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Committee on the Evaluation of the Supplemental Security Income (SSI) Disability Program for Children with Speech Disorders and Language Disorders; Board on the Health of Select Populations; Board on Children, Youth, and Families; Institute of Medicine; Division of Behavioral and Social Sciences and Education; National Academies of Sciences, Engineering, and Medicine; Rosenbaum S, Simon P, editors. Speech and Language Disorders in Children: Implications for the Social Security Administration's Supplemental Security Income Program. Washington (DC): National Academies Press (US); 2016 Apr 6.

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Speech and Language Disorders in Children: Implications for the Social Security Administration's Supplemental Security Income Program.

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2Childhood Speech and Language Disorders in the General U.S. Population

Speech and language disorders in children include a variety of conditions that disrupt children's ability to communicate. Severe speech and language disorders are particularly serious, preventing or impeding children's participation in family and community, school achievement, and eventual employment. This chapter begins by providing an overview of speech and language development and disorders. It then addresses the following topics within the committee's charge: (1) current standards of care for assessing and diagnosing speech and language disorders; (2) causes of and risk factors for these disorders; (3) their prevalence and its relationship to age, development, and gender; and (4) common comorbidities (i.e., other co-occurring conditions).

OVERVIEW OF CHILDHOOD SPEECH AND LANGUAGE DISORDERS

Differentiating Language from Speech

The words “language” and “speech” are often used interchangeably in casual conversation, but in the context of communication disorders, it is important to understand the differences between them. Language refers to the code, or symbol system, for transforming unobservable mental events, such as thoughts and memories, into events that can be perceived by other people. Being a competent language user requires two essential capabilities. One, known as expressive language or language production, is the ability to encode one's ideas into language forms and symbols. The other, known as receptive language or language comprehension, is the ability to understand the meanings that others have expressed using language. People commonly express themselves by speaking and understand others' meanings by listening. However, language also can be expressed and understood in other ways—for example, by reading, writing, and signing (Crystal, 2009).

Speech has a narrower meaning than language because it refers specifically to sounds produced by the oral mechanism, including the lips, tongue, vocal cords, and related structures (Caruso and Strand, 1999). Speech is the most common way to transmit language and, unlike language, can be observed directly. Speech disorders are sometimes mistakenly equated with language disorders, and conversely, normal speech is sometimes assumed to reflect normal language. In fact, speech disorders and language disorders can occur separately or together. For example, a child might have a speech disorder, such as extremely poor articulation, yet have intact language skills. Another child might have a language disorder, such as extremely poor comprehension, yet be able to produce speech sounds normally. Finally, some children have both language disorders and speech disorders. In young children who are producing little if any speech, it can be difficult to determine whether a speech disorder, a language disorder, or both are present. As noted in Chapter 3 on treatment, early intervention for such children generally is designed to facilitate both language and speech skills. When children reach an age that allows each area to be assessed separately, it becomes possible to narrow the focus of treatment according to whether deficits are found only in speech, only in language, or in both.

In this report, the terms “speech disorders,” “language disorders,” and “speech and language disorders” are used (see Box 1-2). The terms “speech disorders” and “language disorders” are used only to refer to these disorders as defined in this chapter, while the term “speech and language disorders” denotes all of the disorders encompassed by these two categories.

Overview of Speech and Language Development and Disorders

The foundations for the development of speech and language begin in utero, with the growth of the anatomical structures and physiological processes that will eventually support sensory, motor, attention, memory, and learning skills. As discussed in the later section of this chapter on causes and risk factors, virtually every factor that threatens prenatal development of the fetus—from genetic abnormalities, to nutritional deficiencies, to exposure to environmental toxins—is associated with an increased risk of developing speech and/or language disorders. Before the end of the prenatal period, fetuses are able to hear, albeit imperfectly, speech and other environmental sounds, and within a few minutes after birth they show special attention to human faces and voices. This early interest in other people appears to set the stage for forming relationships with caregivers, who scaffold the child's growing ability to anticipate, initiate, and participate in social routines (e.g., Locke, 2011). The social experiences and skills that occur during the infant's first months of life are important precursors to pragmatic language skills: the infant first learns to engage in reciprocal interactions and to convey communicative intentions through nonlinguistic means such as gestures, and begins to accomplish these same goals through language forms such as early words. In the first few months of life, infants show improvement in their ability to recognize increasingly detailed patterns of speech, a precursor to linking spoken words with their meanings. Also in the first months of life, infants begin to use their oral mechanisms to produce nonspeech sounds, such as cooing and squealing, as they develop control of their muscles and movements. Thus, they are able to produce increasingly consistent combinations of speech-like sounds and syllables (babbling), a precursor to articulating recognizable words (e.g., Kent, 1999).

Evidence from neurophysiological habituation, neuroimaging, and preferential looking studies shows that children begin to recognize speech patterns that recur in their environments early in the first year of life (Friedrich et al, 2015; Pelucchi et al., 2009; Werker et al., 2012). When tested using behavioral measures, most 12- to 18-month-old children show that they can understand at least a few words in the absence of gestural or other cues to their meaning (e.g., Miller and Paul, 1995). They also can produce at least a few intelligible words during this period (e.g., Squires et al., 2009), showing that they are acquiring both expressive language and speech skills. Their speech skills progress in a systematic fashion over the next few years, as they learn first to say relatively simpler consonants (e.g., “m,” “d,” “n”) and later to say more challenging consonants (e.g., “s,” “th,” “sh”) and consonant clusters (e.g., “bl,” “tr,” “st”) (Shriberg, 1993). Receptive language, expressive language, and speech all develop at a rapid pace through the preschool period as children learn to understand and say thousands of individual words, as well as learn the grammatical (or morpho-syntactic) rules that enable them to understand and produce increasingly lengthy, sophisticated, intelligible, and socially acceptable combinations of words in phrases and sentences (e.g., Fenson et al., 2007). These speech and language skills enable children to achieve communication goals as diverse as understanding a simple story, taking a turn in a game, expressing an emotion, sharing a personal experience, and asking for help (e.g., Boudreau, 2008). By the end of the preschool period, children's ability to understand the language spoken by others and to speak well enough for others to understand them provides the scaffolding for their growing independence.

The end of the preschool period is also when most children show signs that they can think consciously about sounds and words, an ability known as metalinguistic awareness (Kim et al., 2013). Awareness of the phonological (sound) characteristics of words, for example, enables children to identify words that rhyme or words that begin or end with the same speech sound. Such phonological awareness skills have been linked to children's ability to learn that speech sounds can be represented by printed letters—one of the skills necessary for learning to read words (Troia, 2013). Reading requires more than recognizing individual words, however. Competent readers also must understand how words combine to express meanings in connected text, such as phrases, sentences, and paragraphs. Strong evidence shows that children's receptive language skills—such as their knowledge of vocabulary and grammar—are important contributors as well to this aspect of reading comprehension (Catts and Kamhi, 2012; Duke et al., 2013).

In short, by the time children enter elementary school, the speech and language skills they have acquired through listening and speaking provide the foundation for reading and writing. These new literacy skills are critical for learning and social development through the school years and beyond. At the same time, ongoing growth in spoken language skills contributes to building personal and professional relationships and participating independently in society.

It is worth noting that children's speech and language experiences may vary substantially depending on the values and expectations of their culture, community, and family. This point is most obvious for children being raised in multilingual environments, who acquire more than one language. Although the majority of people in the world speak two languages, bilingualism currently is not the norm in the United States, and bilingualism has sometimes been assumed to increase the risk of speech and language disorders. However, there is no evidence that speech or language disorders are more prevalent in bilingual than in monolingual children with similar biological and sociodemographic profiles (Gillam et al., 2013; Goldstein and Gildersleeve-Neumann, 2012; Kohnert and Derr, 2012).

Similarly, some investigators have reported differences in the amounts and kinds of language experienced by children according to their socioeconomic circumstances, and some of these differences have been associated with scores on later tests that emphasize language skills, including tests of vocabulary and verbal intelligence (Hart and Risley, 1995; Hurtado et al., 2014). The language spoken to children certainly influences their language skills, and some aspects of language have been linked to parents' socioeconomic and educational backgrounds (e.g., Hoff, 2013). However, the range of language variations observed to date has not been found to increase the risk of speech or language disorders independent of other factors associated with low socioeconomic status, including inadequate or poor-quality health care, hunger, reduced educational and social resources, and increased exposure to environmental hazards (Harrison and McLeod, 2010; Parish et al., 2010; Pentimonti et al., 2014).

Speech Disorders

As described above, speech refers to the production of meaningful sounds (words and phrases) from the complex coordinated movements of the oral mechanism. Speech requires coordinating breathing (respiration) with movements that produce voice (phonation) and sounds (articulation). Respiration yields a stream of breath, which is set into vibration by laryngeal mechanisms (voice box, vocal cords) to yield audible phonation or voicing. Exquisitely timed and coordinated movements by the articulatory mechanisms, including the jaw, lips, tongue, soft palate, teeth, and upper airway (pharynx), then modify this voiced stream to yield the speech sounds, or phonemes, of the speaker's native language (Caruso and Strand, 1999). Speech disorders are deficits that may prevent speech from being produced at all, or result in speech that cannot be understood or is abnormal in some other way. This broad category includes three main subtypes: speech sound disorders, voice disorders, and stuttering. Speech sound disorders can be further classified into articulation disorders, dysarthria, and childhood apraxia of speech. The speech variations produced by speakers of different dialects and non-native speakers of English are not defined as speech disorders unless they significantly impede communication or educational achievement.

Speech sound disorders, often termed articulation or phonological disorders, are deficits in the production of individual speech sounds, or sequences of speech sounds, caused by inadequate planning, control, or coordination of the structures of the oral mechanism. Dysarthria is a speech sound disorder caused by medical conditions that impair the muscles or nerves that activate the oral mechanism (Caruso and Strand, 1999). Dysarthric speech may be difficult to understand as a result of speech movements that are weak, imprecise, or produced at abnormally slow or rapid rates (Morgan and Vogel, 2008; Pennington et al., 2009). Neuromuscular conditions, including stroke, infections (e.g., polio, meningitis), cerebral palsy, and trauma, can cause dysarthria. Another rare speech sound disorder, childhood apraxia of speech, is caused by difficulty with planning and programming speech movements (ASHA, 2007). Children with this disorder may be delayed in learning the speech sounds expected for their age, or they may be physically capable of producing speech sounds but fail to produce the same sounds correctly when attempting to use them in words, phrases, or sentences.

Voice disorders (also known as dysphonias) occur when the laryngeal structures, including the vocal cords, do not function correctly (Carding et al., 2006). For example, a voice that sounds hoarse or breathy may be due to growths on the vocal cords, allergies, paralysis, infection, or excessive vocal abuse when speaking. A complete inability to produce any sound, called aphonia, may be caused by inflammation, infection, or injury to the vocal cords.

Stuttering (also known as fluency disorder or dysfluency) is a speech disorder that disrupts the ability to speak as smoothly as desired. Dysfluent speech contains an excessive amount of repetitions of sounds, words, and phrases, and involuntary breaks, or “blocks.” Severe stuttering can effectively prevent a speaker from speaking at all; it may also lead to other abnormal physical and emotional behaviors as the speaker struggles to end a particular block or avoid blocks in the future (Conture, 2001).

Language Disorders

As described above, language refers to the code, or system of symbols, for representing ideas in various modalities, including hearing and speaking, reading, and writing. Language may also refer to the ability to interpret and produce manual communication, such as American Sign Language. Language disorders interfere with a child's ability to understand the code, to produce the code, or both (American Psychiatric Association, 2013; WHO, 1992). Children with expressive language disorders have difficulty in formulating their ideas and messages using language. Children with receptive language disorders have difficulty understanding messages encoded in language. Children with expressive-receptive language disorders have difficulty both understanding and producing messages coded in language.

Language disorders may also be classified according to whether they affect pragmatics, semantics, or grammar. Pragmatic language disorders may be seen in children who generally lack social reciprocity, a contributor to the dynamic turn-taking exchanges that typify the earliest communicative interactions (e.g., Sameroff, 2009). A child with a receptive pragmatic language disorder may have difficulty understanding messages that involve abstract ideas, such as idioms, metaphors, and irony. A child with an expressive pragmatic disorder may have difficulty producing messages that are socially appropriate for a given listener or context. A child with a receptive semantic disorder may not understand as many vocabulary words as expected for his or her age, while a child with an expressive semantic disorder may find it difficult to produce the right word to convey the intended meaning accurately. A child with a receptive grammatical deficit may not understand the differences between word endings that indicate concepts such as past (walked) or present (walking), or may not understand complex sentences (e.g., The man that the boy saw was running away). Similarly, a child with an expressive grammatical disorder may produce short, incomplete sentences that lack the grammatical endings or structures necessary to express ideas clearly or completely.

Language disorders can interfere with any of these subsystems, singly or in combination. For example, children with severe pragmatic deficits may appear uninterested in communicating with others. Other children may try to communicate, but suffer from semantic disorders that prevent them from acquiring the words they need to express their messages. Still other children have normal pragmatic skills and vocabularies, but produce grammatical errors when they attempt to combine words into phrases and sentences. Finally, children with phonological disorders may be delayed in learning which sounds belong in words.

As mentioned earlier, language disorders first identified in the preschool period have been linked to learning disabilities when children enter school (Sun and Wallach, 2014). In fact, the Individuals with Disabilities Education Act (IDEA) (Section 300.8) defines a specific learning disability as “a disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, that may manifest itself in the imperfect ability to listen, think, speak, read, write, spell, or to do mathematical calculations.” Strong evidence suggests that early language disorders increase the risk of poor literacy, mental health, and employment outcomes well into adulthood (e.g., Atkinson et al., 2015; Clegg et al., 2015; Law et al., 2009). For this reason, children with a history of language disorders as preschoolers are monitored closely when they enter elementary school, so that services can be provided to those whose language disorders adversely affect literacy, learning, and academic achievement.

Box 2-1 summarizes the major types of speech and language disorders in children.

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BOX 2-1

Types of Speech and Language Disorders in Children.

Co-occurring Speech and Language Disorders

Speech and language disorders may co-occur in children, and in children with severe disorders it is plausible that less obvious deficits in other aspects of development, such as cognitive and sensorimotor processing, may also be implicated. In the first few years of life it may be particularly difficult to determine whether a child's failure to speak is the result of a speech disorder, of a language disorder, or of both. For one thing, many speech and language abilities emerge during the early years of development, and disorders cannot be identified until children have reached the ages at which various speech and language abilities are expected. This difficulty is compounded by the fact that children under the age of approximately 30 months are often difficult to evaluate because they may be reluctant or unable to engage in formal standardized tests of their speech and language skills.

Fortunately, effective treatments for very young nonspeaking children exist that do not depend on differentiating speech from language disorders, and a child's rate of progress in treatment may provide important evidence on the nature and severity of the disorders.

DIAGNOSING SPEECH AND LANGUAGE DISORDERS

Speech and language disorders can accompany or result from any of the conditions that interfere with the development of perceptual, motor, cognitive, or socioemotional function. Accordingly, conditions as varied as Down syndrome, fragile X syndrome, autism spectrum disorder, traumatic brain injury, and being deaf or hard of hearing are known to increase the potential for childhood speech and/or language disorders, and many children with such conditions will also have speech and language disorders. In addition, studies of children with primary speech and language disorders often reveal that they have abnormalities in other areas of development. For example, studies by Brumbach and Goffman (2014) suggest that children with primary language impairment show general deficits in gross and fine motor performance, and such children also show deficits in working memory and procedural learning (Lum et al., 2014). Conversely, some children who have primary speech sound disorders as preschoolers have deficits in reading and spelling during their elementary school years (Lewis et al., 2011). In short, considerable evidence suggests that spoken language skills, including speech sound production, constitute an integrated system and that clear deficits in one area may coexist with deficits in other areas that can compromise future development in language-related domains such as literacy. Intensive monitoring of speech and language development in such children is important for early detection and intervention to lessen the effects of speech and language disorders.

In many children, however, speech and language disorders occur for unknown reasons. In such children, diagnosing speech and language disorders is a complex process that requires assessing not only speech and language skills but also cognitive, perceptual, motor, and socioemotional development; biological, medical, and socioeconomic circumstances; and cultural and linguistic environments. Best-practice guidelines recommend evaluating across multiple domains and obtaining information from multiple sources, including a combination of formal, standardized, or norm-referenced tests; criterion-referenced observations by speech-language pathologists and other professionals; and judgments of familiar caregivers about the child's speech and language competence relative to community expectations for children of the same age (ASHA, 2004; Nelson et al., 2006, 2008; Royal College of Speech & Language Therapists, 2005; Shevell et al., 2003; Wilkinson et al., 2013).

On norm-referenced tests, children's scores are compared with average scores from large, representative samples of children of the same age. Children scoring below a cutoff value are defined as having a deficit, and severity is defined according to how far below average their scores fall. Deficits can range from mild to severe. In clinical practice, scores that fall more than two but less than three standard deviations below the mean are described as severely or extremely low; only 2.14 percent of children would be expected to score this poorly. Scores that fall three or more standard deviations below the mean are extraordinarily low; only 0.13 percent of children would be expected to score this poorly (Urbina, 2014). Figure 2-1 represents these numbers in graphic terms. It shows that only 1 child in 1,000 would be expected to score three or more standard deviations below the mean, and only about 22 children in 1,000 would score more than two but less than three standard deviations below the mean.

FIGURE 2-1. In a normative sample of 1,000 children, only 1 child (shown in orange) is expected to score three or more standard deviations below the mean.

FIGURE 2-1

In a normative sample of 1,000 children, only 1 child (shown in orange) is expected to score three or more standard deviations below the mean. Another 22 children (shown in light green) are expected to score more than two but less than three standard (more...)

In practice, few norm-referenced speech and language tests include a separate severity category for scores that are three or more standard deviations below the mean; all scores two or more standard deviations below the mean are classified together as “severe” or “very low” (Spaulding et al., 2012). As noted in Chapter 1, these clinical criteria for defining severity are not identical to the legal standards for severity specified in the regulations for the Supplemental Security Income (SSI) program, which also considers functional limitations (that are the result of the interactive and cumulative effects of all impairments) to determine the severity. Chapter 4 includes an in-depth review of how children are evaluated for disability in the SSI eligibility determination process.

Norm-referenced testing is not always possible because children may be too young or too disabled to participate in formal standardized testing procedures. In children younger than 3 years and others incapable of formal testing, behaviors and skills are compared with those of typically developing children using criterion-referenced measures or observational checklists (Salvia et al., 2012). Some criterion-referenced measures involve detailed observations of specific skills, such as parent checklists of the number of words that children say. For example, 3-year-old children are expected to say 50 or more different words; those who fail to reach this criterion may be identified as having a significant vocabulary delay. Similarly, by 9-10 months of age, children are expected to communicate with their caregivers using nonlinguistic signals such as pointing and clapping; a 12-month-old who appears uninterested in others and fails to produce such basic communicative precursors to language may be identified as having a significant delay in the pragmatic domain of language. Still other criterion-referenced measures involve more global judgments of whether the child's language abilities are generally commensurate with those of peers, such as asking parents whether they are concerned about their child's ability to talk or understand as well as other children of the same age. In many cases, children are diagnosed as having language delays when their level of performance on some criterion-referenced skill is inconsistent with age to a significant degree, usually defined as a “percentage of delay” relative to chronological age. For example, a 24-month-old with the skills of children half her age (i.e., 12-month-old children) can be described as having a 50 percent delay; if her skills are comparable to those of 18-month-olds, she is described as having a 25 percent delay. In many states, delays of more than 20-25 percent are used to identify children under age 3 years for early intervention under Part C of the 2004 IDEA (Ringwalt, 2015).

Validated norm-referenced tests may not be available for children who are members of cultural and linguistic communities that are not represented adequately in normative samples (e.g., AERA et al., 2014; Roseberry-McKibbin, 2014). In addition, norm-referenced test scores may be influenced by such extraneous factors as additional or confounding deficits (e.g., poor vision, inability to respond actively to test items), fatigue, and emotional state on a given day (Urbina, 2014). Finally, norm-referenced testing may not adequately reflect the functional limitations that speech and language deficits impose on the child's ability to participate in some demanding, real-world contexts. For example, a child with a speech sound disorder may be able to articulate a single word reasonably clearly on a norm-referenced speech test, but be incapable of coordinating the many events necessary to produce an intelligible sentence in fast-paced, dynamic conversation. Similarly, a child with an expressive language disorder may be able to produce single words and short phrases successfully elicited by a norm-referenced test, but be incapable of producing grammatical sentences, much less stories that include them. And a child with a receptive language disorder may understand words presented individually and point to a picture on a norm-referenced test, but be unable to comprehend sentences, especially if the sentences are lengthy, complex, spoken at the normal rate of two to four words per second, or spoken in noisy or distracting environments. For all of these reasons, best diagnostic practices require that evidence from norm- and criterion-referenced testing by professionals be considered in conjunction with judgments made by people who are familiar with the child's usual functioning in his or her daily environment (e.g., Paul and Norbury, 2012).

CAUSES AND RISK FACTORS

This chapter now turns to an overview of known underlying causes of speech and language disorders, followed by a summary of factors that have been associated with an increased risk of speech and language disorders having no known cause. Although prevalence estimates are available for some of the causes described below, and speech and language disorders are frequently mentioned among their sequelae, evidence on the percentage of speech and language disorders attributable solely to the underlying condition is not available. For example, Down syndrome, a chromosomal disorder with a prevalence of 1:700 live births, causes deficits spanning multiple areas of development, including not only speech and language but also cognition and sensorimotor skills, making it difficult to quantify the syndrome's causal role specifically in speech and language disorders.

Speech and Language Disorders with Known Causes

Determining the underlying etiology of a speech or language disorder is essential to providing the child with an appropriate set of interventions and the parents with an understanding of the cause and natural history of their child's disability. A variety of congenital and acquired conditions may result in abnormal speech and/or language development. These conditions include primary disorders of hearing, as well as specific genetic diseases, brain malformation syndromes, inborn errors of metabolism, toxic exposures, nutritional deficiencies, injuries, and epilepsy.

Children who are deaf or hard of hearing provide an especially clear example of the interrelationships among the many causes and consequences of speech and language disorders in childhood (Fitzpatrick, 2015). Because adequate hearing is critically important for developing and using receptive language, expressive language, and speech, being deaf or hard of hearing can lead to speech and language disorders, which in turn contribute to socioemotional and academic disabilities. This is particularly the case when the onset of hearing problems is either congenital or acquired during the first several years of life. Therefore, it is essential that hearing be assessed in children being evaluated for speech and language disorders.

Childhood hearing loss may result from or be associated with a wide variety of causes, which are categorized in Box 2-2. Hearing may be affected by disorders of either the sensory component of the auditory system (i.e., peripheral) or the processing of auditory information within the brain (i.e., central). Peripheral causes may be either unilateral or bilateral and are subdivided into conductive types, which are due to developmental or acquired abnormalities of the structures of the outer or middle ear, and sensorineural types, which are due to a variety of disorders affecting the sound-sensing organ—the cochlea—and its nerve that goes to the brain—the cochlear nerve.

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BOX 2-2

Examples of Conditions Affecting Hearing Early in Life That May Affect the Development of Speech and Language.

Conductive-related causes of reduced hearing levels include congenital structural malformations of the outer and inner ear, consequences of acute or recurrent middle-ear infections, eustachian tube dysfunction, tumors, and trauma. Sensorineural types are even more diverse. A variety of genetic disorders have been identified that affect the function of the cochlea or cochlear nerve, and the disorder may be sporadic or inherited in an autosomal dominant, autosomal recessive, or X-linked manner, depending on the specific gene. Sensorineural types may be secondary to medical illness or even treatments for babies who must be placed in neonatal intensive care units because of either prematurity or a variety of perinatal disorders, such as hypoxia (oxygen deficiency), disturbances of blood flow, infections, or hyperbilirubinemia (excessive bilirubin levels that lead to jaundice and brain dysfunction known as kernicterus). Prenatal infections due to maternal cytomegalovirus, toxoplasmosis, or rubella (TORCH infections) can have a significant congenital impact on the sensorineural hearing mechanism, as can postnatal infectious illnesses such as meningitis (inflammation of membranes around the brain and spinal cord). Ironically, the treatment of meningitis or other bacterial infections with certain antibiotics can result in decreased hearing levels, as some of these life-saving drugs are ototoxic (i.e., harmful to structures of the ear). The impact of antibiotics on central hearing function is much less common in childhood and generally does not lead to total deafness.

The best-recognized cause affecting central hearing is Landau-Kleffner syndrome, or acquired epileptic aphasia, a rare condition that typically presents in early childhood with either minimal speech and language development or loss of previously acquired speech and language due to cortical deafness secondary to persistent epileptiform activity in the electroencephalogram, even in the absence of clinical seizures. Lastly, neonatal hyperbilirubinemia (kernicterus) can impact both sensorineural and central hearing, the latter as a result of dysfunction at the level of the brainstem. Importantly, in addition to the causes described above, many factors that impact hearing are themselves caused by, or co-occur with, underlying conditions that affect other aspects of children's development.

Apart from being deaf or hard of hearing, there are a diverse set of conditions that should be considered as other potential causes of speech and language disorders, as summarized in Box 2-2. As is the case with hearing, abnormal development of anatomic structures critical to the proper generation of speech may lead to speech sound disorders or voice disorders. For example, articulation and phonological disorders may result from cleft palate. A wide variety of genetic syndromes are known to be associated with disordered speech and language development. These include well-characterized conditions that are due to an abnormal number of a specific chromosome, such as Down syndrome (associated with three rather than two copies of chromosome 21) (Tedeschi et al., 2015) or Klinefelter syndrome (which occurs in boys who have a normal Y chromosome together with two or more X chromosomes, rather than one X chromosome).

Well-recognized genetic syndromes due to a mutation in a single gene (such as fragile X syndrome, neurofibromatosis type I, Williams syndrome, and tuberous sclerosis) are associated with speech or language disorders, and current research has demonstrated that alterations in small groups of genes (copy number variations such as 16p11.2 deletion) may increase the risk of a speech or language disability. In general, when indicated by history and clinical examination, these genetic conditions can be detected with clinically available blood-based laboratory tests. Primary malformations of the central nervous system—such as hydrocephalus (an expansion of the fluid-filled cavities within the brain), agenesis of the corpus callosum (the absence of the main structure that connects the right and left hemispheres of the brain), and both gross and microscopic abnormalities of cortical development (cortical dysplasia, an abnormal layering or location of neurons)—also may be associated with speech and language disorders. In general, these primary disruptions in brain anatomy may be diagnosed by magnetic resonance imaging (MRI) and in some cases discovered via an in utero maternal-fetal ultrasound examination.

A variety of prenatal and postnatal toxic exposures may result in abnormal brain development with resultant neurodevelopmental consequences. Maternal alcohol and other substance use are well recognized in this regard, as is postnatal exposure to lead. Similarly, abnormal prenatal growth, postnatal nutritional deprivation, and hypothyroidism (underactive thyroid) have developmental consequences. Injuries to the developing brain, such as perinatal stroke from brain hemorrhages or ischemia (inadequate blood supply), accidental trauma, and nonaccidental trauma (child abuse), must also be considered, as must such neoplastic conditions as primary brain tumors, metastatic disease, and the consequences of oncological therapies (e.g., chemotherapy and radiation). Some children with cerebral palsy (a condition that results in abnormal motor development and that has numerous causes) may also have an associated speech or language disorder. In addition, speech and language disorders may be secondary to poorly controlled epilepsy associated with a variety of causes, including structural abnormalities in cortical development, genetic disorders (e.g., mutations in ion channel genes), and complex epileptic encephalopathies (e.g., West, Lennox-Gastault, or Landau-Kleffner syndromes) (Campbell et al., 2003; Feldman and Messick, 2009).

Box 2-3 presents a listing of examples of speech and language disorders with known causes.

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BOX 2-3

Examples of Speech and Language Disorders with Known Causes.

Risk Factors Associated with Speech and Language Disorders with No Known Cause

In addition to the etiologies described above, a number of variables have been associated with an increased risk of childhood speech and/or language disorders with no known cause. Findings in this literature are somewhat inconsistent (Harrison and McLeod, 2010; Nelson et al., 2006), varying with characteristics of the children examined (e.g., age, phenotype, severity, comorbidity) and with research design features (e.g., sample size, control for confounding, statistical analyses).

Studies of speech and language disorders in children, such as speech sound disorders (Lewis et al., 2006, 2007) and specific language impairment (Barry et al., 2007; Bishop, 2006; Bishop and Hayiou-Thomas, 2008; Rice, 2012; Tomblin and Buckwalter, 1998), show that these conditions are familial (i.e., risk for these disorders is elevated for family members of affected individuals) and that this familiality is partially heritable (i.e., genetic factors shared among biological family members contribute to family aggregation). However, heritability estimates (i.e., the proportion of phenotypic variance that can be attributed to genetic variance) for some speech and language disorders, such as specific language impairment, have been inconsistent (Bishop and Hayiou-Thomas, 2008). For example, twin studies on heritability of language disorders have shown a range of estimates of heritability, from 45 percent for deficient language achievement (Tomblin and Buckwalter, 1998) to 25 percent for specific language impairment (DeThorne et al., 2005). One study of 579 4-year-old twins with low language performance and their co-twins found heritability was greater for more severe language impairment, suggesting a stronger influence of genes at the lower end of language ability (Viding et al., 2004). Finally, a review of twin data found that the environment shared by the twins was “relatively unimportant” in causing specific language impairment compared with genetic factors (Bishop, 2006). Overall, the evidence suggests that susceptibility to speech and language disorders results from interactions between genetic and environmental factors (Newbury and Monaco, 2010).

To date, the evidence best supports a cumulative risk model in which increases in risk are larger for combinations of risk factors than for individual factors (Harrison and McLeod, 2010; Lewis et al., 2015; Pennington and Bishop, 2009; Reilly et al., 2010; Whitehouse et al., 2014). In a study of speech sound disorders, for example, Campbell and colleagues (2003) found that three variables—male sex, low maternal education, and positive family history of developmental communication disorders—were individually associated with increased odds of speech sound disorder, but the odds of such a disorder were nearly eight times larger in a child with all three risk factors than in a child with none of them. Based on a national database in the United Kingdom, Dockrell and colleagues (2014) report higher odds (2.5) of speech, language, and communication needs in boys than in girls, and they document a strong social gradient for childhood speech, language, and communication disorders in which the odds were 2.3 times greater for children entitled to free school lunches and living in more deprived neighborhoods than for children without these factors. It is important to note that risk indices such as odds ratios cannot provide evidence on the proportion of cases of the disorder that are caused by the factor in question, both because they could reflect the influence of some other, unknown causal factor and because they are influenced by the composition of the samples (e.g., base rate, severity) in which they are calculated.

Research has shown a strong association between poverty and developmental delays, such as language delays. For example, in a study of 513 3-year-olds who had been exposed to risk factors that included inadequate income, lack of social supports, poor maternal prenatal care, and high family stress, King and colleagues (2005) found that 10 percent of children—four times the expected 2.5 percent—had severe delays, scoring two or more standard deviations below the mean on a norm-referenced language test. Walker and colleagues (2011) showed that experiences in early life affect the structure and functioning of the brain. For example, a malnourished expectant mother who faces barriers in accessing prenatal care is at risk of having a child who is premature, is small for his or her gestational age, or experiences perinatal complications (Adams et al., 1994; Walker et al., 2011). Children exposed to such factors in the womb are at increased risk for developing a disability such as specific language impairment (Spitz et al., 1997; Stanton-Chapman et al., 2004). Lastly, a variety of other psychosocial factors—including deprivation of appropriate stimuli from parents and caretakers (Akca et al., 2012; Fernald et al., 2013; Hart and Risley, 1995), excess media (television and screen time) exposure (Christakis et al., 2009; Zimmerman et al., 2007), and poor sleep hygiene (Earle and Myers, 2014)—need to be considered as potential risk factors for speech and language disorders.

PREVALENCE

Law and colleagues (2000) found that there existed no systematic synthesis of the evidence concerning the prevalence of pediatric speech and language disorders with primary causes; their observation remains true in 2015 (Wallace et al., 2015). Estimating the prevalence of these disorders with confidence is difficult for several reasons. First, because the characteristics of these disorders differ with age, the diagnostic tools by which they are identified necessarily vary in format, ranging from simple parental reports at the earliest ages to formal standardized testing at later ages. Second, because these disorders can vary in scope—from problems with relatively discrete skills (e.g., producing individual speech sounds) to problems with broader and less observable sets of abilities (e.g., drawing inferences from or comprehending language that is ambiguous, indirect, or nonliteral)—there exists no single diagnostic tool capable of addressing the full range of pediatric speech and language skills. Third, as with many pediatric psychological and behavioral disorders, diagnostic criteria involve integrating observations from multiple sources and time points.

As a result, there currently is no single reference standard for identifying pediatric speech and language disorders of primary origin in children of all ages. Instead, prevalence estimates come from studies that focused on different ages and used different diagnostic tools and criteria. Law and colleagues (2000) found a median prevalence of 5.95 percent in the four studies they reviewed; they observe that this value is consistent with several other estimates, but emphasize the need for caution pending additional evidence from well-designed population studies.

The following subsections describe prevalence estimates from studies that have attempted to distinguish speech disorders from language disorders. However, these estimates also must be viewed with caution, given differences among studies in sample composition and diagnostic criteria.

Speech Disorders

Consistent with the varying expectations for speech skills in children of different ages, estimates of the incidence (i.e., the risk of acquiring a disorder for an individual in a specified population) and prevalence (i.e., the percentage of individuals affected by a disorder in a specified population at a specific point in time) of speech disorders vary according to age, the presence of other neurodevelopmental disorders, and the diagnostic criteria employed.

Most of the literature on the prevalence of speech disorders has focused on children with articulation or phonological disorders due to unknown causes. Shriberg and colleagues (1999, cited in Pennington and Bishop, 2009) report a mean prevalence of 8.2 percent for such disorders; Bishop (2010) estimates prevalence at 10 percent. The prevalence of these disorders varies with age, however, decreasing from 15-16 percent at age 3 (Campbell et al., 2003) to approximately 4 percent at age 6 (Shriberg et al., 1999). Evidence suggests that speech sound disorders affect more boys than girls (Eadie et al., 2015), particularly in early life. In preschoolers, the ratio of affected boys to girls is 2 or 3:1, declining by age 6 to 1.2:1 (Pennington and Bishop, 2009; Shriberg et al., 1999). Although many children with speech sound disorders as preschoolers will progress into the normal range by the time of school entry, the close ties between spoken and written language have motivated many studies of the extent to which speech sound disorders are associated with an increased risk of reading, writing, or spelling disorders. To date, evidence from several studies (e.g., Lewis et al., 2015; Pennington and Bishop, 2009; Skebo et al., 2013) suggests that in comparison with their unaffected peers, children with speech sound disorders but normal-range language skills may have somewhat lower reading scores than their peers, but they rarely meet eligibility criteria for a reading disability (Skebo et al., 2013). However, severity has not been considered to date in studies of the relationship between speech sound disorders and reading skills (Skebo et al., 2013).

Little evidence is available concerning the epidemiology of voice disorders in children (dysphonias) not attributable to other developmental disorders. In a prospective population-based cohort of 7,389 8-year-old British children, 6-11 percent were identified as dysphonic; male sex, number of siblings, asthma, and frequent upper respiratory infections were among the factors associated with an increased risk of voice disorders (Carding et al., 2006).

Stuttering is estimated to have a lifetime incidence of 5 percent but a population prevalence of just under 1 percent (Bloodstein and Ratner, 2008). The prevalence of stuttering before the age of 6 years is much higher than that at later ages; evidence from several sources suggests that rates of natural recovery from stuttering in children before age 6 may be as high as 85 percent (Yairi and Ambrose, 2013). Evidence indicates that stuttering affects only slightly more boys than girls during the preschool period, although higher ratios of affected males to females have been observed at later ages. Finally, approximately 60 percent of cases of developmental stuttering co-occur with other speech and language disorders (Kent and Vorperian, 2013).

Language Disorders

As with speech disorders, estimates of the prevalence of language disorders vary across studies by age, the presence of other neurodevelopmental disorders, and the diagnostic criteria employed. Language disorders with no known cause, sometimes referred to as “specific” (or “primary”) language impairments (e.g., Reilly et al., 2014), are highly prevalent, affecting 6-15 percent of children when identified through formal norm-referenced testing in population-based samples (Law et al., 2000). This is consistent with the cutoff values of 1.0-1.5 standard deviations below the mean employed in several investigations (e.g., Tomblin et al., 1997b). By contrast, prevalence estimates are generally higher when based on parent or teacher reports. For example, in a survey of parents and teachers conducted in a nationally representative sample of 4,983 4- to 5-year-old children in Australia, McLeod and Harrison (2009) found that prevalence estimates based on parent and teacher reports were somewhat higher than those based on norm-referenced testing, with 22-25 percent of children perceived as having deficits in talking (expressive language) and 10-17 percent as having deficits in understanding (receptive language). As noted by Law and colleagues (2000), the discrepancy between prevalence rates defined according to norm- and criterion-referenced methods could be due to a number of factors, including the inability of norm-referenced tests to capture or reflect the child's language functioning in relatively more challenging situations, such as classrooms and conversations.

Language disorders that have no known cause have been reported to affect more boys than girls, but it appears that the gender imbalance is greater in clinical than in population-based samples (e.g., Pennington and Bishop, 2009). For example, the ratio of affected males to females has ranged from 2:1 to 6:1 across several clinical samples, but boys were only slightly more likely to be affected than girls (1.3:1) in a large population-based sample of U.S. kindergarten children (Tomblin et al., 1997b).

As noted earlier, many aspects of literacy depend heavily on the language knowledge and skills that children acquire before they enter school (Catts and Kamhi, 2012), and children with severe language disorders have a substantially increased risk of deficits in reading and academic achievement. Estimates vary, but children diagnosed with language disorders with no known cause as preschoolers are at least four times more likely to have reading disabilities than their unaffected peers (Pennington and Bishop, 2009). Similarly, evidence from a large-scale, prospective methodologically sound cohort study of kindergarteners followed longitudinally showed that the majority of those with language disorders with no known cause continued to exhibit language and/or academic difficulties through adolescence (Tomblin and Nippold, 2014).

One study that helped frame the committee's understanding of prevalence estimates of speech and language disorders was a study of specific language impairment conducted by Tomblin and colleagues (1997b). This study selected a geographic region in the upper Midwest of the United States and sampled rural, suburban, and urban schools within that region. All eligible 5- to 6-year-old children were systematically screened and followed up with diagnostic testing for specific language impairment. Children were not included if they spoke a language other than English, failed a hearing test, or demonstrated low functioning in nonverbal intelligence (suggesting overall lower intellectual functioning). When a cutoff 1.25 standard deviations below the mean (i.e., approximately the 10th percentile, or the lowest 10 percent of the normative sample) on at least two language scores was used, the prevalence rate of specific language impairment was estimated at 7.4 percent of kindergarten children. The prevalence of specific language impairment for boys was 8 percent and for girls was 6 percent.

When the cutoff was set at two standard deviations below the mean (i.e., approximately the 2nd percentile), the prevalence estimate dropped to 1.12 percent. Using 1.25 standard deviations below the mean as the criterion, there were slightly higher rates of specific language impairment among African American and Native American children relative to white and Hispanic children. Only 29 percent of the parents of the kindergarteners diagnosed with specific language impairment reported having been informed that their children had speech or language problems. It is important to note that large-scale epidemiological studies on autism spectrum disorder, learning disorders, and attention deficit hyperactivity disorder have clearly demonstrated that active case-finding strategies lead to higher and more accurate rates of identification of children with neurodevelopmental disorders (Barbaresi et al., 2002, 2005, 2009; CDC, 2014; Katusic et al., 2001) relative to studies depending only on parent reports. Studies that followed this sample of children with specific language impairment into their school years demonstrated that as a group, they also experienced lower academic achievement.

The Tomblin et al. (1997a) study underscores several methodological issues relevant for the current report: differences in severity level for case identification, comorbidity with other disorders considered primary disabilities, and differences in prevalence related to gender and racial or ethnic identity. Subsequent studies with the children included in this study identified low maternal and paternal education and paternal history of speech, learning, or intellectual difficulties as risk factors for specific language impairment (Tomblin et al., 1997a).

Table 2-1 provides a summary of prevalence estimates from the studies of U.S. children that the committee also reviewed. This list is not the result of a meta-analysis, nor is it exhaustive; rather, the table includes a number of well-designed studies that employed clear and consistent definitions. The committee reviewed numerous well-designed studies and meta-analyses from other countries (e.g., Beitchman et al., 1996a,b,c [Canada]; Law et al., 2000 [United Kingdom, others]; McLeod and Harrison, 2009 [Australia]). For the purposes of this study, however, the committee limited the summary of prevalence estimates to U.S. children. Table 2-1 includes the populations and conditions studied, the diagnostic criteria used to identify the conditions, and the prevalence of the conditions (or percent positive). Confidence intervals are included when available. As noted earlier, and as is evident from the table, the studies reviewed vary greatly in terms of ages, diagnostic tools or criteria, and methods used. The estimates presented in the table (in addition to estimates based on national survey data presented in Chapter 5) indicate that speech and language disorders affect between 3 and 16 percent of U.S. children.

TABLE 2-1. Estimates of the Prevalence of Speech and Language Disorders from Studies of U.S. Children.

TABLE 2-1

Estimates of the Prevalence of Speech and Language Disorders from Studies of U.S. Children.

COMMON COMORBIDITIES

An examination of comorbidities (i.e., other co-occurring conditions) of speech and language disorders is complicated by the central role of language and communication in the development and behavior of children and adolescents. Speech and language disorders are a definitional component of certain conditions, most prominently autism spectrum disorder (American Psychiatric Association, 2013). Other neurodevelopmental disorders, including cognitive impairment, are universally associated with varying degrees of delays and deficits in language and communication skills (American Psychiatric Association, 2013). In addition to their co-occurrence with a wide range of neurodevelopmental disorders, speech and language delays in toddlers and preschool-age children are associated with a significantly increased risk for long-term developmental challenges, such as language-based learning disorders (Beitchman et al., 1996a,b,c, 1999, 2001, 2014; Brownlie et al., 2004; Stoeckel et al., 2013; Voci et al., 2006; Young et al., 2002). While specific language impairments (i.e., those not associated with other diagnosable neurodevelopmental disorders) are relatively common, it is likely that substantially greater numbers of children and adolescents experience significant speech and/or language impairment associated with other diagnosable disorders. Finally, speech and language delays and deficits may lead to impairments in other aspects of a child's functional skills (e.g., social interaction, behavior, academic achievement) even when not associated with other diagnosable disorders (Beitchman et al., 1996c, 2001, 2014; Brownlie et al., 2004; Voci et al., 2006; Young et al., 2002). This section, therefore, examines the association of speech and language disorders from the following perspectives: (1) speech and language disorders that are comorbid with other diagnosable disorders, and (2) speech and language disorders in early childhood that confer a quantifiable risk for the later development of comorbid conditions. Together, these two perspectives create a comprehensive picture of the association of speech and language disorders with other neurodevelopmental disorders.

Autism spectrum disorder is a highly prevalent neurodevelopmental disorder, affecting an estimated 1 in 68 8-year-old children in the United States (CDC, 2014). By definition, all children with autism spectrum disorder have deficits in communication, ranging from a complete absence of verbal and nonverbal communication skills, to atypical language (e.g., echolalia or “scripted” language), to more subtle deficits in pragmatic (i.e., social) communication (American Psychiatric Association, 2013). The formal diagnostic criteria for autism spectrum disorder require documentation of deficits in the social-communication domain (American Psychiatric Association, 2013). In clinical practice, when children present with significant delays in the development of communication skills, autism spectrum disorder is one of the primary diagnostic considerations (Myers and Johnson, 2007).

All children and adolescents with intellectual disability have varying degrees of impairment in communication skills (American Psychiatric Association, 2013). Among those with mild intellectual disability, deficits in communication may be relatively subtle, including inability to understand or employ highly abstract language or impairment in social communication. In contrast, children and adolescents with severe or profound levels of intellectual disability may be able only to communicate basic requests, understand concrete instructions, and communicate with simple phrases or single words; others may be unable to employ or understand spoken language. A number of specific genetic disorders are directly associated with varying degrees of intellectual disability together with abnormalities of speech and language (see Box 2-3). Some of these genetic conditions often are also associated with specific profiles of speech and language impairment (Feldman and Messick, 2009). Examples include dysfluent speech in children with Down syndrome, echolalia in boys with fragile X syndrome, and fluent but superficial social language in children with Williams syndrome (Feldman and Messick, 2009).

Language-based learning disorders, including reading and written language disorders, are often associated with speech and language disorders. The association between language impairment and reading disorders has been demonstrated in studies examining the likelihood that family members of subjects with language impairment are at increased risk for reading disorder (Flax et al., 2003). Both epidemiologic and clinic-based studies have demonstrated that children with speech sound disorders and language disorders are at increased risk for reading disorder (Pennington and Bishop, 2009). Similarly, multiple studies have demonstrated a strong association between attention deficit hyperactivity disorder and speech and language disorders (Pennington and Bishop, 2009; Tomblin, 2014).

The comorbidity of speech and language disorders and other neurodevelopmental disorders may not be apparent in pre-school-age children, since these very young children may not yet manifest the developmental lags or symptoms required to make comorbid diagnoses of such conditions as learning disorders and attention deficit hyperactivity disorder. In their prospective community-based study, for example, Beitchman and colleagues (1989) found significant differences in measures of “reading readiness” among 5-year-old children with poor language comprehension compared with children with either high overall speech and language ability or isolated articulation difficulties (Beitchman et al., 1989). Similarly, there was a tendency for 5-year-olds with a combination of low articulation and poor language comprehension to have higher teacher ratings of hyperactivity and inattention and lower maternal ratings of social competence (Beitchman et al., 1989). By age 12, the children who earlier had shown combined deficits in speech and language had significantly lower levels of reading achievement and higher rates of diagnosed psychiatric disorders (57.1 percent versus 23.7 percent for children with normal speech and language at age 5) (Beitchman et al., 1994). By age 19, children with documented language impairment at age 5 had significantly higher rates of reading disorder (36.8 percent versus 6.4 percent), math disorder (53.9 percent versus 12.2 percent), and psychiatric disorders (40 percent versus 21 percent) compared with their peers with normal language ability at age 5 (Young et al., 2002).

In summary, speech and language disorders are frequently identified in association with (i.e., comorbid with) a wide range of other neurodevelopmental disorders. Children with comorbid conditions can be expected to be more severely impaired and to experience greater functional limitations (due to the interactive and cumulative effects of multiple conditions) than children who do not have comorbid conditions. Furthermore, young children with language impairments are at high risk for later manifestation of learning and psychiatric disorders. It is therefore important both to carefully examine the speech and language skills of children with other developmental disorders and to identify other neurodevelopmental disorders among children presenting with speech and language impairment. Among populations of children with conditions as diverse as autism spectrum disorder, attention deficit hyperactivity disorder, traumatic brain injury, and genetic disorders, speech and language disorders may be the most easily identified impairments because of the central role of language and communication in the functional capacity of children and adolescents.

FINDINGS AND CONCLUSIONS

Findings

  • 2-1. Speech and language disorders are prevalent, affecting between 3 and 16 percent of U.S. children. Prevalence estimates vary according to age and the diagnostic criteria employed, but best evidence suggests that approximately 2 percent of children have speech and/or language disorders that are severe according to clinical standards.
  • 2-2. Some speech and language disorders result from known biological causes.
  • 2-3. In many cases, these disorders have no identifiable cause, but factors including male sex and reduced socioeconomic and educational resources have been associated with an increased risk of the disorders.
  • 2-4. Diagnosing speech and language disorders in children is a complex process that requires integrating information on speech and language with information on biological and medical factors, environmental circumstances, and other areas of development.
  • 2-5. Speech and language disorders frequently co-occur with other neurodevelopmental disorders and may be among the earliest symptoms of serious neurodevelopmental conditions.
  • 2-6. Children with severe speech and language disorders have an increased risk of a variety of adverse outcomes, including mental health and behavior disorders, learning disabilities, poor academic achievement, and limited employment and social participation.

Conclusions

  • 2-1. Severe speech and language disorders represent serious threats to children's social, emotional, educational, and employment outcomes.
  • 2-2. Severe speech and language disorders are debilitating at any age, but their impacts on children are particularly serious because of their widespread adverse effects on development and the fact that these negative consequences cascade and build on one another over time.
  • 2-3. Severe speech and language disorders may be one of the earliest detectable symptoms of other serious neurodevelopmental conditions; for this reason, they represent an important point of entry to early intervention and other services.
  • 2-4. It is critically important to identify such disorders for two reasons: first, because they may be an early symptom of other serious neurodevelopmental disorders, and second, so that interventions aimed at forestalling or minimizing their adverse consequences can be undertaken.

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