Neurotransmitter systems and neurotrophic factors in autism: association study of 37 genes suggests involvement of DDC.

Objectives. Neurotransmitter systems and neurotrophic factors can be considered strong candidates for autism spectrum disorder (ASD). The serotoninergic and dopaminergic systems are involved in neurotransmission, brain maturation and cortical organization, while neurotrophic factors (NTFs) participate in neurodevelopment, neuronal survival and synapses formation. We aimed to test the contribution of these candidate pathways to autism through a case-control association study of genes selected both for their role in central nervous system functions and for pathophysiological evidences. Methods. The study sample consisted of 326 unrelated autistic patients and 350 gender-matched controls from Spain. We genotyped 369 tagSNPs to perform a case-control association study of 37 candidate genes. Results. A significant association was obtained between the DDC gene and autism in the single-marker analysis (rs6592961, P = 0.00047). Haplotype-based analysis pinpointed a four-marker combination in this gene associated with the disorder (rs2329340C-rs2044859T-rs6592961A-rs11761683T, P = 4.988e-05). No significant results were obtained for the remaining genes after applying multiple testing corrections. However, the rs167771 marker in DRD3, associated with ASD in a previous study, displayed a nominal association in our analysis (P = 0.023). Conclusions. Our data suggest that common allelic variants in the DDC gene may be involved in autism susceptibility.