Biased paternal transmission of SNAP-25 risk alleles in attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is the most common childhood psychiatric disorder, affecting 5-10% of school-age children. Although the biological basis of this disorder is unknown, twin and family studies provide strong evidence that ADHD has a genetic basis involving multiple genes. A previous study found an association between ADHD and two polymorphisms in the 3' untranslated region (UTR) of SNAP-25, a gene encoding a synaptic vesicle docking protein known to play a role in the hyperactivity observed in the Coloboma mouse strain. In this paper, we test biased transmission of the 3' UTR SNAP-25 haplotype using a larger ADHD sample of 113 families with 207 affected children. Using the transmission disequilibrium test (TDT), we found a trend consistent with biased transmission of the TC haplotype of SNAP-25 in all transmissions and detected a significant distortion (P=0.027) when paternal transmissions were evaluated.