The importance of a post-pubertal gonadotropin deficiency became clear as inverse correlations were detected between FSH and sperm concentration, between FSH and Ad spermatogonia content of the cryptorchid testes, and positive correlations were found between FSH and LH levels, and between LH and presence of Ad spermatogonia. The gene discussed is PLOD1; the disease is Gonadotropin deficiency.