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Klinefelter’s syndrome, 47,XXY or XXY syndrome is a condition caused by a chromosome aneuploidy. Affected individuals have at least two X chromosomes and at least one Y chromosome.[1] Klinefelter’s syndrome is the most common sex chromosome disorder.[2]:549
The principal effects are development of small testicles and reduced fertility. A variety of other physical and behavioral differences and problems are common, though severity varies and many boys and men with the condition have few detectable symptoms. Named after Dr. Harry Klinefelter, an endocrinologist at Massachusetts General Hospital, Boston, Massachusetts, who first described it in 1942[3], it is the second most common disease involving the presence of an extra chromosome. The condition exists in roughly 1 out of every 500 males.[4] Because of the extra chromosome, individuals with the condition are usually referred to as “XXY Males”, or “47, XXY Males”.[5]
Affected males are almost always effectively infertile although advanced reproductive assistance is sometimes possible.[6] Some degree of language learning impairment may be present,[7] and neuropsychological testing often reveals deficits in executive functions.[8] In adults, possible characteristics vary widely and include little to no signs of affectedness, a lanky, youthful build and facial appearance, or a rounded body type with some degree of gynecomastia (increased breast tissue).[9] Gynecomastia is present to some extent in about a third of affected individuals, a slightly higher percentage than in the XY population, but only about 10% of XXY males’ gynecomastia is noticeable enough to require surgery.[10]
The term “hypogonadism” in XXY symptoms is often misinterpreted to mean “small testicles” or “small penis”. In fact, it means decreased testicular hormone/endocrine function. Because of this hypogonadism, patients will often have a low serum testosterone level but high serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels.[11] Despite this misunderstanding of the term, however, it is true that XXY men often also have “microorchidism” (i.e. small testicles).[11]
The more severe end of the spectrum of symptom expression is also associated with an increased risk of germ cell tumors, breast cancer,[12] and osteoporosis,[4] risks shared to varying degrees[13] with females. Additionally, medical literature shows some individual case studies of Klinefelter’s syndrome coexisting with other disorders, such as pulmonary disease, varicose veins, diabetes mellitus, and rheumatoid arthritis, but possible correlations between Klinefelter’s and these other conditions are not well characterized or understood.[citation needed]
In contrast to these potentially increased risks, it is currently thought that rare X-linked recessive conditions occur even less frequently in XXY males than in normal XY males, since these conditions are transmitted by genes on the X chromosome, and people with two X chromosomes are typically only carriers rather than affected by these X-linked recessive conditions.
There are many variances within the XXY population, just as in the most common 46,XY population. While it is possible to characterise 47,XXY males with certain body types, that in itself should not be the method of identification as to whether or not someone has 47,XXY. The only reliable method of identification is karyotype testing.
A karyotype is used to confirm the diagnosis. In this procedure, a small blood sample is drawn. White blood cells are then separated from the sample, mixed with tissue culture medium, incubated, and checked for chromosomal abnormalities, such as an extra X chromosome.
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