Image © Photos.comAttention-deficit/hyperactivity disorder (ADHD) is one of the most widely diagnosed disorders: an estimated 8% to 12% of children are affected worldwide. Although many studies about treatment options have been published, the genetic components that underlie the disorder are still being discovered. A special issue of the American Journal of Medical Genetics, Part B: Neuropsychiatric Genetics, highlights recent research and includes results from the first genome-wide study of patients with ADHD. Genome-wide studies have successfully identified variants associated with obesity and such diseases as age-related macular degeneration, diabetes, and prostate cancer.

Using data from the International ADHD Multicenter Genetics project, one study examined 600,000 genetic markers from more than 900 families. Two single-nucleotide polymorphisms were found to be significant for the specified phenotype and genetic model in the analysis: Rs6565113 and Rs552655.1 Rs6565113 is found in Cadherin 13, which acts as a negative regulator of neural cell growth. Rs552655 is located in GFOD1, a protein thought to be involved in electron transport and metabolic processes. Although the authors were able to identify these “novel genetic associations as viable ADHD candidate genes,” they called for larger studies to confirm their findings and to fully understand the genetic mechanisms that underlie the disorder.

Mick and colleagues2 also examined genome-wide response to treatment with methylphenidate in 187 children with ADHD (mean age, 9.2 years). These researchers examined genetic markers to predict which children would respond favorably to the medication. Although the authors found that “noradrenergic and possibly glutaminergic genes may be involved with response to methylphenidate,” they noted that their findings need to be replicated in larger samples.