Insulin-like Peptide 3 (INSL3) in Men With Congenital Hypogonadotropic Hypogonadism/Kallmann Syndrome and Effects of Different Modalities of Hormonal Treatment: A Single-Center Study of 281 Patients

Context: Insulin-like factor 3 (INSL3) is a testicular hormone secreted during fetal life, the neonatal period, and after puberty. Objective: To measure INSL3 levels in a large series of men with congenital hypogonadotropic hypogonadism (CHH)/Kallmann syndrome (KS), in order to assess its diagnostic value and to investigate its regulation. Patients: We studied 281 CHH/KS patients (91 untreated, 96 receiving T, and 94 receiving combined gonadotropin therapy [human chorionic gonadotropin, hCG, and FSH]) and 72 age-matched healthy men. Methods: Serum INSL3 was immunoassayed with a validated RIA. Results: Mean (+/- SD) INSL3 levels (pg/mL) were 659 +/- 279 in controls and lower (60 +/- 43; P < .001) in untreated CHH/KS patients, with no overlap between the two groups, whenthe threshold of 250 pg/mL was used. Basal INSL3 levels were lower in both untreated CHH/KS men with cryptorchidism than in those with intrascrotal testes and in patients with testicular volumes below 4 mL. Significant positive correlations between INSL3 and both serum total T and LH levels were observed in untreated CHH/KS. Mean INSL3 levels remained low in T-treated CHH/KS patients and were significantly higher in men receiving combined hCG-FSH therapy (P < .001), but the increase was lower cryptorchid patients. FSH-hCG combination therapy or hCG monotherapy, contrary to T and FSH monotherapies, significantly increased INSL3 levels in CHH/KS. Conclusions: INSL3 is as sensitive a marker as T for the evaluation of altered Leydig cell function in CHH/KS patients. INSL3 levels correlate with LH levels in CHH/KS men showing, together with the rise in INSL3 levels during hCG therapy, that INSL3 secretion seems not constitutively secreted during adulthood but is dependence on pituitary LH.