Trisomy 22: What is it? Chromosomal Problems, Effects of Complete Trisomy 22 and Affected Populations

Chromosome problems are a common cause of early pregnancy loss.

Chromosome problems, such as trisomy 22, are by far the most common cause of  miscarriages in the first trimester.

Depending on which chromosome is affected, extra or missing chromosomes (or parts of chromosomes) can cause anything from minor health problems to conditions incompatible with life.

Trisomy 22 is one of the most severe chromosomal disorders.

What does trisomy 22 mean

Trisomy 22 means that a person has three copies of chromosome 22 instead of the expected two copies.

The condition can be complete (meaning all cells in the body are affected) or mosaic (meaning that some cells are affected but not others).

It is also possible to have a partial trisomy 22, that is, two complete copies of chromosome 22 and an additional incomplete copy of only part of the chromosome.

Diagnosis

Trisomy 22 can be diagnosed through genetic testing after miscarriage or stillbirth.

It can be detected prenatally by CVS or amniocentesis, although prenatal test results showing trisomy 22 do not always mean that the baby will be significantly affected.

Effects of complete trisomy 22

Complete trisomy 22 almost always causes a miscarriage in the first trimester; the condition is incompatible with life and there is no chance that a baby with complete trisomy 22 will survive long term.

Researchers believe that trisomy 22 accounts for 3 to 5 percent of all premature miscarriages. The effects of mosaic trisomy 22 can be mild in some individuals and severe in others.

However, prenatal tests that find mosaic trisomy 22 cannot predict the results.

Many babies who appear to have mosaic trisomy 22 on amniocentesis or CVS results have no obvious health problems at birth; babies confirmed with mosaic trisomy 22 at birth are more likely to experience health problems.

Causes

In most people with chromosome 22, trisomy mosaic, the disorder appears to be the result of errors (eg, nondisjunction) during the division of reproductive cells in one of the parents (parental meiosis) or during the cell division after fertilization ( fetal mitosis ).

There have also been reports that the disorder has occurred in association with uniparental disomy, an abnormality in which affected individuals have inherited both copies of a chromosome pair from one parent, rather than one copy from each parent.

If your baby has trisomy 22

If you were told that a baby you aborted had trisomy 22, please be assured that the miscarriage was not your fault and that you could not have done anything to prevent it.

Having a pregnancy affected by trisomy 22 does not mean that you have an increased risk of developing trisomy 22 in a future pregnancy. In most cases, trisomy 22 is the result of random problems in cell division and does not recur.

If you are currently pregnant and have had a CVS showing trisomy 22, it is a good idea to speak with a genetic counselor or doctor who specializes in genetics.

Your baby is unlikely to have complete trisomy 22, and your baby is more likely to have mosaic trisomy 22 or a type of trisomy 22 that is present only in the placenta.

Your doctor may recommend an amniocentesis to shed more light on the situation. When amniocentesis does not confirm trisomy, chances are high that the trisomy is only present in the placenta and the baby is chromosomally normal.

However, there may be an increased risk of intrauterine growth restriction and pregnancy complications due to the abnormal placenta, and you may need additional monitoring for the remainder of your pregnancy.

If amniocentesis confirms mosaicism in the baby, your genetic counselor or other geneticist can give you the most up-to-date information on what to expect.

Affected populations

Chromosome 22, trisomy mosaic, appears to affect women more often than men. Approximately 15 cases have been reported in the medical literature.