Hidden mosaicism in patients with Klinefelter's syndrome: implications for genetic reproductive counselling

BACKGROUND: Most individuals with Klinefelter's syndrome (KS) are azoospermic but residual foci of spermatogenesis have been observed in some patients. However, no consistent predictive factors for testicular sperm extraction success have been established and mosaicism could be a factor to investigate. In this study, we have assessed the degree of mosaicism in somatic and germinal tissues in KS, the meiotic competence of 47,XXY germ cells and the aneuploidy rate of post-reductional cells. METHODS: Five patients with KS previously diagnosed as pure 47,XXY have been studied. Samples from four donors were processed as controls. The chromosome constitution of lymphocytes, buccal mucosa and testicular tissue was assessed by interphase fluorescence in situ hybridization for chromosomes X, Y and 18. In meiotic figures, sex chromosome number and pairing was confirmed. RESULTS: 46,XY cell lines were observed in all patients and tissues analysed. The degree of mosaicism (mean +/- SD) differed among tissues (lowest in lymphocytes: 4.8 +/- 2.5%; highest in Sertoli cells: 42.3 +/- 11.1%). Meiotic figures were found in three cases (KS1, KS2 and KS5), all of them showed an XY complement. Hyperhaploid post-reductional cells were found in all patients (range: 3.3-36.4%) and increased rates versus controls (P < 0.05) were observed. CONCLUSIONS: Diagnosis of homogeneous KS based on lymphocyte karyotyping should be contrasted in other tissues. Mucosa cells could help to better approximate the degree of germ cell mosaicism. Our results indicate that 47,XXY germ cells are not meiotically competent. Increased post-reductional aneuploidy rate is related to meiotic errors in 46,XY cells. Appropriate genetic counselling is recommended in KS.