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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


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

Examples of mosaicism include:


Symptoms vary and are very difficult to predict. Symptoms may not be as severe if you have both normal and abnormal cells.

Exams and Tests

Genetic testing can diagnose mosaicism.

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


Treatment will depend on the type and severity of the disorder. You may need less intense treatment if only some of the cells are abnormal.

Outlook (Prognosis)

How well you do depend on which organs and tissues are affected (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 number 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 number of abnormal cells may only be mildly affected. They may not discover that they have mosaicism until they give birth to a child who has the typical (non-mosaic) form of the disease.

Possible Complications

Complications depend on how many cells are affected by the genetic change.

When to Contact a Medical Professional

A diagnosis of mosaicism may cause confusion and uncertainty. A genetic counselor may help answer any questions about diagnosis and testing.


There is currently no known way to prevent mosaicism.

Alternative Names

Chromosomal mosaicism; Gonadal mosaicism


Stankiewicz P, Lupski JR. Gene, Genomic, and Chromosomal Disorders.  In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 40.

Update Date 11/2/2012

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