The third is the gender-dependent contribution of the TPH-2 gene polymorphism rs4290270 to insomnia and related comorbidities, as a study by Shen et al. (23) reported that the A-A haplotype of rs4290270 and rs7305115 in TPH-2 gene was remarkably overrepresented in women with major depressive disorders compared with the corresponding female controls. Here, TPH2 is linked to insomnia.