What is trisomy 8 mosaicism?

Trisomy 8 mosaicism syndrome (T8mS) is a condition that affects human chromosomes. Specifically, people with T8mS have three complete copies (instead of 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. The condition is sometimes called Warkany syndrome 2.

T8mS is a rare disorder, affecting males more often than females at a ratio of 4-to-1. T8mS is believed to occur in one out of every 25,000-50,000 pregnancies. The chances of having more than one T8mS pregnancy are extremely low.

T8mS is caused by a problem between the sperm and egg in which some cells don’t divide properly. Cells don’t divide at the same time, and chromosomes aren’t distributed properly as a result. This process is called “non-disjunction.” Depending on when the non-disjunction occurs during the baby’s development, the organs and tissues affected by extra chromosomes can vary. The condition is most commonly a chance occurrence, but it is sometimes 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
  • problems with the palate or mouth
  • joint problems and stiffness
  • spinal issues, such as scoliosis
  • kidney problems
  • heart issues
  • bone and structure abnormalities
  • underdeveloped genitals
  • lack of intellectual development
  • extreme stature (either very short or very tall)

T8mS does not always affect intellectual development. Intellectual development will depend, in many ways, on the health of the child during key development stages. Other symptoms of T8mS may cause an infant to have speech or learning delays. But those delays are a result of the child’s physical limitations, not their mental capabilities. Often, children with T8mS “catch up” to their peers in speech and learning. There are cases where individuals with T8mS do not seem to have an intellectual impairment at all.

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. Instead, it just indicates whether T8mS is present.

In most cases, a doctor diagnoses T8mS during pregnancy or early childhood. There are now blood tests that women can take during pregnancy to determine whether the baby they are carrying is likely to have T8mS. If the doctor notices that the baby is measuring small, has only one artery in the umbilical cord, or shows other signs indicating a trisomy, they will prescribe more testing for the baby.

Other kinds of trisomy include Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). All of these syndromes are the result of extra chromosomes in a person’s DNA, but the symptoms of each are vastly different.

Learn more: Triploidy »

There is no cure for T8mS, 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 treat and may require surgery. In some cases, heart surgery is also recommended. A surgeon can often correct palate problems. This will help address any speech delay or impairment.

If most or all cells have the extra chromosome, the condition is 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.

People with T8mS are more likely to develop Wilms’ tumors, a kidney cancer found in children. There is also increased potential to develop myelodysplasias, which are bone marrow conditions. Myeloid leukemia, a form of cancer that affects myeloid tissue, is also a possible complication.

More research is needed to identify the complications that may arise from T8mS. The outcome is hopeful for many children that are born with this syndrome. However, there’s no definitive method of treatment and no way to correct the chromosomal abnormality itself.