Genetics Home > Diagnosing Klinefelter Syndrome
Diagnosing Klinefelter syndrome can be difficult, because not all males carrying the extra chromosome show symptoms. In order to diagnose Klinefelter syndrome, a doctor will perform certain tests. A diagnosis can be made at any time, but the optimal times are shortly after birth or in early childhood. Prenatal testing can also be performed if there is a family history of genetic defects.
Because they often don't appear any different from anyone else, many males with the XXY chromosome arrangement probably never learn of their extra chromosome. However, if a Klinefelter diagnosis is to be made, chances are greatest that it will be made at one of the following times in life:
- Before or shortly after birth
- Early childhood
For males in which Klinefelter syndrome is suspected, a special blood test is recommended to confirm the Klinefelter syndrome diagnosis.
When the doctor suspects that a person has Klinefelter syndrome, he or she may order a special blood test called a karyotype. This test looks at a person's chromosomes and is used to confirm a Klinefelter syndrome diagnosis. The karyotype of a person with Klinefelter syndrome is usually 47,XXY, meaning that an individual has 47 autosomes, two X chromosomes, and a Y chromosome. The usual male karyotype is 46,XY.
In recent years, many males have been diagnosed with Klinefelter syndrome before birth, through amniocentesis or chorionic villus sampling (CVS). In amniocentesis, a sample of the fluid surrounding the fetus is withdrawn. Fetal cells in the fluid are then examined for chromosomal abnormalities. CVS is similar to amniocentesis, except that the procedure is done in the first trimester and the fetal cells needed for examination are taken from the placenta.
Neither procedure is used routinely, except when there is a family history of genetic defects, the pregnant woman is older than 35, or when other medical indications are present.