Attention-deficit hyperactivity disorder and the adrenergic receptors alpha 1C and alpha 2C.

The adrenergic system has been hypothesized to be involved in the etiology of attention-deficit hyperactivity disorder (ADHD) based on pharmacological interventions and animal models. Noradrenergic neurons are implicated in the modulation of vigilance, improvement of visual attention, initiation of adaptive response, learning and memory. In this study we tested the genes for two adrenergic receptors, alpha 1C (ADRA1C) located on chromosome 8p11.2, and alpha 2C (ADRA2C) located on chromosome 4p16, as genetic susceptibility factors in ADHD. For the adrenergic receptor alpha 1C we used a C to T polymorphism that results in a change of Cys to Arg at codon 492 for the linkage study. For the adrenergic receptor alpha 2C gene we examined a dinucleotide repeat polymorphism located approximately 6 kb from the gene. We examined these polymorphisms in a sample of 103 families ascertained through an ADHD proband. Using the transmission disequilibrium test, we did not observe biased transmission of any of the alleles of these polymorphisms. We conclude that the alleles at the polymorphisms tested in these two genes are not linked to the ADHD phenotype in this sample of families.