Mosaicism

Definition

Mosaicism is a condition in which cells within the same person have a different genetic makeup. This condition can affect any type of cell, including:

• Blood cells
• Egg and sperm cells (gametes)
• Skin cells

Alternative Names

Chromosomal mosaicism; Gonadal mosaicism

Causes, incidence, and risk factors

Mosaicism is caused by an error in cell division very early in the development of the unborn baby.

Examples of mosaicism include:

• Mosaic Down Syndrome
• Mosaic Klinefelter Syndrome
• Mosaic Turner Syndrome

Symptoms

Symptoms vary from person to person and are very difficult to predict. When a person has both normal and abnormal cells, problems may not be as severe.

Signs and tests

Mosaicism can be found through chromosome evaluation or microarray analysis. It is usually described as a percentage of the cells examined. Males normally have the chromosomes 46 XY and females normally have the chromosomes 46 XX.

Tests will likely need to be repeated to confirm the results, and to help determine the type and severity of the mosaicism.

Treatment

Treatment will depend on the type of genetic disease. Patients with mosaicism may need less intense treatment than those with the typical form of the disease because only some of their cells are abnormal.

Expectations (prognosis)

The outlook depends on how much the mosaicism has affected the organs and tissues in the body (for example, the brain or heart). It is difficult to predict the effects of having two different cell lines in one person.

In general, patients with a high percentage of abnormal cells have the same outlook as people with the typical form of the disease (those who have all abnormal cells).

Patients with a low percentage of abnormal cells may only be mildly affected. They may not discover that they have mosaicism until they birth to a child who has the typical (non-mosaic) form of the disease.

Complications

Complications vary based on the type and percentage of cells affected by the genetic change.

Calling your health care provider

A diagnosis of mosaicism can cause confusion and uncertainty. A genetic counselor may help you with diagnosis and testing questions.

Prevention

There is currently no known way to prevent mosaicism.

However, there are options for having a child with normal chromosomes. Discuss this information with your doctor.

References

Hall JG. Single-gene and chromosomal disorders. In: Goldman L, Ausiello D. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 39.

Review Date: 2/17/2009

Reviewed by: Chad Haldeman-Englert, MD, Division of Human Genetics, Children's Hospital of Philadelphia, Philadelphia, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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