Clinical and Pathological Heterogeneity of Korean Patients with CAPN3 Mutations

Loss of Calpain 3 dysregulates store-operated calcium entry and its exercise response in mice

Limb-Girdle Muscular Dystrophy R1/2A (LGMD R1/2A) is caused by mutations in the CAPN3 gene encoding Calpain 3, a skeletal-muscle specific, Ca2+-dependent protease. Localization of Calpain 3 within the triad suggests it contributes to Ca2+ homeostasis. Through live-cell Ca2+ measurements, muscle mechanics, immunofluorescence, and electron microscopy (EM) in Capn3 deficient (C3KO) and wild-type (WT) mice, we determined whether loss of Calpain 3 altered Store-Operated Calcium Entry (SOCE) activity. Direct Ca2+ influx measurements revealed loss of Capn3 elicits elevated resting SOCE and increased resting cytosolic Ca2+, supported by high incidence of calcium entry units (CEUs) observed by EM. C3KO and WT mice were subjected to a single bout of treadmill running to elicit SOCE. Within 1HR post-treadmill running, C3KO mice exhibited diminished force production in extensor digitorum longus muscles and a greater decay of Ca2+ transients in flexor digitorum brevis muscle fibers during repetitive stimulation. Striking evidence for impaired exercise-induced SOCE activation in C3KO mice included poor colocalization of key SOCE proteins, stromal-interacting molecule 1 (STIM1) and ORAI1, combined with disappearance of CEUs in C3KO muscles. These results demonstrate that Calpain 3 is a key regulator of SOCE in skeletal muscle and identify SOCE dysregulation as a contributing factor to LGMD R1/2A pathology.

Identification of novel pathogenic variants of Calpain-3 gene in limb girdle muscular dystrophy R1

BACKGROUND

Limb Girdle Muscular Dystrophy R1 (LGMDR1) is an autosomal recessive neuromuscular disease caused by mutations in the calpain-3 (CAPN3) gene. As clinical and pathological features may overlap with other types of LGMD, therefore definite molecular diagnosis is required to understand the progression of this debilitating disease. This study aims to identify novel variants of CAPN3 gene in LGMDR1 patients.

RESULTS

Thirty-four patients with clinical and histopathological features suggestive of LGMD were studied. The muscle biopsy samples were evaluated using Enzyme histochemistry, Immunohistochemistry, followed by Western Blotting and Sanger sequencing. Out of 34 LGMD cases, 13 patients were diagnosed as LGMDR1 by immunoblot analysis, demonstrating reduced or absent calpain-3 protein as compared to controls. Variants of CAPN3 gene were also found and pathogenicity was predicted using in-silico prediction tools. The CAPN3 gene variants found in this study, included, two missense variants [CAPN3: c.1189T > C, CAPN3: c.2338G > C], one insertion-deletion [c.1688delinsTC], one splice site variant [c.2051-1G > T], and one nonsense variant [c.1939G > T; p.Glu647Ter].

CONCLUSIONS

We confirmed 6 patients as LGMDR1 (with CAPN3 variants) from our cohort and calpain-3 protein expression was significantly reduced by immunoblot analysis as compared to control. Besides the previously known variants, our study found two novel variants in CAPN3 gene by Sanger sequencing-based approach indicating that genetic variants in LGMDR1 patients may help to understand the etiology of the disease and future prognostication.

Loss of calpain 3 dysregulates store-operated calcium entry and its exercise response in mice

Limb-Girdle Muscular Dystrophy 2A (LGMD2A) is caused by mutations in the CAPN3 gene encoding Calpain 3, a skeletal-muscle specific, Ca2+-dependent protease. Localization of Calpain 3 within the triad suggests it contributes to Ca2+ homeostasis. Through live-cell Ca2+ measurements, muscle mechanics, immunofluorescence, and electron microscopy (EM) in Capn3 deficient (C3KO) and wildtype (WT) mice, we determined if loss of Calpain 3 altered Store-Operated Calcium Entry (SOCE) activity. Direct Ca2+ influx measurements revealed loss of Capn3 elicits elevated resting SOCE and increased resting cytosolic Ca2+, supported by high incidence of calcium entry units (CEUs) observed by EM. C3KO and WT mice were subjected to a single bout of treadmill running to elicit SOCE. Within 1HR post-treadmill running, C3KO mice exhibited diminished force production in extensor digitorum longus muscles and a greater decay of Ca2+ transients in flexor digitorum brevis muscle fibers during repetitive stimulation. Striking evidence for impaired exercise-induced SOCE activation in C3KO mice included poor colocalization of key SOCE proteins, stromal-interacting molecule 1 (STIM1) and ORAI1, combined with disappearance of CEUs in C3KO muscles. These results demonstrate that Calpain 3 is a key regulator of SOCE in skeletal muscle and identify SOCE dysregulation as a contributing factor to LGMD2A pathology.

Single-centre experience with autosomal recessive limb-girdle muscular dystrophy: case series and literature review

Limb-girdle muscular dystrophy (LGMD) is a group of myopathies that lead to progressive muscle weakness, predominantly involving the shoulder and pelvic girdles; it has a heterogeneous genetic etiology, with variation in the prevalence of subtypes according to the ethnic backgrounds and geographic origins of the populations. The aim of the present study was to analyze a series of patients with autosomal recessive LGMD (LGMD-R) to contribute to a better characterization of the disease and to find the relative proportion of the different subtypes in a Southern Brazil cohort. The sample population consisted of 36 patients with LGMD-R. A 9-gene targeted next-generation sequencing panel revealed variants in 23 patients with LGMD (64%), and it identified calpainopathy (LGMD-R1) in 26%, dysferlinopathy (LGMD-R2) in 26%, sarcoglycanopathies (LGMD-R3-R5) in 13%, telethoninopathy (LGMD-R7) in 18%, dystroglicanopathy (LGMD-R9) in 13%, and anoctaminopathy (LGMD-R12) in 4% of the patients. In these 23 patients with LGMD, there were 27 different disease-related variants in the ANO5, CAPN3, DYSF, FKRP, SGCA, SGCB, SGCG, and TCAP genes. There were different causal variants in different exons of these genes, except for the TCAP gene, for which all patients carried the p.Gln53* variant, and the FKRP gene, which showed recurrence of the p.Leu276Ile variant. We analyzed the phenotypic, genotypic and muscle immunohistochemical features of this Southern Brazilian cohort.

Compound heterozygous CAPN3 variants identified in a family with limb-girdle muscular dystrophy recessive 1

Limb-girdle muscular dystrophy recessive 1 (LGMDR1), a rare subtype of muscular dystrophy, is characterized by progressive muscle weakness and degeneration with a predominant presentation on the shoulder, pelvic and proximal limb muscles. Variants in calcium-activated neutral proteinase 3 (CAPN3), which encodes an enzyme, calpain 3, are considered the major cause of LGMDR1. The present study was conducted to identify the variants responsible for clinical symptoms in a Chinese patient with limb-girdle muscular dystrophies (LGMDs) and explore its genotype-phenotype associations. A series of clinical examinations were conducted, including blood tests and magnetic resonance imaging scans of the lower legs, electromyography and muscle biopsy on the proband diagnosed with muscular dystrophies. Genomic DNA was extracted from the peripheral blood of a three-person family with LGMDs and pathogenic variants detected by whole-exome sequencing (WES) were verified by Sanger sequencing. The WES of this patient revealed compound heterozygous variants in CAPN3, c.2120A>G/p.(Asp707Gly) in exon 20 and c.2201_2202delAT/p.(Tyr734*) in exon 21, which were inherited from his parents and absent from 200 control individuals of similar ethnic origin, indicating that these variants are the pathogenic triggers of the LGMDR1 phenotype. Notably, these CAPN3 sequence variants were related to LGMDR1 pathogenesis in this three-person family. The newly discovered c.2201_2202delAT/p.(Tyr734*) expands the current CAPN3 variant spectrum, improving the understanding of the conditions required to develop molecular diagnostic tools and for genetic counseling, particularly for families with a history of autosomal recessive LGMDs.

Molecular landscape of CAPN3 mutations in limb-girdle muscular dystrophy type R1: from a Chinese multicentre analysis to a worldwide perspective

BACKGROUND

Limb-girdle muscular dystrophy type R1 (LGMDR1) can be caused by recessive CAPN3 mutations accounting for the majority of LGMD. To date, no systemic evaluation has been performed to analyse the detrimental and normal mutations on CAPN3 and its hotspots.

METHODS

CAPN3 variants (n=112) from a total of 124 patients with LGMDR1 recruited in four centres in China were retrospectively analysed. Then external CAPN3 variants (n=2031) from online databases were integrated with our Chinese cohort data to achieve a worldwide perspective on CAPN3 mutations. According to their related phenotypes (LGMDR1 or normal), we analysed consequence, distribution, ethnicity and severity scores of CAPN3 mutations.

RESULTS

Two hotspot mutations were identified including c.2120A>G in Chinese population and c.550del in Europe. According to the integrated dataset, 521 mutations were classified as LGMDR1-related and converged on exons 1, 10, 5, 22 and 13 of CAPN3. The remaining 1585 variants were classified as normal-population related. The deleterious ratio of LGMDR1-relevant variants to total variants in each population was 0.26 on average with a maximum of 0.35 in Finns and a minimum of 0.21 in South Asians. Severity evaluation showed that Chinese LGMDR1-related variants exhibited a higher risk (Combined Annotation Dependent Depletion score +1.10) than that from database patients (p<0.001).

CONCLUSIONS

This study confirmed two hotspots and LGMDR1-related CAPN3 variants, highlighting the advantages in using a data-based comprehensive analysis to achieve a genetic landscape for patients with LGMDR1.

Novel Missense CAPN3 Mutation Responsible for Adult-Onset Limb Girdle Muscular Dystrophy with Calves Hypertrophy

CAPN3 gene encodes for calpain-3; this protein is a calcium-dependent intracellular protease. Deficiency of this enzyme leads to weakness of the proximal limb muscles and pelvic and shoulder girdles, the so-called limb-girdle muscular dystrophy type 2A (LGMD2A). Here, we reported the case of a Tunisian patient with LGMD2A associated with a novel missense mutation (c.T1681C/p.Y561H). A 61-year-old man, with consanguineous parents, was referred for gait difficulties and slowly progressive proximal weakness of the four limbs associated with moderate hypertrophy of the calves but his facial muscles were unaffected. Electromyography showed that the profile was myopathic pattern and creatine kinase (CK) level was high. Muscle biopsy processing included routine histological, immunohistochemical, and Western Blot reactions, using a panel of antibodies directed against dystrophin, dysferlin, calpain-3, sarcoglycan α, β, γ, and δ. For mutation analysis, we designed an NGS-based screening. Immunological analyses demonstrated a total deficiency in calpain-3 and δ-sarcoglycan, and a reduced expression of dysferlin. The genetic study yielded a homozygous missense mutation (c.T1681C) of the 13th exon of the CAPN3 gene. The mutation found in our patient (c.T1681C/p.Y561H) has not been previously reported. It is responsible for complete calpain-3 and δ-sarcoglycan deficiency and reduced dysferlin expression. The genetic study is mandatory in such cases with multiple-protein deficiency and ambiguous results of immune-histology and Western Blot studies.

The clinical spectrum and genetic variability of limb-girdle muscular dystrophy in a cohort of Chinese patients

Background

Limb-girdle muscular dystrophy (LGMD) is a commonly diagnosed hereditary muscular disorder, characterized by the progressive weakness of the limb-girdle muscles. Although the condition has been well-characterized, clinical and genetic heterogeneity can be observed in patients with LGMD. Here, we aimed to describe the clinical manifestations and genetic variability among a cohort of patients with LGMD in South China.

Results

We analyzed the clinical information, muscle magnetic resonance imaging (MRI) findings, and genetic results obtained from 30 patients (24 families) with clinically suspected LGMD. In 24 probands, 38 variants were found in total, of which 18 were shown to be novel. Among the 30 patients, the most common subtypes were dysferlinopathy in eight (26.67%), sarcoglycanopathies in eight [26.67%; LGMD 2C in three (10.00%), LGMD 2D in three (10.00%), and LGMD 2F in two (6.67%)], LGMD 2A in seven (23.33%), followed by LGMD 1B in three (10.00%), LGMD 2I in three (10.00%), and early onset recessive Emery-Dreifuss-like phenotype without cardiomyopathy in one (3.33%). Furthermore, we also observed novel clinical presentations for LGMD 1B, 2F, and 2I patients with hypermobility of the joints in the upper limbs, a LGMD 2F patient with delayed language development, and other manifestations. Moreover, distinct distributions of fatty infiltration in patients with LGMD 2A, dysferlinopathy, and the early onset recessive Emery-Dreifuss-like phenotype without cardiomyopathy were also observed based on muscle MRI results.

Conclusions

In this study, we expanded the clinical spectrum and genetic variability found in patients with LGMD, which provided additional insights into genotype and phenotype correlations in this disease.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0859-6) contains supplementary material, which is available to authorized users.

Integrative variants, haplotypes and diplotypes of the CAPN3 and FRMD5 genes and several environmental exposures associate with serum lipid variables

To determine whether the integrative variants, haplotypes and diplotypes of the calpain 3 (CAPN3) and the FERM domain containing 5 genes (FRMD5) and several environmental exposures are associated with an implication in lipid homeostasis, which are associated with cardiovascular risk. Genotyping of the CAPN3 rs4344713 and FRMD5 rs524908 was performed by Sanger sequencing in 1,640 subjects (Jing, 819 and Han, 821). Multivariate analyses of covariance models that adjusted by age, gender, body mass index (BMI), blood pressure and lifestyle (smoking and drinking), were constructed using variants, haplotypes and diplotypes of the CAPN3 rs4344713 and FRMD5 rs524908 as predictors and changes in lipid variables. Significant associations with low-density lipoprotein cholesterol and apolipoprotein (Apo) B were found. Linkage disequilibrium with each other showed the haplotype-phenotype associations with triglyceride and ApoA1. This study also suggested pleiotropic associations of the CAPN3-FRMD5 diplotypes with lipid variables. As potential confounders, diastolic blood pressure (DBP) and BMI were significantly associated with lipid variables. We conclude that integrative variants, haplotypes and diplotypes of the CAPN3 rs4344713 and FRMD5 rs524908, as well as DBP and BMI are associated with serum lipid variables in the Jing and Han populations.