Bethlem Myopathy

Characteristics

Bethlem myopathy is classified as one of the limb-girdle muscular dystrophies, a group of conditions characterized by progressive muscle weakness and atrophy. The disease was first described by Dutch neurologist Bethlem, after whom it is named. As with other limb-girdle muscular dystrophies, the weakness primarily affects the trunk and the shoulder and pelvic girdle muscles.

What sets Bethlem myopathy apart is the early onset of contractures—permanent shortening of muscles or tendons, often around joints—which can occur even before muscle weakness becomes evident. Commonly affected areas include the muscles that flex the fingers, elbows, ankles, and sometimes the spine. In some cases, contractures are already present at birth, and some infants are born with generalized muscle weakness. This has led to Bethlem myopathy occasionally being grouped under the congenital muscular dystrophies.

Prevalence and Disease Course

Bethlem myopathy is rare, with a few families known to be affected in the Netherlands. Exact prevalence figures are not available. The heart muscle functions normally, and life expectancy does not appear to be reduced. However, involvement of the respiratory muscles can occur relatively early in the disease. By age 50, about 70% of individuals require a wheelchair.

Cause

Bethlem myopathy is inherited in an autosomal dominant manner, meaning that a child of an affected parent has a 50% chance of inheriting the condition. Children who do not inherit the disease cannot carry or pass on the gene. The genetic mutations responsible are located on chromosomes 2 and 21.

Treatment

While no cure currently exists, many interventions can help manage the symptoms and improve quality of life. Maintaining muscle strength and overall physical condition is essential, as is minimizing the risk of joint deformities. Rehabilitation physicians, along with physiotherapists, occupational therapists, and related specialists, play a critical role in managing the disease. Simple advice, assistive devices, or accommodations can often make daily activities easier and enhance independence.