The concept of a hypogonadal–obesity–adipokine cycle is a proposed mechanism behind this association (50, 63, 64): Obesity has been suggested to lead to enhanced aromatisation of androgens to oestrogens by aromatase (CYP19A1, Fig. 2) in adipose tissue, thereby reducing the level of active androgens. The gene discussed is CYP19A1; the disease is obesity due to melanocortin 4 receptor deficiency.