Myosinopathies, or myosin overload myopathies, are a recently described group of genetically determined neuromuscular disorders related to congenital myopathies. Among them, the autosomal dominant form initially described by Nigel Laing in the context of distal myopathies is due to mutations in the MYH7 gene. The latter encodes a heavy chain of myosin expressed in the skeletal muscle and the myocardium. The first motor symptoms are classically present in childhood and result in a fairly characteristic defect in the extension of the big toe (“hanging big toe”).
In an article published in November 2020, Spanish researchers report a study in muscle imaging in 42 patients with myosinopathy linked to the MYH7 gene belonging to thirteen families. Of the five causal mutations found in the MYH7 gene, one suggested a founding effect. The authors confirm the preferential involvement of the muscles of the anterior compartment of the leg (tibialis anterior, long extensor of the big toe, common extensor of the toes) even though it was only the only muscle involvement in 12% of cases. However, other muscle groups, such as the small muscles of the feet, can be affected, thereby expanding the range of phenotypes associated with this gene. Longitudinal observation of the images has also helped establish a natural history of the disease which may prove useful in future trials.