Mosaic Trisomy 22 is a rare chromosome disorder.

Someone with a mosaic condition will have two different types of cells. Mosaic trisomy 22 occurs when a third copy of chromosome 22 (a trisomy) is present in only some cells, resulting in a “mosaic” pattern. The number of cells affected with the extra chromosome can vary,

Mosaicism occurs when a chromosome error happens after fertilization. The zygote (a fertilized egg that develops into an embryo) starts with a normal set of chromosomes, but an error occurs during mitosis (cell division) in one of those early cells (an embryo begins as one cell and divides to make 2, then 4, then 8, and so on). Once the error occurs, every cell afterward will have the same error. The cells with normal chromosomes will also continue to divide.

For people affected with mosaic trisomy 22, it is common to see an uneven development of each side of the body (hemidystrophy), shorter stature, differences in facial features, limb differences, differences in skin pigmentation, hearing loss, heart defects, and developmental delays as well as other features. It is important to remember that not all people with mosaic trisomy 22 will have every feature of the condition and can be impacted differently depending on how many cells are affected by the extra chromosome 22. 

It is impossible to predict how a person with this diagnosis will be impacted, as the number of cells with the extra chromosome 22 is variable. Despite most published cases noting delays in development and cognition, there are reports of normal intellectual development. Researchers have suggested that there is no true correlation between the percentage of trisomic cells and the impact on intellectual development (Abdelgadir, Nowaczyk & Li, 2013; Mazza, et al, 2010).

Less than 45 cases (pre and postnatal) are presented in the medical literature. Some researchers have suggested that it may be under-identified in the population as some people may be mildly affected (Abdelgadir, Nowaczyk & Li, 2013). 

Treatment and support for people with mosaic trisomy 22 will depend on how the condition affects them. For example, people with heart defects may require surgery, and people with developmental delays will require early intervention and support to reach their potential and may benefit from speech and or physical therapies and educational support. As with most of the people in our support group, you will likely be seeing many different specialists. Families supporting individuals with mosaic trisomy 22 will benefit from the services of genetic counsellors and care coordinators to help navigate accessing the right supports.

Mosaic Trisomy 22 Findings may include:

• Intrauterine growth restriction
• Postnatal growth failure – often shorter stature
• Body asymmetry (where one side of the boy develops differently than the other)
• Webbing of the neck
• Differences in facial features
• Congenital heart defects
• Gastrointestinal differences 
• Changes in skin pigmentation
• Differences in skin such as pits, tags or clefts
• Differences in limbs, fingers and toes
• Cranial differences such as microcephaly
• Hearing loss
• Hypotonia (muscle weakness)
• Eye differences
• Dental abnormalities
• Developmental and intellectual disabilities
• Delays in sexual maturity/differences in reproductive organs (missing or abnormally developed ovaries)

The most recent comprehensive review on mosaic trisomy 22 was published in March 2024 by Trevisan et al. You can find a freely accessible copy of the paper here.

Search PUBMED for articles on Mosaic Trisomy 22

National Organization for Rare Disorders Entry on Mosaic Trisomy 22

Join C22C’s Facebook Group to connect with other families.

Mosaic Trisomy 22 Facebook Group (Not affiliated with C22C)

Mosaic Trisomy 22 References