Ehlers-Danlos syndrome and faulty collagen
Ehlers-Danlos syndrome is a group of inherited connective tissue disorders in which, for most types, faulty collagen weakens the supporting tissue of skin, joints and blood vessels.
Remember
Faulty collagen lowers tensile strength (the ability to resist being pulled apart), so skin stretches unusually far, joints slip out of place and vessel walls can tear.
Memory aid
collagen is the steel cable inside a rope
If the cable is faulty, the rope overstretches and frays, as weak collagen lets tissues overstretch.
The Ehlers-Danlos syndromes (EDS) are a group of inherited connective tissue disorders. Connective tissue is the supporting tissue of skin, joints and blood vessels, and collagen is its main protein. Collagen gives skin, ligaments, joint capsules (the tough sleeve around a joint) and blood vessel walls their tensile strength, meaning their ability to resist being pulled apart.
In most types of EDS, a gene involved in the structure, processing or production of collagen is altered. Collagen is also finished after it is made, through enzyme-driven steps, so the syndromes can arise from faults in its structure, processing or production. Tissues that should resist stretching then give way. The result is joint hypermobility (joints that move beyond the normal range), skin that is hyperextensible (it stretches further than normal), and vessel walls that can tear.
In classical EDS the skin extends easily and snaps back after release, which suggests a lack of tensile strength rather than lost elastic recoil (the spring back after stretching). Classical EDS is caused by a harmful change in one of the collagen genes COL1A1, COL5A1 or COL5A2. Vascular EDS involves COL3A1, which encodes type III procollagen (the molecule from which type III collagen is made), a major protein in vessel walls and hollow organs such as the bowel and the uterus. That is why vascular EDS can cause rupture (bursting) of arteries, the bowel and the pregnant uterus. In hypermobile EDS, the most common type, no underlying gene has been identified so far.
Key facts
- Cause
- in most types, a gene involved in the structure, processing or production of collagen is altered.
- Tensile strength
- collagen resists pulling forces in skin, ligaments, joint capsules and vessel walls.
- Classical EDS
- the skin is hyperextensible, snaps back after release and heals with wide scars.
- Vascular EDS
- a change in the COL3A1 gene affects type III procollagen in vessel walls and hollow organs, so arteries, the bowel and the pregnant uterus can rupture.
- Hypermobile EDS
- the most common type, with no underlying gene identified so far.
- Treatment
- at the moment there is no cure for the syndrome, so treatment is supportive.
Exam traps
- Reduced elastin, the protein that lets skin and arteries spring back after stretching, does not explain classical Ehlers-Danlos syndrome, because the skin extends easily and then snaps back, so the fault lies in the tensile strength of collagen, not in recoil.
- Fibrillin-1 faults cause Marfan syndrome, which also brings a risk of aortic tearing, but they do not explain stretchy skin, because fibrillin is a different protein from collagen and Marfan syndrome typically gives a tall frame, long limbs and lens dislocation.
- An autoimmune attack on the lining of the joints, as in rheumatoid arthritis, makes joints swollen, stiff and painful, but it is acquired and does not make skin stretchy, whereas Ehlers-Danlos syndrome is inherited.
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