A replication of the Autism Diagnostic Observation Schedule (ADOS) revised algorithms.

OBJECTIVE: To replicate the factor structure and predictive validity of revised Autism Diagnostic Observation Schedule algorithms in an independent dataset (N = 1,282). METHOD: Algorithm revisions were replicated using data from children ages 18 months to 16 years collected at 11 North American sites participating in the Collaborative Programs for Excellence in Autism and the Studies to Advance Autism Research and Treatment. RESULTS: Sensitivities and specificities approximated or exceeded those of the old algorithms except for young children with phrase speech and a clinical diagnosis of pervasive developmental disorders not otherwise specified. CONCLUSIONS: Revised algorithms increase comparability between modules and improve the predictive validity of the Autism Diagnostic Observation Schedule for autism cases compared to the original algorithms.

Heterogeneous association between engrailed-2 and autism in the CPEA network.

Autism is a neurodevelopmental disorder characterized by an early onset of abnormal social, communicative, and repetitive behavior. Engrailed-2 (EN2) was identified as an autism candidate gene because its influence on cerebellar development in mice parallels neurodevelopmental abnormalities seen in individuals with autism. Studies investigating association between markers at EN2 (chr7q36), a location associated with language disorders, and autism reveal mixed findings. Two positive reports revealed association with two intronic SNPs. Since the associated SNPs were in high linkage disequilibrium and shared similar minor allele frequencies, we chose to test whether one of the SNPs (rs1861972) was associated with autism in three recruiting sites from the NIH Collaborative Programs of Excellence in Autism (CPEA) network. A recessive model revealed significant association with broad autism spectrum disorder. Site specific analyses indicated differential allele transmission by site, despite similar ethnicity, and parental genotypes, suggesting the SNP may contribute to various risk haplotypes. No significant association with autism was found under an additive model for either a broad (autism spectrum disorder) or a narrow (autistic disorder) diagnostic group. Although our findings were not as robust as the previous studies, they suggest that rs1861972 may influence the risk for autism spectrum disorders. Future studies investigating EN2 should consider how the association of variants in this gene with autism could be influenced by differences in phenotype and possible interactions with genotypes at other autism candidate genes.

Discrimination learning and reversal of the conditioned eyeblink reflex in a rodent model of autism.

Offspring of rats exposed to valproic acid (VPA) on gestational day (GD) 12 have been advocated as a rodent model of autism because they show neuron loss in brainstem nuclei and the cerebellum resembling that seen in human autistic cases . Studies of autistic children have reported alterations in acquisition of classical eyeblink conditioning and in reversal of instrumental discrimination learning . Acquisition of discriminative eyeblink conditioning depends on known brainstem-cerebellar circuitry whereas reversal depends on interactions of this circuitry with the hippocampus and prefrontal cortex. In order to explore behavioral parallels of the VPA rodent model with human autism, the present study exposed pregnant Long-Evans rats to 600 mg/kg VPA on GD12 and tested their offspring from Postnatal Day (PND26-31) on discriminative eyeblink conditioning and reversal. VPA rats showed faster eyeblink conditioning, consistent with studies in autistic children . This suggests that previously reported parallels between human autism and the VPA rodent model with respect to injury to brainstem-cerebellar circuitry are accompanied by behavioral parallels when a conditioning task engaging this circuitry is used. VPA rats also showed impaired reversal learning, but this likely reflected "carry-over" of enhanced conditioning during acquisition rather than a reversal learning deficit like that seen in human autism. Further studies of eyeblink conditioning in human autism and in various animal models may help to identify the etiology of this developmental disorder.

Head circumference and height in autism: a study by the Collaborative Program of Excellence in Autism.

Data from 10 sites of the NICHD/NIDCD Collaborative Programs of Excellence in Autism were combined to study the distribution of head circumference and relationship to demographic and clinical variables. Three hundred thirty-eight probands with autism-spectrum disorder (ASD) including 208 probands with autism were studied along with 147 parents, 149 siblings, and typically developing controls. ASDs were diagnosed, and head circumference and clinical variables measured in a standardized manner across all sites. All subjects with autism met ADI-R, ADOS-G, DSM-IV, and ICD-10 criteria. The results show the distribution of standardized head circumference in autism is normal in shape, and the mean, variance, and rate of macrocephaly but not microcephaly are increased. Head circumference tends to be large relative to height in autism. No site, gender, age, SES, verbal, or non-verbal IQ effects were present in the autism sample. In addition to autism itself, standardized height and average parental head circumference were the most important factors predicting head circumference in individuals with autism. Mean standardized head circumference and rates of macrocephaly were similar in probands with autism and their parents. Increased head circumference was associated with a higher (more severe) ADI-R social algorithm score. Macrocephaly is associated with delayed onset of language. Although mean head circumference and rates of macrocephaly are increased in autism, a high degree of variability is present, underscoring the complex clinical heterogeneity of the disorder. The wide distribution of head circumference in autism has major implications for genetic, neuroimaging, and other neurobiological research.

Induction of the homeotic gene Hoxa1 through valproic acid's teratogenic mechanism of action.

BACKGROUND: Valproic acid (VPA) exposure in utero has been associated with an increased risk of both neural tube defects and autism spectrum disorders (ASDs). The terata induced by VPA suggest interference with pattern formation. Retinoic acid produces similar terata and is known to act in part by increasing the expression of Hoxa1. We tested the hypotheses that exposure to VPA would alter the expression of Hoxa1 in rat embryos during times of normal Hoxa1 expression (d10.5-13.5) and that exposure at earlier and later stages would induce inappropriate expression. METHOD: Hoxa1 expression levels were determined by real-time PCR in individual embryos 1 h after exposure on gestational d10, 12, 13, 14, or 15. Additionally, teratogenic (4-yn-VPA) and nonteratogenic analogs of VPA (IE-VPA), retinoic acid (RA), and saline were compared for effects on Hoxa1 expression on d12. Embryos were allowed to develop for 1, 2, 4, 6, or 24 h, to follow the time course of effects. RESULTS: In utero exposure to VPA on gestational d10 and on d12-14 significantly increased the level of Hoxa1 expression compared to saline-exposed embryos at developmental ages prior to, during and after the normal expression period for this gene. On gestational d12, exposures to VPA and 4-yn-VPA significantly increased Hoxa1 expression at all sacrifice times, compared to saline-exposed embryos. RA significantly elevated Hoxa1 expression at all time points except 24-h post-treatment. The nonteratogenic VPA analog, IE-VPA, did not affect Hoxa1 expression. CONCLUSIONS: VPA and 4-yn-VPA exposures elevated Hoxa1 mRNA during its normal expression period and induced expression outside of the normal period. This may explain, in part, how VPA disrupts development.

The teratology of autism.

Autism spectrum disorders affect behaviors that emerge at ages when typically developing children become increasingly social and communicative, but many lines of evidence suggest that the underlying alterations in the brain occur long before the period when symptoms become obvious. Studies of the behavior of children in the first year of life demonstrate that symptoms are often detectable in the first 6 months. The environmental factors known to increase the risk of autism have critical periods of action during embryogenesis. Minor malformations that occur frequently in people with autism are known to arise in the same stages of development. Anomalies reported from histological studies of the brain are consistent with an early alteration of development. Congenital syndromes with high rates of autism include somatic that originate early in the first trimester. In addition, it is possible to duplicate a number of anatomic and behavioral features characteristic of human cases by exposing rat embryos to a teratogenic dose of valproic acid at the time of neural tube closure.

Environmental causes of central nervous system maldevelopment.

The central nervous system is the most vulnerable of all body systems to developmental injury. This review focuses on developmental processes by which the nervous system is formed and how those processes are known or suspected to be injured by toxic agents. The processes discussed are establishment of neuron numbers; migration of neurons; establishment of connections, neurotransmitter activity, and receptor numbers; deposition of myelin; and 2 processes that are prominent in postnatal development, trimming back of connections and postnatal neurogenesis. Our knowledge of the risks of exposure to environmental hazards in childhood and adolescence is minimal. Most of our information concerns the effects of neurotoxicants in prenatal and early postnatal life. More worrisome than our lack of data regarding later stages of development is the minimal effort that we have mounted to protect the public from known neurotoxic agents and that regulations for testing new drugs and chemicals still do not require any assessment of neuroteratologic effects.

Alleles of a reelin CGG repeat do not convey liability to autism in a sample from the CPEA network.

A recent study by Persico et al. [2001: Mol Psychiatry 6:150-159] suggests alleles of a CGG polymorphism, just 5' of the reelin gene (RELN) initiator codon, confer liability for autism, especially alleles bearing 11 or more CGG repeats (long alleles). The association is consistent across both a case-control and family-based sample. We attempted to replicate their finding using a larger, independent family-based sample from the NIH Collaborative Programs of Excellence in Autism (CPEA) Network. In our data, allele transmissions to individuals with autism versus unaffected individuals are unbiased, both when alleles are classified by repeat length and when they are classified into long/short categories. Because of the apparent linkage of autism to chromosome 7q, particularly related to the development of language, we also evaluate the relationship between Reelin alleles and the age at which autism subjects use their first word or first phrase. Neither is significantly associated with Reelin alleles. Our results are not consistent with a major role for Reelin alleles in liability to autism.

Association between the HOXA1 A218G polymorphism and increased head circumference in patients with autism.

BACKGROUND: The HOXA1 gene plays a major role in brainstem and cranial morphogenesis. The G allele of the HOXA1 A218G polymorphism has been previously found associated with autism. METHODS: We performed case-control and family-based association analyses, contrasting 127 autistic patients with 174 ethnically matched controls, and assessing for allelic transmission disequilibrium in 189 complete trios. RESULTS: A, and not G, alleles were associated with autism using both case-control (chi(2) = 8.96 and 5.71, 1 df, p <.005 and <.025 for genotypes and alleles, respectively), and family-based (transmission/disequilibrium test chi(2) = 8.80, 1 df, p <.005) association analyses. The head circumference of 31 patients carrying one or two copies of the G allele displayed significantly larger median values (95.0th vs. 82.5th percentile, p <.05) and dramatically reduced interindividual variability (p <.0001), compared with 166 patients carrying the A/A genotype. CONCLUSIONS: The HOXA1 A218G polymorphism explains approximately 5% of the variance in the head circumference of autistic patients and represents to our knowledge the first known gene variant providing sizable contributions to cranial morphology. The disease specificity of this finding is currently being investigated. Nonreplications in genetic linkage/association studies could partly stem from the dyshomogeneous distribution of an endophenotype morphologically defined by cranial circumference.

Converging evidence for brain stem injury in autism.

The hypothesis that brain stem injury plays a role in the autism spectrum disorders was suggested by evidence that exposure to thalidomide during the earliest stages of brain development increases the risk of autism spectrum disorders. The implications for the embryological origin of autism first led to studies of neuroanatomy in a human case and an animal model and then to examinations of minor craniofacial features in autism. But the general hypothesis had much broader implications. It has now generated studies of the behavioral and neurological symptoms of human patients, of human molecular genetics and population genetics, and of animal behavioral teratology and molecular pharmacology. The collection of this range of data was made possible by adding experts from many fields to the research team. They worked both independently and collaboratively to try to unravel the etiology of autism.