Autistic disorder (AD)1 is a relatively common condition, affecting approximately 0.1% of the population2. It is a chronic and debilitating syndrome characterized by complex behavioural and cognitive deficits, including abnormal social interaction and communication, repetitive behaviour, and atypical information processing. Onset is usually in the middle of the second year of life and always before age 33. AD is part of a broad class of pervasive developmental disorders (PPD) together with Asperger's syndrome (AS) and pervasive f McGill University, Departments of Psychiatry, Neurology and Human Genetics, McGill University, Montreal, QC, Canada; [email protected]

Department of Psychiarty and the Brain Research Centre, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada; [email protected]

development disorder not otherwise specified (PDDNOS). These three entities share most of their symptoms and may be genetically related4.

Although the biological understanding of autism remains limited, the high concordance of the autism phenotype in MZ as compared to DZ twins strongly points to an important role of genes in the determination of autism. Also, the frequent co-morbidity of autism with markers of neurobiological impairment, like mental deficiency and epilepsy, is suggestive of an early neurodevelopmental origin. In recent years, several neuroimaging, neuropathological, and genetic studies have provided new insights into the putative pathogenesis of autism. However, the exact neuronal alterations underlying this disorder remain poorly understood and its treatment is still based on non-specific educational interventions and psychotropic medications. It is hoped that genetic research will identify specific genes increasing the risk for autism and subsequently lead to a better identification of the pathogenic mechanisms, which in turn will provide an early and reliable diagnosis and eventually specific treatments. However, in spite of intensive research in this field, the results of genetic studies remain non-conclusive and poorly replicated. This is particularly disappointing given that the human genome project has provided researchers with extraordinary tools to better investigate the genetic architecture of complex disorders. The purpose of this chapter is to provide an up-to-date view on the genetic results in autism. Subsequently, we briefly discuss the possible reasons for not identifying a greater number of genes implicated in autism and argue that a better knowledge of the biology of autism, particularly synaptic dynamics during development, will help in constructing complex models that may be tested genetically.



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