Is there variable expression in Trisomy 13?
There can be variable expression amongst people with trisomy 13. Babies with trisomy 13 will likely not have every possible symptom. Certain symptoms, like intellectual disability, are predicted to be found in most babies with trisomy 13. Degree of symptom severity may depend on how many cells in the body have three copies of chromosome 13. The term mosaicism is used if not all cells in the body have three copies of chromosome 13. Typically, only blood cells are tested to diagnosis trisomy 13. Some medical professionals believe that individuals with less severe trisomy 13 may have some cells with only 2 copies of chromosome 13 but this is hard to prove since samples of tissue from other parts of the body are not easily available to test. For example, a sample of heart tissue would never be taken from a living person to test the idea that mosaic trisomy is lessening the effects of the condition in a given individual.
Neonatal Netw. 2016;35(1):31-6. doi: 10.1891/0730-0822.214.171.124.Trisomy 13: Changing Perspectives.Macias G, Riley C.