Trisomy 8 mosaicism syndrome (T8mS) is a condition that affects human chromosomes. Specifically, people with T8mS have three complete copies (rather than the typical two) of chromosome 8 in their cells. The extra chromosome 8 appears in some of the cells, but not all. The symptoms of this syndrome vary considerably, ranging from undetectable to, in some cases, severe.
An extra chromosome in all cells is a condition called full or complete trisomy 8, which is deadly and can cause miscarriage during the first trimester of pregnancy.
T8mS is a rare disorder, affecting males more often than females.
Trisomy 8 mosaicism is caused by a problem between the sperm and egg in which some cells don’t divide properly. The condition is a chance occurrence and is not hereditary.
Symptoms of T8mS vary greatly. Some children born with T8mS have severe, highly visible physical symptoms while others display no visible symptoms. Possible symptoms include:
- longer than average head
- wide, deep eyes
- thick lips
- large forehead
- narrow shoulders
- long torso
- narrow pelvis
- deep creases on the hands and feet
- palate (mouth) problems
- joint problems and stiffness
- spinal issues, such as scoliosis
- kidney problems
- heart issues
- bone and structure abnormalities
- underdeveloped genitals
- lack of intellectual development (in some but not all cases)
This condition often goes undiagnosed, because there may be no detectable symptoms. In cases where T8mS is suspected in an infant or adult, the doctor may take a blood or skin sample and perform a cell analysis. This test does not determine the severity of symptoms—rather, it just indicates whether or not it is present.
There is no cure for trisomy 8 mosaicism, but some symptoms of the condition may be treated. Treatment will vary depending on symptoms and severity. Symptoms with no associated health problems (such as facial deformities) may be difficult to properly treat.
If most or all cells have the extra chromosome, this is a condition known as full or complete trisomy 8. Full trisomy 8 is fatal, often leading to miscarriage in the first trimester of pregnancy.>
People with only some of the cells affected can live normal lifespans, as long as other complications from the disorder don’t develop.
Those with T8mS are more likely to develop Wilms’ tumors, a cancer of the kidneys of children. Additionally, there is increased potential to develop myelodysplasias, which are bone marrow conditions, and myeloid leukemia, a form of cancer that affects myeloid tissue.