Klinefelter syndrome is a genetic condition that only affects men and is due to them having an extra ‘X’ sex chromosome and is present in about 1 in 500-1,000 newborn boys; it’s not inherited, but women over the age of 35 are slightly more likely to have boys with this syndrome than younger mothers.
All human genetic material is held on 46 chromosomes, which are identical between the sexes except for the last two chromosomes, the ‘X’ or ‘Y’ that determine our sex:
- Two XX chromosomes is normal for females
- One X and one Y chromosome is normal for males
- In Klinefelter syndrome there’s an extra X (female) chromosome, which results in ‘XXY’
Many boys with Klinefelter syndrome show no symptoms, or they may show some of the possible symptoms after puberty, the degree to which the symptoms are seen varies between individuals, but the chromosomal abnormality means all Klinefelter syndrome men are infertile without specialist help.
- Abnormal body proportions (long legs, short trunk, broad hips) and tall in height
- Muscle weakness, weaker bones, and a lower energy level than other boysi
- Abnormally large breasts and small, firm testes
- A lack of interest in sex, or sexual problems
- Less than the normal amount of pubic, armpit, and facial hair
Infertility is often the reason that a man gets diagnosed with Klinefelter syndrome, and all semen samples from Klinefelter syndrome men reveal no sperm in the sample. Blood tests for hormones will show raised levels of estradiol (one of the estrogens), follicle stimulating hormone (FSH) and luteinizing hormone (LH) and low levels of testosterone, and the definitive test is a chromosome (karyotype) test that shows the extra X chromosome
The genetic variation that causes of the condition is irreversible, however testosterone treatment is an option for those who wish for a more masculine appearance and identity and will increase body hair, energy and sex drive, as well as improve mood and concentration.
As far as fertility is concerned, Klinefelter men are unable to have children without specialist sperm-retrieval techniques that have made it possible for men with Klinefelter syndrome to father a child. By 2010 there had been over 100 successful pregnancies following IVF that used surgically-recovered sperm material from men with Klinefelter syndrome.ii
ii“Should non-mosaic Klinefelter syndrome men be labelled as infertile in 2009?“. Fullerton G, Hamilton M, Maheshwari A. (2010). Hum Reprod. 2010 Mar;25(3):588–97.