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PubMed2004

The genetics of autism.

Autism is a complex, behaviorally defined, static disorder of the immature brain that is of great concern to the practicing pediatrician because of an astonishing 556% reported increase in pediatric prevalence between 1991 and 1997, to a prevalence higher than that of spina bifida, cancer, or Down syndrome. This jump is probably attributable to heightened awareness and changing diagnostic criteria rather than to new environmental influences. Autism is not a disease but a syndrome with multiple nongenetic and genetic causes. By autism (the autistic spectrum disorders [ASDs]), we mean the wide spectrum of developmental disorders characterized by impairments in 3 behavioral domains: 1) social interaction; 2) language, communication, and imaginative play; and 3) range of interests and activities. Autism corresponds in this article to pervasive developmental disorder (PDD) of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition and International Classification of Diseases, Tenth Revision. Except for Rett syndrome--attributable in most affected individuals to mutations of the methyl-CpG-binding protein 2 (MeCP2) gene--the other PDD subtypes (autistic disorder, Asperger disorder, disintegrative disorder, and PDD Not Otherwise Specified [PDD-NOS]) are not linked to any particular genetic or nongenetic cause. Review of 2 major textbooks on autism and of papers published between 1961 and 2003 yields convincing evidence for multiple interacting genetic factors as the main causative determinants of autism. Epidemiologic studies indicate that environmental factors such as toxic exposures, teratogens, perinatal insults, and prenatal infections such as rubella and cytomegalovirus account for few cases. These studies fail to confirm that immunizations with the measles-mumps-rubella vaccine are responsible for the surge in autism. Epilepsy, the medical condition most highly associated with autism, has equally complex genetic/nongenetic (but mostly unknown) causes. Autism is frequent in tuberous sclerosis complex and fragile X syndrome, but these 2 disorders account for but a small minority of cases. Currently, diagnosable medical conditions, cytogenetic abnormalities, and single-gene defects (eg, tuberous sclerosis complex, fragile X syndrome, and other rare diseases) together account for <10% of cases. There is convincing evidence that "idiopathic" autism is a heritable disorder. Epidemiologic studies report an ASD prevalence of approximately 3 to 6/1000, with a male to female ratio of 3:1. This skewed ratio remains unexplained: despite the contribution of a few well characterized X-linked disorders, male-to-male transmission in a number of families rules out X-linkage as the prevailing mode of inheritance. The recurrence rate in siblings of affected children is approximately 2% to 8%, much higher than the prevalence rate in the general population but much lower than in single-gene diseases. Twin studies reported 60% concordance for classic autism in monozygotic (MZ) twins versus 0 in dizygotic (DZ) twins, the higher MZ concordance attesting to genetic inheritance as the predominant causative agent. Reevaluation for a broader autistic phenotype that included communication and social disorders increased concordance remarkably from 60% to 92% in MZ twins and from 0% to 10% in DZ pairs. This suggests that interactions between multiple genes cause "idiopathic" autism but that epigenetic factors and exposure to environmental modifiers may contribute to variable expression of autism-related traits. The identity and number of genes involved remain unknown. The wide phenotypic variability of the ASDs likely reflects the interaction of multiple genes within an individual's genome and the existence of distinct genes and gene combinations among those affected. There are 3 main approaches to identifying genetic loci, chromosomal regions likely to contain relevant genes: 1) whole genome screens, searching for linkage of autism to shared genetic markers in populations of multiplex families (families with >1 affected family member; 2) cytogenetic studies that may guide molecular studies by pointing to relevant inherited or de novo chromosomal abnormalities in affected individuals and their families; and 3) evaluation of candidate genes known to affect brain development in these significantly linked regions or, alternatively, linkage of candidate genes selected a priori because of their presumptive contribution to the pathogenesis of autism. Data from whole-genome screens in multiplex families suggest interactions of at least 10 genes in the causation of autism. Thus far, a putative speech and language region at 7q31-q33 seems most strongly linked to autism, with linkages to multiple other loci under investigation. Cytogenetic abnormalities at the 15q11-q13 locus are fairly frequent in people with autism, and a "chromosome 15 phenotype" was described in individuals with chromosome 15 duplications. Among other candidate genes are the FOXP2, RAY1/ST7, IMMP2L, and RELN genes at 7q22-q33 and the GABA(A) receptor subunit and UBE3A genes on chromosome 15q11-q13. Variant alleles of the serotonin transporter gene (5-HTT) on 17q11-q12 are more frequent in individuals with autism than in nonautistic populations. In addition, animal models and linkage data from genome screens implicate the oxytocin receptor at 3p25-p26. Most pediatricians will have 1 or more children with this disorder in their practices. They must diagnose ASD expeditiously because early intervention increases its effectiveness. Children with dysmorphic features, congenital anomalies, mental retardation, or family members with developmental disorders are those most likely to benefit from extensive medical testing and genetic consultation. The yield of testing is much less in high-functioning children with a normal appearance and IQ and moderate social and language impairments. Genetic counseling justifies testing, but until autism genes are identified and their functions are understood, prenatal diagnosis will exist only for the rare cases ascribable to single-gene defects or overt chromosomal abnormalities. Parents who wish to have more children must be told of their increased statistical risk. It is crucial for pediatricians to try to involve families with multiple affected members in formal research projects, as family studies are key to unraveling the causes and pathogenesis of autism. Parents need to understand that they and their affected children are the only available sources for identifying and studying the elusive genes responsible for autism. Future clinically useful insights and potential medications depend on identifying these genes and elucidating the influences of their products on brain development and physiology.

Autistic Disorder↗
PubMed1995

Autistic regression and disintegrative disorder: how important the role of epilepsy?

At least a third of autistic toddlers regress in language, sociability, play, and often cognition. Many fewer children undergo a similar, unexplained regression after language is fully developed (disintegrative disorder [DD]). Epilepsy or a paroxysmal electroencephalogram (EEG) with/without clinical seizures, including electrical status epilepticus in slow wave sleep (ESES), may be associated, in occasional children, with either selective loss of language (Landau-Kleffner syndrome [LKS]) or with pervasive autistic regression. Fluctuation in language and behavior deficits should raise the suspicion of epilepsy. Review of the literature and of the author's experience suggests that epilepsy probably plays a relatively minor, although non-negligible, pathogenetic role in autistic regression. Multidisciplinary, possibly multi-institutional, longitudinal studies that encompass the regression are needed to sharpen diagnostic criteria to devise more effective therapies.

Autistic Disorder↗
PubMedDate not supplied

Narrative skills of children with communication impairments.

BACKGROUND: Narrative assessment is sensitive to the communication impairments of children with specific language impairment and those with autistic spectrum disorders. Although both groups of children tend to show deficits in narrative, it is unclear whether these deficits are qualitatively different and how language and pragmatic ability may impact on narrative competence. Comparing these two groups of children with children who exhibit pragmatic language impairment without autism may help to clarify these issues. AIMS: This study explored the relationship between structural language ability and pragmatic competence in narrative in children with communication impairments and typically developing children. METHODS AND PROCEDURES: Diagnostic status was determined using the Children's Communication Checklist. All children were asked to generate a narrative to the wordless picture book Frog, Where are You? (Mayer 1969). Narratives were analysed according to their global structure, local linguistic structure and the child's ability to provide evaluative comments, especially about mental or emotional states. OUTCOMES AND RESULTS: No group differences were seen in global structure or evaluation. Children with specific language impairment and autistic disorder made more syntactic errors, and children with autism were significantly more likely to provide ambiguous references in the story. No significant relationships were evident between the Children's Communication Checklist and narrative measures. The complexity of language used was related to evaluation in the clinical groups. CONCLUSIONS: Narrative is a good way of assessing linguistic ability in older children with communication impairments. Core language abilities rather than pragmatic skill or diagnostic status are likely to influence narrative development.

Autistic Disorder↗
PubMed1987

CSF monoamines in autistic syndromes and other pervasive developmental disorders of early childhood.

Spinal fluid concentrations of the three major monoamine metabolites were examined in 25 infantile autistic children and 12 children with other childhood psychoses, and were contrasted with results obtained in normal children and in groups of children with neurological and neurodevelopmental disorders. Autistic children showed absolute and relative increases of the dopamine metabolite homovanillic acid. The group with other childhood psychoses also showed an increase in HVA level; in this group there were also indications of high levels of serotonin and norepinephrine metabolites. The results are discussed in the context of a pathogenetic model for autism involving hyperfunction of dopaminergic nerve fibres in the brain stem-mesolimbic system.

Adolescent↗
PubMed2002

Profiles of everyday executive function in acquired and developmental disorders.

Executive function profiles were examined within and between several clinical disorders via the multi-domain Behavior Rating Inventory of Executive Function (BRIEF; Gioia, Isquith, Guy, & Kenworthy, 2000). Parent ratings of children with Inattentive and Combined types of Attention-Deficit/Hyperactivity Disorder (ADHD-I, ADHD-C), Autistic Spectrum Disorders (ASD), moderate and severe Traumatic Brain Injury (TBI), and Reading Disabilities (RD) were compared with controls. Profile analysis revealed significant (p<.01) and substantial (eta2>.10) differences in global elevations and in profile of scale elevations between diagnostic groups. ASD, ADHD-I and ADHD-C groups exhibited greater elevations across the BRIEF scales than did RD and Severe TBI groups, who were in turn more elevated than Moderate TBI and Control groups. The ADHD-C group was unique in its frequency and severity of inhibitory deficits, while the ASD group was distinguishable by its deficits in flexibility. Within diagnostic groups, relative risk for executive dysfunction was calculated with variability present in the frequency of clinically elevated scales. While the BRIEF captures executive profiles characteristic of specific disorders in the clinical setting, it is not diagnostic in its own right and is best used within the context of a broad based evaluation.

Attention Deficit Disorder with Hyperactivity↗
PubMed1989

Pathophysiologic findings in nonretarded autism and receptive developmental language disorder.

In nonretarded autistic, receptive developmental language disordered, and normal subject groups, we recorded in auditory and visual target detection tasks two neurophysiological components of the event-related brain potential, Nc and P3b. Existent research shows that, in normals, Nc and P3b appear early in development, are associated with attention and memory processes, and are endogenous which means that they are triggered by internal, consciously initiated attentional and cognitive mechanisms and that they can be triggered even by the omission of sensory stimulation so long as it has meaning or importance for the subject. In this report, Nc and P3b were recorded in response to auditory and visual stimulation and to the omission of auditory and visual stimulation. Consistent with the hypothesis that non-retarded autism involves abnormal attentional and cognitive responses to important information, P3b was found to be smaller than normal and Nc was small and often absent in the nonretarded autistic group even under the condition when no auditory language or sensory processing was required. Receptive developmental language disorder has been linked with difficulties in processing sequences of auditory stimuli, and in this study P3b was found to be somewhat enlarged in this group even under the conditions when P3b was elicited by stimuli separated by 1 sec and also when P3b was elicited by the omission of stimulation.

Action Potentials↗
PubMed2003

Association between thimerosal-containing vaccine and autism.

CONTEXT: Mercuric compounds are nephrotoxic and neurotoxic at high doses. Thimerosal, a preservative used widely in vaccine formulations, contains ethylmercury. Thus it has been suggested that childhood vaccination with thimerosal-containing vaccine could be causally related to neurodevelopmental disorders such as autism. OBJECTIVE: To determine whether vaccination with a thimerosal-containing vaccine is associated with development of autism. DESIGN, SETTING, AND PARTICIPANTS: Population-based cohort study of all children born in Denmark from January 1, 1990, until December 31, 1996 (N = 467 450) comparing children vaccinated with a thimerosal-containing vaccine with children vaccinated with a thimerosal-free formulation of the same vaccine. MAIN OUTCOME MEASURES: Rate ratio (RR) for autism and other autistic-spectrum disorders, including trend with dose of ethylmercury. RESULTS: During 2 986 654 person-years, we identified 440 autism cases and 787 cases of other autistic-spectrum disorders. The risk of autism and other autistic-spectrum disorders did not differ significantly between children vaccinated with thimerosal-containing vaccine and children vaccinated with thimerosal-free vaccine (RR, 0.85 [95% confidence interval [CI], 0.60-1.20] for autism; RR, 1.12 [95% CI, 0.88-1.43] for other autistic-spectrum disorders). Furthermore, we found no evidence of a dose-response association (increase in RR per 25 microg of ethylmercury, 0.98 [95% CI, 0.90-1.06] for autism and 1.03 [95% CI, 0.98-1.09] for other autistic-spectrum disorders). CONCLUSION: The results do not support a causal relationship between childhood vaccination with thimerosal-containing vaccines and development of autistic-spectrum disorders.

Autistic Disorder↗
PubMed2006

In vivo 1H-magnetic resonance spectroscopy study of amygdala-hippocampal and parietal regions in autism.

OBJECTIVE: The neural basis for autistic spectrum disorders is unclear, but abnormalities in the development of limbic areas and of glutamate have been suggested. Proton magnetic resonance spectroscopy ((1)H-MRS) can be used to measure the concentration of brain metabolites. However, the concentration of glutamate/glutamine in brain regions implicated in autistic spectrum disorders has not yet been examined in vivo. METHOD: The authors used (1)H-MRS to investigate the neuronal integrity of the amygdala-hippocampal complex and a parietal control region in adults with autistic spectrum disorders and healthy subjects. RESULTS: People with autistic spectrum disorders had a significantly higher concentration of glutamate/glutamine and creatine/phosphocreatine in the amygdala-hippocampal region but not in the parietal region. CONCLUSIONS: Abnormalities in glutamate/glutamine may partially underpin the pathophysiology of autistic spectrum disorders, and the authors confirm earlier reports that limbic areas are metabolically aberrant in these disorders.

Adult↗
PubMed2001

Etiologic determination of childhood developmental delay.

To determine the etiologic yield in young children with developmental delay referred to sub-specialty clinics for evaluation. Over an 18-month period, all children less than 5 years of age referred to the ambulatory pediatric neurology or developmental pediatrics clinics of the Montreal Children's Hospital for initial evaluation of a suspected developmental delay were enrolled. Features evident on history or physical examination were determined at intake as were the laboratory tests (and their rationale) requested by the evaluating physicians. Six months post initial assessment, detailed chart review was undertaken to determine if an etiology was found and the basis for such a determination. Bivariate and multivariate logistic regression was used to test for associations between factors present at intake and successful ascertainment of an underlying etiology. Two hundred and twenty-four children met study criteria. Etiologic yield varied across childhood developmental delay subtypes, and was 44/80 for global developmental delay [GDD] (55%), 13/22 for motor delay [MD] (59.1%), 3/72 for developmental language disorders [DLD] (4.2%), and 1/50 for autistic spectrum disorders [ASD] (2%). For GDD, the presence of historical features or findings on physical examination was associated with greater likelihood for successful etiologic determination with the following items significant in multiple logistic regression analysis; microcephaly, antenatal toxin exposure, focal findings. For MD, physical findings or the co-existence of a cerebral palsy symptom complex predicted a successful search for etiology. For both groups, the severity of the delay did not predict etiologic yield. For both groups, a small number of etiologic categories accounted for the majority of diagnoses made. Etiologic yield in childhood developmental delay is largely dependent on the specific developmental delay subtype. Paradigms for systematic evaluation of this common child health problem can be suggested, however they await validation.

Autistic Disorder↗
PubMed1998

Antipsychotic medication, psychiatric diagnosis and children with intellectual disability: a 12-year follow-up study.

This study is a follow-up to an original survey carried out in the early 1980s of all children with an identified intellectual disability in Cornwall, England. The purpose of this second study was to review the use of antipsychotic medication in these children and to relate it to their various diagnoses. This is a relatively under-researched area, and the few comparable studies in children have not been designed to specify diagnoses, psychiatric or otherwise. A positive relationship between the diagnosis of autistic spectrum disorders in children and the use of antipsychotic medication was one of the important findings which emerged from the research. The possible reasons for this association are discussed.

Adolescent↗
PubMed2004

MMR vaccine and autism: an update of the scientific evidence.

An hypothesis published in 1998 suggested that measles-mumps-rubella vaccine may cause autism as a result of persistent measles virus infection of the gastrointestinal tract. Results of early studies were not supportive and in 2001 a review by the Institute of Medicine concluded that the evidence favors the rejection of a causal relationship at the population level between measles-mumps-rubella vaccine and autistic spectrum disorder. Studies published since the Institute of Medicine report have continued not to find an increased risk of autistic spectrum disorder associated with measles-mumps-rubella. The vaccine also has not been found to be associated with a unique syndrome of developmental regression and gastrointestinal disorders. The evidence now is convincing that the measles-mumps-rubella vaccine does not cause autism or any particular subtypes of autistic spectrum disorder.

Autistic Disorder↗
PubMed2001

Obsessive compulsive behaviour in autism--towards an autistic-obsessive compulsive syndrome?

A portion of autistic patients exhibit compulsive-like behaviours. In addition it has been suggested that serotonin plays a major role in both obsessive compulsive disorder (OCD) and autistic disorder. Other neurohumors such as endogenous opioids and oxytocin have also been implicated in the two disorders. There is also some pharmacological overlap between the two disorders, as well as some similar neuroimaging studies. These similarities and overlaps have led us to propose a putative OCD-autistic disorder, which should be studied in greater detail.

Autistic Disorder↗
PubMedDate not supplied

What's going on? The question of time trends in autism.

Increases in the reported prevalence of autism and autistic spectrum disorders in recent years have fueled concern over possible environmental causes. The author reviews the available survey literature and finds evidence of large increases in prevalence in both the United States and the United Kingdom that cannot be explained by changes in diagnostic criteria or improvements in case ascertainment. Incomplete ascertainment of autism cases in young child populations is the largest source of predictable bias in prevalence surveys; however, this bias has, if anything, worked against the detection of an upward trend in recent surveys. Comparison of autism rates by year of birth for specific geographies provides the strongest basis for trend assessment. Such comparisons show large recent increases in rates of autism and autistic spectrum disorders in both the U.S. and the U.K. Reported rates of autism in the United States increased from < 3 per 10,000 children in the 1970s to > 30 per 10,000 children in the 1990s, a 10-fold increase. In the United Kingdom, autism rates rose from < 10 per 10,000 in the 1980s to roughly 30 per 10,000 in the 1990s. Reported rates for the full spectrum of autistic disorders rose from the 5 to 10 per 10,000 range to the 50 to 80 per 10,000 range in the two countries. A precautionary approach suggests that the rising incidence of autism should be a matter of urgent public concern.

Autistic Disorder↗