RSPO1 and disorder of sexual differentiation: Loss-of-function mutations in WNT4 have been identified in 46,XX individuals that are virilized and lack Müllerian structures [95,96], while loss-of-function mutations in RSPO1 leads to 46,XX DSD with complete sex-reversal [97], or 46,XX ovotesticular DSD, although no information about fertility was reported in these patients [98].