Learn about the structural protein behind connective tissue and vascular EDS
Collagen is the major structural protein of connective tissue and therefore one of the most abundant structural proteins in our body. Collagen is a major structural component of blood vessel walls, the bowel, lungs uterus tendons and also our skin. In addition, collagen plays a large and fundamental role in wound healing after an injury to the skin. To date we identified about 27 different types of collagen.
According to the 2017 International Classification of EDS, there are 13 different types or 'variants' of Ehlers-Danlos syndrome. There are 5 types of collagen involved in, and responsible for, these syndromes. Type 1 collagen is the most abundant form found in the body. It is located in high amounts in the skin, tendons, ligaments and bones. Type 2 collagen is a major component of hyaline cartilage (a form of cartilage found in different parts of the body such as joints). Type 3 collagen is responsible for vascular Ehlers-Danlos syndrome. It is present in blood vessels, lungs, bowel and has a major role in the wound healing process. This explains why the issues of vEDS often include blood vessel injury, bowel perforation and abnormal scar formation. Type 4 and 5 collagen are present in the extracellular matrix and the basement membranes. This is the area that surrounds different cells of the body, helping to anchor them and give them support.
Ehlers-Danlos Syndromes are the result of mutations in the various collagen genes and related processing enzymes (a type of protein) which help create them. This results in various errors in the 'synthesis' (or production of) of the collagen fibers. Or put another way, when collagen is made it is similar to an assembly line process to build a car. 'Processing enzymes' are the factory workers helping to build the final collagen 'product'. If a factory worker forgot to put the engine in the car as it was being built, then that car would not work properly when it reached the end of the assembly line. Similarly, errors in the building process of collagen lead to faulty collagen which doesn't work like its supposed to-- and this is what leads to the disease.
These errors in collagen synthesis will result either in reduction of the amount of the specific collagen or structural defects that impact on the structural integrity of the collagen molecule and therefore impact on their ability to function in a structural support capacity under stress, such as in the case increased blood pressure in our blood vessels, in the skin, the wall of the bowel, uterus lungs, ligaments, tendon and bones etc.
Collagen and its Relationship to EDS
Patients with haploinsufficiency vascular EDS have a different underlying cause of their vEDS. Most vascular EDS patients have one 'normal' type III collagen gene (COL3A1) and one 'abnormal' (or mutated) type III collagen gene. This leads to abnormal collagen fibers, with 7/8ths of the collagen produced being abnormal. Haploinsufficiency vEDS is caused by having one 'normal' type III collagen gene and then one gene that does not produce any collagen. This is known as a 'null mutation'.
Therefore, these patients only produce normal collagen, but in less quantity compared to a person unaffected by vEDS. As a result, haploinsufficiency vEDS tends to have later onset of complications by almost 15 years and extended life expectancy compared to other vEDS patients.
What is Haploinsufficiency vEDS?