Sexual dimorphic effect in the genetic association of monoamine oxidase A (MAOA) markers with autism spectrum disorder.

Autism spectrum disorders are heritable and behaviorally-defined neurodevelopmental disorders having skewed sex ratio. Serotonin as modulator of behavior and implication of serotonergic dysfunction in ASD etiology corroborates that serotonergic system genes are potential candidates for autism susceptibility. In the current study X-chromosomal gene, MAOA responsible for degradation of serotonin is investigated for possible association with ASD using population-based approach. Study covers analysis of 8 markers in 421 subjects including cases and ethnically-matched controls from West Bengal. MAOA marker, rs6323 and various haplotypes formed between the markers show significant association with the disorder. Stratification on the basis of sex reveals significant genetic effect of rs6323 with low activity T allele posing higher risk in males, but not in females. Haplotypic association results also show differential effect both in males and females. Contrasting linkage disequilibrium pattern between pair of markers involving rs6323 in male cases and controls further supports the sex-bias in genetic association. Bioinformatic analysis shows presence of Y-encoded SRY transcription factor binding sites in the neighborhood of rs1137070. C allele of rs1137070 causes deletion of GATA-2 binding site and GATA-2 is known to interact with SRY. This is the first study highlighting male-specific effect of rs6323 marker and its haplotypes in ASD etiology and it suggests sexual dimorphic effect of MAOA in this disorder. Overall results of this study identify MAOA as a possible ASD susceptibility locus and the differential genetic effect in males and females might contribute to the sex ratio differences and molecular pathology of the disorder.