CYP21A2 and endocrine system disorder: Variability in the genotype–phenotype relationship has also been identified for single gene variants in reproductive system syndromes/endocrine disorders (Domenice et al., 2016; Goncalves et al., 2017) in 12 of the 13 (92%) confident genes—ANOS1, AR, CHD7, CYP19A1, CYP21A2, FGF8, FGFR1, KISS1R, LHCGR, NR0B1, NR5A1 and WDR11.