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The official name of this gene is “collagen, type XVIII, alpha 1.”
COL18A1 is the gene's official symbol. The COL18A1 gene is also known by other names, listed below.
The COL18A1 gene provides instructions for making a protein that forms collagen XVIII. Three COL18A1 proteins, called alpha 1 subunits, attach to each other to form collagen XVIII. Collagen XVIII is found in the basement membranes of tissues throughout the body. Basement membranes are thin, sheet-like structures that separate and support cells in these tissues.
There are three versions (isoforms) of the alpha 1 subunit of collagen XVIII, which form three different lengths of the collagen XVIII protein. The short version of collagen XVIII is found in basement membranes throughout the body, including several parts of the eye. The two longer versions are found primarily in the liver. In addition, a piece of collagen XVIII can be cut off to form the protein endostatin. Endostatin is able to block the formation of blood vessels (angiogenesis) and is known as an anti-angiogenic factor.
Little is known about the function of collagen XVIII, but it appears that all of the isoforms are involved in normal development of the eye.
The COL18A1 gene belongs to a family of genes called COL (collagens).
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 a dozen mutations in the COL18A1 gene have been identified in people with Knobloch syndrome, a condition characterized by severe vision problems and a skull defect called an occipital encephalocele. Most COL18A1 gene mutations lead to an abnormally short version of the genetic blueprint used to make the alpha 1 subunit of collagen XVIII. There are a few other mutations that replace single protein building blocks (amino acids) in the protein sequence. Although the process is unclear, the COL18A1 gene mutations result in the loss of collagen XVIII. Most COL18A1 gene mutations affect all isoforms of collagen XVIII, but at least one mutation affects only the short isoform. The loss of one or all isoforms of the collagen XVIII protein likely causes the signs and symptoms of Knobloch syndrome. It is unclear whether endostatin is involved in this condition.
Cytogenetic Location: 21q22.3
Molecular Location on chromosome 21: base pairs 45,405,136 to 45,513,719
The COL18A1 gene is located on the long (q) arm of chromosome 21 at position 22.3.
More precisely, the COL18A1 gene is located from base pair 45,405,136 to base pair 45,513,719 on chromosome 21.
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 COL18A1 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 ; angiogenesis ; basement membranes ; collagen ; gene ; isoforms ; mutation ; protein ; protein sequence ; subunit ; syndrome
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (/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.