Table of Contents
Definition of Klinefelter Syndrome and XXY Chromosome
A chromosomal disorder affecting only males in which there is at least one extra x chromosome. The normal chromosomal configuration for a male is XY; the female configuration is XX. The extra X chromosome in a male, which doctors commonly designate as 47 XXY, dilutes the secondary sexual characteristics.
Men who have Klinefelter’s syndrome often do not produce sperm and thus are infertile (unable to cause pregnancy).
Klinefelter’s syndrome often does not become apparent until a boy enters (or fails to enter) puberty. Secondary sexual characteristics are slow to develop and may appear effeminate, with small genitalia, enlarged breasts (gynecomastia), and little facial hair. learning disorders are also common in boys who have Klinefelter’s syndrome, though researchers are uncertain of the reason for this. Adult men often experience sexual dysfunction such as low libido, erectile dysfunction, and infertility.
The diagnostic path includes blood tests to measure the levels of testosterone, luteinizing hormone (lh), and follicle-stimulating hormone (fsh). Karyotyping, a representation of the chromosomal configuration of the cells, shows the extra X chromosome (and in some men, more than one extra X chromosome).
Treatment is testosterone supplementation to restore to normal the level of testosterone in the blood circulation. Testosterone supplementation generally results in increased masculinization (appearance of secondary sexual characteristics) such as thickened beard growth, deepened voice, enlarged penis and testicles, and increased muscle mass and definition. Treatment is generally lifelong.
Page last reviewed: