Klinefelter Syndrome

Reference work entry

In 1942, Klinefelter et al. published a report on nine men who had enlarged breasts, sparse facial and body hair, small testes, and an inability to produce sperm. In 1959, these men with Klinefelter syndrome were discovered to have an extra sex chromosome (genotype XXY) instead of the usual male sex complement (genotype XY).

Klinefelter syndrome is the most common sex chromosomal disorder associated with male hypogonadism and infertility. Approximately 1 in 500–1,000 males is born with an extra X chromosome. Over 3,000 affected males are born yearly in the USA.

Synonyms and Related Disorders

47,XXY syndrome; Klinefelter syndrome mosaicism (46,XY/47,XXY, 46,XY/48,XXXY, 47,XXY/48,XXXY); Klinefelter syndrome variants (48,XXYY, 48,XXXY, 49,XXXYY, 49,XXXXY); Klinefelter syndrome with structurally abnormal X chromosome [47,X,i(Xq)Y, 47,X,del(X)Y]

Genetics/Basic Defects

  1. 1.

    Caused by at least an additional X chromosome in a male

  2. 2.
    The XXY form of Klinefelter syndrome
    1. a.

      Due to meiotic...


Autism Spectrum Disorder Essential Tremor Preimplantation Genetic Diagnosis Mitral Valve Prolapse Mixed Connective Tissue Disease 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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