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Missense mutations in MYOT encoding the sarcomeric Z‐disk protein myotilin cause three main myopathic phenotypes including proximal limb‐girdle muscular dystrophy, spheroid body myopathy, and late‐onset distal myopathy. We describe a family carrying a heterozygous MYOT deletion (Tyr4_His9del) that clinically was characterized by an early‐adult onset distal muscle weakness and pathologically by a myofibrillar myopathy (MFM). Molecular modeling of the full‐length myotilin protein revealed that the 4‐YERPKH‐9 amino acids are involved in local interactions within the N‐terminal portion of myotilin. Injection of in vitro synthetized mutated human MYOT RNA or of plasmid carrying its cDNA sequence in zebrafish embryos led to muscle defects characterized by sarcomeric disorganization of muscle fibers and widening of the I‐band, and severe motor impairments. We identify MYOT novel Tyr4_His9 deletion as the cause of an early‐onset MFM with a distal myopathy phenotype and provide data supporting the importance of the amino acid sequence for the structural role of myotilin in the sarcomeric organization of myofibers. [ABSTRACT FROM AUTHOR]

Introduction: Limb girdle muscular dystrophies (LGMDs) are characterized by high molecular heterogeneity, clinical overlap, and a paucity of specific biomarkers. Their molecular definition is fundamental for prognostic and therapeutic purposes.Methods: We created an Italian LGMD registry that included 370 molecularly defined patients. We reviewed detailed retrospective and prospective data and compared each LGMD subtype for differential diagnosis purposes.Results: LGMD types 2A and 2B are the most frequent forms in Italy. The ages at disease onset, clinical progression, and cardiac and respiratory involvement can vary greatly between each LGMD subtype. In a set of extensively studied patients, targeted next-generation sequencing (NGS) identified mutations in 36.5% of cases.Conclusion: Detailed clinical characterization combined with muscle tissue analysis is fundamental to guide differential diagnosis and to address molecular tests. NGS is useful for diagnosing forms without specific biomarkers, although, at least in our study cohort, several LGMD disease mechanisms remain to be identified. Muscle Nerve 55: 55-68, 2017. [ABSTRACT FROM AUTHOR]

Mitochondrial disorders are heterogeneous multisystemic disorders due to impaired oxidative phosphorylation causing defective mitochondrial energy production. Common histological hallmarks of mitochondrial disorders are RRFs (ragged red fibres), muscle fibres with abnormal focal accumulations of mitochondria. In contrast with the growing understanding of the genetic basis of mitochondrial disorders, the fate of phenotypically affected muscle fibres remains largely unknown. We investigated PCD (programmed cell death) in muscle of 17 patients with mitochondrial respiratory chain dysfunction. We documented that in affected muscle fibres, nuclear chromatin is condensed in lumpy irregular masses and cytochrome c is released into the cytosol to activate, along with Apaf-1 (apoptotic protease-activating factor 1), caspase 9 that, in turn, activates effector caspase 3, caspase 6, and caspase 7, suggesting the execution of the intrinsic apoptotic pathway. Whereas active caspase 3 underwent nuclear translocation, AIF (apoptosis-inducing factor) mainly stayed within mitochondria, into which an up-regulated Bax is relocated. The significant increase in caspase 2, caspase 3 and caspase 6 activity strongly suggest that the cell death programme is caspase-dependent and the activation of caspase 2 together with PUMA (p53 up-regulated modulator of apoptosis) up-regulation point to a role for oxidative stress in triggering the intrinsic pathway. Concurrently, in muscle of patients, the number of satellite cells was significantly increased and myonuclei were detected at different stages of myogenic differentiation, indicating that a reparative programme is ongoing in muscle of patients with mitochondrial disorders. Together, these data suggest that, in patients with mitochondrial disorders, affected muscle fibres are trapped in a mitochondria-regulated caspase-dependent PCD while repairing events take place. [ABSTRACT FROM AUTHOR]

Autophagy has a large range of physiological functions and its dysregulation contributes to several human disorders, including autoinflammatory/autoimmune diseases such as inflammatory myopathies (IIMs). In order to better understand the pathogenetic mechanisms of these muscular disorders, we sought to define the role of autophagic processes and their relation with the innate immune system in the three main subtypes of IIM, specifically sporadic inclusion body myositis (sIBM), polymyositis (PM), dermatomyositis (DM) and juvenile dermatomyositis (JDM). We found that although the mRNA transcript levels of the autophagy-related genes BECN1, ATG5 and FBXO32 were similar in IIM and controls, autophagy activation in all IIM subgroups was suggested by immunoblotting results and confirmed by immunofluorescence. TLR4 and TLR3, two potent inducers of autophagy, were highly increased in IIM, with TLR4 transcripts significantly more expressed in PM and DM than in JDM, sIBM and controls, and TLR3 transcripts highly up-regulated in all IIM subgroups compared to controls. Co-localization between autophagic marker, LC3, and TLR4 and TLR3 was observed not only in sIBM but also in PM, DM and JDM muscle tissues. Furthermore, a highly association with the autophagic processes was observed in all IIM subgroups also for some TLR4 ligands, endogenous and bacterial HSP60, other than the high-mobility group box 1 (HMGB1). These findings indicate that autophagic processes are active not only in sIBM but also in PM, DM and JDM, probably in response to an exogenous or endogenous ‘danger signal’. However, autophagic activation and regulation, and also interaction with the innate immune system, differ in each type of IIM. Better understanding of these differences may lead to new therapies for the different IIM types. [ABSTRACT FROM AUTHOR]

Facioscapulohumeral muscular dystrophy (FSHD), a common hereditary myopathy, is characterized by atrophy and weakness of selective muscle groups. FSHD is considered an autosomal dominant disease with incomplete penetrance and unpredictable variability of clinical expression within families. Mice overexpressing FRG1 (FSHD region gene 1), a candidate gene for this disease, develop a progressive myopathy with features of the human disorder. Here, we show that in FRG1-overexpressing mice, fast muscles, which are the most affected by the dystrophic process, display anomalous fast skeletal troponin T (fTnT) isoform, resulting from the aberrant splicing of the Tnnt3 mRNA that precedes the appearance of dystrophic signs. We determine that muscles of FRG1 mice develop less strength due to impaired contractile properties of fast-twitch fibers associated with an anomalous MyHC-actin ratio and a reduced sensitivity to Ca2+. We demonstrate that the decrease of Ca2+ sensitivity of fast-twitch fibers depends on the anomalous troponin complex and can be rescued by the substitution with the wild-type proteins. Finally, we find that the presence of aberrant splicing isoforms of TNNT3 characterizes dystrophic muscles in FSHD patients. Collectively, our results suggest that anomalous TNNT3 profile correlates with the muscle impairment in both humans and mice. On the basis of these results, we propose that aberrant fTnT represents a biological marker of muscle phenotype severity and disease progression. [ABSTRACT FROM AUTHOR]

MDs (mitochondrial diseases) are a clinically heterogeneous group of disorders characterized by impairment of the respiratory chain function with altered oxidative phosphorylation. We tested the hypothesis that the function of vascular endothelium is affected by increased oxidative stress in MDs. A total of 12 patients with MDs and pair-matched controls were studied. Endothelial function was assessed by measuring FMD (flow-mediated vasodilation) of brachial and common femoral arteries. The test was repeated after vitamin C (500 mg, twice a day) and E (400 mg, once a day) supplementation for 30 days and 90 days after vitamin withdrawal. FMD was reduced in patients compared with controls [AUC/τ (time-averaged area under the curve) for the brachial artery, 1.05 ± 0.24 compared with 4.19 ± 0.59% respectively, P < 0.001; AUC/τ for the femoral artery, 0.98 ± 0.19 compared with 2.36 ± 0.29% respectively, P = 0.001; values are means ± S.E.M.] and correlated (brachial artery) with plasma lactate (r = -0.63, P < 0.01). Urinary 8-iso-PGF2α (8-iso-prostaglandin F2α) was higher in patients than controls (505.6 ± 85.9 compared with 302.5 ± 38.7 pg/mg of creatinine; P < 0.05) and correlated with plasma lactate (r = 0.70, P < 0.05). Immunohistochemical analysis showed 8-iso-PGF2α staining in MD-affected striated muscle cells and in blood vessels in muscle biopsies of patients. Antioxidant vitamins transiently restored FMD in patients [ΔAUC/τ (change in AUC/τ) for the brachial artery, +1.38 ± 0.49 %, P < 0.05; ΔAUC/τ for the femoral artery, +0.98 ± 0.24 %, P < 0.01] but had no effect on FMD in controls (brachial artery, -1.3 ± 0.63 %; and common femoral artery, -0.58 ± 0.30 %), thus abolishing the differences between patients and controls. The results of the present study indicate that oxidative stress is increased and is, at least partly, responsible for endothelial dysfunction in MDs. [ABSTRACT FROM AUTHOR]

Hearing impairment is common in patients withmitochondrial disorders, affecting over half of all cases at some time in the course of the disease. In some patients, deafness is only part of a multisystem disorder. By contrast, there are also a number of "pure" mitochondrial deafness disorders, the most common probably being maternally inherited. We retrospectively analyzed the last 60 genetically confirmed mitochondrial disorders diagnosed in our Department: 28 had bilateral sensorineural hearing loss, whereas 32 didn't present ear's abnormalities, without difference about sex and age of onset between each single group of diseases. We reported also a case of MELAS patient with sensorineural hearing loss, in which cochlear implantation greatly contributed to the patient's quality of life. Our study suggests that sensorineural hearing loss is an important feature in mitochondrial disorders and indicated that cochlear implantation can be recommended for patients with MELAS syndrome and others mitochondrial disorders [ABSTRACT FROM AUTHOR]