What Are The Variants?
Print Page- 80% – 90% of affected boys have 47,XXY (one additional X chromosome). Most boys with the 47,XXY karyotype have normal intelligence.
- 10% have mosaicism (46,XY/47,XXY). Men with Klinefelter syndrome mosaicism are often fertile and can father a child through modern technology
- Very rare and more serious variants are 48,XXYY; 48,XXXY; 49,XXXYY; 49,XXXXY; 47,X,i(Xq)Y and 47,X,del(X)Y). Boys with these rare variants have mental retardation that increases with more X chromosomes.
Statistics
- Most males who are infertile and have small testicles (grape size) due to a chromosomal disorder have Klinefelter syndrome with a 47,XXY karyotype (extra X and Y chromosomes) or a variant.
- In Australia, 1 in 650 males is born with Klinefelter syndrome. In the U.S.A., 1 in 500-1,000 males has an extra sex chromosome. Klinefelter syndrome is significantly under-diagnosed in the general population. If your healthcare practitioner is unfamiliar with the finer details of Klinefelter syndrome, there is a list of references at the end of this booklet.