INSL3 and Klinefelter syndrome: However, despite its constitutive nature, as also indicated by Albrethsen et al. (24), its high between-individual variance limits more general diagnostic application at the present time, though a consideration of INSL3 thresholds could allow a differentiation in cases of delayed puberty (36), Klinefelter syndrome (37–39), or in older men for functional hypogonadism (17).