USMLE

Klinefelter Syndrome

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Chromosomal Abnormalities
  1. Down Syndrome (Trisomy 21)
  2. Edwards Syndrome (Trisomy 18)
  3. Patau Syndrome (Trisomy 13)
  4. Klinefelter Syndrome
  5. Turner Syndrome
  6. Williams Syndrome
  7. Cri du Chat Syndrome
  8. Imprinting

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.

Find Klinefelter Syndrome and more Chromosomal Abnormalities among Pixorize's visual mnemonics for the USMLE Step 1 and NBME Shelf Exams.