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Environ Health Perspect. 2006 July; 114(7): 1119–1125. Published online 2006 April 6. doi: 10.1289/ehp.8483. | PMCID: PMC1513329 |
Copyright This is an Open Access article: verbatim copying and redistribution of
this article are permitted in all media for any purpose, provided this
notice is preserved along with the article's original DOI Research Children's Health The CHARGE Study: An Epidemiologic Investigation of Genetic and Environmental
Factors Contributing to Autism Irva Hertz-Picciotto,1,2 Lisa A. Croen,3 Robin Hansen,2,4 Carrie R. Jones,1,2 Judy van de Water,2,5 and Isaac N. Pessah2,6 1 Division of Epidemiology, Department of Public Health Sciences, School of Medicine and 2 Medical Investigations of Neurodevelopmental Disorders (MIND) Institute, University of California–Davis, Davis, California, USA 3 Division of Research, Kaiser Foundation Research Institute, Kaiser Permanente, Oakland, California, USA 4 Department of Pediatrics and 5 Department of Rheumatology/Allergy and Clinical Immunology, School of Medicine and 6 Department of Molecular Biosciences, School of Veterinary Medicine, University of California–Davis, Davis, California, USA Received July 8, 2005; Accepted April 6, 2006. Causes and contributing factors for autism are poorly understood. Evidence
suggests that prevalence is rising, but the extent to which diagnostic
changes and improvements in ascertainment contribute to this increase
is unclear. Both genetic and environmental factors are likely to
contribute etiologically. Evidence from twin, family, and genetic studies
supports a role for an inherited predisposition to the development
of autism. Nonetheless, clinical, neuroanatomic, neurophysiologic, and
epidemiologic studies suggest that gene penetrance and expression may
be influenced, in some cases strongly, by the prenatal and early postnatal
environmental milieu. Sporadic studies link autism to xenobiotic
chemicals and/or viruses, but few methodologically rigorous investigations
have been undertaken. In light of major gaps in understanding of
autism, a large case–control investigation of underlying environmental
and genetic causes for autism and triggers of regression has
been launched. The CHARGE (Childhood Autism Risks from Genetics and
Environment) study will address a wide spectrum of chemical and biologic
exposures, susceptibility factors, and their interactions. Phenotypic
variation among children with autism will be explored, as will similarities
and differences with developmental delay. The CHARGE study infrastructure
includes detailed developmental assessments, medical information, questionnaire
data, and biologic specimens. The CHARGE study
is linked to University of California–Davis Center for Children’s
Environmental Health laboratories in immunology, xenobiotic
measurement, cell signaling, genomics, and proteomics. The goals, study
design, and data collection protocols are described, as well as preliminary
demographic data on study participants and on diagnoses of those
recruited through the California Department of Developmental Services
Regional Center System. Keywords: autism, autistic spectrum disorder, developmental delay, environment, genetics, mental retardation, pervasive developmental disorder Autism is a serious neurodevelopmental disorder characterized by impairments
in social interaction, abnormalities in verbal and nonverbal communication, and
restricted, stereotyped interests and behaviors ( American Psychiatric Association 1994). Although a large proportion of individuals with autism manifest abnormal
development from birth, a subset of at least 20–30% experience
a regression with onset between 18 and 24 months of age
after a period of apparently normal development ( Lainhart et al. 2002). Autistic disorder is the most severe form of autism spectrum disorders (ASDs), which
include Asperger’s syndrome and pervasive developmental
disorders (PDDs) not otherwise specified. Approximately 70% of
individuals with autistic disorder have some degree of mental
retardation, and about half are nonverbal or have very impaired speech. Seizures
are present by adolescence in about 30% of children
with ASD, and between 5 and 10% of autism cases occur in
association with other serious medical conditions such as fragile X, tuberous
sclerosis, and Angelman’s syndrome ( Fombonne 2003). Gastrointestinal problems and sleep disturbances are also thought to
be common comorbidities; however, population-based prevalence estimates
for these conditions are currently lacking. Males are four times as
likely as females to have autism, but this ratio approaches one among
individuals with severe cognitive impairment ( Gillberg and Wing 1999). Most individuals with autism cannot live independently as adults ( Rapin 1999). Over the past 20 years, the prevalence of autism has reportedly risen, with
much public debate surrounding the reasons for this increase. Early
reports estimated prevalence at 4–5 per 10,000 births ( Fombonne 1999). Data published in the last few years suggest that autistic disorder
occurs in at least 1–2 per 1,000 births, and the prevalence of
the broader autism spectrum may be as high as 4–6 per 1,000 ( Chakrabarti and Fombonne 2005; Yeargin-Allsopp et al. 2003). The causes and contributing factors for autism are poorly understood. The
number of children with a diagnosis of autism as determined by the
California Department of Developmental Services (DDS) has been rising
continuously for over a decade ( California DDS 2003). Although diagnostic changes and improvements in detection probably contribute
to this increase ( Chakrabarti and Fombonne 2005; Croen et al. 2002), a true rise in incidence may also be occurring ( Blaxill et al. 2003). Evidence for genetic causes is strong, yet concordance in monozygotic
twins suggests that a minimum of 40% of autism cases are likely
to have an environmental cause. No single gene has yet been specifically
linked to autism with replicability, but the disorder is believed
to be polygenic. A few specific environmental factors are associated
with autistic behaviors—prenatal exposures to thalidomide ( Rodier and Hyman 1998), valproic acid ( Christianson et al. 1994), or rubella ( Chess et al. 1978)—but these are likely to play a negligible role, if any, in incident
cases in Western countries over the last decade or so. Results from twin and family studies suggest a strong genetic contribution
to the etiology of autism. Beginning with the classic work by Folstein and Rutter (1977), data from three population-based twin studies have demonstrated a higher
concordance rate among monozygotic compared with dizygotic twins ( Cook 1998). Strong familial aggregation of autism has also been demonstrated. The
sibling recurrence risk (i.e., the probability of developing autism
given a person’s sibling is autistic) has been estimated at 2–14% ( Jorde et al. 1990; Ritvo et al. 1989; Smalley et al. 1988), a 10- to 20-fold increase over the general population prevalence. A
family history of social deficits, language abnormalities, and psychiatric
disorders has also been observed in case–control and clinic-based
studies ( Folstein and Rutter 1988; Piven and Palmer 1999). Linkage, association, and cytogenetic studies have been conducted. Numerous
candidate genes for autism have been suggested based on their functional
role, location within candidate chromosome regions, and positive
associations with the disease ( Korvatska et al. 2002). Replication of findings has been elusive ( Wassink et al. 2004), probably because of the polygenic etiology, heterogeneity of the phenotype, and, assuming
a role for gene–environment interaction, variation
in exposure distributions across populations. An epigenetic
mechanism related to Rett syndrome is also plausible ( Samaco et al. 2005). Genomewide scans to identify regions marked by differing gene expression
are considered key at this stage. One such scan hints at the possible
genetic basis for the well-established sex ratio of four males to
one female ( Stone et al. 2004). A comparison of tuberous sclerosis patients with and without autism
demonstrated 31 genes for which expression differed ( Tang et al. 2004); because both groups shared the tuberous sclerosis diagnosis, the differentially
expressed genes may be related to autism, although they are
not necessarily causal. It is plausible that a substantial proportion
of autism cases could be due to multiple genes interacting with one
or more environmental factors ( Cederlund and Gillberg 2004; Glasson et al. 2004). Neuroanatomic and epidemiologic investigations support a prenatal or early
postnatal origin. Courchesne et al. (1988) observed cerebellar abnormalities consistent with abnormalities in cell
migration between the third and fifth month of gestation. Magnetic resonance
imaging studies point to migrational errors that result in disorganized
columns of the cerebral cortex ( Casanova et al. 2002). Anthropometric indicators, such as brain size and growth trajectory ( Herbert 2005), suggest overall cerebral volume to be larger in mid-childhood, with
growth that accelerates early and then decelerates, although this phenotype
may apply to only a subset of cases. Neuroimaging studies indicate
involvement of specific brain regions, including the amygdala, hippocampus, and
corpus callosum ( Brambilla et al. 2003; Schumann et al. 2004). Studies of environmental factors also relate to the prenatal origin of
autism. Chess et al. (1978) reported that, within a cohort of about 250 children with congenital rubella, 7% were
later diagnosed with autism. A case–control
study using both maternal reports and medical records of illnesses
during pregnancy showed relative risks of 4.1 for influenza and 3.3 for
rubella ( Deykin and MacMahon 1979). Daily maternal smoking during early pregnancy was reported to be linked
to autism in a large case–control epidemiology study (odds
ratio = 1.4; 95% confidence interval, 1.1–1.8) ( Hultman et al. 2002), although in our estimation, these analyses may have inappropriately
adjusted for potentially intermediate variables. The link between autism
and early in utero exposure to thalidomide places the timing of the insult coincident with
neural tube closure in the fourth to fifth week of gestation ( Rodier and Hyman 1998). Case reports of autism in children gestationally exposed to valproic
acid ( Christianson et al. 1994; Rodier et al. 1997; Williams et al. 2001) are concordant with experimental animal studies ( Ingram et al. 2000). A small number of cases of autism after maternal infection with cytomegalovirus ( Markowitz 1983; Stubbs et al. 1984), measles or mumps ( Deykin and MacMahon 1979), or herpes ( Ritvo et al. 1990) as well as one case each of syphilis and toxoplasmosis ( Rutter and Bartak 1971) have been reported. Taken together, the literature suggests a prominent genetic component involving
multiple gene loci, but also a likely contribution from both
chemical and microbial agents. It is likely that further understanding
will require consideration of critical windows during gestation and possibly
early infancy, as well as interactions between genetic or epigenetic
predisposition and environmental factors. In light of the enormous gap in our understanding of the causes of both
autism and developmental delay (DD), a large epidemiologic study was
initiated in 2002. The Childhood Autism Risk from Genetics and the Environment (CHARGE) study
is addressing a wide spectrum of environmental
exposures, endogenous susceptibility factors, and the interplay between
these two ( CHARGE 2006). To structure the search for etiologic factors, we are beginning with known
neurodevelopmental toxicants and hints from the immunologic evidence. Additionally, physiologic differences that might provide clues about
susceptibility and mechanisms are being examined through characterization
of metabolic, immunologic, and gene expression profiles, as well
as genetic polymorphisms. shows five broad classes of exposures of interest: pesticides, metals, persistent
pollutants with known or suspected neurodevelopmental or immunologic
toxicity, medications and other treatments, and infections. Exposures
from both the prenatal and early childhood periods are being
investigated, with data primarily from three sources: a) extensive interviews with parents; b) laboratory analysis of xenobiotics in blood, urine, and hair specimens; and c) prenatal, labor and delivery, neonatal, and pediatric medical records. CHARGE study specimens are analyzed for immunologic, cell activation, xenobiotic, lipomic, and
genomic markers in laboratories of the University
of California–Davis (UC Davis) Center for Children’s
Environmental Health (CCEH) ( Table 1). Metals have been assayed in blood samples from > 300 index children, with
a focus on mercury, lead, arsenic, cadmium, and manganese. Immunologic
profiles are being characterized, including cellular responses
to bacterial antigenic stimulation, general immunoglobulins, and production
of chemokines and cytokines. Already, preliminary results have
demonstrated significant differences between children with autism and
children from the general population in leptin concentrations (Ashwood
P, Kwong C, Hansen R, Hertz-Picciotto I, Croen L, Krakowiak P, et al., unpublished
observations). | Table 1Biospecimen use for susceptibility and exposure markers.a |
A detailed lipomics screen is being applied to the plasma from the first
few hundred children. Affymetrix GeneChip microarrays (Affymetrix, Santa
Clara, CA) have been generated from an initial sample of children
and analyzed to determine whether a genomic fingerprint for autism can
be identified; results will be replicated on a further set. Brominated
flame retardants are being measured in 80–100 children, and
metabolites of pyrethroid pesticides will be evaluated in urine specimens. The CHARGE study also benefits from CCEH hypothesis-driven experimental
research on animal models for autism in mice and non-human primates and in vitro investigations of immune and neurogenic cells aimed at uncovering molecular
mechanisms. A common database coordinates the archival, retrieval, and
analysis of samples, and the combination of population-based epidemiology
with state-of-the-art molecular and cellular methods provides
a powerful basis for interdisciplinary collaborative research. With
future funding, the CHARGE study will undertake targeted evaluation of
candidate genes, such as those responsible for regulation of xenobiotic
metabolizing enzymes, cell signaling in both neurons and immune cells, and
immune cell activation. Currently, the study is also characterizing phenotypic variation within
the autism case group and relating these phenotypes to the exposures
and physiologic profiles of interest. For example, we have begun to compare
immune function in regressive autism (children who have lost previously
acquired social or language skills) with those with early onset (children
who never acquired those skills). Other phenotypic subtypes
include, for example, high versus low cognitive function and presence
versus absence of gastrointestinal symptoms, macrocephaly, and sleep
disturbances. Design and Subject Recruitment The CHARGE study appears to be the first large-scale, population-based
epidemiologic investigation focusing primarily on environmental exposures, as
well as their interactions with genes, as underlying causes for
autism. It uses the case–control design, which provides the
most efficient sampling for studies of conditions that are rare or of
multifactorial etiology. A further advantage is the focus on a specific
outcome, which translates into close scrutiny of diagnoses and rigorous
measurement for the most highly suspect risk factors. The CHARGE study population is sampled from three strata: children with
autism (full-syndrome autism, not those with a “spectrum disorder”), children
with DD but not autism, and children selected
from the general population without regard for developmental characteristics. All
participating children (currently > 500, with an ultimate
goal of between 1,000 and 2,000) meet the following criteria: a) between the ages of 24 and 60 months, b) living with at least one biologic parent, c) having a parent who speaks English or Spanish, d) born in California, and e) residing in the catchment areas of a specified list of regional centers (RCs) in
California. No further exclusions are made based on genetics
or family phenotype. Children with autism and children with mental retardation or DD are identified
through RCs that contract with the California DDS to determine
eligibility and coordinate services for persons with developmental disabilities. Eligibility
in the DDS/RC system does not depend on citizenship
or financial status. Thus, the system is widely used across socioeconomic
levels and racial/ethnic groups. Referrals are from pediatricians, other
clinical providers, schools, friends, and family members. The DDS/RC system is mandated to provide services for individuals with
autism, as well as for those with other PDDs who have mental retardation (IQ < 70) or
are substantially handicapped. One investigation estimated
that 75–80% of the total population of children
with an autism diagnosis in the state were enrolled in the DDS system ( Croen et al. 2002). Among preschoolers, the figure may be lower, with fewer mild cases. Additionally, this
proportion may decline with recent changes to eligibility
requirements that emphasize the extent of disability. Children
with Asperger’s or PDDs not otherwise specified without mental
retardation are not generally eligible for DDS/RC services and therefore
are not actively recruited into the CHARGE study. Potential cases of autism for the CHARGE study are defined as those who
are eligible for services based on a DDS/RC diagnosis of autism. Families
with a child who has received a diagnosis but is not in the RC system
are also invited. The second study group, children with DD, is likewise
drawn from those determined eligible for services based on a diagnosis
of mental retardation or DD. Children 0–3 years of age
who are at risk for DD or disability can receive RC services under the
Early Start program and are also eligible to be in the second CHARGE
study group. The DD children must meet the above inclusion criteria but
are not age- or sex-matched to the children with autism. Staff of the RCs contact parents of children with autism or DD, provide
them an information packet, and explain how they can participate in the
CHARGE study. For those who are interested, permission is obtained
for the study staff to telephone the families and schedule appointments. The
children then undergo further testing (see below) to confirm their
diagnoses. The third group consists of children from the general population identified
from state birth files. Throughout the study, we generate random
samples of children meeting the study eligibility criteria according to
their birth certificate information. This group is frequency-matched
to the age, sex, and broad residential RC catchment area distribution
of the autism cases. Using names and social security numbers in birth
certificate files, study personnel attempt to locate current contact
information and then initiate a recruitment effort. Data collection protocols Participation involves assessments of cognitive and social development, a
medical examination, biologic specimen collection, and completion of
an exposure interview and several self-administered questionnaires. Other
components include maternal and child medical records review and
abstractions. Table 2 summarizes the protocols, other than specimen and medical record collection. | Table 2Data collection protocol for CHARGE study: three developmental groups of
children. |
CHARGE study children are assessed at the UC Davis Medical Investigations
of Neurodevelopmental Disorders (MIND) Institute; a small percentage
were seen at the UCLA Neuropsychiatric Institute. Standardized clinical
assessments are administered to confirm the child’s diagnostic
group. Autism cases are assessed using diagnostic tools widely accepted
for research: the Autism Diagnostic Interview–Revised (ADI-R) ( Le Couteur et al. 2003; Lord et al. 1994, 1997) and the Autism Diagnostic Observation Schedules (ADOS) ( Lord et al. 2000, 2003). The ADI-R is a standardized, semistructured 2- to 3-hr interview with
caregivers of individuals with autism or PDDs. It yields summary scores
in the following domains: qualitative impairments in reciprocal social
interaction, communication, and repetitive behaviors and stereotyped
patterns. Published values for interrater reliability are good, with
kappa values ranging between 0.62 and 0.89 ( Lord et al. 2003). The ADOS is a semistructured, standardized assessment of children in which
the examiner observes the social interaction, communication, play, and
imaginative use of materials. The ADOS requires approximately 30 min
and includes four possible modules; the examiner chooses the one that
best matches the expressive language level of the individual child
to prevent a relatively low level of language ability from impeding accurate
measurement. Diagnostic algorithms are available for autism or
for broader ASDs/PDDs ( Lord et al. 2003). The ADOS provides measures in the following domains: reciprocal social
interactions, communication, stereotyped behaviors and restricted interests, and
play. All kappa values for interrater reliability exceeded 0.60. All
CHARGE clinical assessment personnel are trained and have
attained research reliability on the ADI-R and the ADOS. Cognitive function is measured in all children (those with autism or DD
and the general population controls) using the Mullen Scales of Early
Learning (MSEL) ( Mullen 1995). The MSEL is a standardized developmental test of children 3–60 months
of age. The MSEL consists of five subscales: gross motor, fine
motor, visual reception, expressive language, and receptive language. The
MSEL allows for separate standard verbal and nonverbal summary
scores to be constructed. The five MSEL scales demonstrate satisfactory
internal consistency (0.75–0.83), internal reliability (0.91), test–retest
reliability (0.71–0.96), and inter-rater
reliability (0.91–0.99) ( Mullen 1995). Adaptive function is assessed by parental interview using the Vineland
Adaptive Behavior Scales (VABS) ( Sparrow et al. 1984). The VABS is the most widely used instrument for assessment of adaptive
behavior across the lifespan and covers the domains of socialization (interpersonal
relationships, play and leisure time, and coping skills), daily
living skills (personal, domestic, and community skills), motor
skills (gross and fine motor), and communication (receptive, expressive, and
written communication), with developmentally ordered skills
for each area. The scale is norm referenced, and recent supplemental
norms have been published for individuals with autism ( Carter et al. 1998). Psychometric properties of the instrument include excellent internal
consistency (0.90–0.98), test–retest reliability ( r = 0.78–0.92), and interrater reliability ( r = 0.87 for young children). Before the clinic visit, the parent is mailed the consent form to review
and several self-administered forms to complete, including the Aberrant
Behavior Checklist, a standardized checklist constructed to rate inappropriate
and maladaptive behaviors in developmentally delayed individuals ( Aman and Singh 1994); Multiple Language Questionnaire to determine what languages are used
at home; Child Development Questionnaire (CDQ), consisting of 31 questions
regarding acquisition and loss of language and skills, a subset
of the Early Development Questionnaire ( Ozonoff et al. 2005) to examine loss of developmental skills; and structured questionnaires
about gastrointestinal symptoms and sleep habits of the child (developed de novo). Parents are also sent a list of autoimmune diseases with a description
of each, so that they can prepare to respond to questions about family
history of these disorders during the clinic visit. All instruments
and forms are administered in either English or Spanish, depending on
the language in which the parent or child feels most comfortable. The
CHARGE study employs trained bilingual/bicultural staff for every phase
of the study. At the clinic, the psychometric assessments are administered, a family
medical history with an emphasis on mental health and autoimmune disorders
is taken, and a family characteristics questionnaire is used to document
developmental and other aspects of the broader phenotype in immediate
family members. Physical and neurologic exams are completed; dysmorphology
and growth or neurologic abnormalities are recorded. Finally, blood
specimens are collected at the end of the clinic visit. The
parent is asked to bring in urine specimens for the child and immediate
family members. For families of children recruited from the nonautistic groups, the protocol
is essentially identical, except that the ADI-R and ADOS are not
routinely administered. The Social Communication Questionnaire (SCQ) was
developed from the ADI-R to screen children for evidence of features
of ASDs. If the score on the SCQ is above 15, the ADI-R and ADOS are
administered on a second visit. Final autism case status is defined as meeting criteria on the communication, social, and
repetitive behavior domains of the ADI-R and scoring
at or above the total cutoff for autistic disorder on the ADOS module 1 or 2. Analyses
will be conducted for cases meeting criteria for autistic
disorder, as well as for a broader definition of impairment encompassing
ASDs. A similar approach will be used for mental retardation/DD: Children
obtaining an MSEL composite score of < 69 and a VABS
composite score of < 70 will be classified as meeting strict criteria
for DD. Separate from the clinic visit, we conduct a telephone interview with the
primary caregiver regarding periconceptional, prenatal, and early childhood
exposures and experiences. The interview of approximately 1 hr 40 min
covers the following areas: demographics; mother’s medical
history; mother’s reproductive and pregnancy history; index
pregnancy, including use of reproductive technology for conception; maternal
illnesses and medications during index pregnancy; metals, diet, and
household product use; child’s illnesses and medications; maternal
lifestyle information; residential history; and occupational
history of the mother and father. An index time period is defined
as 3 months before pregnancy to the end of pregnancy or, if the child
was breast-fed, until weaning. Information on medications, metals, household
products, and the occupational and residential histories focuses
on this index period. Blood and urine specimens are collected from the index child, parents, and
siblings. For any family member from whom blood is not obtained, an
attempt is made to collect buccal swabs for DNA extraction. Hair specimens
are collected from the index child and from the mother if her hair
is long enough to potentially contain information about exposures
during the pregnancy or lactation period. If the parent saved locks from
the child’s first haircut, we request a few strands. Additionally, neonatal
blood spots from the index child will be obtained from
the newborn screening specimen archive maintained by the Genetic Disease
Branch of the California Department of Health Services (Richmond, CA). Medical records are procured and abstracted for information about procedures, medications
and other treatments, and conditions at birth of the
index child. Obstetric/gynecology/prenatal clinic and mental health
provider records are obtained for the mother. Similarly, labor and delivery, neonatal, pediatric, and specialty clinic medical records are procured. Dental
records are sought for the confirmation of mercury amalgams. The study complies with all applicable requirements regarding human subjects
and is approved by the institutional review boards for the State
of California and the University of California. Informed consent is obtained
before collection of any data. Preliminary data on participants and their diagnoses Full recruitment into the CHARGE study began in late 2003. More than 520 children
and their families have enrolled in the CHARGE study at the
time of this writing. This includes > 360 recruited because of an
RC diagnosis of autism, > 50 with an RC diagnosis of DD (recruitment
began later for this group), and > 120 from the general population. By
the end of the first 5 years of funding, we expect to have a total
of approximately 650–700 children enrolled. Among contacted
families of children with autism, 20% were ineligible, 22% refused, and 58% agreed to participate. Among general population
families with whom we made contact, 22% were ineligible, 41% refused, and 36% agreed to join the study. Among children with a diagnosis of autism recruited from RCs, after assessment
by CHARGE study personnel, 64% met criteria on both the
ADOS and ADI-R. Among those 3 or 4 years of age who are California DDS
eligible based on their diagnosis of autism, 64% meet criteria
on both instruments, another 9% meet criteria on the ADOS
alone, and a further 14% on the ADI-R alone, for a total of 87%. Additionally, among the remainder, 6% meet criteria
for ASD based on both examinations (scores at least 7 on ADOS module 1 or
at least 8 on ADOS module 2, and meets cutoff in ADI-R for section
D and either section A or B, and falls within 2 points on the other
section of A or B); another 5% meet criteria for ASD based on
either ADI-R alone or ADOS alone. Fewer than 2% would not be classified
as being on the spectrum. Among those recruited through RCs with a diagnosis of DD, the percentage
that showed delay in both adaptive and cognitive domains was 64%, with
another 6% that met the cutoff on at least one of the
tests. Among those who entered the study with a diagnosis of DD, 3% met
criteria for autism and another 8% met criteria for
ASD. Another phenotypic distinction we are investigating is early-onset versus
regressive autism, as defined by the language and social regression
questions on the ADI-R and the CDQ. Using a broad definition of regression
that includes loss of previously attained language and/or social
skills ( Ozonoff et al. 2005), close to 50% of the CHARGE children with a confirmed diagnosis
of autism had regression. Finally, Table 3 provides basic demographic information about the CHARGE study sample, based
on data from the birth certificate. This table also provides comparison
information about the pool of births from which we recruit the
general population controls. Compared with this pool, mothers who participate
are older, more highly educated, and more likely to have private
health insurance. Participant mothers of general population controls
are also more likely to have been born in the United States. The children
were more likely to be twins. In further work, the autistic and
DD participants will be compared with their respective pools. | Table 3Demographics in CHARGE study (%). |
Community partnership A community advisory council (CAC) was formed early in the development
of this project to maximize participation in the research by parents, clinicians, service
providers, advocacy organizations, and RC and DDS
staff. Parental suggestions regarding the collection of specimens and
information from younger siblings of affected children were incorporated
into the study design. The CAC meets regularly to hear updates on study
progress and provide input. CAC members have given critical advice
on data collection instruments, ways to make the clinical protocol as
child-friendly and special-needs–friendly as possible, and strategies
to enhance recruitment. The CHARGE study is building an infrastructure that will support multiple
investigations of autism and related neurodevelopmental disorders. The
psychometric evaluations and clinical examinations combined with extensive
exposure information and biologic specimens represent rich resources
for research on etiology and phenotypic expression of these disorders
and make possible the comprehensive approach needed to advance
understanding of autism and DD. In our clinical assessments of > 300 children
identified with autism in the California DDS system, we have
confirmed the diagnosis in 87%, suggesting that the large increases
in DDS system clients with autism over the last decade or two
is unlikely to be due to overdiagnosis in younger cohorts. Although several large birth cohort studies recently initiated or in progress
will be able to examine factors that predict autism, the number
of cases of autism in the CHARGE study may be comparable with what is
expected in birth cohorts of 100,000 (i.e., we have enrolled > 360 children
with autism and are continuing recruitment). In contrast with
large cohort studies with dispersed populations, we are able to confirm
diagnoses using standardized instruments administered by a small, well-trained
clinical assessment team. Additionally, in cohort studies
attempting to address a wide range of health and developmental outcomes, the
exposures and factors measured will not necessarily have been
chosen for relevance to autism. The specimen bank is currently being used by several laboratories that
are part of the UC Davis CCEH. In this first stage, xenobiotic and biochemical
profiles of children with autism are being compared with those
of unaffected children, and comparisons are being made between different
autism phenotypes. As distinguishing features emerge, the second
stage will be to determine whether any differences in biomarkers were
present at birth, using the neonatal blood spots where possible. Data
and specimens will be made available to qualified researchers with targeted, worthwhile
hypotheses not being addressed by CCEH and CHARGE investigators. Limitations of this study must be recognized. Much of the information will
be gathered retrospectively. The only biologic specimens prospectively
collected (i.e., before diagnosis) are the newborn blood spots and, for
some children, baby hair locks. Similarly, questionnaires on use
of pesticides and other household products will be retrospective and
hence subject to reporting/recall bias. Thus, the large birth cohort
studies under way or in preparation will complement the CHARGE study by
providing fully prospective data, although they are subject to the limitations
described above. Nevertheless, in the CHARGE study, medical
records will yield prospectively recorded data on treatments, illnesses, and
prescription medications. Other unbiased, relevant sources of
information on xenobiotics include blood measurements that represent cumulative
exposures for persistent compounds and California’s
Pesticide Use Reporting system, which documents commercial pesticide applications
that can be linked to participant residences during critical
time windows. Although sporadic studies have identified specific environmental factors
that have been associated with autism, no previous effort has attempted
to address the broad spectrum of environmental factors that may, in
combination with genetic susceptibility, affect development and severity
of this condition in the population. The CHARGE study is charting
new territory in the investigation of etiologic factors for autism and
DD. The goal of the CHARGE study is to understand causes of autism and
DD, both genetic and environmental, in order to reduce their incidence
in the future. The design combines a large population-based sample
of children with different patterns of development; standardized diagnostic
assessments of autism, cognitive development, and adaptive behavior
by trained assessors; medical and neurologic examinations; detailed
reviews of medical records; and an extensive set of questionnaires
describing phenotypic characteristics and environmental exposures from
preconception through early childhood. Currently, it is unique in its
emphasis on environmental factors and its tight linkage with state-of-the-art
laboratories of the UC Davis CCEH that enable us to address biologic
markers of xenobiotic exposures, immunologic responses, and gene
expression. Other features include active community involvement, an
ethnically diverse pool of participants, and inclusion of developmentally
delayed children in addition to general population controls. Finally, the
collaboration by CHARGE study investigators with other population-based
autism epidemiologic efforts currently under way, such as the
national Centers for Autism and Developmental Disabilities Research
and Epidemiology (CADDRE) study, will create valuable opportunities for
replication and perhaps data pooling. - Aman MG, Singh NN. 1994. Aberrant Behavior Checklist—Community. Supplementary Manual. East
Aurora, NY:Slosson Educational Publications.
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