Klinefelter Syndrome
Klinefelter SyndromeKlinefelter syndrome, also called testicular dysgenesis, is the phenotype of the 47,XXY genotype and is characterized by male hypogonadism and infertility. Klinefelter Syndrome is probably the most common chromosomal variation found in humans. In random surveys, it is found to appear about once in every 500 to one in every 1,000 live born males. Since the largest percentage of these men would have never been diagnosed otherwise, it shows that in many cases affected individuals lead healthy, normal lives with no particular medical or social questions. Klinefelter Syndrome is diagnosed through a karyotype; a chromosome analysis usually done on a blood sample.
Klinefelter Syndrome is caused by a chromosome variation involving the sex chromosomes. The person with Klinefelter Syndrome is a male who, because of this chromosome variation, has a hormone imbalance. While Dr. Harry Klinefelter accurately described this condition in 1942, it was not until 1956 that other researchers reported that many boys with this description had 47 chromosomes in each cell of their bodies instead of the usual number of 46. This extra sex (X) chromosome causes the distinctive make-up of these boys. All men have one X chromosome and one Y chromosome, but sometimes a variation will result in a male with an extra X. This is Klinefelter Syndrome and is often written as 47,XXY. There are other, less common variations such as 48,XXYY; 48,XXXY; 49,XXXXY; and XY/XXY mosaic. All of these are considered Klinefelter Syndrome variants.
The major effect of the extra X chromosome in boys with Klinefelter Syndrome seems to be the function of the testes. The testes produce the major male sex hormone testosterone and the amount of this hormone may be decreased in boys with Klinefelter Syndrome. When these boys reach 10-12 years of age, it is helpful to measure their blood hormone levels periodically (e.g., yearly) to see if they are normal. If the testosterone level is low, resulting in diminished sexual changes which boys otherwise undergo during puberty, or if other characteristics are present which seem to point to poor metabolism of the existing hormone levels, then treatment with male sex hormones is usually very beneficial.
The most common form of treatment involves administering depotestosterone, a synthetic form of testosterone, by injection once a month. The dose gradually needs to be increased and given more frequently as the boys get older. Treatment should result in normal progression of physical and sexual development, including pubic hair growth, an increase in the size of the penis and scrotum (but not the testes), beard growth, deepening of the voice, and increase in muscle bulk and strength.
Because they often don't appear any different from anyone else, many XXY males probably never learn of their extra chromosome. However, if they are to be diagnosed, chances are greatest at one...
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