FGF9 and disorder of sexual differentiation: In human foetal gonad cultures dysregulation of FGFR-mediated signalling affects testicular development58, and some emerging evidence suggests that variants in the FGF9 pathway may contribute to DSD, with mutations in FGFR2 described in an XY individual with gonadal dysgenesis59, and a gain of FGF9 copy number in one SRY-negative 46,XX male patient60.