Klinefelter's syndrome occurs in males, typically with the 47 XXY genotype. It is the most common sex chromosome disorder, affecting 1 in 500 males



(1) 47 XXY

(2) mosaics with 46XY and 47 XXY

(3) 48 XXXY


Clinical features:

(1) small testes with a firm consistency due to testicular fibrosis

(2) decreased spermatogenesis with infertility

(3) gynecomastia

(4) increased armspan, being greater than height by 2 cm or more

(5) increased height (postpubertal height > 184 cm) due to increased leg length, with the length from hip to soles at least 2 inches greater than the length from head to hips


Laboratory Findings:

(1) increased gonadotropins (LH, FSH)

(2) decreased free testosterone (total testosterone may be normal)

(3) decreased inhibin B in serum

(4) Barr bodies in nuclei on buccal cell smears (except in mosaics)


Additional findings:

(1) decreased facial and pubic hair

(2) decreased penis size

(3) learning disabilities

(4) anxiety and neuroses

(5) osteoporosis

(6) adult onset diabetes mellitus

(7) taurodontism with teeth having a thinning of the surface and enlargement of the pulp

(8) weakness and fatigue

(9) erectile dysfunction


Genetic testing:

(1) peripheral blood karyotyping to detect an extra X chromosome

(2) if the peripheral blood karyotyping is negative and mosaicism is suspected, then testicular biopsy with karyotyping may be warranted.


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