DOPAMINE DRD4 RECEPTOR POLYMORPHISM AND ATTENTION-DEFICIT HYPERACTIVITY DISORDER

A polymorphism in the dopamine receptor 4 gene (DRD4) has been related to novelty seeking, Tourette's syndrome, and attention deficit hypera ctivity disorder (ADHD). The variability is in a 48-bp repeat in exon 3 of the gene (a transmembrane region). This study examined the relati on of the 7-repeat (ie, high-risk) allele to questionnaire-based diagn oses of ADHD (both combined type and inattentive type). Several positi ve findings were obtained for ADHD-inattentive type. In an association test, the 7-repeat allele occurred more frequently in children with A DHD-inattentive type than in control children. In genetically discorda nt sibling pairs, the sibling with a greater number of 7-repeat allele s displayed more inattentive symptoms than his/her co-sibling with few er 7-repeat alleles. For ADHD-combined type, the 7-repeat allele frequ ency was greater than that in the control sample. However, a quantitat ive transmission disequilibrium test yielded no significant linkage of the 7-repeat allele with hyperactive-impulsive symptoms. A categorica l TDT yielded no significant findings, but the number of transmissions was small, especially for ADHD-inattentive type.