Bethlem myopathy

Overview

Bethlem myopathy sits within the congenital muscular dystrophies, specifically a related group known as collagen VI-related dystrophy (COL6-RD) — Bethlem is the mildest condition in that family. It causes gradually worsening muscle weakness alongside joint stiffness, most often starting in childhood, and is caused by changes in one of three genes: COL6A1, COL6A2 or COL6A3.

Symptoms

Onset is usually in childhood, though it can appear anywhere from birth to adulthood. Early signs include low muscle tone, unusually flexible ('bendy') joints, muscle weakness, and reaching milestones like sitting or walking a bit later than expected. Weakness tends to be most noticeable around the hips and shoulders, making it harder to lift the arms, get up from sitting, or climb stairs.

Joint stiffness — contractures — commonly affects the wrists, fingers, elbows and Achilles tendons, and some people go on to develop scoliosis. A distinctive feature is skin involvement: because collagen VI is present in skin as well as muscle, cuts and wounds can heal slowly and leave thick, raised keloid scars. Breathing muscles can weaken too, which is worth monitoring even when limb strength seems fine.

Inheritance

Most cases follow an autosomal dominant pattern, where a single changed copy of the gene from either parent is enough to cause the condition. A rarer recessive form exists too, needing a changed copy from both parents, and sometimes the condition appears with no family history at all.

Getting a diagnosis

Diagnosis typically combines a physical exam, muscle imaging (ultrasound or MRI), and a genetic blood test checking the three COL6 genes — genetic testing is the test that actually confirms it. A muscle biopsy is sometimes used as well.

Management and outlook

A multidisciplinary team, usually including a neurologist, is the standard approach. Physiotherapy and gentle exercise — swimming and walking are often recommended — help maintain strength, mobility and breathing capacity. Orthotic devices, splints and braces help manage contractures and scoliosis, with surgery reserved for more severe cases.

Respiratory function is worth monitoring regularly, since the skin/muscle connection doesn't extend protection to the lungs. Most people gradually need some mobility support — a stick, frame or wheelchair — by mid-to-late adulthood, though this varies a great deal. An annual flu vaccine is recommended, alongside the pneumococcal vaccine for anyone using overnight breathing support.