Chromosome 22q11.2 duplication syndrome

Causes

What gene change causes 22q11.2 duplication syndrome?

Chromosomes are made up mostly of DNA, and are the structures in the body's cells that carry genetic information (known as genes), which direct the body how to grow and develop. Humans have 46 chromosomes in most cells of their body, which are arranged in 23 pairs. The first 22 pairs of chromosomes are called autosomes and are numbered 1-22. The 23rd pair is known as the sex chromosomes (XX for female and XY for male). Each chromosome has a short (p) arm and a long (q) arm, and sections known as bands are numbered on the p and q arm (like the house number on a street).

Individuals with 22q11.2 duplication syndrome have an extra copy of a small piece of chromosome 22 on the long arm (q) of this chromosome, labeled, q11.2. The typical duplication (extra genetic material) at 22q11.2 results in a person having an additional 3 megabases (3 Mb) of DNA or an extra 30-40 genes.

Not everyone with 22q11.2 duplication has the exact same area of chromosome 22q duplicated. Some people have larger duplications (from 4-6 Mb), where a small number of affected individuals have a shorter duplication in the same region. The size of the duplication will also change the number of genes involved, with larger duplications meaning that more genes are involved and smaller duplications meaning that fewer genes are involved in the duplication. Variation in the size of the specific duplication (and therefore which genes are involved) may contribute to some of the differences seen between individuals who have 22q11.2 duplication syndrome.

The function of all of the genes involved in 22q11.2 duplication syndrome are not well understood. It is not currently known why duplication in these genes causes the health and developmental problems in some individuals with 22q11.2 duplication syndrome, and why others with 22q11.2 duplication syndrome do not have any obvious physical, medical or developmental differences as a result of having this duplication. It is possible that having extra copies of these genes leads to some of the symptoms seen in 22q11.2 duplication syndrome. Since so little is known about the function of many of the genes in this region, researchers are working to determine which duplicated genes may contribute to the developmental delay and other problems that can affect people with 22q11.2 duplication syndrome.

The medical specialty commonly involved in diagnosing and providing care for individuals with chromosome changes, including 22q11.2 duplication syndrome, is medical genetics. If you are interested in finding out more about medical genetics services in your area, you may be able to ask you primary care physician for a referral. The National Society of Genetic Counselors website includes a searchable "Find a Genetic Counselor" directory, which may help you locate a genetic counselor in the United States or Canada.

References
  • Unique. (2012). 22q11.2 duplications. Retrieved February 20, 2016, from http://www.rarechromo.org/information/Chromosome%2022/22q11.2%20duplications%20FTNW.pdf
  • Firth HV. 22q11.2 Duplication. 2009 Feb 17 [Updated 2013 Nov 21]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016. Available from: http://www.ncbi.nlm.nih.gov/books/NBK3823/
  • Genetics Home Reference. (2011). 22q11.2 duplication. Retrieved February 20, 2016, from http://ghr.nlm.nih.gov/condition/22q112-duplication

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