The Relationship Between Tryptophan Hydroxylase-2 Gene with Primary Insomnia and Depressive Symptoms in the Han Chinese Population

BACKGROUND: Insomnia often coexists with depression, and there is compelling evidence for a genetic component in the etiologies of both disorders. AIMS: To investigate the relationship between exonic variant (rs4290270) in the tryptophan hydroxylase-2 gene and primary insomnia and symptoms of depression in Han Chinese. STUDY DESIGN: Case-control study. METHODS: This study included 152 patients with primary insomnia and 164 age- and gender-matched normal controls. All patients were investigated by polysomnography for 2 consecutive nights. The depressive symptoms were measured by using a 20-item Zung Self-rating Depression Scale. Sleep quality was assessed with the Pittsburgh Sleep Quality index. The genotypes of the TPH-2 gene polymorphism rs4290270 were determined by the polymerase chain reaction-restriction fragment length polymorphism method. RESULTS: The genotype distributions of the tryptophan hydroxylase-2 gene polymorphism rs4290270 were in Hardy-Weinberg equilibrium in both patients and controls (p>0.05). The allele and genotype distributions of this variant were comparable between patients and controls in all subjects and between genders (all p>0.05). The impact of rs4290270 on self-rating depression scale score changes was statistically significant (p=0.002), with carriers of the A/A genotype having the highest self-rating depression scale score (mean ± standard deviation: 52.73±12.88), followed by the A/T genotype (50.94±11.29, p=0.35) and the T/T genotype (43.48±7.78, p<0.01), and this impact was more obvious in women (p<0.001). CONCLUSION: The tryptophan hydroxylase-2 gene polymorphism rs4290270 may not be a susceptibility locus for primary insomnia in Han Chinese, but it may be a marker of depressive symptoms.