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Researchers have not determined which genes on the X chromosome are associated with most of the features of Turner syndrome. People with Turner syndrome caused by X chromosome mosaicism are said to have mosaic Turner syndrome. Some people with Turner syndrome have a chromosomal change in only some of their cells, which is known as mosaicism. Turner syndrome can also occur if one of the X chromosomes is partially missing or rearranged rather than completely absent. The missing genetic material affects development before and after birth.Ībout half of individuals with Turner syndrome have monosomy X, which means each cell in the individual's body has only one copy of the X chromosome instead of the usual two. Turner syndrome results when one normal X chromosome is present in cells and the other sex chromosome is missing or structurally altered. People typically have two sex chromosomes in each cell: generally, females have two X chromosomes, while males have one X chromosome and one Y chromosome. Turner syndrome is related to the X chromosome, which is one of the two sex chromosomes. Developmental delays, nonverbal learning disabilities, and behavioral problems are possible, although these characteristics vary among affected individuals. Most people with Turner syndrome have normal intelligence. Complications associated with these heart defects can be life-threatening.
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One-third to one-half of individuals with Turner syndrome are born with a heart defect, such as a narrowing of the large artery that leaves the heart ( coarctation of the aorta ) or abnormalities of the valve that connects the aorta to the heart (the aortic valve). A small percentage of people with Turner syndrome retain normal ovarian function through young adulthood.Ībout 30 percent of individuals with Turner syndrome have extra folds of skin on the neck ( webbed neck ), a low hairline at the back of the neck, puffiness or swelling ( lymphedema ) of the hands and feet, skeletal abnormalities, or kidney problems. Many affected individuals do not undergo puberty unless they receive hormone therapy, and most are unable to become pregnant naturally. The ovaries develop normally at first, but egg cells usually die prematurely and most ovarian tissue breaks down before birth. Reduced functioning of the ovaries, the female reproductive organs that produce egg cells (oocytes) and female sex hormones, is also very common. The most common feature of Turner syndrome is short stature, which becomes evident by about age 5. Females typically have two X chromosomes, but in individuals with Turner syndrome, one copy of the X chromosome is missing or altered. Turner syndrome is a chromosomal condition that affects development in people who are assigned female at birth.