Furthermore, in patients with Klinefelter syndrome, T levels and the AR gene CAG polymorphisms, consisting of a polyglutamine stretch of variable lengths within the N-terminal domain of the receptor, encoded by a variable number of CAG triplets in exon 1 of the AR gene located on the X chromosome, which reduce the AR sensitivity, are not associated with osteoporosis, despite the well-known relationship between hypogonadism and reduced BMD [23]. This evidence concerns the gene AR and hypogonadism.