- Fetal abnormalities such as cystic hygroma (fluid around the neck), or incidentally when a routine amniocentesis is performed (e.g., for advanced maternal age)
- Webbed neck (excess skin) or lymphedema (swelling of hands and feet) in newborns
- Specific heart problems in infants
- Slow growth and/or short stature
- Delayed puberty or amenorrhea (lack of menstrual cycles)
- Infertility or menstrual irregularities
Turner Syndrome (TS) is a chromosome abnormality affecting about 1 in every 2,000 female births and up to10% of miscarriages. TS is characterized clinically by short stature, ovarian failure, and a variety of other features such as extra neck skin, heart abnormalities, mild hearing loss, and others. Genetically, TS is due to the absence of all or part of one sex chromosome, usually one X. This abnormality, also called monosomy X, is denoted medically as the 45,X (older literature used XO) karyotype, as opposed to the usual 46,XX female karyotype. Many, perhaps most, girls and women with TS are actually mosaic, meaning that they have cells with more than one karyotype. Often there is a mix of 46,XX and 45,X cells, and in this case the resulting clinical abnormalities tend to be milder than in 45,X TS. Mosaicism, especially 45,X/46,XX, is frequently detected by prenatal diagnosis (amnicentesis). Occasionally there is mosaicism for cells containing Y chromosome material – but not enough to cause male sexual features. Girls with TS and Y chromosome mosaicism are at increased risk of developing a tumor of the gonads and should have their non-functioning ovaries removed. Molecularly, most TS features result from having one rather than two copies of certain X chromosome genes. To date, one gene called SHOX has been clearly implicated in TS. Loss of one copy of SHOX is the main cause of short stature in TS. Identification of TS genes may lead to better treatments for short stature and other symptoms. (This article was provided by Dr. Andrew Zinn) How reliable are the FISH and the Karyotype tests? What is the life expectancy of a woman with Turner syndrome? How often does Turner syndrome occur? Is Turner syndrome inherited? What does “mosaic” mean?Mosaicism is defined as “a condition in which tissues of genetically different types occur in the same organism”. For individuals with Turner Syndrome, it means that the second X chromosome is not entirely missing. In a person with mosaic Turner Syndrome, some cells have the normal number of 46 chromosomes, but other cells are missing one X or there are structural defects in the second X.
Many different karyotypes fall under the category of “mosaic”. Some of the most common mosaic karyotypes are 45,X/46,XX and 45,X/46,XY. Other variations include:
- Partial deletions: This occurs when part of the chromosome is missing.
- Isochromosomes: The centromere, or center part of the chromosome, is upposed to separate a short arm from a long arm. An isochromosome means that the two arms are of equal length and the information in each one is genetically identical.
- Ring chromosomes: This occurs when the chromosome breaks at each end, loses its end segments and curls around to form a ring shape.
While there is still some question as to how and when any form of Turner Syndrome occurs, it is believed that mosaicism always occurs after fertilization, when the embryo has between 2 and 100 cells. At this point, many organ systems and other tissues are still forming, and some systems may have the normal karyotype, while others may adopt the new or “abnormal” karyotype, resulting in an individual with mosaic Turner Syndrome.
People with Turner Syndrome should be familiar with their karyotypes for a variety of reasons. Generally speaking, individuals with 45,X/46,XX mosaicism have fewer and less severe symptoms of TS compared to individuals with 45,X karyotypes. Unfortunately, it is impossible to know what percentage of 45,X and 46,XX cells there are in various organs such as the heart, brain or kidneys. So, for each individual, the severity of Turner Syndrome characteristics is unpredictable. For those with karyotypes that include all or part of a Y chromosome, it is important to investigate the possibility of tumors that can develop in the ovaries.
Because the severity and frequency of Turner Syndrome features can vary from individual to individual, it is important to discuss your karyotype and its implications with a qualified physician.
When asked about mosaicism and its implications for those with Turner Syndrome, Dr. Andrew Zinn, Associate Professor of Internal Medicine at the University of Texas Southwestern Medical School and Chair of the Medical Advisory Board stated, “I really believe in diagnosing and treating the patient, and not the karyotype… the problems associated with Turner Syndrome should be treated no differently in women with mosaic versus non-mosaic karyotypes.