OBJECTIVEAttention deficit hyperactivity disorder (ADHD), a common behavior disorder of childhood, is a highly heterogeneous disease frequently accompanied by various mental disorders, including disruptive behavior disorder (DBD). Studies show that children suffering from ADHD with DBD are at higher risk of antisocial personality, substance abuse, and social adaptations disorder at their adulthood. The dopamine beta hydroxylase (DbetaH) is the key enzyme to ADHD since it catalyzes the conversion of dopamine to norepinephrine, and dysfunction there of is believed to be one of the causes of the disorder. To explore the association between DBH gene and ADHD complicated with or without DBD, the authors analyzed the transmission of a novel polymorphism DBH -1021C-->T, which is found associated with plasma DbetaH activity, in ADHD nuclear families using transmission disequilibrium test (TDT).

METHODSConsensus diagnoses were based on the DSM-IV. The samples included those from 292 Chinese Han nuclear families with ADHD probands. Genotypes of DBH -1021C-->T polymorphism were determined by PCR amplification, endonuclease digesting and electrophoresis. The transmission of DBH -1021C-->T polymorphism in ADHD nuclear families with or without DBD was analyzed by TDT.

RESULTSThe results showed that there was transmission disequilibrium between DBH-1021C-->T polymorphism and ADHD with or without DBD. In ADHD comorbid with DBD, T allele was preferentially transmitted (P < 0.05); and in ADHD without DBD, so was the C allele (P < 0.05). Among the three subtypes of ADHD, only ADHD-C subtype with DBD had an increased transmission of T allele (P < 0.05).

CONCLUSIONThere is an association between DBH gene and ADHD comorbid with or without DBD, but the preferential transmission alleles are different. The low activity T allele is increased to transmit in ADHD with DBD, while the high activity C allele is preferentially transmitted in ADHD without DBD. The results support the proposition that the genetic mechanism is different between ADHD comorbid with or without DBD. We also found that only ADHD-C subtype with DBD is associated with DBH -1021C-->T polymorphism in three subtypes of ADHD, which may suggest that there is a more intense relationship between DBD and ADHD-C subtype.