No association of the DRD2 polymorphism and attention deficit hyperactivity disorder in the Irish population

Attention Deficit Hyperactivity Disorder (ADHD) is a common disorder of childhood characterized by inattention, excessive motor activity, impulsivity, and distractibility. It is associated with serious disability in children, adolescents and adults. Pharmacological and biochemical studies have suggested a dopaminergic and nor-adrenergic systems involvement. The DRD2 polymorphisms 'TaqI' and Ser-Cys/ 311 have been implicated in the aetiology of alcoholism, schizophrenia and other psychiatric disorders. It was postulated that Ser-Cys/311might produce conformational change of the receptor by forming new disulphide bond. Functional analysis of the Ser-Cys showed that the rare Cys variant is markedly less effective in inhibiting cAMP synthesis. We investigated the transmission of both polymorphisms in ADHD cases from Ireland using the haplotype based haplotype relative risk design. There was slight and non-significant preferential transmission of the 'TaqI' allele1( 2=1.8,p=0.18) and Ser-Cys/311(Ser allele) ( 2=1.74,p=0.18) A larger sample would be required to confirm or discard this observation.