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1.

Spinocerebellar ataxia 1

Spinocerebellar ataxia type 1 (SCA1) is characterized by progressive cerebellar ataxia, dysarthria, and eventual deterioration of bulbar functions. Early in the disease, affected individuals may have gait disturbance, slurred speech, difficulty with balance, brisk deep tendon reflexes, hypermetric saccades, nystagmus, and mild dysphagia. Later signs include slowing of saccadic velocity, development of up-gaze palsy, dysmetria, dysdiadochokinesia, and hypotonia. In advanced stages, muscle atrophy, decreased deep tendon reflexes, loss of proprioception, cognitive impairment (e.g., frontal executive dysfunction, impaired verbal memory), chorea, dystonia, and bulbar dysfunction are seen. Onset is typically in the third or fourth decade, although childhood onset and late-adult onset have been reported. Those with onset after age 60 years may manifest a pure cerebellar phenotype. Interval from onset to death varies from ten to 30 years; individuals with juvenile onset show more rapid progression and more severe disease. Anticipation is observed. An axonal sensory neuropathy detected by electrophysiologic testing is common; brain imaging typically shows cerebellar and brain stem atrophy. [from GeneReviews]

MedGen UID:
155703
Concept ID:
C0752120
Disease or Syndrome
2.

Glycogen storage disease, type II

Pompe disease is classified by age of onset, organ involvement, severity, and rate of progression. Infantile-onset Pompe disease (IOPD; individuals with onset before age 12 months with cardiomyopathy) may be apparent in utero but more typically onset is at the median age of four months with hypotonia, generalized muscle weakness, feeding difficulties, failure to thrive, respiratory distress, and hypertrophic cardiomyopathy. Without treatment by enzyme replacement therapy (ERT), IOPD commonly results in death by age two years from progressive left ventricular outflow obstruction and respiratory insufficiency. Late-onset Pompe disease (LOPD; including: (a) individuals with onset before age 12 months without cardiomyopathy; and (b) all individuals with onset after age 12 months) is characterized by proximal muscle weakness and respiratory insufficiency; clinically significant cardiac involvement is uncommon. [from GeneReviews]

MedGen UID:
5340
Concept ID:
C0017921
Disease or Syndrome
3.

Werdnig-Hoffmann disease

Spinal muscular atrophy (SMA) is characterized by muscle weakness and atrophy resulting from progressive degeneration and loss of the anterior horn cells in the spinal cord (i.e., lower motor neurons) and the brain stem nuclei. The onset of weakness ranges from before birth to adolescence or young adulthood. The weakness is symmetric, proximal > distal, and progressive. Before the genetic basis of SMA was understood, it was classified into clinical subtypes; however, it is now apparent that the phenotype of SMN1-associated SMA spans a continuum without clear delineation of subtypes. Poor weight gain with growth failure, restrictive lung disease, scoliosis, joint contractures, and sleep difficulties are common complications. [from GeneReviews]

MedGen UID:
21913
Concept ID:
C0043116
Disease or Syndrome
4.

Charcot-Marie-Tooth disease, demyelinating, type 1b

Charcot-Marie-Tooth disease is a sensorineural peripheral polyneuropathy. Affecting approximately 1 in 2,500 individuals, Charcot-Marie-Tooth disease is the most common inherited disorder of the peripheral nervous system (Skre, 1974). Autosomal dominant, autosomal recessive, and X-linked forms have been recognized. Classification On the basis of electrophysiologic properties and histopathology, CMT has been divided into primary peripheral demyelinating (type 1, or HMSNI) and primary peripheral axonal (type 2, or HMSNII) neuropathies. The demyelinating neuropathies classified as CMT type 1 are characterized by severely reduced motor NCVs (less than 38 m/s) and segmental demyelination and remyelination with onion bulb formations on nerve biopsy. The axonal neuropathies classified as CMT type 2 are characterized by normal or mildly reduced NCVs and chronic axonal degeneration and regeneration on nerve biopsy (see CMT2A1; 118210). Distal hereditary motor neuropathy (dHMN) (see 158590), or spinal CMT, is characterized by exclusive motor involvement and sparing of sensory nerves (Pareyson, 1999). McAlpine (1989) proposed that the forms of CMT with very slow nerve conduction be given the gene symbol CMT1A (118220) and CMT1B, CMT1A being the gene on chromosome 17 and CMT1B being the gene on chromosome 1. CMT2 was the proposed symbol for the autosomal locus responsible for the moderately slow nerve conduction form of the disease (axonal). For a phenotypic description and discussion of genetic heterogeneity of the various subtypes of CMT, see CMTX1 (302800), CMT2A1 (118210), CMT3 (DSS; 145900), CMT4A (214400), and CMTDIB (606482). Genetic Heterogeneity of Autosomal Dominant Demyelinating CMT1 Autosomal dominant demyelinating CMT1 is genetically heterogeneous disorder and can be caused by mutations in different genes (see CMT1A, 118220; CMT1C, 601098; CMT1D, 607678), CMT1E (607734), CMT1F (607734), and CMT1G (618279). See also 608236 for a related phenotype characterized by isolated slowed nerve conduction velocities (NCVs). [from OMIM]

MedGen UID:
124377
Concept ID:
C0270912
Disease or Syndrome
5.

Merosin deficient congenital muscular dystrophy

Merosin-deficient congenital muscular dystrophy is an autosomal recessive form of muscular dystrophy characterized by muscle weakness apparent at birth or in the first 6 months of life. Patients show hypotonia, poor suck and cry, and delayed motor development; most never achieve independent ambulation. Most patients also have periventricular white matter abnormalities on brain imaging, but mental retardation and/or seizures occur only rarely (summary by Xiong et al., 2015). [from OMIM]

MedGen UID:
224728
Concept ID:
C1263858
Disease or Syndrome
6.

Nemaline myopathy 3

Nemaline myopathy (referred to in this entry as NM) is characterized by weakness, hypotonia, and depressed or absent deep tendon reflexes. Muscle weakness is usually most severe in the face, the neck flexors, and the proximal limb muscles. The clinical classification defines six forms of NM, which are classified by onset and severity of motor and respiratory involvement: Severe congenital (neonatal) (16% of all individuals with NM). Amish NM. Intermediate congenital (20%). Typical congenital (46%). Childhood-onset (13%). Adult-onset (late-onset) (4%). Considerable overlap occurs among the forms. There are significant differences in survival between individuals classified as having severe, intermediate, and typical congenital NM. Severe neonatal respiratory disease and the presence of arthrogryposis multiplex congenita are associated with death in the first year of life. Independent ambulation before age 18 months is predictive of survival. Most children with typical congenital NM are eventually able to walk. [from GeneReviews]

MedGen UID:
777997
Concept ID:
C3711389
Disease or Syndrome
7.

Severe X-linked myotubular myopathy

X-linked myotubular myopathy (X-MTM), also known as myotubular myopathy (MTM), is characterized by muscle weakness that ranges from severe to mild. Approximately 80% of affected males present with severe (classic) X-MTM characterized by polyhydramnios, decreased fetal movement, and neonatal weakness, hypotonia, and respiratory failure. Motor milestones are significantly delayed and most individuals fail to achieve independent ambulation. Weakness is profound and often involves facial and extraocular muscles. Respiratory failure is nearly uniform, with most individuals requiring 24-hour ventilatory assistance. It is estimated that at least 25% of boys with severe X-MTM die in the first year of life, and those who survive rarely live into adulthood. Males with mild or moderate X-MTM (~20%) achieve motor milestones more quickly than males with the severe form; many ambulate independently, and may live into adulthood. Most require gastrostomy tubes and/or ventilator support. In all subtypes of X-MTM, the muscle disease is not obviously progressive. Female carriers of X-MTM are generally asymptomatic, although manifesting heterozygotes are increasingly being identified. In affected females, symptoms range from severe, generalized weakness presenting in childhood, with infantile onset similar to affected male patients, to mild (often asymmetric) weakness manifesting in adulthood. Affected adult females may experience progressive respiratory decline and ultimately require ventilatory support. [from GeneReviews]

MedGen UID:
98374
Concept ID:
C0410203
Congenital Abnormality
8.

Alagille syndrome 1

Alagille syndrome (ALGS) is a complex multisystem disorder involving primarily the liver, heart, eyes, face, and skeleton. The clinical features are highly variable, even within families. The major clinical manifestations of ALGS are cholestasis, characterized by bile duct paucity on liver biopsy; congenital cardiac defects, primarily involving the pulmonary arteries; posterior embryotoxon in the eye; typical facial features; and butterfly vertebrae. Renal and central nervous abnormalities also occur. Mortality is approximately 10%, with vascular accidents, cardiac disease, and liver disease accounting for most of the deaths. [from GeneReviews]

MedGen UID:
365434
Concept ID:
C1956125
Disease or Syndrome
9.

Smith-Magenis syndrome

Smith-Magenis syndrome (SMS) is characterized by distinctive physical features (particularly facial features that progress with age), developmental delay, cognitive impairment, behavioral abnormalities, sleep disturbance, and childhood-onset abdominal obesity. Infants have feeding difficulties, failure to thrive, hypotonia, hyporeflexia, prolonged napping or need to be awakened for feeds, and generalized lethargy. The majority of individuals function in the mild-to-moderate range of intellectual disability. The behavioral phenotype, including significant sleep disturbance, stereotypies, and maladaptive and self-injurious behaviors, is generally not recognized until age 18 months or older and continues to change until adulthood. Sensory issues are frequently noted; these may include avoidant behavior, as well as repetitive seeking of textures, sounds, and experiences. Toileting difficulties are common. Significant anxiety is common as are problems with executive functioning, including inattention, distractibility, hyperactivity, and impulsivity. Maladaptive behaviors include frequent outbursts / temper tantrums, attention-seeking behaviors, opposition, aggression, and self-injurious behaviors including self-hitting, self-biting, skin picking, inserting foreign objects into body orifices (polyembolokoilamania), and yanking fingernails and/or toenails (onychotillomania). Among the stereotypic behaviors described, the spasmodic upper-body squeeze or "self-hug" seems to be highly associated with SMS. An underlying developmental asynchrony, specifically emotional maturity delayed beyond intellectual functioning, may also contribute to maladaptive behaviors in people with SMS. [from GeneReviews]

MedGen UID:
162881
Concept ID:
C0795864
Disease or Syndrome
10.

Charcot-Marie-Tooth disease, type IA

For a general phenotypic description and a discussion of genetic heterogeneity of Charcot-Marie-Tooth disease type 1, see CMT1B (118200). CMT1A is the most common form of CMT. The average age of onset of clinical symptoms is 12.2 +/- 7.3 years. Slow nerve conduction velocity (NCV) less than 38 m/s is highly diagnostic and is a 100% penetrant phenotype independent of age (Lupski et al., 1991, 1992). [from OMIM]

MedGen UID:
75727
Concept ID:
C0270911
Disease or Syndrome
11.

Peroxisome biogenesis disorder 1A (Zellweger)

Zellweger spectrum disorder (ZSD) is a phenotypic continuum ranging from severe to mild. While individual phenotypes (e.g., Zellweger syndrome [ZS], neonatal adrenoleukodystrophy [NALD], and infantile Refsum disease [IRD]) were described in the past before the biochemical and molecular bases of this spectrum were fully determined, the term "ZSD" is now used to refer to all individuals with a PEX gene defect regardless of phenotype. Individuals with ZSD usually come to clinical attention in the newborn period or later in childhood. Affected newborns are hypotonic and feed poorly. They have distinctive facies, congenital malformations (neuronal migration defects associated with neonatal-onset seizures, renal cysts, and bony stippling [chondrodysplasia punctata] of the patella[e] and other long bones), and liver disease that can be severe. Infants with severe ZSD are significantly impaired and typically die during the first year of life, usually having made no developmental progress. Individuals with intermediate/milder ZSD do not have congenital malformations, but rather progressive peroxisome dysfunction variably manifest as sensory loss (secondary to retinal dystrophy and sensorineural hearing loss); neurologic involvement (ataxia, polyneuropathy, and leukodystrophy); liver dysfunction; adrenal insufficiency; and renal oxalate stones. While hypotonia and developmental delays are typical, intellect can be normal. Some have osteopenia; almost all have ameleogenesis imperfecta in the secondary teeth. [from GeneReviews]

MedGen UID:
1648474
Concept ID:
C4721541
Disease or Syndrome
12.

Ataxia-oculomotor apraxia type 1

Ataxia with oculomotor apraxia type 1 (AOA1) is characterized by childhood onset of slowly progressive cerebellar ataxia, followed by oculomotor apraxia and a severe primary motor peripheral axonal motor neuropathy. The first manifestation is progressive gait imbalance (mean age of onset: 4.3 years; range: 2-10 years), followed by dysarthria, then upper-limb dysmetria with mild intention tremor. Oculomotor apraxia, usually noticed a few years after the onset of ataxia, progresses to external ophthalmoplegia. All affected individuals have generalized areflexia followed by a peripheral neuropathy and quadriplegia with loss of ambulation about seven to ten years after onset. Hands and feet are short and atrophic. Chorea and upper-limb dystonia are common. Intellect remains normal in some individuals; in others, different degrees of cognitive impairment have been observed. [from GeneReviews]

MedGen UID:
395301
Concept ID:
C1859598
Disease or Syndrome
13.

Fukuyama congenital muscular dystrophy

Fukuyama congenital muscular dystrophy (FCMD) is characterized by hypotonia, symmetric generalized muscle weakness, and CNS migration disturbances that result in changes consistent with cobblestone lissencephaly with cerebral and cerebellar cortical dysplasia. Mild, typical, and severe phenotypes are recognized. Onset typically occurs in early infancy with poor suck, weak cry, and floppiness. Affected individuals have contractures of the hips, knees, and interphalangeal joints. Later features include myopathic facial appearance, pseudohypertrophy of the calves and forearms, motor and speech delays, intellectual disability, seizures, ophthalmologic abnormalities including visual impairment and retinal dysplasia, and progressive cardiac involvement after age ten years. Swallowing disturbance occurs in individuals with severe FCMD and in individuals older than age ten years, leading to recurrent aspiration pneumonia and death. [from GeneReviews]

MedGen UID:
140820
Concept ID:
C0410174
Disease or Syndrome
14.

Charcot-Marie-Tooth disease, type 2A2A

Charcot-Marie-Tooth hereditary neuropathy type 2A (CMT2A) is a classic axonal peripheral sensorimotor neuropathy characterized by earlier and more severe involvement of the lower extremities than the upper extremities, distal upper-extremity involvement as the neuropathy progresses, more prominent motor deficits than sensory deficits, and normal (>42 m/s) or only slightly decreased nerve conduction velocities (NCVs). Postural tremor is common. Most affected individuals develop symptoms in the first or second decade. It has recently been suggested that CMT2A represents more than 90% of the severe dominant CMT2 cases. However, milder late-onset cases and unusual presentations have also been described. [from GeneReviews]

MedGen UID:
1648317
Concept ID:
C4721887
Disease or Syndrome
15.

Ataxia with vitamin E deficiency

Ataxia with vitamin E deficiency (AVED) generally manifests in late childhood or early teens between ages five and 15 years. The first symptoms include progressive ataxia, clumsiness of the hands, loss of proprioception, and areflexia. Other features often observed are dysdiadochokinesia, dysarthria, positive Romberg sign, head titubation, decreased visual acuity, and positive Babinski sign. The phenotype and disease severity vary widely among families with different pathogenic variants; age of onset and disease course are more uniform within a given family, but symptoms and disease severity can vary even among sibs. [from GeneReviews]

MedGen UID:
341248
Concept ID:
C1848533
Disease or Syndrome
16.

Charcot-Marie-Tooth disease type 2C

The TRPV4-associated disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within and between both groups is considerable. Bilateral progressive sensorineural hearing loss (SNHL) can occur in both. The three neuromuscular disorders (mildest to most severe): Charcot-Marie-Tooth disease type 2C (CMT2C). Scapuloperoneal spinal muscular atrophy (SPSMA). Congenital distal spinal muscular atrophy (CDSMA). The neuromuscular disorders are characterized by a progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures. The six skeletal dysplasias: Mildest: Familial digital arthropathy-brachydactyly. Intermediate: Autosomal dominant brachyolmia. Spondylometaphyseal dysplasia, Kozlowski type. Spondyloepiphyseal dysplasia, Maroteaux type. Most severe: Parastremmatic dysplasia. Metatropic dysplasia. The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the TRPV4-associated disorders life span is normal; in the most severe it is shortened. [from GeneReviews]

MedGen UID:
342947
Concept ID:
C1853710
Disease or Syndrome
17.

Charcot-Marie-Tooth disease, type 4A

GDAP1-related hereditary motor and sensory neuropathy (GDAP1-HMSN) is a peripheral neuropathy (also known as a subtype of Charcot-Marie-Tooth disease) that typically affects the lower extremities earlier and more severely than the upper extremities. As the neuropathy progresses, the distal upper extremities also become severely affected. Proximal muscles can also become weak. Age at onset ranges from infancy to early childhood. In most cases, disease progression causes disabilities within the first or second decade of life. At the end of the second decade, most individuals are wheelchair bound. Disease progression varies considerably even within the same family. The neuropathy can be either of the demyelinating type with reduced nerve conduction velocities or the axonal type with normal nerve conduction velocities. Vocal cord paresis is common. Intelligence is normal. Life expectancy is usually normal, but on occasion may be reduced because of secondary complications. [from GeneReviews]

MedGen UID:
347821
Concept ID:
C1859198
Disease or Syndrome
18.

Lowe syndrome

Lowe syndrome (oculocerebrorenal syndrome) is characterized by involvement of the eyes, central nervous system, and kidneys. Dense congenital cataracts are found in all affected boys and infantile glaucoma in approximately 50%. All boys have impaired vision; corrected acuity is rarely better than 20/100. Generalized hypotonia is noted at birth and is of central (brain) origin. Deep tendon reflexes are usually absent. Hypotonia may slowly improve with age, but normal motor tone and strength are never achieved. Motor milestones are delayed. Almost all affected males have some degree of intellectual disability; 10%-25% function in the low-normal or borderline range, approximately 25% in the mild-to-moderate range, and 50%-65% in the severe-to-profound range of intellectual disability. Affected males have varying degrees of proximal renal tubular dysfunction of the Fanconi type, including low molecular-weight (LMW) proteinuria, aminoaciduria, bicarbonate wasting and renal tubular acidosis, phosphaturia with hypophosphatemia and renal rickets, hypercalciuria, sodium and potassium wasting, and polyuria. The features of symptomatic Fanconi syndrome do not usually become manifest until after the first few months of life, except for LMW proteinuria. Glomerulosclerosis associated with chronic tubular injury usually results in slowly progressive chronic renal failure and end-stage renal disease between the second and fourth decades of life. [from GeneReviews]

MedGen UID:
18145
Concept ID:
C0028860
Disease or Syndrome
19.

Infantile neuroaxonal dystrophy

PLA2G6-associated neurodegeneration (PLAN) comprises a continuum of three phenotypes with overlapping clinical and radiologic features: Infantile neuroaxonal dystrophy (INAD). Atypical neuroaxonal dystrophy (atypical NAD). PLA2G6-related dystonia-parkinsonism. INAD usually begins between ages six months and three years with psychomotor regression or delay, hypotonia, and progressive spastic tetraparesis. Many affected children never learn to walk or lose the ability shortly after attaining it. Strabismus, nystagmus, and optic atrophy are common. Disease progression is rapid, resulting in severe spasticity, progressive cognitive decline, and visual impairment. Many affected children do not survive beyond their first decade. Atypical NAD shows more phenotypic variability than INAD. In general, onset is in early childhood but can be as late as the end of the second decade. The presenting signs may be gait instability, ataxia, or speech delay and autistic features, which are sometimes the only evidence of disease for a year or more. Strabismus, nystagmus, and optic atrophy are common. Neuropsychiatric disturbances including impulsivity, poor attention span, hyperactivity, and emotional lability are also common. The course is fairly stable during early childhood and resembles static encephalopathy but is followed by neurologic deterioration between ages seven and 12 years. PLA2G6-related dystonia-parkinsonism has a variable age of onset, but most individuals present in early adulthood with gait disturbance or neuropsychiatric changes. Affected individuals consistently develop dystonia and parkinsonism (which may be accompanied by rapid cognitive decline) in their late teens to early twenties. Dystonia is most common in the hands and feet but may be more generalized. The most common features of parkinsonism in these individuals are bradykinesia, resting tremor, rigidity, and postural instability. [from GeneReviews]

MedGen UID:
82852
Concept ID:
C0270724
Disease or Syndrome
20.

Charcot-Marie-Tooth disease, type 4J

Charcot-Marie-Tooth neuropathy type 4J (CMT4J) is a peripheral neuropathy characterized by childhood onset (manifest as clumsy gait) with accelerated limb weakness and muscle atrophy during the teen or adult years that is typically asymmetric and can involve both distal and proximal limb muscles. Although sensory symptoms are minimal, examination may reveal decreased response to touch, pin prick, or vibration distally. Bulbar and cranial nerve functions are often spared; intellect is normal. [from GeneReviews]

MedGen UID:
370808
Concept ID:
C1970011
Disease or Syndrome
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