The pituitary-thyroid axis in Klinefelter's syndrome.

Conventional thyroid function indices (serum T4, T3, TSH and thyroidal RAIU before and after TSH) appeared to be normal in most of 25 clinically euthyroid patients with chromatine positive Klinefelter's syndrome. Administration of TRH, however, revealed a decreased TSH reserve in the Klinefelter patients, both off or on testosterone treatment, in comparison to euthyroidal eugondal male controls. Preliminary data suggest that this blunted TSH respnse to TRH is not a characteristic of Klinefelter's syndrome per se but might be caused by the concurrent hypergonadotrophism. Despite the blunted TSH response, the TRH mediated T3 response in the Klinefelter patients was about equal to that in the male controls.