Contrary to the assumption that temperature-dependent effects on cryptorchid gonads damage undescended testes before sexual maturation is complete, recent evidence aligns with the idea that germ cell loss, resulting in infertility in cryptorchidism, is a consequence of alterations in the Piwi pathway and the derepression of transposons (36). The gene discussed is PIWIL4; the disease is cryptorchidism.