Background: The Circadian Locomotor Output Cycles Kaput (CLOCK) T3111C polymorphism has been associated with several psychiatric disorders, including mood disorders and schizophrenia, which are linked to specific personality traits. We investigated the relationship between the personality traits measured by the Temperament and Character Inventory (TCI) and the C3111T polymorphism of the CLOCK gene in healthy Japanese subjects. Methods: The sample population contained 1,092 healthy subjects (age = 27.4 ± 8.7 years) who completed the TCI. Genomic DNA was isolated from whole blood and genotyped using the TaqMan allele-specific assay method. The associations between the gene polymorphisms and TCI scores were evaluated by one-way analysis of variance and multiple regression analysis. We also compared the TCI scores between the C allele carrier (C/T and C/C genotypes) and non-carrier (T/T genotype) groups using Student’s t test. Males and females were analyzed separately. Results: There was no significant association between the C3111T genotype and any TCI score, but multiple regression analyses revealed significant but opposite associations between reward dependence and the C3111T polymorphism in males and females (p = 0.032, β = 0.087 and p = 0.05, β = –0.087, respectively). Similarly, when we compared the TCI scores of CLOCK C3111T C carrier and non-carrier subjects, we found that male C allele carriers had significantly higher reward dependence scores than non-carriers (p = 0.02). Conclusion: Our findings suggest that the CLOCK C3111T polymorphism may affect personality traits in healthy Japanese subjects.

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