Clinical characteristics: Laing distal myopathy is characterized by early-onset weakness (usually before age 5 years) that initially involves the dorsiflexors of the ankles and great toes and then the finger extensors, especially those of the third and fourth fingers. Weakness of the neck flexors is seen in most affected individuals and mild facial weakness is often present. After distal weakness has been present for more than ten years, mild proximal weakness may be observed. Life expectancy is normal.
Diagnosis/testing: The diagnosis of Laing distal myopathy is established in a proband with suggestive findings and a heterozygous pathogenic variant in MYH7 identified by molecular genetic testing.
Management: Treatment of manifestations: Physiotherapy to prevent or treat tightening of the Achilles tendon is helpful. In more advanced cases, lightweight splinting of the ankle (e.g., with an ankle-foot orthosis) can be useful. Standard medical treatment under the supervision of a cardiologist is recommended for cardiomyopathy; surgical stabilization of the spine is used to treat kyphoscoliosis.
Surveillance: Annual neurologic examination; repeat electrocardiogram and echocardiogram if symptoms of cardiac insufficiency occur; regular evaluation for scoliosis/kyphoscoliosis (especially during rapid growth); respiratory assessment if symptoms suggest sleep-related respiratory insufficiency and obstructive sleep apnea.
Genetic counseling: Laing distal myopathy is an autosomal dominant disorder. Approximately 65%-70% of affected individuals have an affected parent; de novo pathogenic variants in MYH7 account for 30%-35% of individuals with Laing distal myopathy. If a parent of the proband is affected and/or is known to have the pathogenic variant identified in the proband, the risk to the sibs of inheriting the pathogenic variant is 50%. Once the MYH7 pathogenic variant has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing for Laing distal myopathy are possible.
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