From mini-puberty to pre-puberty: early impairment of the hypothalamus–pituitary–gonadal axis with normal testicular function in children with non-mosaic Klinefelter syndrome

Purpose: Klinefelter syndrome (KS) is a genetic disorder caused by the presence of an extra X chromosome in males. The aim of this study was to evaluate the hypothalamic–pituitary–gonadal (HPG) axis and the clinical profile of KS boys from mini-puberty to early childhood. Patients and methods: In this retrospective, cross-sectional, population study, 145 KS boys and 97 controls aged 0–11.9 years were recruited. Serum FSH, LH, testosterone (T), Inhibin B (INHB), sex hormone binding globulin (SHBG) and anti-Müllerian hormone (AMH) were determined. Auxological parameters were assessed. To better represent the hormonal and clinical changes that appear in childhood, the entire population was divided into 3 groups: ≤ 6 months (group 1; mini-puberty); > 6 months and ≤ 8 years (group 2; early childhood); > 8 and ≤ 12 years (group 3; mid childhood). Results: During mini-puberty (group 1), FSH and LH were significantly higher in KS infants than controls (p < 0.05), as were INHB and T (respectively p < 0.0001 and p < 0.005). INHB was also significantly higher in KS than controls in group 2 (p < 0.05). AMH appeared higher in KS than in controls in all groups, but the difference was only statistically significant in group 2 (p < 0.05). No significant differences were found in height, weight, testicular volume, and penile length. Conclusions: No hormonal signs of tubular or interstitial damage were found in KS infants. The presence of higher levels of gonadotropins, INHB and testosterone during mini-puberty and pre-puberty may be interpreted as an alteration of the HPG axis in KS infants.