What causes Klinefelter Syndrome

Klinefelter syndrome occurs after the mother’s egg is fertilized. Chromosome pairs are supposed to separate, so that two daughter cells receive one chromosome each. In Klinefelter syndrome, the pair does not disjoin (separate). Both of the chromosomes in the pair go to one daughter cell. The other daughter cell receives none. This problem happens more frequently in older mothers, and is called meiotic nondisjunction.

As a result of this genetic problem, the Klinefelter syndrome baby develops an abnormal pituitary gland, testicles, and hypothalamus portion of the brain. The boy’s testicles degenerate, so they often cannot produce enough sperm in later life. Healthy tissue is replaced by clear, glassy collagen fibers, called hyaline. The boy has scar tissue (fibrosis) in his seminiferous tubules, where his sperm form.

Feminine breasts develop in late puberty for 50% of Klinefelter syndrome adolescents. Urine tests show elevated gonadotropin levels, which mean the male is sterile. Psychosocial problems and low self-esteem result from the feminizing effects of the hormone estradiol.