Instituto Valenciano de Microbiología

Masía El Romeral
Ctra. de Bétera a San Antonio Km. 0.3
46117 Bétera (Valencia)
Phone. 96 169 17 02
Fax 96 169 16 37
CIF B-96337217


Klinefelter syndrome - Chromosome X

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

Other physical changes associated with Klinefelter syndrome may include radioulnar synostosis, clinodactyly in the fifth finger and flat feet; hypotonia and coordination problems that delay the development of motor skills. Older children and adults with Klinefelter syndrome tend to be taller and have a higher risk of developing type 2 diabetes, blood clots, tremors, breast cancer and systemic lupus erythematosus, although the likelihood of developing these alterations is similar that of women in the general population. In addition, children with Klinefelter syndrome may have learning disabilities and delays in speech and language development. Also, they 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 males have one X chromosome and one 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, often preventing the normal functioning of the testes and reducing testosterone levels. Most people with an additional X chromosome have the characteristics described above, although some have 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 Klinefelter syndrome, tend to cause more intense signs and symptoms than classic Klinefelter syndrome. In addition to affecting male sexual development, variants of Klinefelter syndrome are associated with intellectual disability, distinctive facial features, skeletal abnormalities, poor coordination, and severe speech problems. As the number of additional sex chromosomes increases, so does the risk of these health problems. Some people with features of Klinefelter syndrome have the extra X chromosome in only some of their cells; in these individuals, the alteration is described as the mosaic Klinefelter syndrome (46, XY / 47, XXY). People with mosaic Klinefelter syndrome may have milder signs and symptoms, depending on the number of cells that have an extra X chromosome.

The Klinefelter syndrome and its variants are not inherited; These chromosomal changes generally occur as random events during the formation of the reproductive cells in one of the parents. An error in cell division called absence of disjunction leads to 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 result of the absence of disjunction. If one of these atypical reproductive cells contributes to a child's genetic makeup, the child will have one or more additional X chromosomes in each of the body's cells. The mosaic 46, XY / 47, XXY is not inherited either. It is presented as a random event at the beginning of cell division during fetal development. As a result, some of the body's cells have one X chromosome and one 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 the alterations associated with Klinefelter syndrome, by detecting additional X chromosomes.

Recommended samples: blood extracted with EDTA for separation of blood leukocytes, or card impregnated with dried blood sample (IVAMI can mail the card to deposit the blood sample).