With respect to gonadotrophin deficiency, a GnRH stimulation test, with GnRH-induced maximal LH cutoff of 4.3 IU/L, together with a testicular volume cutoff of 1.1 mL, and basal inhibin B concentration <35 pg/mL, have been proposed as the most effective discriminators of congenital hypogonadotropic hypogonadism (CHH) from delayed puberty in adolescent males (17). This evidence concerns the gene PLOD1 and congenital hypogonadotropic hypogonadism.