Klinefelter syndrome (KS) is the most common sex chromosomal disorder in men. Most of these patients show the 47,XXY karyotype, whereas approximately 15% of them are mosaics with variable phenotype. A 39-year-old male investigated for primary infertility, was clinically normal with small firm testes and elevated levels of FSH, LH and low level of testosterone. Total azoospermia was confirmed on semen analysis. Testicular histopathology revealed no spermatogenesis and absence of germ cells. Karyotype from whole blood culture showed cells with 47,XXY/46,XX/ 45,X/48,XXXY/ 46,XY mosaicism. The predominant cell line was 47,XXY (83.67%). This was confirmed by fluorescence in situ hybridization (FISH). Also the presence of a small population of cells with the 48,XXXY and 45,X karyotypes was detected by FISH. This case illustrates the utility of FISH as an adjunct to conventional cytogenetics in assess the chromosome copy number in each cell line of a mosaic.
Keywords: Fluorescent in situ Hybridization; Karyotype; Klinefelter Syndrome; Mosaicism.