Klinefelter Syndrome, also known as 47,XXY or XXY, is a chromosomal disorder caused by the presence of an extra X chromosome in males.
This additional X chromosome becomes inactivated as a Barr body. Patients are phenotypically male, but have poor testicular function. Specifically, patients have abnormal Sertoli and Leydig cells, with testicular atrophy.
Labs reveal decreased testosterone and inhibin B levels, and a compensatory increase in FSH and LH levels. Estrogen levels are also increased due to increased FSH/LH stimulation Patients classically are infertile, with degenerative seminiferous tubules and azoospermia. Patients typically have a characteristically tall stature and gynecomastia. Pathology reveals pseudoadenomatous clusters of Leydig cells and hyalinized seminiferous tubules.
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