Mutations in myotilin cause myofibrillar myopathy.
ABSTRACT The term myofibrillar myopathy (MFM) is a noncommittal term for a pathologic pattern of myofibrillar dissolution associated with accumulation of myofibrillar degradation products and ectopic expression of multiple proteins. Ultrastructural studies implicate the Z-disk as the site of the initial pathologic change, and mutations in two Z-disk-related proteins, desmin and alphaB-crystallin, have been identified in a minority of patients with MFM. The authors' objective was to determine whether mutations in myotilin, a key Z-disk component and the disease protein in limb-girdle muscular dystrophy (LGMD) 1A, are another cause of MFM.
The authors used histochemical, immunocytochemical, ultrastructural, and mutation analysis.
The authors detected four missense mutations in 6 of 57 patients with MFM in the serine-rich exon 2 of MYOT, where the two previously identified LGMD1A mutations are located. Three mutations were novel, and one had been previously identified in LGMD1A. Each patient had evidence for neuropathy, and at least three kinships had associated cardiomyopathy. Distal weakness greater than proximal weakness was present in three patients. Except for minor differences, the morphologic features were similar to those in other patients with MFM.
1) Mutations in myotilin cause MFM; 2) exon 2 of MYOT is a hotspot for mutations; 3) peripheral neuropathy, cardiomyopathy, and distal weakness greater than proximal weakness are part of the spectrum of myotilinopathy; 4) not all cases of myotilinopathy have a limb-girdle phenotype; and 5) the molecular basis of the majority of MFM cases remains to be discovered.
SourceAvailable from: Gabrielle Christine Geddes[Show abstract] [Hide abstract]
ABSTRACT: Myofibrillar myopathies (MFMs) are a heterogeneous group of neuromuscular disorders distinguished by the pathological hallmark of myofibrillar dissolution. Most patients present in adulthood, but mutations in several genes including BCL2-associated athanogene 3 (BAG3) cause predominantly childhood-onset disease. BAG3-related MFM is particularly severe, featuring weakness, cardiomyopathy, neuropathy, and early lethality. While prior cases reported either neuromuscular weakness or concurrent weakness and cardiomyopathy at onset, we describe the first case in which cardiomyopathy and cardiac transplantation (age eight) preceded neuromuscular weakness by several years (age 12). The phenotype comprised distal weakness and severe sensorimotor neuropathy. Nerve biopsy was primarily axonal with secondary demyelinating/remyelinating changes without "giant axons." Muscle biopsy showed extensive neuropathic changes that made myopathic changes difficult to interpret. Similar to previous cases, a p.Pro209Leu mutation in exon 3 of BAG3 was found. This case underlines the importance of evaluating for MFMs in patients with combined neuromuscular weakness and cardiomyopathy. Copyright © 2015 Elsevier B.V. All rights reserved.Neuromuscular Disorders 02/2015; DOI:10.1016/j.nmd.2015.01.009 · 3.13 Impact Factor
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ABSTRACT: Desmin is a muscle-specific intermediate filament protein which forms a network connecting the sarcomere, T tubules, sarcolemma, nuclear membrane, mitochondria and other organelles. Mutations in the gene coding for desmin (DES) cause skeletal myopathies often combined with cardiomyopathy, or isolated cardiomyopathies. The molecular pathomechanisms of the disease remain ambiguous. Here, we describe and comprehensively characterize two DES mutations found in Polish patients with a clinical diagnosis of desminopathy. The study group comprised 16 individuals representing three families. Two mutations were identified: a novel missense mutation (Q348P) and a small deletion of nine nucleotides (A357_E359del), previously described by us in the Polish population. A common ancestry of all the families bearing the A357_E359del mutation was confirmed. Both mutations were predicted to be pathogenic using a bioinformatics approach, including molecular dynamics simulations which helped to rationalize abnormal behavior at molecular level. To test the impact of the mutations on DES expression and the intracellular distribution of desmin muscle biopsies were investigated. Elevated desmin levels as well as its atypical localization in muscle fibers were observed. Additional staining for M-cadherin, α-actinin, and myosin heavy chains confirmed severe disruption of myofibrill organization. The abnormalities were more prominent in the Q348P muscle, where both small atrophic fibers as well large fibers with centrally localized nuclei were observed. We propose that the mutations affect desmin structure and cause its aberrant folding and subsequent aggregation, triggering disruption of myofibrils organization.PLoS ONE 12/2014; 9(12):e115470. DOI:10.1371/journal.pone.0115470 · 3.53 Impact Factor