Mutations In RYR1 Gene Research Articles

Congenital Myopathy Due to RyR1 Gene Mutation in a Newborn Masquerading as a Consequence of Hypoxic-ischemic Encephalopathy

Background: Congenital myopathies may be a cause of prolonged and persistent hypotonia and weakness in a newborn, which may be overlooked as a neurological consequence of hypoxic-ischemic encephalopathy. We report such a neonate which turned out to be a case of central core myopathy. Clinical Description: A female neonate born at 38 weeks of gestation suffered birth asphyxia and was referred at 25 days of life due to a persistent need for respiratory support. A review of history revealed that the mother had decreased fetal movements during the third trimester and polyhydramnios. On examination, the baby had a frog-like posture with a paucity of proximal movements with preserved distal movements. Considering the possibility of a congenital myopathy, investigations were carried out. The whole-exome sequencing revealed heterozygous nonsense variation in exon 20 of the RyR1 gene, thus diagnosing the infant as a case of congenital core myopathy. Management and Outcome: The baby was managed with supportive care including ventilatory and nutritional support. Baby remained ventilator dependent, but ultimately succumbed to complications by 2 months of age. Conclusions: A high index of suspicion is required in a newborn with birth asphyxia having unusually persistent hypotonia, thorough clinical examination and appropriate genetic testing can help in identifying an underlying congenital myopathy.

Therapeutic effects of novel type1 ryanodine receptor inhibitor on skeletal muscle diseases

Type 1 ryanodine receptor (RyR1) plays a key role in Ca2+ release from the sarcoplasmic reticulum (SR) during excitation-contraction coupling of skeletal muscle. Mutations in RyR1 hyperactivate the channel to cause malignant hyperthermia (MH). MH is a serious complication characterized by skeletal muscle rigidity and elevated body temperature in response to commonly used inhalational anesthetics. Thus far, more than 300 mutations in RyR1 gene have been reported in patients with MH. Some heat stroke triggered by exercise or environmental heat stress is also related to MH mutations in the RyR1 gene. The only drug approved for ameliorating the symptoms of MH is dantrolene, which has been first developed in 1960s as a muscle relaxant. However, dantrolene has several disadvantages for clinical use: poor water solubility which makes rapid preparation difficult in emergency situations and long plasma half-life, which causes long-lasting side effects such as muscle weakness. Here we show that a novel RyR1-selective inhibitor, 6,7-(methylenedioxy)-1-octyl-4-quinolone-3-carboxylic acid (Compound 1, Cpd1), effectively rescues MH and heat stroke in new mouse model relevant to MH. Cpd1 has great advantages of higher water solubility and shorter plasma half-life compared to dantrolene. Our data suggest that Cpd1 has the potential to be a promising new candidate for effective treatment of patients carrying RyR1 mutations.

Recessive RYR1-related centronuclear myopathy with congenital chylothorax in a Japanese male child

Abstract Introduction: The severity of RYR1-related centronuclear myopathy (CNM) is typically intermediate between the most severe X-linked myotubular myopathy and mildly severe DNM2-related centronuclear myopathy. We report a Japanese male patient with recessive RYR1-related CNM that was exceedingly severe compared to previously reported cases and had congenital chylothorax, which is a very rare complication of congenital myopathy. Patient concerns: A male neonate from non-consanguineous Japanese parents presented with generalized hypotonia and respiratory distress at birth. Diagnosis: Muscle biopsy of the vastus lateralis showed typical features of CNM. The next-generation sequencing assay detected RYR1 gene mutations, which were c.5989G>A (p.E1997K) and c.1441-2A>G. These findings confirmed the diagnosis of recessive RYR1-related CNM. Chest radiography showed bilateral pleural effusions at birth, which was diagnosed as chylothorax on laboratory examination. Interventions: Mechanical ventilation and tube feeding were initiated. Chylothorax was managed with drainage and treatment with octreotide acetate. Outcomes: His clinical course was so rapidly progressive that he could not move his fingers even when he was one year of age. Conclusion: Congenital chylothorax with congenital myopathy can be considered an indicator of a severe phenotype, and its presence may indicate poor prognosis.

Vplyv suplementácie betaínu a kreatínmonohydrátu na chemické zloženie,oxidačnú stabilitu a kvalitu mäsa ošípaných heterozygótnych v géne RYR1

The aim of this study was to evaluate an effect of betaine and creatine monohydrate supplementation on chemical composition, meat quality, and oxidative stability of pork in pigs genotyped on mutation in RYR1 gene. Totally, sixty pigs – crosses of Lx(HAxPN) were involved in the experiment. Pigs were divided to one homozygous (NN) – control (C1), and three heterozygous (Nn) groups, each group including 15 animals. One group of Nn pigs was the control (C2) and two Nn groups were experimental. Control groups received a standard diet without supplement. Experimental groups were fed the same composition as controls but with supplement of betaine – BET (1.25 g/kg of feed) or creatine monohydrate - CMH (2.0 g/kg of feed) for thirty days prior to slaughter. Pigs C2 had worse meat quality, especially pH45, colour L* and drip loss (P<0.05), than homozygous C1 pigs. Dietary supplementation with betaine increased initial pH and decreased drip loss in Nn group (P<0.05) compared to C2 group. Supplementary CMH also increased pH45 and had a tendency to lowering the drip loss (P=0.058). Both feed additives substantially improved oxidative stability of pork, especially after 120 min incubation (P<0.01), compared to control C2 pigs.

Dominant or recessive mutations in the RYR1 gene causing central core myopathy in Brazilian patients.

Central Core Disease (CCD) is an inherited neuromuscular disorder characterized by the presence of cores in muscle biopsy. CCD is caused by mutations in the RYR1 gene. This gene encodes the ryanodine receptor 1, which is an intracellular calcium release channel from the sarcoplasmic reticulum to the cytosol in response to depolarization of the plasma membrane. Mutations in this gene are also associated with susceptibility to Malignant Hyperthermia (MHS).In this study, we evaluated 20 families with clinical and histological characteristics of CCD to identify primary mutations in patients, for diagnosis and genetic counseling of the families.We identified variants in the RYR1 gene in 19/20 families. The molecular pathogenicity was confirmed in 16 of them. Most of these variants (22/23) are missense and unique in the families. Two variants were recurrent in two different families. We identified six families with biallelic mutations, five compound heterozygotes with no consanguinity, and one homozygous, with consanguineous parents, resulting in 30% of cases with possible autosomal recessive inheritance. We identified seven novel variants, four of them classified as pathogenic. In one family, we identified two mutations in exon 102, segregating in cis, suggesting an additive effect of two mutations in the same allele.This work highlights the importance of using Next-Generation Sequencing technology for the molecular diagnosis of genetic diseases when a very large gene is involved, associated to a broad distribution of the mutations along it. These data also influence the prevention through adequate genetic counseling for the families and cautions against malignant hyperthermia susceptibility.

An integration-free iPSC line SDQLCHi025-A from a girl with multiminicore disease carrying compound heterozygote mutations in RYR1 gene.

Peripheral blood mononuclear cells for reprogramming in this work were donated by a girl with clinically and genetically diagnosed multiminicore disease harboring compound heterozygote mutations of RYR1 gene. Induced pluripotent stem cells (iPSCs) were obtained by non-integrating episomal vectors containing OCT4, SOX2, KLF4, BCL-XL and c-MYC. The iPSC line (SDQLCHi025-A) presented pluripotent cell morphology, high mRNA levels of pluripotency markers, differentiation potential in vitro, a normal karyotype, and carrying RYR1 gene mutations.

Effects of RYR1 gene mutation on the health, welfare, carcass and meat quality in slaughter pigs

This study assessed the effects of RYR1 mutation on the health, welfare, and carcass and meat quality in slaughter pigs. Any signs of pneumonia, pleurisy, pericarditis, and liver milk spots were recorded as present or absent. At exsanguination, blood samples were collected and RYR1 genotype, blood lactate and glucose concentrations were determined. The following carcass quality traits were measured: live, hot and cold carcass weights, backfat thickness, loin muscle thickness, lean meat content and skin lesion score. pH and temperature of M. longissimus dorsi and M. semimembranosus were measured 45 minutes postmortem. Nn pigs were more affected by pneumonia, had higher blood lactate and glucose concentrations and more developed rigor mortis than NN pigs. NN pigs had lower daily weight gain, produced lighter carcasses, more fat and less meat than Nn pigs. Meat obtained from Nn pigs was of a lower quality class than meat obtained from NN pigs, as shown by the lower pH and higher temperatures measured 45 minutes post mortem in both muscles and higher prevalence of pale, soft and exudative meat. In conclusion, the presence of a mutant n allele in pigs positively affected carcass quality traits, but had a deleterious effect on health, welfare and meat quality.

CONGENITAL MYOPATHIES: GENERAL AND RYR1: P.45A new congenital myopathy with multiple structured cores

Congenital myopathies are a heterogeneous group of inherited muscle disorders characterised by the presence of distinctive morphological features on skeletal muscle biopsy. Cores myopathies show the presence of cores, corresponding to well-delimited rounded areas devoid of oxidative staining. AD RYR1 and MYH7 gene mutations have been found in central core and eccentric cores disease patients. Nevertheless, several cores myopathy patients remain genetically unsolved. Our patient was the third child born to healthy non-consanguineous parents. He had mild hypotonia and sucking difficulties at birth. At two months, he developed progressive cardiac failure spontaneously resolved at 6 month. Successive cardiac follow-up was normal. The patient developed progressive diffuse weakness and scoliosis with normal cognitive skills. He underwent Achilles tendons tenotomy at 14 years and arthrodesis at 16 years, followed by gait loss. He showed progressive respiratory involvement and he underwent tracheostomy at 35 years. Last clinical examination at 46 years revealed profound amyotrophy, bilateral ptosis, mild facial weakness, nasal speech and high-arched palate. There was a profound proximal and distal muscle weakness (2 to 3 MRC), and axial weakness of neck flexor and extensor (2 MRC). Whole body MRI demonstrated diffuse and severe muscle atrophy and fat replacement. The respected muscles where masseter, pterigoidian, shoulder rotators, right biceps and triceps, pelvic girdle and bilateral hamstring muscles. Muscle biopsy of the left deltoid at 9 years demonstrated the presence of multiple and well defined round areas devoid of oxidative staining in every muscle fibers, and type 1 fibers uniformity. Muscle biopsy of left radialis muscle at 46 years revealed great fiber size variability with the presence of numerous small fibers. Oxidative staining disclosed the presence multiple core areas often clustered at the periphery of muscle fibers. Electron microscopy studies of both muscle biopsies showed multiple and large areas composed by 'out or register' sarcomeres with jagged Z-lines, corresponding to structured core lesions. Exome sequencing failed to reveal pathogenic mutations in the known myopathies genes. In conclusion we described a congenital myopathy with atypical multiple structured cores not linked to RYR1 and MYH7 genes.

Effect of sex and RYR1 gene mutation on the muscle proteomic profile and main physiological biomarkers in pigs at slaughter

Gender and RYR1 gene mutation might have an effect on the muscle metabolic characteristics and on the animal's stress at slaughter, which could influence the process of muscle-to-meat conversion. Forty-eight pigs were distributed in a design including two factors: sex (male/female) and RYR1 genotype (NN/Nn). At slaughter, physiological blood biomarkers and muscle proteome were analyzed and carcass and meat quality traits were registered. Females had higher serum levels of glucose, urea, C-reactive protein “CRP”, Pig-MAP and glutation-peroxidase “GPx” and lower levels of lactate, showed faster muscle pH decline and higher meat exudation. RYR1 mutation increased serum creatinine, creatine kinase and CRP and decreased GPx. The proteomic study highlighted significant effects of gender and RYR1 genotype on proteins related to fibre composition, antioxidant defense and post mortem glycolytic pathway, which correlate to differences of meat quality. This study provides interesting information on muscle biomarkers of the ultimate meat quality that are modulated by the animal's individual susceptibility to stress at slaughter.

Case of Recurrent, Severe Rhabdomyolysis with Chronic Pain and Dysphagia Cause by Novel Mutation in RYR1 Gene (P5.064)

Case of Recurrent, Severe Rhabdomyolysis with Chronic Pain and Dysphagia Cause by Novel Mutation in RYR1 Gene (P5.064)

Functional Characterization of a Central Core Disease RyR1 Mutation (p.Y4864H) Associated with Quantitative Defect in RyR1 Protein.

Background:Central Core Disease (CCD) is a congenital myopathy often resulting from a mutation in RYR1 gene. Mutations in RyR1 can increase or decrease channel activity, or induce a reduction in the amount of protein. The consequences of a single mutation are sometimes multiple and the analysis of the functional effects is complex.Objective:The consequences of the p.Y4864H mutation identified in a CCD patient have been studied regarding both RyR1 function and amount.Methods:The amount of RyR1 in human and mouse muscles was evaluated using qRT-PCR and quantitative Western blot, and calcium release was studied using calcium imaging on primary cultures. The results were compared between human and mouse.Results:The p.Y4864H mutation induced an alteration of calcium release, and in addition was associated to a reduction in the amount of RyR1 in the patient’s muscle. This suggests two possible pathophysiological mechanisms: the alteration of calcium release could result from a modification of the channel properties of RyR1 or from a RyR1 reduction. In order to discriminate between the two hypotheses, we used the heterozygous RyR1 knockout (RyR1+/–) mouse model showing a comparable RyR1 protein reduction. No reduction in calcium release was observed in primary muscle culture from these mice, and no muscle weakness was measured.Conclusions:Because the reduction in the amount of RyR1 protein has no functional consequences in the murine model, the muscle weakness observed in the patient is most likely the result of a modification of the calcium channel function of RyR1 due to the p.Y4864H mutation.

Acute rhabdomyolysis and inflammation.

Rhabdomyolysis results from the rapid breakdown of skeletal muscle fibers, which leads to leakage of potentially toxic cellular content into the systemic circulation. Acquired causes by direct injury to the sarcolemma are most frequent. The inherited causes are: i) metabolic with failure of energy production, including mitochondrial fatty acid ß-oxidation defects, LPIN1 mutations, inborn errors of glycogenolysis and glycolysis, more rarely mitochondrial respiratory chain deficiency, purine defects and peroxysomal α-methyl-acyl-CoA-racemase defect (AMACR), ii) structural causes with muscle dystrophies and myopathies, iii) calcium pump disorder with RYR1 gene mutations, iv) inflammatory causes with myositis. Irrespective of the cause of rhabdomyolysis, the pathology follows a common pathway, either by the direct injury to sarcolemma by increased intracellular calcium concentration (acquired causes) or by the failure of energy production (inherited causes), which leads to fiber necrosis. Rhabdomyolysis are frequently precipitated by febrile illness or exercise. These conditions are associated with two events, elevated temperature and high circulating levels of pro-inflammatory mediators such as cytokines and chemokines. To illustrate these points in the context of energy metabolism, protein thermolability and the potential benefits of arginine therapy, we focus on a rare cause of rhabdomyolysis, aldolase A deficiency. In addition, our studies on lipin-1 (LPIN1) deficiency raise the possibility that several diseases involved in rhabdomyolysis implicate pro-inflammatory cytokines and may even represent primarily pro-inflammatory diseases. Thus, not only thermolability of mutant proteins critical for muscle function, but also pro-inflammatory cytokines per se, may lead to metabolic decompensation and rhabdomyolysis.

G.P.49: RYR1 mutations in adults with acute rhabdomyolysis episodes

Recurrent rhabdomyolysis episodes in adults are commonly caused by glycogenosis or fatty-acid oxidation disorders. However, in many cases the etiology remains unknown, and recently mutations in RYR1 appeared as a possible cause of exercise induced rhabdomyolysis. We studied 14 adults who presented acute rhabdomyolysis (CK above 10,000 UI/l) triggered by exercise or fever, in whom McArdle disease, fatty acid oxidation disorders, and LPIN1 mutations were excluded. All patients underwent muscle biopsy in order to screen RYR1 mutation on cDNA. Potentially pathogenic mutations in RYR1 gene were detected in 5 unrelated patients. Mutations were the following: p.Val4847Leu, p.G593R, p R3539H, Gly2434Arg, p.Gln3461Pro, p.A1352T, p.A933T and p.Ser1342Gly. Two patients presented each 2 and 3 heterozygous variants. Baseline CK levels were elevated in all cases but one (400–700 UI/l). None of them complained of myalgia or exercise intolerance. Rhabdomyolysis were triggered by weight-training in two patients, viral infection in two cases, and retinoic acid treatment in the last case. Higher recorded CK levels were between 28,000 and 94,000 UI/l, without renal failure. Three patients had a unique episode, whereas two other had several rhabdomyolysis episodes. Muscle biopsies were either normal, or showed moderate structure disorganization. Two siblings of a patient, the father of another patient, and the brother of a third patient, also presented mutations in the RYR1 gene and high baseline CK level. Per-anesthetic malignant hyperthermia was noticed in a grand-mother of one patient. Mutations in RYR1 gene should be systematically searched in patients with exercise or fever induced rhabdomyolysis episodes, after having excluded common metabolic disorders. This diagnostic implies major consequences for genetic counselling in the families, due to the potential risk of anesthetic malignant for the patients and their relatives.

G.P.47: Severe congenital myopathy with central nuclei and novel RYR1 gene mutations

Congenital myopathies with centrally placed nuclei are a heterogenous group of diseases and mutations in the genes associated with centronuclear or myotobular myoapthy and even myotonia dystrophica congenita have been all well described. Recently, there have been reports of <i>RYR1</i> gene mutations associated with congenital myopathy with central nuclei without cores. We report a 17year old wheelchair-bound girl who presented at birth with severe generalized weakness, ptosis, ophthalmoplegia and profound facial and bulbar weakness. All findings have lasted throughout her life requiring tracheostomy and life-long nocturnal ventilation (at 17years FVC is 39% of predicted, and FEV1 33%) as well as placement of G-tube. Her CK has been repeatedly normal, EMG was myopathic. Muscle biopsy at 4months of age showed 91.2% fiber type I predominance and centrally placed nuclei in 10–15% of muscle fibers. EM showed focal myofribrillary disarray. DNA analysis of <i>MTM1</i> and <i>DNM2</i> genes revealed no mutations but she was found to have two novel heterozygous mutations in <i>RYR1</i> gene: in exon 21 c2682G>A, and, in exon 66 c.9859C>T (p.Arg3287Cys). Severe myopathy with central nuclei and <i>RYR1</i> mutations without cores requiring life-long ventilatory support has been reported in four other cases. The findings will be compared with the current case with focus on respiratory therapy. Our case of severe congenital myopathy with central nuclei and novel mutations in <i>RYR1</i> gene emphasizes the genetic and phenotypic heterogeneity of congenital muscle diseases associated with central nuclei. Apart from genes associated with CNM and MTM (i.e. <i>DNM2, BIN1</i> and <i>MTM1</i>) one needs to search for mutations in <i>RYR1</i> gene as well.

P.4.13 Central core disease (CCD): Improving the screening for mutations in RYR1 gene

Central core disease (CCD) is a congenital myopathy, characterized by the presence of central core-like areas in muscle fibers. Patients with RYR-related CCD usually have mild or moderate axial and proximal weakness, hypotonia and motor developmental delay. CCD is associated with susceptibility to malignant hyperthermia (MH), and both conditions have been linked to mutations in human RYR1 gene, which encodes a calcium release channel known as ryanodine receptor (RyR1). RYR1 mutational spectrum linked with CCD includes more than 200 described mutations mostly heterozygous dominant missense mutations and minor deletions or duplications. Definite diagnosis of CCD is done by clinical history and evaluation, histopathological analyses of muscle biopsy and, recently, genetic testing of gene’s “hot spots”, because RYR1 is a large gene and direct sequencing of each exon is laborious. Here, we tested Multiplex Ligation-dependent Probe Amplification (MLPA) as an alternative and simple method for screening patients with histological diagnosis or family history of CCD. This technique uses high-performance PCR to quantify up to 45 transcripts in small human DNA samples. It is based on annealing of two hemi-probes into its complementary sequence and was designed to detect the 33 most common mutations in RYR1 gene. From 41 patients diagnosed with CCD in three different institutions, 24 (58,5%) had mutations found in direct sequencing and 11 (26,8%) in MLPA. Seventeen patients (41,5%) had consistent results: 6 (14,6%) had their mutation diagnosed with sequencing and MLPA and neither method was able to find mutations in 11 patients (26,8%). Mutations in exon 101 were the most prevalent in sequencing (11 patients) and MLPA (4 patients). MLPA had shown to be a relevant tool to help diagnosing CCD; moreover, it is especially useful in diagnosing family members of patients with known mutations detectable by MLPA. Financial support: FAPESP-CEPID, CNPQ-INCT, FINEP.

P.4.12 Association of two mutations in the RYR1 gene in central core disease: Recessive or modifying effect?

Central core disease (CCD) is a congenital myopathy, characterized by the presence of central core-like areas in muscle fibers. Patients usually have mild or moderate axial and proximal weakness, hypotonia and motor developmental delay. CCD is associated with mutations in human RYR1 gene, which encodes a calcium release channel known as ryanodine receptor (RyR1). Here we present a family diagnosed with CCD with distinct phenotypes. A 48-year old female was referred to our service with clinical features suggesting a congenital myopathy. Histological analysis confirmed the diagnosis of CCD. Nine exons from the C-terminal region of RYR1 were screened for mutations in the index case. Two different missense mutations were identified: c.14256 A>C in exon 98 and c.14693 T>C in exon 102. Trans position of the 2 mutations was confirmed because patient's daughter, mother and sister carried the exon 98 mutation, but not the one in exon 102. The mutation in exon 102 have already been described as pathogenic, and is compatible with both severe and mild phenotypes, observed as intra and inter family variability. On the other hand, the c.14256 A>C mutation in exon 98 is a single nucleotide variation and its clinical significance is still untested. Considering the fact that patient's relatives showed no CCD phenotype, it could be inferred that this polymorphism alone is not responsible for the disease. Moreover, the effect of association of this polymorphism to exon 102's pathogenic mutation is not clear. Further studies about patients with both exon 98 polymorphism and exon 102 mutation could help establishing a better relation between these two findings. The case described above illustrates the present reality where new methods for wide genome screening are becoming more accessible and able to identify a great variety of mutations and polymorphisms in patients and their families. FAPESP-CEPID, CNPq-INCT, FINEP.

P.4.14 A novel mutation in RYR1 gene for central core disease in a Chinese family

Central core disease (CCD) is a mild, non-progressive or slowly progressive congenital myopathy with proximal symmetrical muscle weakness. CCD is transmitted as an autosomal dominant or recessive trait and at least one gene responsible is the ryanodine receptor gene at chromosome 19q13.1. Here we report the clinical and myopathological changes in a Chinese family with central core disease in an autosomal dominant pattern. The proband showed early onset congenital myopathy with severe contractures, delayed motor milestones, both proximal and distal muscle weakness, normal serum creatine kinase (CK), a non-progressive course, with muscle biopsy findings of central cores and in addition, marked proliferation of connective and adipose tissue, and variation in fibre size. The mother and the younger sister of the proband had similar but mild symptoms with the proband. Molecular genetic analysis showed a heterozygous sequence change in exon 102 (c.14692G > A; p.Gly4897Asp) in RYR1 gene not previously reported. The uncommon clinical distribution of weakness and the severe morphological abnormalities on muscle histology, which had some features of a muscular dystrophy had never been reported in an autosomal dominant CCD family.

Divergence in clinical presentation of Dynamin2-caused centronuclear myopathy is associated with mutations in distinct parts of the DNM2 gene

Centronuclear myopathy (CM) is a heterogeneous group of congenital myopathies with onset from birth to adult ages. Autosomal recessive CM is caused by RYR1 and BIN1 (Amphiphysin) gene mutations, whereas Dynamin2 (DNM2) mutations cause dominant CM.

Ryanodine Receptor RYR1 Gene Mutations in African American Men with Hypertrophied Muscles and Persistently Elevated Serum Creatine Kinase (S05.004)

Ryanodine Receptor RYR1 Gene Mutations in African American Men with Hypertrophied Muscles and Persistently Elevated Serum Creatine Kinase (S05.004)

C.P.4 Congenital fiber type disproportion with myofibrillar disorganization and altered internal nuclei is caused by RYR1 mutation

Mutations in the gene encoding skeletal muscle ryanodine receptor (RYR1) have been implicated in various forms of neuromuscular diseases including congenital myopathy. There is a broad range of clinical and pathological features including central core disease, congenital neuromuscular disease with uniform type 1, multiminicore disease, core-rod myopathy, and malignant hyperthermia susceptibility. Here we describe a group of patients with RYR1 mutations showing a unique muscle pathology. We chose seven unrelated Japanese patients among 12,000 frozen muscle biopsies in NCNP, based on the characteristic pathological findings including fiber type disproportion), marked type 1 fiber predominance, and scattered fibers with abnormal internal nuclei. On NADH-TR stain, myofibrillar disorganization was commonly seen. Unique fibers characterized by darkly-stained central portion with multiple small vacuoles were seen in three patients. On electron microscopy, center of muscle fibers were frequently occupied by aggregations of enlarged, vacuolated sarcoplasmic reticulum and abnormal shaped nuclei. Clinically, all seven patients showed axial and proximal dominant muscle weakness of variable severity from neonatal period, and often required respiratory supports. Muscle weakness was stable or rather improved during childhood. In addition, some patients revealed ptosis and/or ophthalmoparesis. All patients had compound heterozygous mutations in the central portion of RYR1 distributed between 18 and 66. In conclusion, mutations in RYR1 gene are associated with a unique myopathy characterized as congenital fiber type disproportion associated with myofibrillar disorganization and altered internal nuclei. These pathological changes may be closely related to degeneration of sarcoplasmic reticulum.