Abstract. Twenty four boys with Klinefelter syndrome, 18 of whom were diagnosed prepubertally, were observed until adulthood. Onset of puberty, as judged from testicular enlargement and pubic hair development, occurred between 11 to 14 years in the above 18 patients. By the age of 17 pubic hair, penile length and height had reached the adult stage in all patients, but arrest of testicular growth was noted at midpuberty, 13 years, with maximal mean (+_ SD) volume attained being 3.5 4-1.5 ml. The first conscious ejaculation was reported to have occurred between 13 to 16 years in 10 patients and in the remaining 4 between 17 to 18 years of age. Sperm counts obtained after the age of 18 revealed azospermia or severe oligospermia in all patients except one, who had a sperm count of 30 • 106/ml. The hypothalamic-pituitary-gonadal axis, assessed by LH-RH and hCG stimulation tests, was found to be normal in prepuberty and during early pubertal stages. From mid-puberty the basal levels of plasma FSH and the response to LH-RIt showed a gradual increase above the normal. Towards late puberty (> 15 years) basal and peak levels of LH were above normal with a concomitant decrease in the basal level of testosterone and its response to hCG.These findings indicate that during childhood and early puberty function of the hypothalamic-pituitary-gonadal axis is normal in Klinefelter syndrome, allowing the onset of pubertal signs at the appropriate age, and that until late puberty there is a relative preservation of function in the testicular Leydig cells, permitting the normal sequential development of the androgen-dependent pubertal signs. The measurement of testicular testosterone reserve by means of hCG stimulation constitutes a useful aid in determining when and if testosterone replacement therapy should be instituted. Key words: Klinefelter syndrome -PubertyThe clinical, hormonal and histological picture of Klinefelter syndrome has been given wide attention in the literature since the original description published in 1942 [13]. Histological studies indicate that testicular damage is already present in the perinatal and prepubertal periods [15,21]. The progression of these changes during puberty has been found to lead to faulty spermatogenesis [10] as well as a decrease in testosterone production and secretion by the testes [14,31] with signs of hypovirilization in most of these patients [8].Reprint requests to: Prof. Z. Laron, Institute of Pediatric and Adolescent Endocrinology, Beilinson Medical Center, Petah Tikva 49 100, Israel Presented here are the findings made during long-term follow-up in 24 patients with Klinefelter syndrome, most of whom had been diagnosed before puberty. It was the aim of this study to investigate the sequence of the clinical and hormonal changes taking place and their inter-relationships, before and during puberty. Patients and MethodsThe patient material comprised 24 patients in all of whom the diagnosis of Klinefelter syndrome was confirmed by chromosomal studies. In 18, diagnosis was made before ...

Data obtained during long-term follow-up of 68 girls with premature thelarche were analysed. In 85% onset was before the age of 2 years, in 30.8% being present at birth. In 44.1% there was a regression after 3 2/12 +/- 2 8/12 years (SD). Basal levels of plasma FSH and response to LH-RH were significantly higher than prepubertal controls (1.93 +/- 1.56 vs. 0.8 +/- 0.1 mU/ml and peaks 12.3 +/- 5.4 vs. 7.9 +/- 1.0 mU/ml respectively; p less than 0.001). Twenty-seven of 52 patients tested had increased plasma estradiol and in 27 of 40 patients tested, urocytograms or vaginal smear showed estrogenization. Basal levels of LH and response to LH-RH were prepubertal. The girls with premature thelarche were significantly taller than normal controls of the same age (p less than 0.001). These results suggest that premature thelarche is an incomplete form of precocious sexual development probably due to derangement in the maturation of the hypothalamo-pituitary-gonadal axis which results in a higher than normal secretion of FSH, as well as a defect in the peripheral sensitivity to the sex hormones.

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