Myopathic EDS (mEDS) is one of the 13 types of a group of inherited connective tissue disorders. These disorders, known collectively as Ehlers-Danlos syndrome, or EDS, are caused by mutations in genes that encode for collagen and collagen-related proteins.
The various types of EDS all target the connective tissue that provide structure to joints, skin, and blood vessels.
What causes mEDS?
mEDS is caused by mutations in the COL12A1 gene that encodes for type 12 collagen. Type 12 collagen is required for the structural integrity and function of the skeletal muscles because it interacts with other structural proteins such as decorin, cartilage oligomeric matrix protein, fibromodulin, and tenascin. The mutation affects these interactions and results in weak muscles with defective structures.
This type of EDS may also be caused by mutations in other genes not yet known to be associated with it.
How is mEDS inherited?
mEDS is inherited in either an autosomal recessive or autosomal dominant manner. In general, individuals with a single copy of the mutated COL12A1 gene show milder symptoms than those who have a mutation in both copies of COL12A1. Autosomal dominant inheritance occurs when one gene copy with this mutation is inherited from either the father or the mother, and a normal gene copy is passed along from the other parent. In the case of autosomal recessive inheritance, a mutant copy of the COL12A1 gene is inherited from each parent. In such cases, both parents must carry the mutation, but they may or may not show any symptoms.
What are the symptoms of mEDS?
The hallmark symptoms of mEDS are muscle weakness in early childhood associated with large contractures — permanent tightening of the muscles — of the knee, hip, and elbow joints, also called proximal joints. People with mEDS also usually have hypermobility of the joints of the ankles, wrists, feet, and hands, known as the distal joints. Muscle weakness tends to improve with age.
Other symptoms include soft skin and atrophic scarring, which is an indented scar in the skin. mEDS also is linked to delays in motor development and myopathy, symptoms of which can include muscle weakness, cramps, stiffness, and spasms.
How is mEDS diagnosed?
The hallmark features of mEDS are critical for an initial diagnosis. Genetic testing to confirm the presence of mutations in the COL12A1 gene is required for a diagnosis. Sometimes, a whole-exome sequencing may be performed to test for mutations in all genes in one single test. This also allows the identification of any mutations in genes such as COL6A1, COL6A2, COL6A3 genes, which cause other diseases like Bethlem myopathy and Ullrich congenital muscular dystrophy.
Should no COL12A1 mutations be found, alternative disorders — like other forms of EDS, Bethlem, or Ullrich — should be considered.
How is mEDS treated?
People with mEDS need to be monitored for respiratory issues. If they have nocturnal hypoventilation, which is abnormally slow breathing during sleep, they may require assisted non-invasive ventilation at night.
Last updated: Nov. 5, 2019
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