INSL3 and cryptorchidism: Knockout experiments in mice clearly show independent requirements for INSL3/RXFP2 and androgens in testicular descent (16, 17); nevertheless causative mutations in INSL3, RXFP2, AR (androgen receptor) or the Leydig cell regulator NR5A1 (steroidogenic factor-1), are rare in cases of cryptorchidism (18, 19).