Imaging‐based evaluation of pathogenicity by novel DNM2 variants associated with centronuclear myopathy

Abstract

A centronuclear myopathy (CNM) is a group of inherited congenital diseases showing clinically progressive muscle weakness associated with the presence of centralized myonuclei, diagnosed by genetic testing and muscle biopsy. The gene encoding dynamin 2, DNM2, has been identified as a causative gene for an autosomal dominant form of CNM. However, the information of a DNM2 variant alone is not always sufficient to gain a definitive diagnosis as the pathogenicity of many gene variants is currently unknown. In this study, we identified five novel DNM2 variants in our cohort. To establish the pathogenicity of these variants without using clinicopathological information, we used a simple in cellulo imaging‐based assay for T‐tubule‐like structures to provide quantitative data that enable objective determination of pathogenicity by novel DNM2 variants. With this assay, we demonstrated that the phenotypes induced by mutant dynamin 2 in cellulo are well correlated with biochemical gain‐of‐function features of mutant dynamin 2 as well as the clinicopathological phenotypes of each patient. Our approach of combining an in cellulo assay with clinical information of the patients also explains the course of a disease progression by the pathogenesis of each variant in DNM2‐associated CNM.

Centronuclear Myopathy Caused by Defective Membrane Remodelling of Dynamin 2 and BIN1 Variants

“…The fission activities of dynamin have been mainly measured based on its GTPase activity and most of the CNM-associated dynamin 2 mutants have been identified as gain-of-function mutants. Interestingly, our quantitative analyses on T-tubule like structures reconstituted in cellulo showed a good correlation between membrane fission activities of CNM-associated variants and pathogenicity [ 91 ]. Thus, our approach using simple in vitro and in cellulo assays together with genetic and clinicopathological analyses should contribute to a more precise diagnosis of pathogenicity, especially when muscle biopsy samples are unavailable ( Figure 4 ).…”

Benefits of therapy by dynamin-2-mutant-specific silencing are maintained with time in a mouse model of dominant centronuclear myopathy

“…1 AD-CNM results from heterozygous mutations in the DNM2 gene, which encodes dynamin 2 (DNM2), 2,3 and to date, 37 mutations (mainly missense) have been identified. 2,[4][5][6][7][8][9][10][11] Dominant DNM2 mutations also cause rare cases of Charcot-Marie-Tooth pe-ripheral neuropathy (CMT) (MIM: 606482) 12 and hereditary spastic paraplegia. 13 DNM2 belongs to the superfamily of large guanosine triphosphatases (GTPases) and is involved in endocytosis and intracellular vesicle trafficking through its role in deformation of biological membranes by oligomerization at the neck of membranes invagination, leading to the release of vesicles.…”

Phenotypic Spectrum of DNM2 -Related Centronuclear Myopathy

“…[13][14][15][16] Our understanding of tissue-specific mechanisms causing these different phenotypes is limited but suggests that CNM is caused by a gain of function mechanism, whereas CMT generally results from a loss of function mechanism. 10,[16][17][18] DNM2 encodes the large GTPase dynamin 2 that plays a role in many cellular functions, particularly membrane trafficking. 19,20 In DNM2-related CNM, most mutations cluster in the middle and pleckstrin homology (PH) domains of dynamin 2, leading to reduced inhibition of GTPase activity (Figure 1A).…”

“…[22][23][24][25] There has been significant progress in understanding disease mechanisms of DNM2-related CNM resulting in proof of principle and preclinical studies for several therapeutic approaches, 5,26 including antisense oligonucleotide-mediated DNM2 knockdown. However, the clinical variability and small numbers of reported patients 18,[27][28][29][30][31][32][33][34] pose a challenge to defining the natural history of this rare disorder. This retrospective case series study aims to further describe the phenotypic variability of DNM2-related CNM, highlight underreported clinical features, and evaluate genotype-phenotype correlation.…”

“…13-16 Our understanding of tissue-specific mechanisms causing these different phenotypes is limited but suggests that CNM is caused by a gain of function mechanism, whereas CMT generally results from a loss of function mechanism. 10,16-18…”