Preclinical studies have demonstrated the relevance of adrenergic α2A receptor on the attentional process and the mechanism of action of methylphenidate hydrochloride. Several molecular genetic investigations suggest a role for the adrenergic α2A receptor gene (ADRA2A) in attention-deficit/hyperactivity disorder (ADHD), especially in the inattentive dimension. However, the effect of ADRA2A in the response to methylphenidate in humans has not been previously investigated, to our knowledge.
To evaluate the association between the ADRA2A –1291 C>G polymorphism and the clinical response to methylphenidate treatment in children and adolescents with ADHD.
A pharmacogenomic study was undertaken between November 1, 2002, and May 1, 2004, using a nonrandom assignment, quasi-experimental design.
An ADHD outpatient program at a university hospital in Brazil.
One hundred six patients consecutively diagnosed as having ADHD were genotyped for the ADRA2A –1291 C>G polymorphism and were included in the analyses.
Short-acting methylphenidate administered in increasing dosages until no further clinical improvement was detected or until limited adverse effects occurred.
Main Outcome Measures
The primary outcome measure was the parent-rated inattentive subscale of the Swanson, Nolan, and Pelham Scale version IV. Secondary outcome measures included the Barkley Side Effect Rating Scale and the parent-rated hyperactivity-impulsivity subscale of the Swanson, Nolan, and Pelham Scale version IV. Scales were applied by child psychiatrists blinded to genotype at baseline and at 1 and 3 months of treatment.
A significant interaction effect between the presence of the G allele and treatment with methylphenidate over time on inattentive scores was detected during the 3 months of treatment (n = 106; F2,198 = 4.30; P = .02).
We documented the effect of the G allele at the ADRA2A –1291 C>G polymorphism on the improvement of inattentive symptoms with methylphenidate treatment in children and adolescents with ADHD. Our findings provide clinical evidence for the involvement of the noradrenergic system in the modulation of methylphenidate action.