Circannual variations of plasma thyrotropin in Klinefelter's syndrome.

The aim of this study was to explore the occurrence of abnormalities in the circannual thyrotropin (TSH) rhythm in Klinefelter's syndrome (KS). For 3 years, 69 healthy adult males and 73 patients with KS, usually living in Sardinia, were studied by a cross-sectional design. Plasma samples were taken between 08.00 and 09.00 h and TSH was radioimmunoassayed. First, the mean (+/- SD) of the data, grouped for each month of the year, was estimated to seek any macroscopic annual variation. Then, a cosine function was fitted to the single serially independent data by the single cosinor method in order to test for any statistically significant rhythm and, if the no-rhythm assumption is rejected, to describe the circannual parameters. Our patients showed circannual mean TSH concentrations lower than controls (p less than 0.001) without any statistically significant circannual rhythm, which was instead apparent in normal subjects with the annual crest time in December (95% CL November-February). Our results support the hypothesis that in KS the impaired TSH secretion may be related to abnormalities in the hypothalamic-pituitary coordination of the circannual rhythmicity of this hormone.