ESR1 and type 2 diabetes mellitus: In men with E2 deficiency due to a mutation in the cytochrome P450 aromatase gene (Cyp19a1), which catalyzes the aromatization of androgens to E2, or E2 resistance, caused by a point mutation in the ERα gene (ESR1), the following have been reported: increased total cholesterol level, the development of insulin resistance, impaired glucose tolerance, type 2 diabetes mellitus, and impaired vasodilatation (27–31).