Klinefelter syndrome

Klinefelter syndrome is a chromosomal condition in which a person typically has an extra X chromosome, often resulting in a 47,XXY karyotype. It can affect sexual development, fertility, and other traits, with wide variation among individuals.

47,XXY: A chromosome complement containing two X chromosomes and one Y chromosome. This is the most common chromosome pattern associated with Klinefelter syndrome.
Karyotype: An organized display of an individual's chromosomes used to examine their number and structure. Chromosome analysis can confirm an XXY or mosaic chromosome pattern.
46,XY: The typical chromosome complement of a male, with one X chromosome and one Y chromosome. It provides the chromosome-pattern comparison for the common 47,XXY karyotype.
Azoospermia: The absence of sperm in semen. Many adults with Klinefelter syndrome have little or no sperm in the ejaculate.
Meiosis: The cell-division process that produces eggs or sperm with half the usual chromosome number. Errors in chromosome separation during meiosis can produce a gamete with an extra X.
Sex chromosome aneuploidy: A chromosome-number difference involving one or more sex chromosomes. Klinefelter syndrome is one form of this broader class of chromosome conditions.
Prenatal diagnosis: Testing during pregnancy to assess fetal health or identify genetic and chromosomal conditions. Prenatal tests may identify an extra X chromosome before birth.
46,XX: The typical chromosome complement of a female, with two X chromosomes and no Y chromosome. It helps distinguish the usual XX pattern from sex-chromosome variations such as XXY.
Hypogonadism: Reduced function of the gonads, including insufficient production of sex hormones or gametes. Testicular dysfunction is a frequent feature of the condition.
Nondisjunction: Failure of chromosomes or chromatids to separate properly during cell division. This chromosome-separation error can lead to an XXY chromosome complement.

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