Potential Role of Genetic Variants in the Etiology of ADHD Comorbid With Tic Disorders.

To evaluate the role of the adrenergic receptor alpha-2A gene () in the genetic etiology of ADHD comorbid with tic disorders (ADHD+TD). Two single nucleotide polymorphisms (SNPs) of were genotyped and analyzed in 936 normal controls and 1,815 ADHD probands, including 1,249 trios. Approximately 16% of the ADHD probands also had a diagnosis of TD. No significant association was found between and ADHD in general. Case-control analyses indicated different allelic and genotypic distributions of rs553668 between ADHD+TD and controls in males. Family-based association tests showed that the G allele of rs1800544, the A allele of rs553668, and the GA haplotype consisting of these two SNPs were overtransmitted in the ADHD+TD trios, especially in males. Moreover, the allelic/genotypic distribution and allelic transmission were different between ADHD+TD and ADHD without TD. may be associated with ADHD+TD, especially in males.