SNPs in, for example, the drug metabolic enzyme cytochrome P450 19A1 (CYP19A1) and the estrogen receptor 1 (ERS1) gene have been related to the risk for AI-related side effects, but mainly in relation to the development of arthralgias, menopausal symptoms, and osteoporosis [69,70,71]. The gene discussed is CYP19A1; the disease is osteoporosis.