Objective: To examine the association between CLOCK gene T3111C polymorphism with attention deficit hyperactivity disorder (ADHD) and ADHD related sleep disturbances in children.
Methods: One hundred and sixty-six unrelated children with ADHD diagnosed according to DSM-IV criteria and a control group of 150 normal children were enrolled in this study. Parents filled out the Sleep Disturbance Scale for Children (SDSC). Genotype and allele frequencies of T3111C of the CLOCK gene were examined by PCR-restriction fragment length polymorphisms (PCR-RFLP).
Results: There were significant differences in the genotype and allele frequencies of T3111C of the CLOCK gene between the ADHD and control groups (P<0.05). C allele frequency in the ADHD group was significantly higher than in the control group (χ2=7.254, P=0.007, OR=1.740, 95%CI=1.160-2.612). The ADHD children with sleep disturbances were found to have higher C allele frequency than those without sleep disturbances (χ2=13.052, P<0.001, OR=2.766, 95%CI=1.573-4.865).
Conclusions: There is an association between CLOCK gene T3111C polymorphism and both ADHD and related sleep disturbances in children. The individuals with C allele are susceptible to ADHD as well as ADHD related sleep disturbances.