BACKGROUND: The circadian locomotor output cycles kaput (CLOCK) gene encodes protein regulation circadian rhythm and also plays some roles in neural transmitter systems including the dopamine system. Several lines of evidence implicate a relationship between attention-deficit hyperactivity disorder (ADHD), circadian rythmicity and sleeping disturbances. A recent study has reported that a polymorphism (rs1801260) at the 3'-untranslated region of the CLOCK gene is associated with adult ADHD. METHODS: To investigate the association between the polymorphism (rs1801260) in ADHD, two samples of ADHD probands from the United Kingdom (n = 180) and Taiwan (n = 212) were genotyped and analysed using within-family transmission disequilibrium test (TDT). Bonferroni correction procedures were used to just for multiple comparisons. RESULTS: We found evidence of increased transmission of the T allele of the rs1801260 polymorphism in Taiwanese samples (P = 0.010). There was also evidence of preferential transmission of the T allele of the rs1801260 polymorphism in combined samples from the Taiwan and UK (P = 0.008). CONCLUSION: This study provides evidence for the possible involvement of CLOCK in susceptibility to ADHD.
