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The official name of this gene is “collagen, type IX, alpha 2.”
COL9A2 is the gene's official symbol. The COL9A2 gene is also known by other names, listed below.
The COL9A2 gene provides instructions for making part of a large molecule called type IX collagen. Collagens are a family of proteins that strengthen and support connective tissues, such as skin, bone, cartilage, tendons, and ligaments. In particular, type IX collagen is an important component of cartilage, which is a tough, flexible tissue that makes up much of the skeleton during early development. Most cartilage is later converted to bone, except for the cartilage that continues to cover and protect the ends of bones and is present in the nose and external ears.
Type IX collagen is made up of three proteins that are produced from three distinct genes: one α1(IX) chain, which is produced from the COL9A1 gene, one α2(IX) chain, which is produced from the COL9A2 gene, and one α3(IX) chain, which is produced from the COL9A3 gene. Type IX collagen is more flexible than other types of collagen molecules and is closely associated with type II collagen. Researchers believe that the flexible nature of type IX collagen allows it to act as a bridge that connects type II collagen with other cartilage components. Studies have shown that type IX collagen also interacts with the proteins produced from the MATN3 and COMP genes.
The COL9A2 gene belongs to a family of genes called COLPG (collagen proteoglycans). It also belongs to a family of genes called PG (proteoglycans).
A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genefamilies) in the Handbook.
At least five mutations in the COL9A2 gene have been shown to cause dominant multiple epiphyseal dysplasia, a disorder of cartilage and bone development that primarily affects the ends of the long bones in the arms and legs (epiphyses). All of these mutations disrupt how genetic information is spliced together to make the blueprint for producing the α2(IX) chain. These mutations, called splice-site mutations, change one DNA building block (nucleotide) near an area of the gene called exon 3. These mutations in the COL9A2 gene result in the deletion of 12 protein building blocks (amino acids) from the α2(IX) chain. It is not known how mutations in COL9A2 cause the signs and symptoms of dominant multiple epiphyseal dysplasia.
At least one mutation in the COL9A2 gene has been found to cause the characteristic features of Stickler syndrome, including a distinctive facial appearance, eye abnormalities, hearing loss, and joint problems. The identified mutation is a complex change that deletes eight DNA building blocks (base pairs) and inserts four others (written as c.843_c.846 + 4del8). This mutation is predicted to lead to the production of an abnormally short, nonfunctional version of the α2(IX) chain. Studies suggest that without this chain, functional collagen IX is not produced. A lack of type IX collagen disrupts the development of connective tissues throughout the body, resulting in the signs and symptoms of Stickler syndrome.
When the features of Stickler syndrome result from mutations in the COL9A2 gene, the condition is sometimes called type V Stickler syndrome or autosomal recessive Stickler syndrome. (Autosomal recessive inheritance means two copies of the gene in each cell must be altered to cause the condition.)
At least one mutation in the COL9A2 gene increases an individual's risk for intervertebral disc disease, one of the most common sources of lower back pain. This mutation substitutes the amino acid tryptophan for the amino acid glutamine at position 326 in the α2(IX) chain. This mutation is commonly known as the Trp2 allele and is sometimes written as Glu326Trp. The amino acid tryptophan is rarely found in collagen molecules, and its inclusion likely alters the structure or function of type IX collagen.
Cytogenetic Location: 1p33-p32
Molecular Location on chromosome 1: base pairs 40,766,162 to 40,782,938
The COL9A2 gene is located on the short (p) arm of chromosome 1 between positions 33 and 32.
More precisely, the COL9A2 gene is located from base pair 40,766,162 to base pair 40,782,938 on chromosome 1.
See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.
You and your healthcare professional may find the following resources about COL9A2 helpful.
You may also be interested in these resources, which are designed for genetics professionals and researchers.
See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
acids ; allele ; amino acid ; autosomal ; autosomal recessive ; cartilage ; cell ; collagen ; deletion ; DNA ; dysplasia ; exon ; gene ; inheritance ; joint ; molecule ; mutation ; nucleotide ; protein ; recessive ; syndrome ; tissue
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://www.ghr.nlm.nih.gov/glossary).
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? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.