Defects in genes regulating gonadal development and causing gonadal dysgenesis, either complete or partial, or gonadal sex reversal include a large groups of genes in 46,XY DSD (e.g., ARX, ATRX, CBX2, DAX1, DHH, DMRT1, EMX2, ESR2, FGFR2, GATA4, HHAT, MAP3K1, NR5A1, SOX9, SRY, TSPYL1, WNT4, WT1, ZFPM2, and ZNRF3) as well as in 46,XX DSD (e.g., BMP15, FGF9, FOXL2, NR2F2, NR5A1, NUP107, RSPO1, SOX3, SOX9, SOX10, SRY, and WNT4) [3,28]. The gene discussed is ESR2; the disease is disorder of sexual differentiation.