Klinefelter syndrome - X chromosome

Klinefelter syndrome (KS), also known as XXY syndrome or XXY trisomy, is a chromosomal disorder that affects male physical and cognitive development. Its signs and symptoms vary among affected individuals, and may include small testicles that do not produce enough testosterone, which causes delayed puberty or incomplete puberty; gynecomastia; decreased muscle mass and bone density; reduction of facial and body hair; infertility; cryptorchidism; hypospadias and micropenis.

Other physical changes associated with Klinefelter syndrome may include radioulnar sinostosis, clinodactyly in the fifth finger and flat feet; hypotonia and coordination problems that delay the development of motor skills. Older children and adults affected by this syndrome tend to be higher and have a higher risk of developing type 2 diabetes, osteoporosis, rheumatoid arthritis, blood clots, tremor, breast cancer and systemic lupus erythematosus, although the likelihood of manifesting these alterations is similar to that of women in the general population. In addition, children with Klinefelter syndrome may have learning difficulties and delayed speech and language development. They also tend to be calm, sensitive and assertive, although personality characteristics vary among affected individuals.

Klinefelter syndrome is a disease related to the X and Y chromosomes. People usually have two sex chromosomes in each cell: women have two X chromosomes (46, XX), and men have an X chromosome and a Y chromosome (46, XY). Frequently, Klinefelter syndrome is due to the presence of an extra copy of the X chromosome in each cell (47, XXY). Additional copies of genes on the X chromosome interfere with male sexual development, and usually interfere with the normal functioning of the testicles, reducing testosterone levels. Most people with an additional X chromosome have the characteristics described above, although some cases show few or no associated signs or symptoms.

Some people with features of Klinefelter syndrome have more than one extra sex chromosome in each cell (for example, 48, XXXY or 49, XXXXY). These alterations, which are often called variants of the Klinefelter syndrome, tend to cause more intense signs and symptoms than the classic syndrome. On the other hand, in addition to affecting male sexual development, variants of Klinefelter syndrome are associated with intellectual disability, distinctive facial features, skeletal abnormalities, difficulties in coordination and serious problems in speech ability. As the number of additional sex chromosomes increases, so does the risk of these alterations. Some people with features of Klinefelter syndrome have the extra X chromosome only in some of their cells. In these individuals the disorder is described as mosaic Klinefelter syndrome (46, XY / 47, XXY), and the signs and symptoms may be milder, depending on the number of cells that have an additional X chromosome.

Klinefelter syndrome and its variants are not inherited, but these chromosomal changes generally occur as random events during the formation of reproductive cells in one of the parents. An error in cell division, called absence of disjunction, results in a reproductive cell with an abnormal number of chromosomes. For example: a reproductive cell can obtain one or more additional copies of the X chromosome as a result of the absence of disjunction. If one of these atypical reproductive cells contributes to the genetic composition of a child, the child will have one or more additional X chromosomes in each of the body's cells. For its part, the mosaic 46, XY / 47, XXY is not inherited either and is presented as a random event at the beginning of cell division during fetal development. As a consequence, some of the body's cells have an X chromosome and a Y chromosome (46, XY), and other cells have an extra copy of the X chromosome (47, XXY).

Tests performed in IVAMI: in IVAMI we perform the detection of disorders associated with Klinefelter syndrome (KS), by means of the detection of additional X chromosomes.

Recommended samples: non-coagulated blood obtained with EDTA for separation of blood leukocytes.