Integrated Functional Analysis Implicates Syndromic and Rare Copy Number Variation Genes as Prominent Molecular Players in Pathogenesis of Autism Spectrum Disorders

Abstract

Autism Spectrum Disorders (ASD) are caused by disrupted neurodevelopment leading to socio-communication and behavioural abnormalities. Although genetic anomalies like Copy Number Variations (CNV) have been implicated in ASD, their overall genomic landscape and pathogenicity remain elusive. Therefore, we created a CNV map for ASD using 9337 cases and 5650 controls from SFARI database, statistically marked genomic regions with high and low frequencies of CNVs (i.e., common and rare CNV regions respectively), performed gene function enrichment for CNV genes, built functional networks, pathways and examined their expression in brain tissues. Information thus obtained were cumulatively integrated using a weighted scoring strategy to rank CNV regions by their neuro-functional attributes. Subsequently, we mapped 105 genic CNV regions across 20 chromosomes. They encompassed 537 genes, of which only 59 (11%) genes were identified with Single Nucleotide Variations (SNV) in ASD subjects through sequencing and functional studies, which indicated that diverse sets of genes were affected by CNVs and SNVs in ASD. Overall, syndromic CNV regions displayed the most prominent neuronal functions. While common CNV regions were found in loci 15q11.2, 16p11.2, 22q11.21, 15q13.2-13.3, rare CNV regions in loci 4p16.3, 9q34.3, 7q11.23, 17p11.2 contributed significantly to protein interaction networks and were highly expressed in brain. Enriched CNV genes were clustered in six functional categories with either direct roles in neurodevelopment or auxiliary roles like cellular signalling via MAPK pathway, cytoskeletal organization and transport or immune regulation. Mechanisms through which these molecular systems could independently or in combination trigger an ASD phenotype were predicted.