Abstract
BackgroundMyosin heavy chain 7 (MYH7)-related myopathies are emerging as an important group of muscle diseases of childhood and adulthood, with variable clinical and histopathological expression depending on the type and location of the mutation. Mutations in the head and neck domains are a well-established cause of hypertrophic cardiomyopathy whereas mutation in the distal regions have been associated with a range of skeletal myopathies with or without cardiac involvement, including Laing distal myopathy and Myosin storage myopathy. Recently the spectrum of clinical phenotypes associated with mutations in MYH7 has increased, blurring this scheme and adding further phenotypes to the list. A broader disease spectrum could lead to misdiagnosis of different congenital myopathies, neurogenic atrophy and other neuromuscular conditions.ResultsAs a result of a multicenter Italian study we collected clinical, histopathological and imaging data from a population of 21 cases from 15 families, carrying reported or novel mutations in MYH7. Patients displayed a variable phenotype including atypical pictures, as dropped head and bent spine, which cannot be classified in previously described groups. Half of the patients showed congenital or early infantile weakness with predominant distal weakness. Conversely, patients with later onset present prevalent proximal weakness. Seven patients were also affected by cardiomyopathy mostly in the form of non-compacted left ventricle. Muscle biopsy was consistent with minicores myopathy in numerous cases. Muscle MRI was meaningful in delineating a shared pattern of selective involvement of tibialis anterior muscles, with relative sparing of quadriceps.ConclusionThis work adds to the genotype-phenotype correlation of MYH7-relatedmyopathies confirming the complexity of the disorder.Electronic supplementary materialThe online version of this article (doi:10.1186/s13023-016-0476-1) contains supplementary material, which is available to authorized users.
Highlights
Myosin heavy chain 7 (MYH7)-related myopathies are emerging as an important group of muscle diseases of childhood and adulthood, with variable clinical and histopathological expression depending on the type and location of the mutation
Skeletal myopathies due to MYH7 mutations were initially classified in two main subgroups according to clinical and pathological findings: myosin storage myopathy (MSM, MIM 608358) and Laing distal myopathy (LDM, MIM 160500)
MYH7 mutations often lead to a distal myopathy starting at lower limb To date 327 mutations in MYH7 have been reported in the related mutation database, myoMAPR and it has becoming clear that alterations in MYH7 are no longer an uncommon cause of skeletal myopathy
Summary
Myosin heavy chain 7 (MYH7)-related myopathies are emerging as an important group of muscle diseases of childhood and adulthood, with variable clinical and histopathological expression depending on the type and location of the mutation. Additional phenotypes have been reported over the years, including a scapulo-peroneal or limb-girdle muscle form with or without morphological features of myosin storage [3], multi-minicore disease with variable cardiac involvement [4, 5] and families with morphological features suggestive of congenital fiber type disproportion [6, 7]. These disorders are either due to de novo mutations or inherited in a dominant fashion cases with autosomal recessive inheritance have seldom been reported [8, 9]
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