What’s mosaicism?

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Mosaicism is a condition in which an individual’s cells are genetically variegated. Also known as gonadal or chromosomal mosaicism, this condition is congenital and can affect any cell type. Resulting from improper cell division in utero, treatment depends on the type of genetic condition. The prognosis for an individual with mosaicism depends on how their organs and tissues are affected.

Cells that are typically affected by this condition include blood, skin, and reproductive cells. Mosaicism can manifest as a variety of syndromes such as Turner, Klinefelter and Down. Symptoms associated with these conditions are difficult to predict and vary in severity.

Mosaicism can be diagnosed by karyotyping or chromosome analysis. Each sex typically has 46 chromosomes, with males having an XY mating and females an XX mating. When an individual has a form of mosaicism, the pairing or number of chromosomes may be abnormal.

Turner syndrome is a condition that affects females and results from the absence of the usual pair of XX chromosomes. Cells within the individual are missing a portion or all of a single X chromosome. Symptoms of Turner syndrome include short height, no periods, and a broad, flat chest. Newborns with Turner syndrome may have a wide, webbed neck or outstretched hands and feet.

Tests conducted to confirm a diagnosis of this condition may include an echocardiogram, pelvic exam, and ultrasound of the kidneys and reproductive organs. Treatment for Turner syndrome may include giving estrogen replacement therapy and growth hormone. Complications associated with Turner syndrome include obesity, high blood pressure, and kidney problems.

Klinefelter syndrome is characterized by the presence of an additional X chromosome in a male with the normal XY chromosome structure. Males with this condition may experience symptoms including small genitalia, abnormally proportioned extremities, and lack of body hair. In some cases, Klinefelter may not be diagnosed until adulthood, when infertility issues may arise.
Tests used to confirm a Klinefelter syndrome diagnosis include a sperm count and blood tests to measure male hormone levels. Treatment for this condition may include testosterone therapy. Males with Klinefelter syndrome may experience complications including depression, learning disabilities, or the development of an autoimmune disease, such as rheumatoid arthritis or lupus.

Individuals with Down syndrome have an extra chromosome, which, in most cases, is chromosome 21. Also called trisomy 21, this form of mosaicism is the most common cause of birth defects. Those with this condition may exhibit a range of symptoms that vary in severity. Common physical indicators of this condition include a flattened nose, small features, large hands, and an abnormally shaped head. The characteristics of this condition extend beyond the physical to impact emotional, social, and sometimes, psychological development.
The delayed development that children with Down syndrome experience can contribute to problems such as learning disabilities, impulsive behavior, and shortened attention span. Frustration and anger at their delayed development can manifest in behavioral problems, including aggression. Secondary conditions including hypothyroidism, heart defects, and joint problems have been known to occur.

An initial diagnosis of Down syndrome is usually made at birth, but further tests may be administered to confirm it. Tests including an echocardiogram, blood tests for chromosomal analysis, and chest X-rays are usually used. Individuals with this form of mosaicism should be monitored as a precautionary measure to screen for the development of secondary conditions. While there is no treatment for Down syndrome, individuals with birth defects may require corrective surgery to restore and promote function. Complications associated with this condition include hearing and vision problems, heart and gastrointestinal problems, and sleep apnea.

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