In addition to common polymorphisms and gene variations that cause a decrease in BMD and lead to the development of osteoporosis, there are also rare genetic variants that may contribute to a predisposition to osteoporosis at an early age, such as TNFRSF11, Col1a1, Col1a2, ESR1, LRP5, FONG, and ARHGEF3, but they are quite rare [63,64,65,66]. The gene discussed is ESR1; the disease is osteoporosis.