Mild Clinical Features and Histopathologically Atypical Cores in Two Korean Families with Central Core Disease Harboring RYR1 Mutations at the C-Terminal Region

Gene Panel Sequencing Identifies a Novel RYR1 p.Ser2300Pro Variant as Candidate for Malignant Hyperthermia with Multi-Minicore Myopathy

Malignant hyperthermia (MH), a rare autosomal dominant pharmacogenetic disorder of skeletal muscle calcium regulation, is triggered by sevoflurane in susceptible individuals. We report a Korean having MH with multi-minicore myopathy functionally supported by RYR1-mediated intracellular Ca2+ release testing in B lymphocytes. A 14-year-old boy was admitted for the evaluation of progressive torticollis accompanied by cervicothoracic scoliosis. During the preoperative drape of the patient for the release of the sternocleidomastoid muscle under general anesthesia, his wrist and ankle were observed to have severe flexion contracture. The body temperature was 37.1 °C. To treat MH, the patient was administered a bolus of dantrolene intravenously (1.5 mg/kg) and sodium bicarbonate. After a few minutes, muscle rigidity, tachycardia, and EtCO2 all resolved. Next-generation panel sequencing for hereditary myopathy identified a novel RYR1 heterozygous missense variant (NM_000540.2: c.6898T > C; p.Ser2300Pro), which mapped to the MH2 domain of the protein, a hot spot for MH mutations. Ex vivo RYR1-mediated intracellular Ca2+ release testing in B lymphocytes showed hypersensitive Ca2+ responses to isoflurane and caffeine, resulting in an abnormal Ca2+ release only in the proband, not in his family members. Our findings expand the clinical and pathological spectra of information associated with MH with multi-minicore myopathy.

Characterization of congenital myopathies at a Korean neuromuscular center

INTRODUCTION

Congenital myopathies are muscle diseases characterized by specific histopathologic features, generalized hypotonia from birth, and perinatal complications, although some cases develop during childhood or, rarely, in adulthood. We undertook this study to characterize congenital myopathies among patients registered at our institution.

METHODS

Clinical, histopathologic, and genetic features were evaluated in 34 patients recruited for this study.

RESULTS

The majority of patients experienced a childhood onset, and no disease-related mortality was recorded during follow-up. Functional outcomes were no better for those with late-onset disease, indicating later disease progression can be significant. Nemaline myopathy was the most frequent pathology, followed by central core disease and centronuclear myopathy. Among the 18 (54.5%) genetically confirmed patients, NEB and RYR1 mutations were the most common, followed by DNM2 mutations.

DISCUSSION

This study shows features not previously reported and suggests that congenital myopathy should be considered an important issue among adult patients. Muscle Nerve 58: 235-244, 2018.

Clinical and Pathologic Findings of Korean Patients with RYR1-Related Congenital Myopathy

Background and Purpose

This study was designed to investigate clinical and pathologic characteristics of five Korean patients with RYR1-related congenital myopathy (CM).

Methods

Five patients from unrelated families were diagnosed with RYR1-related CM via direct or targeted sequencing of RYR1. Their clinical, mutational, and pathologic findings were then analyzed.

Results

Seven different mutations were identified, including two novel mutations: c.5915A>T and c.12250C>T. All of the patients presented at infancy with proximal dominant weakness and delayed motor milestones. Other clinical findings were scoliosis in three patients, winged scapula in two, hip dislocation in one, and pectus excavatum in one. Ophthalmoplegia was observed in one patient with a novel recessive mutation. Two of three muscle specimens revealed a myopathic pattern with core.

Conclusions

We have identified a novel compound heterozygous RYR1 mutation and demonstrated clinical and pathologic findings in five Korean patients with RYR1-related CM.