Trisomy Disorders

Trisomy 22

Posted on: October 30, 2008

What is chromosome 22?

Chromosome 22 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 22 is the second smallest human chromosome, spanning about 49 million base pairs (the building material of DNA) and representing between 1.5 and 2 percent of the total DNA in cells.

In 1999, researchers working on the Human Genome Project announced they had determined the sequence of base pairs that make up this chromosome. Chromosome 22 was the first human chromosome to be fully sequenced.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 22 likely contains between 500 and 800 genes.

Genes on chromosome 22 are among the estimated 20,000 to 25,000 total genes in the human genome.

There are many conditions related to genes on chromosome 22.

What chromosomal conditions are related to chromosome 22?

The following conditions are caused by changes in the structure or number of copies of chromosome 22.

22q11.2 deletion syndrome
Most people with 22q11.2 deletion syndrome are missing about 3 million base pairs on one copy of chromosome 22 in each cell. The deletion occurs near the middle of the chromosome at a location designated as q11.2. This region contains about 30 genes, but many of these genes have not been well characterized. A small percentage of affected individuals have shorter deletions in the same region.

The loss of one particular gene, TBX1, is thought to be responsible for many of the characteristic features of 22q11.2 deletion syndrome, such as heart defects, an opening in the roof of the mouth (a cleft palate), distinctive facial features, and low calcium levels. A loss of this gene does not appear to cause learning disabilities, however. Other genes in the deleted region are also likely to contribute to the signs and symptoms of 22q11.2 deletion syndrome.

other chromosomal conditions
Other changes in the number or structure of chromosome 22 can have a variety of effects, including mental retardation, delayed development, physical abnormalities, and other medical problems. These changes include an extra piece of chromosome 22 in each cell (partial trisomy), a missing segment of the chromosome in each cell (partial monosomy), and a circular structure called ring chromosome 22 that is caused by the breakage and reattachment of both ends of the chromosome.

Cat-eye syndrome is a rare disorder most often caused by a chromosomal change called an inverted duplicated 22. A small extra chromosome is made up of genetic material from chromosome 22 that has been abnormally duplicated (copied). The extra genetic material causes the characteristic signs and symptoms of cat-eye syndrome, including an eye abnormality called ocular iris coloboma (a gap or split in the colored part of the eye), small skin tags or pits in front of the ear, heart defects, kidney problems, and, in some cases, delayed development.

A rearrangement (translocation) of genetic material between chromosomes 9 and 22 is associated with several types of blood cancer (leukemia). This chromosomal abnormality, which is commonly called the Philadelphia chromosome, is found only in cancer cells. The Philadelphia chromosome has been identified in most cases of a slowly progressing form of blood cancer called chronic myeloid leukemia, or CML. It also has been found in some cases of more rapidly progressing blood cancers (acute leukemias). The presence of the Philadelphia chromosome can help predict how the cancer will progress and provides a target for molecular therapies.

Is there a standard way to diagram chromosome 22?

Geneticists usediagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome’s relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope.These bands are used to describe the location of genes on each chromosome.

Ideogram of chromosome 22 See How do geneticists indicate the location of a gene? in the Handbook. Where can I find additional information about chromosome 22?

You may find the following resources about chromosome 22 helpful.

You may also be interested in these resources, which are designed for genetics professionals.

Where can I find general information about chromosomes?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding chromosome 22?

acute ; base pair ; calcium ; cancer ; chromosome ; chronic ; cleft palate ; coloboma ; deletion ; DNA ; gene ; genome ; kidney ; learning disability ; leukemia ; mental retardation ; monosomy ; palate ; rearrangement ; ring chromosomes ; sign ; symptom ; translocation ; trisomy

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

References (13 links) 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

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Complete Trisomy 22

http://www.nt.net/~a815/fullt22.htm

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Chromosome 22 Central

SUPPORT FOR
CHROMOSOME 22 RELATED DISORDERS

237 Kent Avenue
Timmins, Ontario CANADA
P4N 3C2
(705) 268-3099
a815@c22c.org

http://www.c22c.org/

.…………………….

Chromosome 22 related Syndromes

http://ibis-birthdefects.org/start/digeorge.htm

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Trisomy 22 Interest Board

http://members.boardhost.com/Stephanie/

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Human Chromosome 22 Project Overview

http://www.sanger.ac.uk/HGP/Chr22/

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National Organization for Rare Disorders, Inc.

Chromosome 22, Trisomy Mosaic

Important
It is possible that the main title of the report Chromosome 22, Trisomy Mosaic is not the name you expected. Please check the
synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.

Synonyms

  • Trisomy 22 Mosaic
  • Trisomy 22 Mosaicism Syndrome

Disorder Subdivisions

  • None

General DiscussionChromosome 22, Trisomy Mosaic is a rare chromosomal disorder in which chromosome 22 appears three times (trisomy) rather than twice in some cells of the body. The term “mosaic” indicates that some cells contain the extra chromosome 22, whereas others have the normal chromosomal pair.

The range and severity of associated symptoms and findings may vary, depending upon the percentage of cells with the chromosomal abnormality. However, characteristic features typically include growth delays, mental retardation, unequal development of the two sides of the body (hemidystrophy), and webbing of the neck. Affected individuals may also have abnormal outward deviation of the elbows upon extension (cubitus valgus), multiple pigmented moles or birthmarks (nevi), distinctive malformations of the head and facial (craniofacial) area, and other physical abnormalities..

………………………..

Resources Support Organization for Trisomy 18, 13, and Related Disorders
2982 South Union Street
Rochester, NY 14624-1926
Tel: (716)594-4621
Fax: (716)594-4621
Tel: (800)716-7638
Email: barbv@trisomy.org

Internet: http://www.trisomy.org

March of Dimes Birth Defects Foundation
1275 Mamaroneck Avenue
White Plains, NY 10605
Tel: (914)428-7100
Fax: (914)997-4763
Tel: (888)663-4637
TDD: (914)997-4764
Email: Askus@marchofdimes.com

Internet: http://www.marchofdimes.com

The Arc (a national organization on mental retardation)
1010 Wayne Ave
Suite 650
Silver Spring, MD 20910
Tel: (301)565-3842
Fax: (301)565-3843
Tel: (800)433-5255
TDD: (817)277-0553
Email: info@thearc.org

Internet: http://thearc.org/

National Organization for Rare Disorders, Inc.
55 Kenosia Ave
PO Box 1968
Danbury, CT 06813-1968
Tel: (203)744-0100
Fax: (203)798-2291
Tel: (800)999-6673
TDD: (203)797-9590
Email: orphan@rarediseases.org

Internet: http://www.rarediseases.org

American Heart Association
National Center
7272 Greenville Avenue
Dallas, TX 75231-4596
Tel: (214)373-6300
Fax: (214)373-0268
Tel: (800)242-8721
Email: inquire@heart.org

Internet: http://www.americanheart.org

Support Organization for Trisomy 13/18 and Related Disorders, UK
7 Orwell Road
Petersfield
Hampshire, Intl GU31 4LQ
United Kingdom
Tel: 0121-351-3122
Email: enquiries@soft.org.uk

Internet: http://www.soft.org.uk

UNIQUE – Rare Chromosome Disorder Support Group
P.O. Box 2189
Caterham
Surrey, Intl CR3 5GN
United Kingdom
Tel: 4401883 330766
Fax: 4401883 330766
Email: info@rarechromo.org

Internet: http://www.rarechromo.org

Congenital Heart Disease Resource Page
Web Site on the Internet

Email: sheri.berger@csun.edu

Internet: http://www.bamdad.com/sheri/

For a Complete Report

This isan abstract of a report from the National Organization for Rare Disorders, Inc. ® (NORD). A copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see

http://www.rarediseases.org/search/rdblist.html

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