Objective To precisely characterize the chronology of testicular endocrine function impairment during childhood and adolescence in patients with Klinefelter syndrome.
Design Retrospective chart review.
Patients A total of 29 boys with Klinefelter syndrome with up to 12·3 years follow-up.
Measurements Clinical features and serum hormone levels were analysed during follow-up.
Results Of the 29 patients, 16 were prepubertal and 13 had already entered puberty at their first visit. Fifteen patients were followed up through late puberty. Before puberty, LH, FSH, testosterone, anti-Müllerian hormone (AMH) and inhibin B were within the expected range in almost all cases. However, levels of the inhibin α-subunit precursor Pro-αC were in the lowest levels of the normal range in most cases. During puberty, FSH levels increased earlier and more markedly than LH. Inhibin B and AMH declined to abnormally low or undetectable levels in advanced pubertal stages. Although testosterone and Pro-αC levels were within the reference ranges in most cases, they were abnormally low for the observed LH values.
Conclusions In Klinefelter syndrome, a mild Leydig cell dysfunction is present from early childhood in most cases and persists throughout puberty. Sertoli cell function is normal until mid puberty, when a dramatic impairment is observed.