Klinefelter syndrome occurs only in males and results from an abnormality of one of the sex chromosomes. The condition is usually characterized by the presence of an extra X chromosome. Klinefelter syndrome is estimated to occur in about one in 1,000 live born males and is found in all races, ethnic groups, and socioeconomic classes.
Chromosomes are thin strands of genetic material found in cell nuclei.
Chromosomes contain genetic information that is passed from parents to children and determine a person's unique, hereditary characteristics. In a fertilized egg, one chromosome from each pair of autosomes originates from the mother's egg, the other from the father's sperm. Eggs normally contain a single X chromosome. Sperm cells may contain either an X or Y chromosome. If a sperm bearing the X chromosome fertilizes the egg, the fetus will develop into a female.