The symptoms depend on what genetic change is mosaic.

For example, if a person has two populations of cells -- one normal and one missing an X chromosome -- the symptoms are usually milder versions of those seen in Turner syndrome. Turner syndrome results when 100% of cells lack an X chromosome. If only a fraction of cells lack this chromosome, the symptoms will vary from milder to none at all. The severity increases as the percentage of mosaicism increases. If 90% of cells are abnormal, symptoms are likely; if only 10% are abnormal, the person may be unaware that anything is wrong.

Gonadal mosaicism is a different situation. In that case, the mosaicism is in the parent's ovaries or testes. Any individul egg or sperm either has the mutation or not. Therefore, if conception involves one of these mutant sex cells, the resultant child will not be mosaic, but will simply have the genetic disease caused by that particular mutation.

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.