What is the pathophysiology of Klinefelter syndrome?

Updated: Mar 23, 2020
  • Author: Germaine L Defendi, MD, MS, FAAP; Chief Editor: Luis O Rohena, MD, MS, FAAP, FACMG  more...
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The X chromosome carries genes that have a role in many organ systems, playing a part, for example, in testes function, brain development, and growth. [9] Consequences of an extra X chromosome, usually acquired through a nondisjunctional error during parental gametogenesis, include hypogonadism, gynecomastia, and psychosocial behavioral concerns.

The addition of more than one extra X or Y chromosome to a normal male karyotype results in variable cognitive and physical abnormalities. As the number of supernumerary X chromosomes increases, somatic and cognitive development are more likely to be affected. Skeletal and cardiovascular abnormalities can become increasingly severe. Gonadal development is particularly susceptible to each additional X chromosome, resulting in seminiferous tubule dysgenesis and infertility, as well as hypoplastic and malformed genitalia, as seen in polysomy X males. A form of primary testicular failure occurs in males with Klinefelter Syndrome, with elevated gonadotropin levels due to lack of feedback inhibition by the pituitary gland.

Moreover, mental capacity diminishes with additional X chromosomes. The intelligence quotient (IQ) score is reduced by approximately 15 points for each supernumerary X chromosome, but conclusions about reduced mental capacity must be drawn cautiously. All major areas of development, including expressive and receptive language and coordination, are affected by extra X chromosome material.

A study by van Rijn et al indicated that information processing becomes more difficult in individuals with a 47,XXY karyotype as the social load related to the task increases. For example, with regard to visuospatial processing, which was associated with no social load, 17% of subjects in the study had trouble with the task, while in terms of facial recognition (medium social load) and facial expression of emotion (high social load), 26% and 33% of individuals, respectively, encountered difficulties. [10]

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