Practice question

Klinefelter syndrome sex chromosome aneuploidy 47,XXY most common among newborn males about 1 in 660 births, often underdiagnosed until adolescence adulthood due subtle phenotype. Presentation includes tall stature with long legs disproportionate, small firm testes under 4 ml volume, hypergonadotropic hypogonadism reduced testosterone, gynecomastia breast enlargement, azoospermia infertility due seminiferous tubule dysgenesis, variable language learning difficulties but intelligence usually normal range. Supernumerary X undergoes inactivation forming Barr body partially compensating dosage, permitting viability similar autosomal trisomies small chromosomes. Origin may be maternal or paternal nondisjunction event.