CYP19A1 and hyperinsulinemic hypoglycemia, familial, 4: There is great heterogeneity in the literature about the role of CYP19A1 gene variants and, consequently, in the difference that these genotypes cause in aromatase activity; there are several polymorphisms in CYP19A1 that are associated with aromatase deficiency and others related to CYP19A1 aromatase excess syndrome.