Overall, a certain degree of gonadal dysfunction (ranging from isolated increase of FSH to hypogonadism or pubertal arrest) was recorded in 84.5% of the patients following TBI, 51.4% after a busulfan-based conditioning and 31.6% after cyclophoshamide/fludarabine, whereas no abnormal findings were found among the 18 patients exposed to treosulfan. This evidence concerns the gene BRD2 and hypogonadism.