Heterozygous CAPN3 missense variants causing autosomal-dominant calpainopathy in seven unrelated families

Variants in CAPN3 Causing Autosomal Dominant Limb-Girdle Muscular Dystrophy Combined With Calpain-3 Deficiency

Limb-girdle muscular dystrophy Type 2A/R1 or calpain-3 deficiency is the most common autosomal recessive limb-girdle muscular dystrophy. However, in recent years, autosomal dominant cases and families with calpain-3 deficiency have been reported, and there is an emerging interest in looking for single variants in the calpain-3 gene in mildly to moderately affected patients with limb-girdle muscular dystrophy without biallelic gene variants in CAPN3. Here, we report four cases with creatine kinase levels above 1500 U/L, mild-to-moderate proximal weakness, waddling gait, and scapular winging. Two patients, a son and his father, are heterozygous for the CAPN3 variant c.304C>T; p.(Pro102Ser), which has previously been reported in patients with compound heterozygous variants in CAPN3. The third and fourth patients were heterozygous for c.1371C>G; p.(Asn457Lys) and c.1490C>T; p.Ala497_Glu508del, respectively, neither of which has been reported before. All four patients had a near-complete loss of calpain-3 as determined by western blotting. While inherited autosomal dominant calpainopathy has now been firmly established, additional single cases of dominant calpainopathy are likely to emerge; some will be associated with clinical findings from parents or siblings, while others will arise from spontaneous mutations, but nevertheless with similar clinical findings of mild-to-moderate proximal weakness, increased level of creatine kinase, and near-complete loss of calpain-3 protein in affected individuals. This report expands the known number of variants causing dominant calpainopathy from 8 to 11 that appears to exclusively reside in two out of four domains that make up calpain-3. This information could aid in determining whether a CAPN3 variant of unknown significance is pathological.

Case report: A single novel calpain 3 gene variant associated with mild myopathy

Recessively inherited limb-girdle muscular dystrophy type 1, caused by mutations in the calpain 3 gene, is the most common limb-girdle muscular dystrophy worldwide. Recently, cases of autosomal dominant calpainopathy have been described. A man was referred to our neurological outpatient clinic at the age of 54 for persistent hyperCKemia (>1000 U/l) associated with muscle fatigue and myalgia. Clinical examination revealed mild proximal weakness in the lower limbs. His brother exhibited a moderate increase in serum creatine kinase levels (up to 2000 U/l) without other signs of myopathy. Their father experienced slowly progressive lower limb weakness after the age of 50. The calpain 3 variant c.1478G>A (p.Arg493Gln) in the heterozygous state was identified in both brothers. In silico modeling studies predict that this substitution may disrupt protein folding. This represents the first description of the heterozygous p.Arg493Gln calpain 3 variant as a potential cause of mild calpainopathy.

A Patient with Calpainopathy Carrying Compound Heterozygous Mutations of a De Novo Pathogenic Variant of c.1333G>A and a Novel Variant of c.1331C>T in CAPN3

Calpainopathy is primarily an autosomal recessive inherited myopathy; however, dominantly inherited cases with a pathogenic variant of c.1333G>A have been reported. A 13-year-old Japanese girl presented with toe walking and elevated serum creatine kinase levels. Genetic panel testing revealed compound heterozygosity for c.1333G>A and a novel variant of c.1331C>T in CAPN3, leading to a diagnosis of calpainopathy. A genetic analysis of her parents revealed the possibility that c.1333G>A was de novo. In this patient, the onset age was earlier than that of the reported autosomal dominant cases, suggesting the influence of the novel variant in the contralateral allele.

MRI for the diagnosis of limb girdle muscular dystrophies

PURPOSE OF REVIEW

In the last 30 years, there have many publications describing the pattern of muscle involvement of different neuromuscular diseases leading to an increase in the information available for diagnosis. A high degree of expertise is needed to remember all the patterns described. Some attempts to use artificial intelligence or analysing muscle MRIs have been developed. We review the main patterns of involvement in limb girdle muscular dystrophies (LGMDs) and summarize the strategies for using artificial intelligence tools in this field.

RECENT FINDINGS

The most frequent LGMDs have a widely described pattern of muscle involvement; however, for those rarer diseases, there is still not too much information available. patients. Most of the articles still include only pelvic and lower limbs muscles, which provide an incomplete picture of the diseases. AI tools have efficiently demonstrated to predict diagnosis of a limited number of disease with high accuracy.

SUMMARY

Muscle MRI continues being a useful tool supporting the diagnosis of patients with LGMD and other neuromuscular diseases. However, the huge variety of patterns described makes their use in clinics a complicated task. Artificial intelligence tools are helping in that regard and there are already some accessible machine learning algorithms that can be used by the global medical community.

Dominantly inherited muscle disorders: understanding their complexity and exploring therapeutic approaches

Treatments for disabling and life-threatening hereditary muscle disorders are finally close to becoming a reality. Research has thus far focused primarily on recessive forms of muscle disease. The gene replacement strategies that are commonly employed for recessive, loss-of-function disorders are not readily translatable to most dominant myopathies owing to the presence of a normal chromosome in each nucleus, hindering the development of novel treatments for these dominant disorders. This is largely due to their complex, heterogeneous disease mechanisms that require unique therapeutic approaches. However, as viral and RNA interference-based therapies enter clinical use, key tools are now in place to develop treatments for dominantly inherited disorders of muscle. This article will review what is known about dominantly inherited disorders of muscle, specifically their genetic basis, how mutations lead to disease, and the pathomechanistic implications for therapeutic approaches.

The CAPN3 p.Lys 254del variant is not always associated with dominant CAPN3-related muscular dystrophy

INTRODUCTION/AIMS

Limb-girdle muscular dystrophy R1 (LGMDR1) calpain 3-related usually presents as a recessively transmitted weakness of proximal limb-girdle muscles due to pathogenic variants in the CAPN3 gene. Pathogenic variants in this gene have also been found in patients with an autosomal dominantly inherited transmission pattern (LGMDD4). The mechanism underlying this difference in transmission patterns has not yet been elucidated. Camptocormia, progressive limb weakness, myalgia, back pain, and increased CK levels are common clinical features associated with dominant forms. The p.Lys254del pathogenic variant was associated with camptocormia in two LGMDD4 families. This study aimed to present carriers found in recessively transmitted LGMDR1 families bearing the p.Lys254del variant that do not show muscle weakness.

METHODS

DNA sequencing was performed on exon 5 of CAPN3 in family members to establish the carrier status of the pathogenic variant. They were evaluated clinically and MRI was performed when available.

RESULTS

Two families presented with the p.Lys254del pathogenic variant in a homozygous or compound heterozygous state. Family members carrying only the pathogenic variant in the heterozygous state did not demonstrate the myopathic characteristics described in dominant patients. Camptocormia and other severe clinical symptoms were not observed.

DISCUSSION

We conclude that the p.Lys254del pathogenic variant per se cannot be solely responsible for camptocormia in dominant patients. Other undisclosed factors may regulate the phenotype associated with the dominant inheritance pattern in CAPN3 pathogenic variant carriers.

Identification and functional characterization of a novel heterozygous splice‑site mutation in the calpain 3 gene causes rare autosomal dominant limb‑girdle muscular dystrophy

Limb-girdle muscular dystrophies are a group of extremely heterogenous neuromuscular disorders that manifest with gradual and progressive weakness of both proximal and distal muscles. Autosomal dominant limb-girdle muscular dystrophy (LGMDD4) or calpainopathy is a very rare form of myopathy characterized by weakness and atrophy of both proximal and distal muscles with a variable age of onset. LGMDD4 is caused by germline heterozygous mutations of the calpain 3 (CAPN3) gene. Patients with LGMDD4 often show extreme phenotypic heterogeneity; however, most patients present with gait difficulties, increased levels of serum creatine kinase, myalgia and back pain. In the present study, a 16-year-old male patient, clinically diagnosed with LGMDD4, was investigated. The proband had been suffering from weakness and atrophy of both of their proximal and distal muscles, and had difficulty walking and standing independently. The serum creatine kinase levels (4,754 IU/l; normal, 35-232 IU/l) of the patient were markedly elevated. The younger sister and mother of the proband were also clinically diagnosed with LGMDD4, while the father was phenotypically normal. Whole exome sequencing identified a heterozygous novel splice-site (c.2440-1G>A) mutation in intron 23 of the CAPN3 gene in the proband. Sanger sequencing confirmed that this mutation was also present in both the younger sister and mother of the proband, but the father was not a carrier of this mutation. This splice-site (c.2440-1G>A) mutation causes aberrant splicing of CAPN3 mRNA, leading to the skipping of the last exon (exon 24) of CAPN3 mRNA and resulting in the removal of eight amino acids from the C-terminal of domain IV of the CAPN3 protein. Hence, this splice site mutation causes the formation of a truncated CAPN3 protein (p.Trp814*) of 813 amino acids instead of the wild-type CAPN3 protein that consists of 821 amino acids. This mutation causes partial loss of domain IV (PEF domain) in the CAPN3 protein, which is involved in calcium binding and homodimerization; therefore, this is a loss-of-function mutation. Relative expression of the mutated CAPN3 mRNA was reduced in comparison with the wild-type CAPN3 mRNA in the proband, and their younger sister and mother. This mutation was also not present in 100 normal healthy control individuals of the same ethnicity. The present study reported the first case of CAPN3 gene-associated LGMDD4 in the Chinese population.

Genetic findings in Czech patients with limb girdle muscular dystrophy

Limb girdle muscular dystrophies (LGMD) are a genetically heterogeneous group of muscular dystrophies. The study presents an overview of molecular characteristics of a large cohort of LGMD patients who are representative of the Czech LGMD population. We present 226 LGMD probands in which 433 mutant alleles carrying 157 different variants with a supposed pathogenic effect were identified. Fifty-four variants have been described only in the Czech LGMD population so far. LGMD R1 caplain3-related is the most frequent subtype of LGMD involving 53.1% of patients with genetically confirmed LGMD, followed by LGMD R9 FKRP-related (11.1%), and LGMD R12 anoctamin5-related (7.1%). If we consider identified variants, then all but five were small-scale variants. One large gene deletion was identified in the LAMA2 gene and two deletions in each of CAPN3 and SGCG. We performed comparison our result with other published studies. The results obtained in the Czech LGMD population clearly differ from the outcome of other LGMD populations in two aspects-we have a more significant proportion of patients with LGMD R1 calpain3-related and a smaller proportion of LGMD R2 dysferlin-related.

Family and literature analysis demonstrates phenotypic effect of two variants in the calpain-3 gene

Both, recessive (LGMD R1) and dominant (LGMD D4) inheritance occur in calpain 3-related muscular dystrophy. We report a family with calpain-related muscular dystrophy caused by two known variants in the calpain 3 gene (CAPN3, NM_000070.3; (I) c.700G>A, p.Gly234Arg and (II) c.1746-20C>G, p.?). Three family members are compound heterozygous and exhibit a relatively homogeneous phenotype characterized by progressive proximal weakness starting in the third to fourth decade of life in the shoulder girdle and spreading to the legs. Two family members affected only by the p.Gly234Arg heterozygous missense variants show a different phenotype characterized by severe exertional myalgia without overt pareses. We conclude that in our family, the missense variant causes a severe myalgic phenotype without pareses that is aggravated by the second intronic variant and put these findings in the context of previous studies of the same variants.

The Limb-Girdle Muscular Dystrophies

PURPOSE OF REVIEW

The limb-girdle muscular dystrophies (LGMDs) are a group of inherited muscle disorders with a common feature of limb-girdle pattern of weakness, caused by over 29 individual genes. This article describes the classification scheme, common subtypes, and the management of individuals with LGMD.

RECENT FINDINGS

Advances in genetic testing and next-generation sequencing panels containing all of the LGMD genes have led to earlier genetic confirmation, but also to more individuals with variants of uncertain significance. The LGMDs include disorders with autosomal recessive inheritance, which are often due to loss-of-function mutations in muscle structural or repair proteins and typically have younger ages of onset and more rapidly progressive presentations, and those with autosomal dominant inheritance, which can have older ages of presentation and chronic progressive disease courses. All cause progressive disability and potential loss of ability to walk or maintain a job due to progressive muscle wasting. Certain mutations are associated with cardiac or respiratory involvement. No disease-altering therapies have been approved by the US Food and Drug Administration (FDA) for LGMDs and standard treatment uses a multidisciplinary clinic model, but recessive LGMDs are potentially amenable to systemic gene replacement therapies, which are already being tested in clinical trials for sarcoglycan and FKRP mutations. The dominant LGMDs may be amenable to RNA-based therapeutic approaches.

SUMMARY

International efforts are underway to better characterize LGMDs, help resolve variants of uncertain significance, provide consistent and improved standards of care, and prepare for future clinical trials.

Quantitative muscle MRI captures early muscle degeneration in calpainopathy

To evaluate differences in qMRI parameters of muscle diffusion tensor imaging (mDTI), fat-fraction (FF) and water T2 time in leg muscles of calpainopathy patients (LGMD R1/D4) compared to healthy controls, to correlate those findings to clinical parameters and to evaluate if qMRI parameters show muscle degeneration in not-yet fatty infiltrated muscles. We evaluated eight thigh and seven calf muscles of 19 calpainopathy patients and 19 healthy matched controls. MRI scans were performed on a 3T MRI including a mDTI, T2 mapping and mDixonquant sequence. Clinical assessment was done with manual muscle testing, patient questionnaires (ACTIVLIM, NSS) as well as gait analysis. Average FF was significantly different in all muscles compared to controls (p < 0.001). In muscles with less than 8% FF a significant increase of FA (p < 0.005) and decrease of RD (p < 0.004) was found in high-risk muscles of calpainopathy patients. Water T2 times were increased within the low- and intermediate-risk muscles (p ≤ 0.045) but not in high-risk muscles (p = 0.062). Clinical assessments correlated significantly with qMRI values: QMFM vs. FF: r = - 0.881, p < 0.001; QMFM versus FA: r = - 0.747, p < 0.001; QMFM versus MD: r = 0.942, p < 0.001. A good correlation of FF and diffusion metrics to clinical assessments was found. Diffusion metrics and T2 values are promising candidates to serve as sensitive early and non-invasive methods to capture early muscle degeneration in non-fat-infiltrated muscles in calpainopathies.

Identification of a novel heterozygous DYSF variant in a large family with a dominantly-inherited dysferlinopathy

AIMS

Dysferlinopathy is an autosomal recessive muscular dystrophy, caused by bi-allelic variants in the gene encoding dysferlin (DYSF). Onset typically occurs in the second to third decade and is characterised by slowly progressive skeletal muscle weakness and atrophy of the proximal and/or distal muscles of the four limbs. There are rare cases of symptomatic DYSF variant carriers. Here, we report a large family with a dominantly inherited hyperCKaemia and late-onset muscular dystrophy.

METHODS AND RESULTS

Genetic analysis identified a co-segregating novel DYSF variant [NM_003494.4:c.6207del p.(Tyr2070Metfs*4)]. No secondary variants in DYSF or other dystrophy-related genes were identified on whole genome sequencing and analysis of the proband's DNA. Skeletal muscle involvement was milder and later onset than typical dysferlinopathy presentations; these clinical signs manifested in four individuals, all between the fourth and sixth decades of life. All individuals heterozygous for the c.6207del variant had hyperCKaemia. Histological analysis of skeletal muscle biopsies across three generations showed clear dystrophic signs, including inflammatory infiltrates, regenerating myofibres, increased variability in myofibre size, and internal nuclei. Muscle magnetic resonance imaging revealed fatty replacement of muscle in two individuals. Western blot and immunohistochemical analysis of muscle biopsy demonstrated consistent reduction of dysferlin staining. Allele-specific quantitative PCR analysis of DYSF mRNA from patient muscle found that the variant, localised to the extreme C-terminus of dysferlin, does not activate post-transcriptional mRNA decay.

CONCLUSIONS

We propose that this inheritance pattern may be underappreciated and that other late-onset muscular dystrophy cases with mono-allelic DYSF variants, particularly C-terminal premature truncation variants, may represent dominant forms of disease.

Hereditary cerebral small vessel disease: Assessment of a HTRA1 variant using protein stability predictors and 3D modelling

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is an autosomal recessive vascular disorder caused by biallellic variants in HTRA1. Recently, it has been reported that several heterozygous mutations in HTRA1 are responsible for a milder late-onset cerebral small vessel disease (CSVD) with an autosomal dominant pattern of inheritance. The majority of them are missense that affects the Htr1A protease activity due to a dominant-negative effect caused by defective trimerization or monomer activation. The molecular mechanism related to the structural destabilization of the protein supports the practical utility of integrating computational stability predictors to prioritize candidate variants in this gene. In this work, we report a family with several members diagnosed with subcortical ischemic events and progressive cognitive impairment caused by the novel c.820C > G, p.(Arg274Gly) heterozygous variant in HTRA1 segregating in an autosomal dominant manner and propose its molecular mechanism by a three-dimensional model of the protein's structure.

CAPN3 c.1746-20C>G variant is hypomorphic for LGMD R1 calpain 3-related

The investigated intronic CAPN3 variant NM_000070.3:c.1746-20C>G occurs in the Central and Eastern Europe with a frequency of >1% and there are conflicting interpretations on its pathogenicity. We collected data on 14 patients carrying the CAPN3 c.1746-20C>G variant in trans position with another CAPN3 pathogenic/likely pathogenic variant. The patients compound heterozygous for the CAPN3 c.1746-20C>G variant presented a phenotype consistent with calpainopathy of mild/medium severity. This variant is most frequent in the North/West regions of Russia and may originate from that area. Molecular studies revealed that different splicing isoforms are produced in the muscle. We hypothesize that c.1746-20C>G is a hypomorphic variant with a reduction of RNA and protein expression and only individuals having a higher ratio of abnormal isoforms are affected. Reclassification of the CAPN3 variant c.1746-20C>G from variant with a conflicting interpretation of pathogenicity to hypomorphic variant explains many unidentified cases of limb girdle muscular dystrophy R1 calpain 3-related in Eastern and Central Europe.

Transcriptomic Evidence of the Immune Response Activation in Individuals With Limb Girdle Muscular Dystrophy Dominant 2 (LGMDD2) Contributes to Resistance to HIV-1 Infection

LGMDD2 is a rare form of muscular dystrophy characterized by one of the three heterozygous deletions described within the TNPO3 gene that result in the addition of a 15-amino acid tail in the C-terminus.TNPO3 is involved in the nuclear import of splicing factors and acts as a host cofactor for HIV-1 infection by mechanisms not yet deciphered. Further characterization of the crosstalk between HIV-1 infection and LGMDD2 disease may contribute to a better understanding of both the cellular alterations occurring in LGMDD2 patients and the role of TNPO3 in the HIV-1 cycle. To this regard, transcriptome profiling of PBMCs from LGMDD2 patients carrying the deletion c.2771delA in the TNPO3 gene was compared to healthy controls. A total of 545 differentially expressed genes were detected between LGMDD2 patients and healthy controls, with a high representation of G protein-coupled receptor binding chemokines and metallopeptidases among the most upregulated genes in LGMDD2 patients. Plasma levels of IFN-β and IFN-γ were 4.7- and 2.7-fold higher in LGMDD2 patients, respectively. An increase of 2.3-fold in the expression of the interferon-stimulated gene MxA was observed in activated PBMCs from LGMDD2 patients after ex vivo HIV-1 pseudovirus infection. Thus, the analysis suggests a pro-inflammatory state in LGMDD2 patients also described for other muscular dystrophies, that is characterized by the alteration of IL-17 signaling pathway and the consequent increase of metallopeptidases activity and TNF response. In summary, the increase in interferons and inflammatory mediators suggests an antiviral environment and resistance to HIV-1 infection but that could also impair muscular function in LGMDD2 patients, worsening disease evolution. Biomarkers of disease progression and therapeutic strategies based on these genes and mechanisms should be further investigated for this type of muscular dystrophy.

Current and Future Approaches to Classify VUSs in LGMD-Related Genes

Next-generation sequencing (NGS) has revealed large numbers of genetic variants in LGMD-related genes, with most of them classified as variants of uncertain significance (VUSs). VUSs are genetic changes with unknown pathological impact and present a major challenge in genetic test interpretation and disease diagnosis. Understanding the phenotypic consequences of VUSs can provide clinical guidance regarding LGMD risk and therapy. In this review, we provide a brief overview of the subtypes of LGMD, disease diagnosis, current classification systems for investigating VUSs, and a potential deep mutational scanning approach to classify VUSs in LGMD-related genes.

Targeted Next-Generation Sequencing Reveals Mutations in Non-coding Regions and Potential Regulatory Sequences of Calpain-3 Gene in Polish Limb-Girdle Muscular Dystrophy Patients

Limb–girdle muscular dystrophy type R1 (LGMDR1) is caused by mutations in CAPN3 and is the most common type of recessive LGMD. Even with the use of whole-exome sequencing (WES), only one mutant allele of CAPN3 is found in a significant number of LGMDR patients. This points to a role of non-coding, intronic or regulatory, sequence variants in the disease pathogenesis. Targeted sequencing of the whole CAPN3 gene including not only intronic, 3′ and 5′ UTRs but also potential regulatory regions was performed in 27 patients suspected with LGMDR1. This group included 13 patients with only one mutated CAPN3 allele detected previously with exome sequencing. A second rare variant in the non-coding part of CAPN3 was found in 11 of 13 patients with previously identified single mutation. Intronic mutations were found in 10 cases, with c.1746-20C>G variant present in seven patients. In addition, a large deletion of exons 2–8 was found in one patient. In the patients with no causative mutation previously found, we detected rare CAPN3 variants in 5 out of 10 patients and in two of them in a compound heterozygous state. Rare variants within putative regulatory sequences distant from the CAPN3 gene were found in 15 patients, although in 11 of these cases, other variants are deemed causative. The results indicate that intronic mutations are common in Polish LGMDR patients, and testing for non-coding mutations in CAPN3 should be performed in apparently single heterozygous patients.

A recurrent rare intronic variant in CAPN3 alters mRNA splicing and causes autosomal recessive limb-girdle muscular dystrophy-1 in three Pakistani pedigrees

Autosomal recessive limb-girdle muscular dystrophy-1 (LGMDR1) is an autosomal recessive disorder characterized by progressive weakness of the proximal limb and girdle muscles. Biallelic mutations in CAPN3 are reported frequently to cause LGMDR1. Here, we describe 11 individuals from three unrelated consanguineous families that present with typical features of LGMDR1 that include proximal muscle wasting, weakness of the upper and lower limbs, and elevated serum creatine kinase. Whole-exome sequencing identified a rare homozygous CAPN3 variant near the exon 2 splice donor site that segregates with disease in all three families. mRNA splicing studies showed partial retention of intronic sequence and subsequent introduction of a premature stop codon (NM_000070.3: c.379 + 3A>G; p.Asp128Glyfs*15). Furthermore, we observe reduced CAPN3 expression in primary dermal fibroblasts derived from an affected individual, suggesting instability and/or nonsense-mediated decay of mutation-bearing mRNA. Genome-wide homozygosity mapping and single-nucleotide polymorphism analysis identified a shared haplotype and supports a possible founder effect for the CAPN3 variant. Together, our data extend the mutational spectrum of LGMDR1 and have implications for improved diagnostics for individuals of Pakistani origin.

An integrated approach to the evaluation of patients with asymptomatic or minimally symptomatic hyperCKemia

Introduction/Aims

Currently, there are no straightforward guidelines for the clinical and diagnostic management of hyperCKemia, a frequent and nonspecific presentation in muscle diseases. Therefore, we aimed to describe our diagnostic workflow for evaluating patients with this condition.

Methods

We selected 83 asymptomatic or minimally symptomatic patients with persistent hyperCKemia for participation in this Italian multicenter study. Patients with facial involvement and distal or congenital myopathies were excluded, as were patients with suspected inflammatory myopathies or predominant respiratory or cardiac involvement. All patients underwent a neurological examination and nerve conduction and electromyography studies. The first step of the investigation included a screening for Pompe disease. We then evaluated the patients for myotonic dystrophy type II–related CCTG expansion and excluded patients with copy number variations in the DMD gene. Subsequently, the undiagnosed patients were investigated using a target gene panel that included 20 genes associated with isolated hyperCKemia.

Results

Using this approach, we established a definitive diagnosis in one third of the patients. The detection rate was higher in patients with severe hyperCKemia and abnormal electromyographic findings.

Discussion

We have described our diagnostic workflow for isolated hyperCKemia, which is based on electrodiagnostic data, biochemical screening, and first‐line genetic investigations, followed by successive targeted sequencing panels. Both clinical signs and electromyographic abnormalities are associated with increased diagnostic yields.

[Calpainopathies: state of the art and therapeutic perspectives]

Calpainopathies are inherited limb-girdle muscular dystrophies, most often following an autosomal recessive (AR) transmission. Autosomal dominant (AD) forms with less severe presentation are increasingly reported. Calpainopathies with autosomal recessive (AR) mutations of the calpain3 gene (CAPN3) are associated with limb girdle muscular dystrophy type R1 (LGMD-R1, OMIM 253600) also referred to as LGMD-2A according to the old nomenclature. LGMD-R1 is the commonest form of all LGMDs, with an estimated prevalence of 10 to 70 cases per million inhabitants, that is a cohort of between 670 and 4,200 patients in France theoritically. Patients present a symmetrical proximal axial myopathy manifesting itself between the first and second decade. The clinical course is variable. The level of Creatine- Kinase (CK) is usually high and there is no cardiac involvement. From a therapeutic perspective, the autosomal recessive form of calpainopathy is quite suitable to gene replacement strategies; the viability of recombinant AAV-mediated calpain 3 transfer has been demonstrated in animal models and clinical trials are expected in the coming years. Meanwhile, natural history studies are needed to prepare for future clinical trials.