Impaired Autophagy in Retinal Pigment Epithelial Cells Induced from iPS Cell of Distal Myopathy with Rimmed Vacuole Patient.

OBJECTIVE: We generated induced pluripotent stem (iPS) cells from a patient with distal myopathy with rimmed vacuoles (DMRV), in which sialic acids synthesis is reported to be defective. In this study, we examined whether the differentiation to retinal pigment epithelial (RPE) cells and autophagy was affected in the patient derived cells. METHODS: Patient derived iPS cells were established through the transduction of re-programming factors into peripheral mononuclear cells via retrovirus vectors. RPE cells were induced from iPS cells through aggregation culture. Then the autophagy induced by amino acid starvation was estimated by measuring LC3-containing "puncta" structure. RESULTS: A 3D aggregate culture of patient-derived iPS cells resulted in some irregular shapes, and the aggregate contained large vacuoles filled with lipid droplets and cellular components such as damaged mitochondria. RPE cells induced from patient-derived iPS cells showed impaired autophagy flux under amino acid starvation. CONCLUSION: These findings were similar to those of sialidosis patient-derived iPS cells, in which cleavage of terminal sialic acids in oligosaccharide chains is defective. This suggests that the control of both the addition and removal of sialic acids are pivotal for autophagy progression.

Clinical myopathy in patients with nephropathic cystinosis.

BACKGROUND: Nephropathic cystinosis is a lysosomal storage disorder. Patient survival years after renal transplantation has revealed systemic complications including distal myopathy and dysphagia. METHODS: We evaluated 20 adult patients with nephropathic cystinosis using patient-reported and clinical outcome measures. Standard motor measures, video fluoroscopy swallow studies, and tests of respiratory function were performed. We also used Rasch analysis of an initial survey to design a 16-item survey focused on upper and lower extremity function, which was completed by 31 additional patients. RESULTS: Distal myopathy and dysphagia were common in patients with nephropathic cystinosis. Muscle weakness ranges from mild involvement of intrinsic hand muscles to prominent distal greater than proximal weakness and contractures. CONCLUSIONS: In addition to further characterization of underlying dysphagia and muscle weakness, we propose a new psychometrically devised, disease specific, functional outcome measures for distal myopathy in patients with nephropathic cystinosis.

Cystinosis distal myopathy, novel clinical, pathological and genetic features.

Nephropathic cystinosis is an autosomal recessive lysosomal disease in which cystine cannot exit the lysosome to complete its degradation in the cytoplasm, thus accumulating in tissues. Some patients develop a distal myopathy involving mainly hand muscles. Myopathology descriptions from only 5 patients are available in the literature. We present a comprehensive clinical, pathological and genetic description of 3 patients from 2 families with nephropathic cystinosis. Intrafamiliar variability was detected in one family in which one sibling developed a severe distal myopathy while the other sibling did not show any signs of skeletal muscle involvement. One of the patients was on treatment with Cysteamine for over 12 years but still developed the usual complications of nephropathic cystinosis in his twenties. Novel pathological findings consisting in sarcoplasmic deposits reactive for slow myosin were identified. Three previously known and one novel mutation are reported. Nephropathic cystinosis should be included in the differential diagnosis of distal myopathies in those with early renal failure. Novel clinical and pathological features are reported here contributing to the characterization of the muscle involvement in nephropathic cystinosis.

Distal Myopathies: Case Studies.

About 15% of myopathies present with distal weakness. Lack of sensory deficit, and preservation of sensory responses and deep tendon reflexes, favors a myopathic cause for distal weakness. Electromyogram confirms this diagnosis. Profuse spontaneous discharges are common in inflammatory, metabolic, and myofibrillar myopathy (MFM). If the clinical picture indicates a specific disease such as facioscapulohumeral muscular dystrophy (FSHD), genetic testing provides the quickest diagnosis. Otherwise, muscle biopsy can distinguish specific features. The common causes of myopathic distal weakness are FSHD, myotonic dystrophy, and inclusion body myositis. Other causes include MFM, distal muscular dystrophies, metabolic myopathies, and congenital myopathies.

Distal weakness with respiratory insufficiency caused by the m.8344A > G "MERRF" mutation.

The m.8344A>G mutation in the mt-tRNA(Lys) gene, first described in myoclonic epilepsy and ragged red fibers (MERRF), accounts for approximately 80% of mutations in individuals with MERRF syndrome. Although originally described in families with a classical syndrome of myoclonus, ataxia, epilepsy and ragged red fibers in muscle biopsy, the m.8344A>G mutation is increasingly recognised to exhibit marked phenotypic heterogeneity. This paper describes the clinical, morphological and laboratory features of an unusual phenotype in a patient harboring the m.8344A>G 'MERRF' mutation. We present the case of a middle-aged woman with distal weakness since childhood who also had ptosis and facial weakness and who developed mid-life respiratory insufficiency necessitating non-invasive nocturnal ventilator support. Neurophysiological and acetylcholine receptor antibody analyses excluded myasthenia gravis whilst molecular genetic testing excluded myotonic dystrophy, prompting a diagnostic needle muscle biopsy. Mitochondrial histochemical abnormalities including subsarcolemmal mitochondrial accumulation (ragged-red fibers) and in excess of 90% COX-deficient fibers, was seen leading to sequencing of the mitochondrial genome in muscle. This identified the m.8344A>G mutation commonly associated with the MERRF phenotype. This case extends the evolving phenotypic spectrum of the m.8344A>G mutation and emphasizes that it may cause indolent distal weakness with respiratory insufficiency, with marked histochemical defects in muscle. Our findings support consideration of screening of this gene in cases of indolent myopathy resembling distal limb-girdle muscular dystrophy in which screening of the common genes prove negative.

GNE myopathy: a personal trip from bedside observation to therapeutic trials.

The trip is not over yet as definite therapy for GNE myopathy is not yet available. Also the exact mechanisms by which GNE defects lead to isolated muscle disease in humans are not fully recognized. But in the Gaetano Conte lecture of 2013 I have tried to describe how much a progress was made in several research laboratories and clinical institutes in the investigation of this unique myopathy.

[Miyoshi distal muscular dystrophy (Miyoshi myopathy)].

We present an overview of autosomal recessive distal muscular dystrophy (ARDMD), including recent molecular genetic findings. ARDMD is often referred to as Miyoshi-type distal muscular dystrophy (MDMD) or Miyoshi myopathy (MM). The onset of MDMD occurs in early adulthood. Muscle atrophy is most dominant in distal leg muscles, especially the flexor muscles, i.e., gastrocnemius and soleus. As MDMD advances, muscle atrophy progresses to the thigh and hip muscles. Toe standing is impaired but heel standing can still be accomplished early in the disease course. This is followed by difficulty in standing and walking. The patients rarely become confined to bed. Serum creatine kinase level is markedly elevated, e.g., 100 times the upper limit of the normal range early in the disease course. Pre-symptomatic patients may also have high creatine kinase levels. Heterozygous individuals may have only slightly elevated creatine kinase levels. Recent development revealed that MDMD and LGMD2B are both caused by mutations in the dysferlin gene (DYSF). C1939G, G3370T, 3746delG, and 4870delT are reported to be common mutations among patients with MDMD. The dysferlin protein is presumably involved in the repair of muscle cell membranes. Among the patients reported originally by Miyoshi et al., 3 affected individuals from 3 different families were confirmed carriers of dysferlin mutations. Additionally, 1 heterozygous individual was identified. Although MDMD and LGMD2B are caused by the mutation of the same gene, ARDMD is characterized by initial involvement of leg flexors while LGMD2B is characterized by involvement of the proximal leg muscles. The difference in the distribution becomes obscure as the 2 diseases progress. The temporal profiles of functional impairment in the 2 diseases are reportedly very similar. When MDMD is suspected, it is important to carefully observe the relevant leg, more specially the flexor muscle group.

[Animal model of distal myopathy with rimmed vacuoles/hereditary inclusion body myopathy and preclinical trial with sugar compounds].

Sialic acids are terminal sugars of glycolipids and glycoproteins and are involved in several cellular processes. Sialic acid biosynthesis occurs in the cytosol, where UDP-N-acetylglucosamine (GlcNAc) is sequentially converted to N-acetylmannosamine (ManNAc) 6-phosphate by UDP-GlcNAc-2-epimerase/ManNAc kinase enzymes, both of which are encoded by the GNE gene. Since the only existing mouse model of DMRV/hIBM (Gne(-/-)hGNED176VTg) exhibited decreased sialic acid levels in most organs, DMRV/hIBM is thought to be secondary to the metabolic defect in sialic acid production. Theoretically, replenishing sialic acid could be employed as a therapeutic option. It has been reported that N-acetylneuraminic acid (NeuAc) and ManNAc are well incorporated into cells and converted to sialic acid. Thus, we evaluated the efficacy and safety of ManNAc, NeuAc, and sialyllactose in the Gne(-/-)hGNED176VTg, by orally administering these agents to mice from 5-15 weeks continuously until they reached 54-57 weeks of age. The treatment showed beneficial effects in terms of survival rate, overall motor performance, myofiber size, ex vivo skeletal muscle contractile properties, and pathology. These low-dose compounds showed acceptable kidney and liver toxicity profiles. Thus our results show that the oral therapy with NeuAc and ManNAc or their derivatives is safe and effective in preventing myopathic symptoms in Gne(-/-)hGNED176VTg mice, and could be considered as a guide for further therapeutic trials.

[Development of therapy for distal myopathy with rimmed vacuoles].

Distal myopathy with rimmed vacuoles (DMRV), also called hereditary inclusion body myopathy, is an autosomal recessive disorder caused by homozygous or compound heterozygous missense mutations in GNE which encodes a protein with two enzymatic activities in sialic acid biosynthesis: UDP-GlcNAc 2-epimerase and ManNAc kinase. The disease starts from 1540 years and is slowly progressive. DMRV preferentially affects tibialis anterior and hamstrings muscles, and has characteristic findings in muscle pathology which include rimmed vacuoles, tubulofilamentous inclusions, deposition of amyloid, and phosphorylated tau. We generated DMRV mice (Gne -/- hGNE D176V-Tg) by crossmating Gne knock-out heterozygous mouse and human GNE p.D176V transgenic mouse. This model mouse recapitulates DMRV clinically, pathologically, and biochemically by developing muscle weakness and atrophy from 21 weeks, amyloid deposition from 31 weeks, and rimmed vacuoles and phosphorylated tau from 41 weeks while having lifelong hyposialylation. We gave three types of GNE metabolites, ManNAc, NeuAc and sialyllactose, to DMRV mice orally from 15 weeks until 55 weeks of age. Sialic acid supplementation almost completely precluded the disease and virtually no sign of DMRV was seen even at 55 weeks of age, indicating that decreased sialic acid is the cause of myopathic phenotype and sialic acid supplementation can prevent the disease process.

Hereditary inclusion-body myopathy: clues on pathogenesis and possible therapy.

Hereditary inclusion-body myopathy (h-IBM), or distal myopathy with rimmed vacuoles (DMRV), is an autosomal recessive disorder with onset in early adult life and a progressive course leading to severe disability. h-IBM/DMRV is due to mutations of a gene (GNE) that codes for a rate-limiting enzyme in the sialic acid biosynthetic pathway. Despite the identification of the causative gene defect, it has not been unambiguously clarified how GNE gene mutations impair muscle metabolism. Although numerous studies have indicated a key role of hyposialylation of glycoproteins in h-IBM/DMRV pathogenesis, others have demonstrated new and unpredicted functions of the GNE gene, outside the sialic acid biosynthetic pathway, that may also be relevant. This review illustrates the clinical and pathologic characteristics of h-IBM/DMRV and the main clues available to date concerning the possible pathogenic mechanisms and therapeutic perspectives of this disorder.

Perspectives on distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy: contributions from an animal model. Lack of sialic acid, a central determinant in sugar chains, causes myopathy?

Distal myopathy with rimmed vacuoles (DMRV) or hereditary inclusion body myopathy (hIBM) is an adult onset slowly progressive myopathy secondary to mutations in the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene that encodes a bifunctional enzyme which catalyzes the rate-limiting step in sialic acid biosynthesis. Many hypotheses have been proposed to explain why patients develop weakness and atrophy, but are most views are obscure and thus are still considered controversial, partly because of the lack of an appropriate model with which these theories could be clarified. In this review, we briefly summarize the progress in DMRV research, and highlight efforts of researchers in generating the animal model for this myopathy.

Proximal weakness of lower limbs as the sole presentation of hyperthyroidism: report of one case.

Most children with acute or chronic flaccid limb weakness have a disorder of motor unit. However, it is very important to exclude cerebral or other upper motor neuron disorders before we approach such patients as pure muscle disorders. In general, neuropathy results in distal limb weakness, myopathy manifests with proximal weakness. There are exceptions, however. Accurate diagnosis in this wide array of disorders is dependent on a careful clinical assessment followed by the appropriate investigations. Here we report a 14-year-old girl who presented with progressive difficulty in rising up from the floor for one month. Neurological examination revealed an obese, clumsy but clear girl with stable vital signs. The muscle power of neck and upper limbs was normal. There was positive Gower sign, but the toe and heel gaits were acceptable. The initial blood work and motor/sensory nerve conduction velocity were unremarkable. Further study for thyroid function showed a hyperthyroid state. The proximal myopathy recovered soon after medical treatment. There were no other symptoms, and signs indicating hyperthyroidism and proximal myopathy of lower limbs was the isolated clinical feature. Hyperthyroid myopathy is common in hyperthyroidism, but is unusual as the sole presenting symptom.

[Cystinosis: an infrequent cause of distal myopathy]. / Cistinosis: una causa infrecuente de miopatía distal.

INTRODUCTION: Cystinosis is a hereditary disease with clinical symptoms that are caused by the accumulation of cystine crystals in different tissues. Distal vacuolar myopathy has been reported as one of its later complications. CASE REPORT: Here, we present the case of a 20-year-old male diagnosed with cystinosis at the age of 2 years, with severe renal involvement that required a transplant. The patient gradually developed weakness and atrophy of the muscles in his hands. Neurophysiological and histological studies enabled a diagnosis of distal vacuolar myopathy to be established, and electron microscopy revealed deposits of cystine crystals. CONCLUSIONS: Cystinosis must be included within the differential diagnosis of distal myopathies. Timely treatment with cysteamine could prevent the development of this complication.