Laing distal myopathy

Alternate names

Laing early-onset distal myopathy; Myopathy distal, type 1

Definition

Laing distal myopathy is a slowly progressive muscle disorder that tends to begin in childhood.

Epidemiology

Although Laing distal myopathy is thought to be rare, its prevalence is unknown. Several families with the condition have been identified worldwide.

Cause

Laing distal myopathy is caused by mutations in the MYH7 gene. The MYH7 gene provides instructions for making a protein that is found in heart (cardiac) muscle and in type I skeletal muscle fibers. In cardiac and skeletal muscle cells, the protein produced from the MYH7 gene forms part of a larger protein called type II myosin.

Gene mutations

• Researchers have proposed that these mutations alter the structure of myosin in skeletal muscles, which prevents it from interacting with other proteins.
• The abnormal myosin gradually impairs the function of type I skeletal muscle fibers.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

This condition is inherited in an autosomal dominant fashion.

Signs and symptoms

• Early symptoms include weakness in the feet and ankles, followed by weakness in the hands and wrists.
• Weakness in the feet leads to tightening of the Achilles tendon, an inability to lift the big toe, and a high-stepping walk.
• Weakness in the hands makes it more difficult to lift the fingers, especially the third and fourth fingers.
• As the muscle weakness slowly progresses over the course of many years, other muscles of the body (e.g., neck, face, legs, hips, and shoulders) weaken.
• Other findings include scoliosis and cardiomyopathy in up to one third of individuals.

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

• Foot dorsiflexor weakness(Foot drop)
• Toe extensor amyotrophy

30%-79% of people have these symptoms

• Abnormal mitochondria in muscle tissue
• Abnormality of the calf musculature(Abnormal calf muscles)
• Distal muscle weakness(Weakness of outermost muscles)
• Gait disturbance(Abnormal gait)
• High palate(Elevated palate)
• Mildly elevated creatine kinase
• Minicore myopathy
• Myalgia(Muscle ache)
• Neck muscle weakness(Floppy neck)
• Progressive muscle weakness
• Scoliosis
• Talipes cavus equinovarus
• Type 1 muscle fiber predominance
• Weakness of orbicularis oculi muscle

5%-29% of people have these symptoms

• Dilated cardiomyopathy(Stretched and thinned heart muscle)
• EMG: myopathic abnormalities
• Proximal muscle weakness(Weakness in muscles of upper arms and upper legs)
• Proximal muscle weakness in lower limbs

Diagnosis

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.<ref>Lamont P, Laing NG. Laing Distal Myopathy. 2006 Oct 17 [Updated 2021 Feb 4]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2021. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1433/</ref>[1]. Laboratory findings

• Serum creatine kinase concentration is usually normal, but may in rare cases be as high as eight times the upper limit of normal.
• Nerve conduction studies are normal.
• Electromyographic findings are nonspecific, with occasional fibrillation potentials but no prolonged or large motor unit potentials

Treatment

• Treatment may include physiotherapy to prevent tightening of the Achilles tendon and splinting of the ankle.<ref>Lamont P, Laing NG. Laing Distal Myopathy. 2006 Oct 17 [Updated 2021 Feb 4]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2021. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1433/</ref>[2].
• Annual neurologic examinations, evaluations for scoliosis, and regular assessments of cardiac and respiratory functions may be necessary.

References

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NIH genetic and rare disease info

• NIH info on Laing distal myopathy

Laing distal myopathy is a rare disease.

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