Klinefelters syndrome (KS) is the most frequent form of sex chromosome aneuploidy. The classic form of KS is associated with a 47,XXY karyotype. Mosaic forms of KS are thought to occur in approximately 10% mainly in the form of 46,XX/47,XXY. Other forms of mosaicism are rare among which the 46,XX/47,XXY form is very rare and can manifest as an ambiguous genitalia at birth as reported in our case.
A full term child presented at birth an hypospadias with a cured penis of 2.5 cm length, the scrotum was well developed with the two gonads present inside. There was no other physical abnormalities. Ultrasound imagining confirmed the presence of two gonads in the scrotum and didnt found internal female genitalia. The hormonal assessment performed at three months found normal gonadotropins levels (LH=10.74 Mu/ml, FSH=5.19 Mu/ml) and a normal testosterone response after HCG stimulation (before HCG = 2.87 nmol/l, after HCG =16.12 nmol/l). The karyotype found a 46,XX/47,XXY mosaic.
Mosaic forms of KS may explain the wide clinical spectrum of this disease. The 46,XX/47,XXY form may account for the more severe form with ambiguous genitalia as reported in our case.