Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
Klinefelter syndrome, named after Dr. Harry Klinefelter who first identified it, is a chromosomal problem where a person with an XY genotype - biologically a male - inherits at least one extra X-chromosome, and sometimes a few extra ones.
Having an extra X chromosome makes the testicular cells generate less testosterone, which is the hormone responsible for primary sex characteristics like development of the sex organs as well as secondary sex characteristics like height and body shape.
It’s worth mentioning up front, that we’re using the term male here, rather than boy or man, to talk about the biological category of a person’s sex rather than a person’s gender identity.
Now, in puberty, in both males and females, the hypothalamus starts to release more gonadotropin releasing hormone, which gets the pituitary gland to release luteinizing hormone and follicle-stimulating hormone.
In males, these hormones affect the Leydig cells and the Sertoli cells.
To main balance or homeostasis, testosterone reduces gonadotropin releasing hormone and luteinizing hormone, and Sertoli cells release the hormone inhibin which inhibits release of follicle-stimulating hormone.
In Klinefelter syndrome, this hormone balance is altered.
The extra X-chromosome interrupts the normal function of the Sertoli and Leydig cells.
This means that levels of luteinizing hormone and follicle stimulating hormone increase.