MYH7-related scapuloperoneal myopathy

Alternate names

Scapuloperoneal myopathy, MYH7-related; MYH7-related late-onset scapuloperoneal syndrome; MYH7-related late-onset SPMD; MYH7-related late-onset scapuloperoneal muscular dystrophy

Definition

MYH7-related scapuloperoneal myopathy is an inherited muscular dystrophy characterized by weakness and wasting of the muscles in the lower legs and the area of the shoulder blades. In some individuals, facial muscles may also be affected.

Cause

• MYH7-related scapuloperoneal myopathy is caused by mutations in the MYH7 gene.
• This gene, located on chromosome 14q12, provides instructions for making a protein known as the cardiac beta (β)-myosin heavy chain.
• This protein is found in heart (cardiac) muscle and in type I skeletal muscle fibers.
• Type I fibers, which are also known as slow-twitch fibers, are one of two types of fibers that make up skeletal muscles.
• Type I fibers are the primary component of skeletal muscles that are resistant to fatigue.
• For example, muscles involved in posture, such as the neck muscles that hold the head steady, are made predominantly of type I fibers.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

Autosomal dominant inheritance is suggested in these cases.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

• Elevated serum creatine kinase(Elevated blood creatine phosphokinase)
• Foot dorsiflexor weakness(Foot drop)
• Increased endomysial connective tissue
• Increased variability in muscle fiber diameter
• Shoulder girdle muscle weakness(Weak shoulder muscles)
• Tibialis muscle weakness

30%-79% of people have these symptoms

• Centrally nucleated skeletal muscle fibers
• Decreased Achilles reflex
• Decreased patellar reflex(Decreased knee jerk reflex)
• Difficulty walking(Difficulty in walking)
• EMG: myopathic abnormalities
• Hand muscle weakness
• Pes cavus(High-arched foot)
• Scapular winging(Winged shoulder blade)
• Shoulder girdle muscle atrophy(Shoulder girdle muscle wasting)
• Steppage gait(High stepping)
• Upper limb amyotrophy

5%-29% of people have these symptoms

• Abnormal cardiac septum morphology
• Abnormal left ventricular function
• Abnormality of the foot musculature(Abnormal foot muscles)
• Arrhythmia(Abnormal heart rate)
• Beevor's sign
• Chronic pulmonary obstruction
• Enlargement of the ankles
• Facial palsy(Bell's palsy)
• Heart murmur(Heart murmurs)
• Hyperlordosis(Prominent swayback)
• Hypertension
• Intellectual disability(Mental deficiency)
• Left anterior fascicular block
• Limitation of movement at ankles
• Limited hip movement
• Limited neck flexion(Limited neck flexibility)
• Limited shoulder movement
• Limited wrist extension
• Muscle fiber splitting
• Muscle spasm
• Myopathic facies
• Pes planus(Flat feet)
• Proximal lower limb amyotrophy(Wasting of thigh muscle)
• Triceps weakness

Treatment

There is no standard course of treatment for scapuloperoneal myopathy. Some patients may benefit from physical therapy or other therapeutic exercises.

NIH genetic and rare disease info

• NIH info on MYH7-related scapuloperoneal myopathy

MYH7-related scapuloperoneal myopathy is a rare disease.

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