Expanding the clinical-pathological and genetic spectrum of RYR1-related congenital myopathies with cores and minicores: an Italian population study

Abstract

Mutations in the RYR1 gene, encoding ryanodine receptor 1 (RyR1), are a well-known cause of Central Core Disease (CCD) and Multi-minicore Disease (MmD). We screened a cohort of 153 patients carrying an histopathological diagnosis of core myopathy (cores and minicores) for RYR1 mutation. At least one RYR1 mutation was identified in 69 of them and these patients were further studied. Clinical and histopathological features were collected. Clinical phenotype was highly heterogeneous ranging from asymptomatic or paucisymptomatic hyperCKemia to severe muscle weakness and skeletal deformity with loss of ambulation. Sixty-eight RYR1 mutations, generally missense, were identified, of which 16 were novel. The combined analysis of the clinical presentation, disease progression and the structural bioinformatic analyses of RYR1 allowed to associate some phenotypes to mutations in specific domains. In addition, this study highlighted the structural bioinformatics potential in the prediction of the pathogenicity of RYR1 mutations. Further improvement in the comprehension of genotype-phenotype relationship of core myopathies can be expected in the next future: the actual lack of the human RyR1 crystal structure paired with the presence of large intrinsically disordered regions in RyR1, and the frequent presence of more than one RYR1 mutation in core myopathy patients, require designing novel investigation strategies to completely address RyR1 mutation effect.

Keywords: Central core disease; Genotype–phenotype correlations; Multi-minicore disease; Neuromuscular disorder; Protein modelling; RYR1-related myopathies.

Fig. 1

Muscle biopsy stained with COX from patients with core myopathy. In each panel is reported the patient #, the RYR1 mutation and RyR1 protein domain where the mutation is located. Central core (CC) (single or multiple, centrally or peripherally located) are shown in patient #2, 3, 47, 23, 21, 22, 67 and 56. In patient #56 a minority of muscle fibers showed CC where minicores (Mm) (multiple, small randomly distributed areas with focal loss of mitochondrial activity) were more abundant. Patient #22 showed both CC and Mm where patient #31 muscle biopsy showed only Mm. Neither the RYR1 mutation nor the RyR1 protein domain predict the ratio between CC and Mm

Fig. 2

Histogram showing the proportion of patients manifesting specific phenotypes. Patients are grouped based on the mutated domain; each domain is colored following the legend on the top of the figure. A. Manifestations during pregnancy or at the birth. B. Muscular manifestations. C. Osteoarticular manifestations. D. Respiratory involvement

Fig. 3

Schematic representation of RyR1 monomer functional domains. RyR1 sequence is presented as yellow bar with functional regions represented as colored boxes. Domain structural organization is presented on top. Dotted lines highlight regulative regions where red implies inhibition and green activation of the channel. Arrows represent the position for each mutation (frameshift mutations not shown). New mutations modelled in silico are wrote in red and marked with * when predicted as pathogenic, in green marked with # when benign

Fig. 4

Cartoon representation of the human RyR1 structure. Front and top views of RyR1 tetramer assembly. Different colors represent each monomer. On right side, isolated RyR1 monomer colored by functional domains with mutations noted and grouped accordingly (frameshift mutations not shown). New mutations modelled in silico are wrote in red and marked with * when predicted as pathogenic, in green marked with # when benign