Mosaicism

Mosaicism Diagnosis & Tests

Signs, like symptoms, depend on which genetic change is mosaic. When mosaicism results from mutation during embryonic or fetal growth, one part of the body may have signs or symptoms of a genetic disease, while another part of the body may be normal.

For chromosomal mosaicism, the test is called a karyotype (an analysis of your chromosomes). Both the number and structure of the chromosomes is examined. If two different populations are found, the blood test is usually repeated to make sure the result is accurate. If it is, mosaicism is diagnosed.

For gonadal mosaicism that could cause a genetic disease in the offspring (such as a single gene disorder), the appropriate tests are the same as if the genetic change was present in 100% of the cells. DNA analysis can be done on a man's sperm to look for gonadal mosaicism, but no testing is routinely available for women with gonadal mosaicism. This is because it is difficult to obtain a woman's eggs for testing.

Mosaicism is an example where it is often helpful to do genetic testing on cells from different parts of the body. For example, studying cells from inside the cheek (buccal smear) or from the skin in addition to blood cells. This helps to determine if one part of or fraction of the body is mosaic.