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The official name of this gene is “transthyretin.”
TTR is the gene's official symbol. The TTR gene is also known by other names, listed below.
The TTR gene provides instructions for producing a protein called transthyretin. This protein transports vitamin A (retinol) and a hormone called thyroxine throughout the body. To transport thyroxine, four transthyretin proteins must be attached (bound) to each other to form a four-protein unit (tetramer). To transport retinol, transthyretin must form a tetramer and also bind to retinol binding protein. Transthyretin is produced primarily in the liver. A small amount of this protein is produced in an area of the brain called the choroid plexus and in the light-sensitive tissue that lines the back of the eye (the retina).
More than 100 mutations in the TTR gene have been found to cause transthyretin amyloidosis. Nearly all of these mutations change one protein building block (amino acid) in the transthyretin protein. The most common mutation found in people with transthyretin amyloidosis replaces the amino acid valine with the amino acid methionine at position 30 in the transthyretin protein (written as Val30Met or V30M). This mutation is seen most commonly in the Portuguese and Swedish populations, although it is found in affected people worldwide. Another common mutation replaces the amino acid valine with the amino acid isoleucine at position 122 in the transthyretin protein (written as Val122Ile or V122I). It is estimated that 3 percent to 3.9 percent of African Americans and 5 percent of some West African populations have this mutation.
Most of the TTR gene mutations that cause transthyretin amyloidosis are thought to alter the structure of transthyretin, impairing its ability to bind to other transthyretin proteins and altering its normal function.
In elderly people, deposits of transthyretin protein cause a condition called senile systemic amyloidosis. People with this condition do not have a mutation in the TTR gene; for reasons that are unclear, the transthyretin protein abnormally begins to form protein deposits. The most common place for amyloidosis in people with this condition is the heart, causing slowly progressive heart failure. Other sites of amyloidosis may include the lungs, blood vessels, and kidneys. It is estimated that 10 percent to 25 percent of people older than 80 have senile systemic amyloidosis.
Cytogenetic Location: 18q12.1
Molecular Location on chromosome 18: base pairs 31,591,766 to 31,599,023
The TTR gene is located on the long (q) arm of chromosome 18 at position 12.1.
More precisely, the TTR gene is located from base pair 31,591,766 to base pair 31,599,023 on chromosome 18.
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 TTR 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.
amino acid ; amyloidosis ; choroid ; choroid plexus ; gene ; heart failure ; hormone ; isoleucine ; methionine ; mutation ; protein ; retina ; tissue ; valine
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.