Bethlem myopathy is a milder form of congenital muscular dystrophy caused by mutations in the COL6A1, COL6A2, or COL6A3 genes, which encode for components of a protein called collagen type 6.
Bethlem myopathy progresses slowly and can appear at any age. The disease symptoms may appear before birth or may be so subtle that they may not be recognized until well into adulthood. In general, most patients start having symptoms during the first or second decade of life.
The main symptoms seen in patients with Bethlem myopathy are:
- Low muscle tone (hypotonia) and stiff neck (torticollis) that may develop during infancy. These symptoms may be present prenatally in addition to decreased fetal movements, but may be recognized in retrospect.
- Developmental delays and delayed motor milestones during early childhood. For example, babies with Bethlem myopathy may learn to sit or walk by themselves later than usual.
- Contractures or tightness in the finger joints or Achilles tendon. Patients may also show flexion contractures of the wrists, elbows, and ankles. The contractures may appear and disappear in various joints.
- Cardiac problems.
- Respiratory problems. These are rare but patients may need nighttime respiratory support in later life.
- Follicular hyperkeratosis may be seen in some patients. These are unusual skin features such as small bumps around the elbows, soft and velvety skin on the palms and soles, and keloid formation, where wounds split open with little bleeding and widen over time to create shallow scars.
- Walking difficulty. Nearly two-thirds of the patients over age 50 will need to use a walker, cane, or wheelchair.
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