is a trisomy affecting the ninth chromosome. Full trisomy 9 would mean that all of the cells in the baby’s body and placenta had three copies of chromosome 9. It is also possible to have partial trisomy 9, meaning there are two full copies of the ninth chromosome plus an additional partial copy. A third type of trisomy 9 involves mosaicism, meaning that the trisomy is present in some of the body’s cells but other cells have a normal set of chromosomes.
Prognosis of Trisomy 9:
Full trisomy 9 is always fatal; most babies with full trisomy 9 are miscarried in the first trimester. Those that make it to birth typically will not survive more than a few months, with most dying in the first week of life. Partial trisomy 9 and mosaic trisomy 9 have a more uncertain prognosis. Many babies with mosaic trisomy 9 die in infancy due to the health problems caused by the disorder, and those that survive usually have severe developmental impairments. Partial trisomy 9 may not affect the baby’s life expectancy, but affected babies may have a range of common health and developmental problems.
The cause of trisomy 9 is an error in cell division affecting either the sperm or egg, meaning that the problem is already present at conception. Sometimes a phenomenon known as trisomy correction can occur very early in embryonic development, leading some cells to be unaffected by trisomy. Researchers believe this is the origin of mosaic trisomy disorders. No one is sure what causes the cell division errors and why some babies experience trisomy correction whereas others do not.
Researchers have not identified any risk factors for having a baby affected by trisomy 9. The condition appears to occur randomly. The only exception is if either parent has a condition known as balanced translocation affecting chromosome 9, which could increase the risk of having a baby with partial trisomy 9, but partial trisomy 9 is relatively rare compared to other types.
Diagnosis of trisomy 9 could come in the form of followup testing after a miscarriage, which could reveal that the miscarried baby had trisomy 9. It is also possible to receive the diagnosis during pregnancy by either CVS or amniocentesis. Screening tests can show that a baby may be more likely to have a genetic disorder, but diagnoses can only be confirmed by genetic testing.