The biological function of the INSL3/RXFP2 receptor pair was first discovered in the early 2000s when Insl3−/− or Rxfp2−/− male mice were shown to develop cryptorchidism, or undescended testes, characterized by the failure of the male gonad to descend into the scrotal position during embryonic development. The gene discussed is RXFP2; the disease is cryptorchidism.