Genetic pathways to autism spectrum disordersAuthor(s): Sunil Q Mehta, Erika L Nurmi
Over the past several decades, progress in understanding the genetic basis of autism spectrum disorder (ASD) has dramatically altered our conception of its genetic architecture. Once believed to be an oligogenic disorder of common susceptibility variants, autism is now considered to be a collection of distinct ‘autisms’ marked by profound genetic heterogeneity. While twin and family studies have demonstrated a strong genetic etiology, genome-wide linkage and association studies have been limited by the extreme underlying heterogeneity. Genome-wide association studies have identified a few variants with small effects on ASD risk, but no common variants that clearly explain the few replicated linkage signals have been identified, suggesting that common variation is unlikely to play a central role. Recent successes in characterizing genetic risk have been driven by technological advances permitting the identification of de novo variants, both single-nucleotide variants and copy number variants, occurring in sporadic autism. The power to detect modest, rare inherited effects has been achieved through growing sample sizes through large collaborations; however, the inherited risk of ASD remains largely uncharted. Several hundred risk genes for ASD have been proposed, many linked via shared physiologic pathways. While many investigators now estimate that the number of autism risk genes will reach the thousands, pathway analysis will facilitate the understanding of ASD pathophysiology, the identification of novel risk genes and the development of clinically actionable targets. Molecular diagnosis has become possible for many ASD subtypes and will continue to expand. Targeted interventions will be developed and individualized based on diagnostic data and the growing appreciation of the biology of autism.