The term "Klinefelter syndrome" typically applies to adolescent or adult males with at least one additional X chromosome (usually 47, XXY) that have the signs and symptoms associated with the condition. Not all people with a 47, XXY chromosome finding (karyotype) have Klinefelter syndrome, and not all people with this karyotype necessarily identify as males.
As of 2011, there were 13 reported cases of people with a 47, XXY karyotype and female physical appearance. Despite having a female physical appearance, many of these people had testes and did not have a uterus. In 8 of these 13 cases, further testing revealed that they had complete androgen insensitivity syndrome (CAIS). People with CAIS are typically genetically male but their body is unable to respond to certain male sex hormones (called androgens). As a result they may have mostly female sex characteristics, or signs of both male and female sexual development. Given that a 47, XXY karyotype is not a rare finding, it is possible for people to have this karyotype as well as CAIS.
Another 3 of the women were found to be missing the SRY gene on their Y chromosome (called SRY negative). The SRY gene provides instructions for a protein that causes a fetus to develop as male. If a person is missing the SRY gene, they will develop as female.. This can occur in people with a 46, XY male karyotype, as well.
In the remaining 2 cases of women with a 47, XXY karyotype, the reason for their female development was reportedly not identified. In these reports, the people were not classified as having Klinefelter syndrome. They were referred to as "47, XXY females" or as having a "Klinefelter variant."
Last updated: 10/13/2015
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