Genetic factors may create a predisposition to the disease in patients with premature ejaculation. In the classic study by Bernhard Schapiro, people with a high number of family members suffering from premature ejaculation were predisposed to develop premature ejaculation. Therefore, genes may also be involved in the etiology of PE. A study by Jern P et al. on 3946 twins (18-48 years old, mean age 29.9 years) found a moderate genetic predisposition (28%) for genetic factors in the development of PE, and further studies evaluated the genotype of the 5-hydroxytryptamine transporter gene, which is polymorphic and has a relationship with the development of PE, and also with the application of SSRIs for the treatment of PE. Animal experiments showed that mice lacking the endothelial-type nitric oxide synthase gene developed PE symptoms, while lack of the heme oxygenase gene G2 resulted in delayed ejaculation and non-ejaculation.