<prompt> Genetic defect in Klinefelters syndrome?XYYXXYXXXXO  <response>: Ans. b XXY Ref. H-17th2340KLINEFELTERS SYNDROME Most common chromosomal disorder associated with testicular dysfunction and male infertilty. 1 in 1000 live-bom males. Azoospermia is the rule in men with Klinefelter syndrome who have the 47, XXY karyotype. Testicular histology :hyalinization of seminiferous tubules and absence of spermatogenesis. But number of Leydig cells appears to increase. Testosterone is decreased and estradiol is increased. Features:- Undervirilization and gynecomastia- Markedly reduced testicular volumes 1-2 mL- Osteoporosis. Increased risk of:- Breast cancer- NHL- Lung cancer. Reduced risk of:- Prostate cancer. 