What causes classical-like EDS?
Classical-like EDS is caused by mutations in the TNXB gene. This gene provides instructions to build a protein called tenascin-X, which supports the function of collagen. Collagen is a family of proteins that is an integral part of the connective tissue. Tenascin-X supports the structure of muscles, joints, skin, and organs. Defects in the tenascin-X protein lead to the symptoms of classical-like EDS, such as joint hypermobility and soft skin.
In some individuals, classical-like EDS is caused by large deletions of genetic material, in which case the TNXB gene and the nearby CYP21A2 gene are both deleted. Mutations in CYP21A2 lead to congenital adrenal hyperplasia, a genetic condition that affects the adrenal glands. These glands produce hormones and are found above the kidneys.
How is classical-like EDS inherited?
Classical-like EDS is inherited in an autosomal recessive manner. That means that both copies of the TNXB gene (one from the father and one from the mother) have to be mutated for the condition to manifest. When both parents carry one copy of the mutated TNXB gene, their child has a 25% chance of inheriting classical-like EDS. There is a 50% chance of the child inheriting one mutated copy from either parent in which case they become a carrier. A carrier is usually symptom-free but can pass on the mutation to the next generation. In some rare cases, individuals with one mutated TNXB gene copy show symptoms similar to hypermobile EDS.
What are the symptoms of classical-like EDS?
Common symptoms of classical-like EDS include:
- joint hyperflexibility
- hypotonia (low or weak muscle tone)
- weak upper arm and upper leg muscles
- easy bruising
- muscle aches
- hyperelastic and thin skin
- skeletal muscle degeneration
- sensory neuropathy (damage to sensory nerves)
- joint pain
How is classical-like EDS diagnosed?
As in other types of EDS, diagnosing classical-like EDS can be challenging. It usually involves an assessment of the patient’s medical history, a detailed analysis of the symptoms, a physical exam, and a genetic test to confirm the diagnosis.
The physical exam is very individualized and dependent on the patient’s symptoms. Because joint hypermobility occurs in more than 80% of classical-like EDS patients, the exam usually involves measuring joint hypermobility, using the Beighton scoring system. This is a scale that measures the angle that the patients can comfortably reach by bending the joints of their thumbs, fingers, elbows, spine, and knees. A score of 5 or higher indicates joint hypermobility.
A genetic test can detect mutations and is performed to confirm a diagnosis of EDS. The test can also identify the type of EDS (i.e., classical-like EDS) by detecting mutations in the TNXB gene. (Other types of EDS are caused by mutations in different genes.)
How is classical-like EDS treated?
As with other types of EDS, there is currently no cure for classical-like EDS, and treatments focus on managing the symptoms of the disease.
Last updated: Oct. 25, 2019
Ehlers-Danlos News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.