Laing distal myopathy is a rare genetic disorder causing slowly progressing weakness in the skeletal muscles. The term “distal” means the weakness begins in muscles farthest from the body’s center, impacting the feet and hands first. Symptoms often appear in early childhood, and the condition progresses gradually over many decades.
Genetic Origins of Laing Distal Myopathy
The underlying cause of Laing distal myopathy is a mutation in the MYH7 gene. This gene provides instructions for a protein component of type II myosin, which is important for muscle contraction. This protein is found in cardiac muscle and type I skeletal muscle fibers, also known as slow-twitch fibers. Slow-twitch fibers are fatigue-resistant and are common in muscles that support posture, such as those in the neck.
Mutations in the MYH7 gene alter the myosin protein’s structure, disrupting its interaction with other proteins and impairing muscle fiber function. The condition is inherited in an autosomal dominant pattern, meaning one copy of the mutated gene from a parent is enough to cause the disorder. This gives an affected individual a 50% chance of passing the condition to each child.
In some cases, the mutation occurs spontaneously in an individual with no family history of the disorder; these are known as de novo mutations. Although the MYH7 gene is active in heart muscle, cardiac problems are not a feature for most people with this condition.
Recognizing the Symptoms
The first signs of Laing distal myopathy appear in early childhood, often before age five, but onset can range into the early twenties. The first symptom is weakness in the muscles that lift the front of the foot and the big toe. This leads to “foot drop,” causing a high-stepping walk and an increased risk of tripping.
Months or years later, weakness develops in the hands and wrists, making it difficult to extend the fingers, particularly the third and fourth. A distinctive feature is the early involvement of the neck flexor muscles. This weakness can make it difficult to lift the head from a lying position, such as when getting out of bed. Mild weakness in facial muscles may also be present.
About ten years after the first symptoms, mild weakness may begin to affect proximal muscles closer to the body’s core, like the hips and shoulders. Despite this progression, most individuals retain their mobility throughout life, and life expectancy is normal.
The Diagnostic Process
Diagnosis begins with a clinical evaluation, including a physical exam and a review of personal and family medical history. The specific pattern of weakness provides strong clues, but because other disorders can present similarly, further testing is required. The definitive diagnosis is made through molecular genetic testing, which analyzes DNA to identify a mutation in the MYH7 gene. Doctors may use a multigene panel that screens for many genetic causes of distal myopathy at once.
Other tests can support the diagnosis or rule out other conditions. An electromyography (EMG) measures the electrical activity of muscles to confirm the weakness originates in the muscle itself. Blood tests for the creatine kinase (CK) enzyme are also common, and in this condition, CK levels are normal or only mildly elevated. Due to the high accuracy of genetic testing, a muscle biopsy is now rarely necessary.
Management and Supportive Care
There is no cure for Laing distal myopathy, so treatment focuses on managing symptoms and maintaining function and quality of life. A team of specialists, often led by a neurologist, creates a tailored management plan. Regular follow-up appointments monitor progression and allow for adjustments to interventions.
Physical therapy is a primary component of care, aiming to maintain muscle strength and flexibility. Therapists design exercise programs to prevent or treat the tightening of tendons, like the Achilles tendon, that can result from foot drop. Occupational therapy helps individuals develop strategies and use adaptive tools for daily activities affected by hand and finger weakness.
Assistive devices are important for managing mobility. Lightweight ankle-foot orthoses (AFOs) are prescribed to counteract foot drop. These braces fit inside a shoe to hold the foot in a neutral position, improving walking safety and reducing fall risk.