Abstract Study question Do testis-specific cells have a normal karyotype in regions with spermatogonia (SPG) and ongoing spermatogenesis non-mosaic Klinefelter Syndrome (KS) patients? Summary answer While SPG Sertoli (SC) 46,XY spermatogenesis, most Leydig (LC) peritubular myoid (PTMC) 47,XXY karyotype. What is known already Although the majority of KS patients azoospermic, some focal (FS) can ...