The heterogeneity of the androgen phenotype in the steroid synthesis pathway may be attributed to differences in the activity of important enzymes; for example, in hyperandrogenic PCOS patients, the activities of 17 and 20 lyases and 3β-hydroxysteroid dehydrogenase II (3β-HSD) increase, while aromatase activity bound to the Δ4 pathway decreases (de Medeiros et al., 2015). The gene discussed is CYP19A1; the disease is polycystic ovary syndrome.