Symptoms Bethlem myopathy

The first symptoms of Bethlem myopathy can present at any time from birth through to adulthood and are variable. In childhood, these symptoms can be hypotonia (floppiness) and joint laxity (double jointedness), muscle weakness, delayed achievement of motor milestones such as sitting unaided or walking.

Joint contractures are common in Bethlem myopathy, typically affecting the wrists, fingers, elbows and Achilles tendons. Some stiffness of the spine can also develop over the years.

Other symptoms such as poor stamina/exercise intolerance and difficulty rising from a seated position and climbing stairs are related to the proximal muscle weakness evident in Bethlem myopathy.

As collagen VI is found in the skin as well as the muscles, individuals with Bethlem myopathy have a tendency for scars which heal slowly or become thickened and elevated (keloid formation). The surfaces of the arms and legs can feel ‘rough’ or ‘bumpy’ owing to ‘keratosis pilaris’ which commonly occurs in the skin.

The main complications in Bethlem myopathy are the progression of joint contractures (tightness), increased proximal limb (hip and shoulder girdle) weakness and, to a much lesser extent, a decline in lung function. Physiotherapy and a regimen of stretching can help to prevent or slow the progression of joint contractures. Some adults will become dependent on walking aids (cane, crutches or wheelchair) for walking outdoors.

Lung function in individuals with Bethlem myopathy should be monitored. If indicated (depending on the respiratory function values), overnight sleep studies could be required. Rarely, adults with Bethlem myopathy develop sleep hypoventilation for which night-time non-invasive ventilation (NIV) will be necessary.