Lisa A. Croen

Genetic Heritability and Shared Environmental Factors Among Twin Pairs With Autism

CONTEXT Autism is considered the most heritable of neurodevelopmental disorders, mainly because of the large difference in concordance rates between monozygotic and dizygotic twins. OBJECTIVE To provide rigorous quantitative estimates of genetic heritability of autism and the effects of shared environment. DESIGN, SETTING, AND PARTICIPANTS Twin pairs with at least 1 twin with an autism spectrum disorder (ASD) born between 1987 and 2004 were identified through the California Department of Developmental Services. MAIN OUTCOME MEASURES Structured diagnostic assessments (Autism Diagnostic Interview-Revised and Autism Diagnostic Observation Schedule) were completed on 192 twin pairs. Concordance rates were calculated and parametric models were fitted for 2 definitions, 1 narrow (strict autism) and 1 broad (ASD). RESULTS For strict autism, probandwise concordance for male twins was 0.58 for 40 monozygotic pairs (95% confidence interval [CI], 0.42-0.74) and 0.21 for 31 dizygotic pairs (95% CI, 0.09-0.43); for female twins, the concordance was 0.60 for 7 monozygotic pairs (95% CI, 0.28-0.90) and 0.27 for 10 dizygotic pairs (95% CI, 0.09-0.69). For ASD, the probandwise concordance for male twins was 0.77 for 45 monozygotic pairs (95% CI, 0.65-0.86) and 0.31 for 45 dizygotic pairs (95% CI, 0.16-0.46); for female twins, the concordance was 0.50 for 9 monozygotic pairs (95% CI, 0.16-0.84) and 0.36 for 13 dizygotic pairs (95% CI, 0.11-0.60). A large proportion of the variance in liability can be explained by shared environmental factors (55%; 95% CI, 9%-81% for autism and 58%; 95% CI, 30%-80% for ASD) in addition to moderate genetic heritability (37%; 95% CI, 8%-84% for autism and 38%; 95% CI, 14%-67% for ASD). CONCLUSION Susceptibility to ASD has moderate genetic heritability and a substantial shared twin environmental component.

The Changing Prevalence of Autism in California

We conducted a population-based study of eight successive California births cohorts to examine the degree to which improvements in detection and changes in diagnosis contribute to the observed increase in autism prevalence. Children born in 1987-1994 who had autism were identified from the statewide agency responsible for coordinating services for individuals with developmental disabilities. To evaluate the role of diagnostic substitution, trends in prevalence of mental retardation without autism were also investigated. A total of 5038 children with full syndrome autism were identified from 4,590,333 California births, a prevalence of 11.0 per 10,000. During the study period, prevalence increased from 5.8 to 14.9 per 10,000, for an absolute change of 9.1 per 10,000. The pattern of increase was not influenced by maternal age, race/ethnicity, education, child gender, or plurality. During the same period, the prevalence of mental retardation without autism decreased from 28.8 to 19.5 per 10,000, for an absolute change of 9.3 per 10,000. These data suggest that improvements in detection and changes in diagnosis account for the observed increase in autism; whether there has also been a true increase in incidence is not known.

Neuropeptides and neurotrophins in neonatal blood of children with autism or mental retardation.

There has been little exploration of major biologic regulators of cerebral development in autism. In archived neonatal blood of children with autistic spectrum disorders (n = 69), mental retardation without autism (n = 60), or cerebral palsy (CP, n = 63) and of control children (n = 54), we used recycling immunoaffinity chromatography to measure the neuropeptides substance P (SP), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase–activating polypeptide (PACAP), calcitonin gene–related peptide (CGRP), and the neurotrophins nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), neurotrophin 3 (NT3), and neurotrophin 4/5 (NT4/5). Neonatal concentrations of VIP, CGRP, BDNF, and NT4/5 were higher (ANOVA, all p values < 0.0001 by Scheffe test for pairwise differences) in children in the autistic spectrum and in those with mental retardation without autism than in control children. In 99% of children with autism and 97% with mental retardation, levels of at least one of these substances exceeded those of all control children. Concentrations were similar in subgroups of the autistic spectrum (core syndrome with or without mental retardation, other autistic spectrum disorders with or without mental retardation) and in the presence or absence of a history of regression. Among children with mental retardation, concentrations did not differ by severity or known cause (n = 11, including 4 with Down syndrome). Concentrations of measured substances were similar in children with CP as compared with control subjects. SP, PACAP, NGF, and NT3 were not different by diagnostic group. No measured analyte distinguished children with autism from children with mental retardation alone. In autism and in a heterogeneous group of disorders of cognitive function, overexpression of certain neuropeptides and neurotrophins was observed in peripheral blood drawn in the first days of life.

Autism spectrum disorders in relation to distribution of hazardous air pollutants in the san francisco bay area.

Objective To explore possible associations between autism spectrum disorders (ASD) and environmental exposures, we linked the California autism surveillance system to estimated hazardous air pollutant (HAP) concentrations compiled by the U.S. Environmental Protection Agency. Methods Subjects included 284 children with ASD and 657 controls, born in 1994 in the San Francisco Bay area. We assigned exposure level by census tract of birth residence for 19 chemicals we identified as potential neurotoxicants, developmental toxicants, and/or endocrine disruptors from the 1996 HAPs database. Because concentrations of many of these were highly correlated, we combined the chemicals into mechanistic and structural groups, calculating summary index scores. We calculated ASD risk in the upper quartiles of these group scores or individual chemical concentrations compared with below the median, adjusting for demographic factors. Results The adjusted odds ratios (AORs) were elevated by 50% in the top quartile of chlorinated solvents and heavy metals [95% confidence intervals (CIs), 1.1–2.1], but not for aromatic solvents. Adjusting for these three groups simultaneously led to decreased risks for the solvents and increased risk for metals (AORs for metals: fourth quartile = 1.7; 95% CI, 1.0–3.0; third quartile = 1.95; 95% CI, 1.2–3.1). The individual compounds that contributed most to these associations included mercury, cadmium, nickel, trichloroethylene, and vinyl chloride. Conclusions Our results suggest a potential association between autism and estimated metal concentrations, and possibly solvents, in ambient air around the birth residence, requiring confirmation and more refined exposure assessment in future studies.

The CHARGE study: an epidemiologic investigation of genetic and environmental factors contributing to autism.

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.

Descriptive Epidemiology of Autism in a California Population: Who Is at Risk?

We investigated the association between selected infant and maternal characteristics and autism risk. Children with autism born in California in 1989-1994 were identified through service agency records and compared with the total population of California live births for selected characteristics recorded on the birth certificate. Multivariate models were used to generate adjusted risk estimates. From a live birth population of more than 3.5 million, 4381 children with autism were identified. Increased risks were observed for males, multiple births, and children born to black mothers. Risk increased as maternal age and maternal education increased. Children born to immigrant mothers had similar or decreased risk compared with California-born mothers. Environmental factors associated with these demographic characteristics may interact with genetic vulnerability to increase the risk of autism.

Sleep problems in children with autism spectrum disorders, developmental delays, and typical development: a population-based study

This study compared parent‐reported sleep characteristics in 2‐ to 5‐year‐old children with autism spectrum disorders (ASD) to children with other developmental delays (DD) and typical development (TD). We included 529 children (303 ASD [167 males], 63 DD [46 males], and 163 TD [134 males]) enrolled in the CHARGE study, an ongoing population‐based case–control study. The mean age of participants was 3.6 years (standard deviation, 0.8 years). ASD diagnosis was confirmed with Autism Diagnostic Interview‐Revised (ADI‐R) and Autism Diagnostic Observation Schedules (ADOS). Cognitive and adaptive functioning was assessed using Mullen Scales of Early Learning (MSEL) and Vineland Adaptive Behavior Scales (VABS), respectively. Demographic, medical and sleep history information were ascertained from California birth records, telephone interview, medical assessments at clinic visit, and parent‐administered questionnaires. Fifty‐three percent of children with ASD had at least one frequent sleep problem, followed by 46% of children with DD, and 32% of the TD group (P < 0.0001). Exploratory factor analyses of sleep history data yielded two factors: sleep onset problems and night waking. Children with ASD had marginally higher sleep onset factor scores and significantly higher night waking factor scores compared with the TD group. Factor scores for children with DD were intermediate between the ASD and TD groups. Cognitive or adaptive development did not predict severity of sleep problems in the ASD group.

Racial and ethnic variations in the prevalence of orofacial clefts in California, 1983-1992.

To investigate variations in the prevalence of oral cleft anomalies according to parental race and ethnicity and maternal country of birth, the authors analyzed a cohort of 2,221,755 live births and fetal deaths delivered between 1983 and 1992 to residents of California. A total of 2,329 cleft lip with or without cleft palate (CL +/- P) cases and 1,475 cleft palate alone (CP) cases were identified by the California Birth Defects Monitoring Program, a population-based registry. Compared to Whites, the prevalence of CL +/- P was lower among African Americans (prevalence ratio (PR) = 0.56, 95% confidence interval (CI) = 0.45-0.69), higher among Native Americans (PR = 1.81, CI = 1.20-2.69), and the same among the Japanese (PR = 1.07, CI = 0.62-1.82) and Chinese (PR = 0.96, CI = 0.71-1.29). The risk of CL +/- P was slightly lower among the offspring of foreign-born Chinese women relative to U.S.-born Chinese women (PR = 0.71, CI = 0.33-1.57), and slightly higher among foreign-born Filipinos relative to their U.S.-born counterparts (PR = 1.37, CI = 0.57-3.53), although confidence intervals around these risk estimates were wide owing to sparse data. For CP, lower prevalences were observed among African Americans (PR = 0.72, CI = 0.58-0.91) and Hispanics (PR = 0.77, CI = 0.67-0.87) than among Whites. The risk of CP was higher among foreign-born Filipinos compared to U.S.-born Filipinos (PR = 1.52, CI = 0.58-4.33), although the confidence interval around this estimate included unity. These prevalence variations may reflect differences in both environmental and genetic factors affecting clefting risk.

A Comparison of Health Care Utilization and Costs of Children With and Without Autism Spectrum Disorders in a Large Group-Model Health Plan

OBJECTIVE. Data on the current costs of medical services for children with autism spectrum disorders are lacking. Our purpose for this study was to compare health care utilization and costs of children with and without autism spectrum disorders in the same health plan. PATIENTS AND METHODS. Participants included all 2- to 18-year-old children with autism spectrum disorders (n = 3053) and a random sample of children without autism spectrum disorders (n = 30529) who were continuously enrolled in the Kaiser Permanente Medical Care Program in northern California between July 1, 2003, and June 30, 2004. Data on health care utilization and costs were derived from health plan administrative databases. MAIN OUTCOME MEASURES. Outcome measures included mean annual utilization and costs of health services per child. RESULTS. Children with autism spectrum disorders had a higher annual mean number of total clinic (5.6 vs 2.8), pediatric (2.3 vs 1.6), and psychiatric (2.2 vs 0.3) outpatient visits. A higher percentage of children with autism spectrum disorders experienced inpatient (3% vs 1%) and outpatient (5% vs 2%) hospitalizations. Children with autism spectrum disorders were nearly 9 times more likely to use psychotherapeutic medications and twice as likely to use gastrointestinal agents than children without autism spectrum disorders. Mean annual member costs for hospitalizations (

Predictors of outcome in perinatal arterial stroke: A population-based study

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