Ehlers-Danlos Syndrome, Classical Type
What is Ehlers-Danlos syndrome, classical type?
Ehlers-Danlos syndrome is a group of inherited disorders that affect connective tissue, the tissue that binds and supports the body's muscles, ligaments, organs, and skin. The classical type is characterised by highly elastic, soft, and doughy skin; unusual scarring; and loose joints. This type of Ehlers-Danlos syndrome combines the types formerly called I and II.
Ehlers-Danlos syndrome, classical type is a subtype of Ehlers-Danlos syndrome.
People with the disorder have smooth, velvety skin that is stretchy, fragile, and easily bruised. Wounds often split open with little bleeding, heal slowly, and leave characteristic thin, wide scars ("cigarette paper" scars). People with this condition also have loose joints with an unusually large range of movement (hypermobility). As a result, joints are prone to dislocation, sprains, and early-onset arthritis. Noncancerous fibrous growths on pressure points (such as elbows) and fatty growths on the forearms and shins are also common.
Other signs of the disorder include weak muscle tone in infants due to hypermobility, which can make them seem "floppy" and delay the development of motor skills such as sitting, standing, and walking. As many as half of people with classical Ehlers-Danlos syndrome have a condition called mitral valve prolapse, which affects blood flow between the chambers of the heart.
How common is Ehlers-Danlos syndrome, classical type?
The classical type is one of the most common forms of Ehlers-Danlos syndrome. It probably affects 1 in 20,000 to 40,000 people.
What genes are related to Ehlers-Danlos syndrome, classical type?
Mutations in the COL1A1, COL1A2, COL5A1, COL5A2, and TNXB genes cause Ehlers-Danlos syndrome, classical type.
Alterations in the COL5A1 gene are most common, accounting for 30 percent to 50 percent of cases. Less commonly, mutations in the COL5A2, COL1A1, and COL1A2 genes cause the condition. The proteins produced by all four genes make up larger molecules called collagens. Collagens provide structure and strength to connective tissue throughout the body. When one of the proteins is altered by a gene mutation, collagen molecules cannot be assembled correctly, and the signs and symptoms of Ehlers-Danlos syndrome result.
A small number of people have mutations in both copies of another gene, TNXB. They have signs and symptoms similar to the classical type of Ehlers-Danlos syndrome, but without unusual scarring. The protein made by the TNXB gene, tenascin-X, is involved in the assembly of collagen and elastic fibers (which provide flexibility to connective tissue). Mutations in the TNXB gene disrupt the normal organisation of connective tissue, leading to the features of Ehlers-Danlos syndrome.
How do people inherit Ehlers-Danlos syndrome, classical type?
This condition is usually inherited in an autosomal dominant pattern, which means one copy of the altered gene is sufficient to cause the disorder. In the rare cases caused by TNXB mutations, the condition has shown an autosomal recessive pattern of inheritance, which means two copies of the gene must be altered for a person to be affected by the disorder.
What other names do people use for Ehlers-Danlos syndrome, classical type?
- Classical Ehlers-Danlos syndrome
- EDS I
- EDS II
- Ehlers-Danlos syndrome, gravis type
- Ehlers-Danlos syndrome, mild classic type
- Ehlers-Danlos syndrome, mitis type
- Ehlers-Danlos syndrome, severe classic type
- Ehlers-Danlos syndrome, type I
- Ehlers-Danlos syndrome, type II