Muscular Dystrophy, Limb-Girdle, Autosomal Recessive 1

A number sign (#) is used with this entry because of evidence that autosomal recessive limb-girdle muscular dystrophy-1 (LGMDR1), previously symbolized LGMD2A, is caused by homozygous or compound heterozygous mutation in the gene encoding the proteolytic enzyme calpain-3 (CAPN3; 114240) on chromosome 15q15.

Heterozygous mutation in the CAPN3 gene can cause autosomal dominant limb-girdle muscular dystrophy-4 (LGMDD4; 618129), which has a later onset and milder features.

Description

Autosomal recessive limb-girdle muscular dystrophy-1 affects primarily the proximal muscles, resulting in difficulty walking. The age at onset varies, but most patients show onset in childhood, and the disorder is progressive. Other features may include scapular winging, calf pseudohypertrophy, and contractures (summary by Mercuri et al., 2005).

Genetic Heterogeneity of Autosomal Recessive Limb-Girdle Muscular Dystrophy

Autosomal recessive LGMD is genetically heterogeneous.

LGMDR2 (253601), previously symbolized LGMD2B, is caused by mutation in the dysferlin gene (DYSF; 603009) on 2p13. LGMDR3 (608099), previously symbolized LGMD2D, is caused by mutation in the alpha-sarcoglycan gene (SGCA; 600119) on 17q21. LGMDR4 (604286), previously symbolized LGMD2E, is caused by mutation in the beta-sarcoglycan gene (SGCB; 600900) on 4q12. LGMDR5 (253700), previously symbolized LGMD2C, is caused by mutation in the gamma-sarcoglycan gene (SGCG; 608896) on 13q12. LGMDR6 (601287), previously symbolized LGMD2F, is caused by mutation in the delta-sarcoglycan gene (SGCD; 601411) on 5q33. LGMDR7 (601954), previously symbolized LGMD2G, is caused by mutation in the TCAP gene (604488) on 17q12. LGMDR8 (254110), previously symbolized LGMD2H, is caused by mutation in the TRIM32 gene (602290) on 9q33. LGMDR9 (607155), previously symbolized LGMD2I, is caused by mutation in the FKRP gene (606596) on 19q13. LGMDR10 (608807), previously symbolized LGMD2J, is caused by mutation in the titin gene (TTN; 188840) on 2q31. LGMDR11 (609308), previously symbolized LGMD2K, is caused by mutation in the POMT1 gene (607423) on 9q34. LGMDR12 (611307), previously symbolized LGMD2L, is caused by mutation in the ANO5 gene (608662) on 11p14. LGMDR13 (611588), previously symbolized LGMD2M, is caused by mutation in the FKTN gene (607440) on 9q31. LGMDR14 (613158), previously symbolized LGMD2N, is caused by mutation in the POMT2 gene (607439) on 14q24. LGMDR15 (613157), previously symbolized LGMD2O, is caused by mutation in the POMGNT1 gene (606822) on 1p34. LGMDR16 (613818), previously symbolized LGMD2P, is caused by mutation in the DAG1 gene (128239) on 3p21. LGMDR17 (613723), previously symbolized LGMD2Q, is caused by mutation in the PLEC1 gene (601282) on 8q24. LGMDR18 (615356), previously symbolized LGMD2S, is caused by mutation in the TRAPPC11 gene (614138) on 4q35. LGMDR19 (615352), previously symbolized LGMD2T, is caused by mutation in the GMPPB gene (615320) on 3p21. LGMDR20 (616052), previously symbolized LGMD2U, is caused by mutation in the ISPD gene (614631) on 7p21. LGMDR21 (617232), previously symbolized LGMD2Z, is caused by mutation in the POGLUT1 gene (615618) on 3q13. LGMDR22 (254090), also known as Ullrich congenital muscular dystrophy, is caused by mutation in one of the collagen VI genes (120220, 120240, 120250). LGMDR23 (618138) is caused by mutation in the LAMA2 gene (156225) on 6q22. LGMDR24 (618135) is caused by mutation in the POMGNT2 gene (614828) on 3p22. LGMDR25 (616812), previously symbolized LGMD2X, is caused by mutation in the BVES gene (604577) on 6q21.

Some forms of autosomal recessive LGMD were reclassified by Straub et al. (2018). LGMD2R was reclassified as a form of myofibrillar myopathy (MFM1; 601419). For forms previously designated LGMD2W and LGMD2Y, see 616827 and 617072, respectively.

For a discussion of autosomal dominant LGMD, see LGMDD1 (603551).

Nomenclature

At the 229th ENMC international workshop, limb-girdle muscular dystrophy was defined as 'a genetically inherited condition that primarily affects skeletal muscle leading to progressive, predominantly proximal muscle weakness at presentation caused by a loss of muscle fibres. To be considered a form of limb girdle muscular dystrophy the condition must be described in at least two unrelated families with affected individuals achieving independent walking, must have an elevated serum creatine kinase activity, must demonstrate degenerative changes on muscle imaging over the course of the disease, and have dystrophic changes on muscle histology, ultimately leading to end-stage pathology for the most affected muscles' (Straub et al., 2018).

Straub et al. (2018) reviewed, reclassified, and/or renamed forms of LGMD. The proposed naming formula was 'LGMD, inheritance (R or D), order of discovery (number), affected protein.'

Clinical Features

In a large study of patients with different forms of muscular dystrophy, Chung and Morton (1959) delineated the common features of limb-girdle muscular dystrophy. Onset usually occurred in childhood, but sometimes in maturity or middle age. Involvement was first evident in either the pelvic or, less frequently, the shoulder girdle, often with asymmetry of wasting when the upper limbs were first involved. Spread from the lower to the upper limbs or vice versa occurred within 20 years. Pseudohypertrophy of the calves was uncommon, but may have been counterfeited by a stocky build or wasting of the vasti. The rate of progression was variable, but severe disability with inability to walk was seen within 20 to 30 years of onset. Contractures and facial weakness occurred in some in late stages. Age at death was variable with the largest number of patients dying in middle age. In the analysis of Chung and Morton (1959), 59% of cases of limb-girdle muscular dystrophy could be ascribed to autosomal recessive inheritance; the remainder were sporadic cases of unknown etiology.

Richard et al. (1999) reviewed the clinical information on 163 LGMD2A patients with calpain-3 mutations. They noted that Fardeau et al. (1996) had defined precise clinical features, first noted in patients from Reunion Island. LGMD2A was characterized mainly by a symmetric, very selective atrophic involvement of limb-girdle and trunk muscles, with the gluteus maximus and thigh adductors being most affected. The same pattern of muscle involvement was also reported for three-fourths of the examined metropolitan French patients, with occasionally minor variations around this pattern. Similar findings were found in LGMD2A patients of Turkish or Basque origin. Mean age at onset was 13.7 years (range, 2 to 40 years) and the mean age at loss of walking ability was 17.3 years (range, 5 to 39 years). No sex difference was evident in age at onset or disease progression.

Using linkage studies to characterize 13 Brazilian families with autosomal recessive LGMD, Passos-Bueno et al. (1996) found that the approximately 33% of families had LGMD2A and 33% had LGMD2B (LGMDD2), whereas 17% had LGMD2D (LGMDR3), and less than 10% had LGMD2C (LGMDR5). Patients with LGMD2B appeared to have the mildest phenotype, with an average age at onset that was significantly later than for patients with LGMD2A.

Passos-Bueno et al. (1999) studied 140 patients from 40 Brazilian families with one of 7 autosomal recessive limb-girdle muscular dystrophies. All LGMD2E (LGMDR4) and LGMD2F (LGMDR6) patients had a severe phenotype; considerable inter- and intrafamilial variability was observed in all other types of LGMD. Comparison between 40 LGMD2A patients and 52 LGMD2B patients showed that LGMD2A patients had a more severe course and higher frequency of calf hypertrophy (86% vs 13%), and that LGMD2B patients were more likely to be unable to walk on toes (70% vs 18%).

Mercuri et al. (2005) reported skeletal muscle MRI findings of 7 patients with LGMD2A who had early contractures. The 3 younger patients were able to walk independently and had selective impairment of the adductor magnus and semimembranosus muscles. The 4 older patients all had restricted ambulation and had similar involvement of the adductor magnus as well as more diffuse involvement of the posterolateral thigh muscles and vastus intermedius. Two 'control' patients with LGMD2A without contractures showed similar muscle involvement. Mercuri et al. (2005) suggested that patients with LGMD2A have a somewhat unique pattern of muscle involvement on MRI, which may serve to differentiate the disorder from Emery-Dreifuss muscular dystrophy (EDMD; see, e.g., 616516) and Bethlem myopathy (BTHLM; see 158810), both of which have phenotypic similarities to LGMD2A.

LGMD2A is characterized by a wide variability in clinical features and rate of progression. Patients with 2 null mutations usually have a rapid course, but in the remaining cases (2 missense mutations or compound heterozygote mutations) prognosis is uncertain. Fanin et al. (2007) conducted a systematic histopathologic, biochemical, and molecular investigation of 24 LGMD2A patients, subdivided according to rapid or slow disease progression to determine if some parameters could correlate with disease progression. They found that muscle histopathology score and the extent of regenerating and degenerating fibers could be correlated with a rate of disease course. Comparison of clinical and muscle histopathologic data between LGMD2A and 4 other types of LGMD (LGMD2B-E) also gave another significant result. They found that LGMD2A has significantly lower levels of dysmorphic features (i.e., degenerating and regenerating fibers) and higher levels of chronic changes (i.e., lobulated fibers) compared with other LGMDs, particularly LGMD2B. Fanin et al. (2007) concluded that these results might explain the observation that atrophic muscle involvement seems to be a clinical feature peculiar to LGMD2A patients.

Eosinophilic Myositis

Krahn et al. (2006) reported 6 unrelated patients originally diagnosed with eosinophilic myositis based on skeletal muscle biopsy in the first decade of life (age at diagnosis 3 to 11 years). All patients presented initially with increased serum creatine kinase. Skeletal muscle biopsies showed focal inflammatory lesions with eosinophilic infiltration and no evidence of parasites; some biopsies showed necrotic fibers. Clinically, 1 patient had only motor fatigability, 2 had mild motor clumsiness, and 1 had difficulty walking on heels. Two of the older patients, ages 16 and 11, respectively, had more significant muscle weakness. Three patients had hypereosinophilia on peripheral blood count. Western blot analysis of 1 patient showed loss of calpain-3. All patients were found to have homozygous or compound heterozygous mutations in the CAPN3 gene (see, e.g., 114240.0006). Krahn et al. (2006) suggested that eosinophilic myositis may be an early and transient feature in calpainopathies, because it was not present in biopsies from older patients with typical LGMD2A.

Krahn et al. (2011) reported 5 additional patients with an initial diagnosis of eosinophilic myositis who were found to be homozygous or compound heterozygous for CAPN3 mutations. One adult presented with progressive proximal weakness in her early twenties. The other 4 patients were children who presented in the first decade with increased serum creatine kinase and blood eosinophilia, which was intermittent in 2 cases. In addition, a 5-year-old boy with 2 CAPN3 mutations who presented with proximal muscle weakness of the lower limbs was found to have a focal lymphocytic infiltrate of CD8+ T cells on muscle biopsy. In a retrospective analysis of muscle biopsies from 17 patients with genetically confirmed LGMD2A, Krahn et al. (2011) identified inflammatory changes with presence of eosinophils in 5 patients. The average disease duration at biopsy for patients without or with eosinophils was 13.9 and 6 years, respectively. The findings highlighted eosinophilic infiltration as an early component in primary calpainopathy.

Pathogenesis

Richard et al. (1995) noted that the identification of CANP3 as a defective gene in LGMD2A suggested a novel pathologic mechanism leading to a muscular dystrophy in which the disorder is caused by mutations affecting an enzyme and not a structural component of muscle tissue. They suggested that the defect may have regulatory consequences, perhaps in signal transduction.

Diagnosis

Among 58 patients with LGMD2A confirmed by mutation analysis, Fanin et al. (2004) found that 46 (80%) had a variable degree of calpain-3 protein deficiency determined by immunoblot analysis, and 12 (20%) had normal amounts of calpain-3. The probability of having LGMD2A was very high (84%) when patients had a complete calpain-3 deficiency and progressively decreased with increasing amounts of protein detected. CAPN3 gene mutations were identified in 46 of 69 (67%) patients with calpain-3 protein deficiency and in 12 of 139 (9%) patients with normal calpain-3 protein. Patients with severe, early-onset disease usually had no calpain-3 protein, but absent or markedly reduced protein levels were also detected in patients with adult onset. However, almost all patients with normal calpain-3 levels had late or adult onset of the disorder.

The diagnosis of calpainopathy is obtained by identifying calpain-3 protein deficiency or mutations in the CALPN3 gene. However, in many patients with LGMD2A, loss-of-function mutations cause enzymatic inactivation of calpain-3 while protein quantity remains normal. The identification of such patients is difficult unless a functional test suggests pursuing a search for mutations. Fanin et al. (2007) used a functional in vitro assay to test calpain-3 autolytic function in a large series of muscle biopsy specimens from patients with unclassified LGMD/hyperCKemia who had been shown to have normal calpain-3 protein quantity. Of 148 muscle biopsy specimens tested, 17 (11%) had lost normal autolytic function. The CAPN3 gene mutations were identified in 15 of the 17 patients (88%), who accounted for about 20% of the total patients with LGMD2A diagnosed in their series.

Blazquez et al. (2008) performed a retrospective diagnostic study of CAPN3 mRNA expression in peripheral blood of 26 unrelated patients with LGMD2A, including 14 with known biallelic CAPN3 mutations and 12 with only 1 CAPN3 mutation identified through DNA analysis. The results of peripheral blood mRNA analysis confirmed the known mutations. In addition, 7 (25%) of 28 mutations identified by analyzing white blood cell mRNA were splice site mutations that modified the CAPN3 transcript, but would not have been detected by direct DNA sequencing of coding regions. However, 4 different mRNA transcripts were identified in white blood cells, compared to only 1 known to be expressed in skeletal muscle tissue. These different isoforms were produced by alternative splicing of exons 6, 15, and 16 of the CAPN3 gene. Blazquez et al. (2008) concluded that while analysis of CAPN3 mutations at the mRNA level in peripheral blood is useful, the diagnosis must be confirmed by DNA studies, since the results could be discordant mainly because of nonsense-mediated decay of truncated transcripts.

By molecular screening, Fanin et al. (2009) identified 66 different CAPN3 mutations in 94 of 519 patients with LGMD. Of those with mutations, 73% had a quantitative protein defect, 16% had a functional protein defect, and 11% had normal protein quantity. Conversely, CAPN3 mutations were found in 80% of patients with a quantitative defect on western blot analysis and in 88% of patients with a functional defect of calpain-3 on skeletal muscle biopsy. In addition, CAPN3 mutations were found in 10 (5.6%) of 178 patients with normal CAPN3 quantity. Fanin et al. (2009) concluded that systematic investigation for LGMD2A in patients should involve biochemical assays and muscle biopsy evaluation to determine which patients are suitable for genetic analysis.

Differential Diagnosis

Walton and Nattrass (1954) introduced the term 'limb-girdle muscular dystrophy' as part of a classification that achieved wide acceptance and did much to resolve earlier confusion. Over the next 30 years it became clear that many inherited and acquired disorders could produce a similar clinical picture, such as nemaline myopathy (e.g., 256030), central core disease (117000), thyrotoxic myopathy, various scapuloperoneal syndromes (e.g., 181430), chronic polymyositis, and, spinal muscular atrophy (e.g., 253300). Many of the early reported cases of 'limb-girdle' muscular dystrophy likely had one of these conditions.

Attempting total ascertainment of LGMD in the Lothian area of Scotland, Yates and Emery (1985) collected 10 index cases of adult-onset (at or after age 18) LGMD. In the 10 sibships, only 1 had a second case; however, in this family the 2 brothers may have had Becker muscular dystrophy (BMD; 300376). Assuming recessive inheritance, there was a significant deficiency of affected persons and a great preponderance of males (9 out of 10).

Arikawa et al. (1991) analyzed diagnostic muscle biopsies in 41 cases with the clinical diagnosis of limb-girdle muscular dystrophy at the National Institute of Neuroscience in Tokyo. Using immunofluorescence, immunoblot analysis, and PCR analysis to examine diagnostic muscle biopsies, they identified 5 male patients with an abnormal dystrophin (300377) pattern diagnostic of Becker muscular dystrophy and 2 female patients with dystrophin patterns consistent with a manifesting carrier of Duchenne muscular dystrophy (DMD; 310200). Thus, 17% of the limb-girdle patients showed a 'dystrophinopathy,' with 31% (4/13) of isolated males misclassified and 13% (2/15) of isolated females misclassified. The study emphasized the clinical overlap between LGMD and dystrophinopathies and reinforced the necessity of dystrophin protein and gene studies for accurate clinical diagnosis.

Clinical Management

Daniele et al. (2007) provided a review of therapeutic strategies in various forms of LGMD, including ongoing studies in gene therapy.

Mapping

In an inbred population descended from French settlers of the Island of Reunion, Beckmann et al. (1991) mapped the LGMD locus to proximal 15q by demonstration of linkage to D15S25 (lod score = 5.52 at theta = 0.0). In studies of the Old Order Amish in Indiana, Young et al. (1991, 1992) found linkage to 15q15-q22 (maximum lod score of 5.92 at theta = 0.08).

Passos-Bueno et al. (1993) found informative results in 8 of 11 large Brazilian LGMD families of different racial backgrounds: linkage to 15q markers was established in 2 of these families and excluded in 6 others, indicating genetic heterogeneity.

By screening the CEPH YAC libraries with probes flanking the LGMD2 locus within a 7-cM interval, Fougerousse et al. (1994) refined the cytogenetic LGMD2A locus to 15q15.1-q21.1. Allamand et al. (1995) constructed a physical map of the 7-cM region 15q15.1-q21.1 by means of a 10- to 12-Mb continuum of overlapping YAC clones and localized the LGMD2A gene to the proximal part of this region in both Amish families and families from the Island of Reunion. Analysis of the interrelated pedigrees from Reunion revealed at least 6 different carrier haplotypes, suggesting that multiple LGMD2A mutations may segregate in this population.

Genetic Heterogeneity

Beckmann (1991) identified several families with recessive LGMD in which linkage with 15q was excluded, indicating genetic heterogeneity.

Allamand et al. (1995) found unexpected genetic heterogeneity of LGMD among the Indiana Amish; linkage of LGMD to chromosome 15 was excluded in 6 Amish kindreds from southern Indiana. Notably, these 6 kindreds were related by multiple consanguineous links to the same northern Indiana families in which involvement of chromosome 15 was previously demonstrated (Young et al., 1992). Allamand et al. (1995) also excluded the form of autosomal recessive muscular dystrophy related to a locus on 2p (LGMD2B) as the site of the mutation in the southern Indiana Amish. Lim et al. (1995) demonstrated that the mutation in the individuals with LGMD in the southern Indiana Amish involved the beta-sarcoglycan gene (600900.0001); this form was referred to as limb-girdle muscular dystrophy type 2E.

Inheritance

LGMDR1 is an autosomal recessive disorder.

The Reunion Paradox

Richard et al. (1995) referred to the unexpected presence of multiple independent mutations rather than a single founder mutation in the small inbred population on Reunion Island as the 'Reunion paradox.' To explain the paradox, they proposed a digenic inheritance model, i.e., only in the presence of specific alleles at a permissive second unlinked locus (e.g., a compensatory, partially redundant, regulatory, or modifier gene) would there be expression of calpain mutations. Since one would need mutations at both loci to be affected, the disease prevalence would remain low. Under this model, members of the Reunion Island community would have a disease-associated allele at the hypothesized second locus at high frequency, or even fixed, as a result of genetic drift. Such conditions would explain the apparent complete penetrance of the calpain mutations. Complete penetrance of this disease in the Amish and in the other described LGMD2A pedigrees would also be under the control of the second locus. If this model were true, there would be fewer selected pressures against the appearance of CAPN3 mutations as a result of the conditional penetrance. The digenic inheritance model would predict that in a number of kindreds, there will be healthy individuals with 2 mutant calpain genes. (Digenic inheritance of retinitis pigmentosa (608133) has been reported; see 180721 and 179605.)

In discussing the digenic model of Richard et al. (1995), van Ommen (1995) suggested that polygenic disease may be less complex than often thought and that the interaction between 1 major gene and 1 or a few modifiers may explain much of complex genetics.

Zlotogora et al. (1996) suggested that multiple mutations in a single specific gene in a small geographic area may be a common phenomenon. They referred to 3 different iduronidase (252800) mutations causing Hurler syndrome (607014) in 4 different non-Jewish families in the Galilee region of Israel (Bach et al., 1993) and 5 different mutations in the arylsulfatase A gene (607574) causing metachromatic leukodystrophy (250100), occurring on at least 3 different haplotypes in the same region (Heinisch et al., 1995). Zlotogora et al. (1996) suggested that the occurrence of multiple mutations in the calpain gene among Reunion Island patients may be an example of a high mutation rate in the gene coupled with selective advantage to carriers.

Beckmann (1996) offered rebuttal to the explanation of the 'Reunion paradox' by Zlotogora et al. (1996) and defended their previously reported digenic model. He stated that to that time a total of 7 distinct calpain mutations had been identified among Reunion Island patients with limb-girdle muscular dystrophy.

Molecular Genetics

By a mutation screen in families with autosomal recessive limb-girdle muscular dystrophy type 2A, Richard et al. (1995) identified biallelic mutations in the CAPN3 gene, including nonsense, splice site, frameshift, and missense mutations (see, e.g., 114240.0001-114240.0003). The mutations segregated with the disorder in the families. Six of the mutations were found within an inbred population on Reunion Island, located in the Indian Ocean, and haplotype analysis suggested the existence of at least 1 more mutation in the group. The occurrence of multiple independent mutations in the isolated population on Reunion Island rather than the finding of an expected founder mutation was referred to as the 'Reunion paradox' by Richard et al. (1995). They suggested that LGMD2A, instead of being a monogenic disorder, might have a more complex inheritance pattern in which expression of calpain mutations is dependent on genetic background, either nuclear or mitochondrial (see INHERITANCE).

Richard et al. (1999), who referred to this disorder as 'calpainopathy,' stated that 97 distinct pathogenic CAPN3 mutations had been identified: 4 nonsense mutations, 32 deletions/insertions, 8 splice site mutations, and 53 missense mutations, together with 12 polymorphisms and 5 unclassified variants. The mutations, most of which represented private variants, were distributed along the entire length of the CAPN3 gene.

Fanin et al. (2005) identified mutations in the CAPN3 gene in 70 (33%) of 214 patients with limb-girdle muscular dystrophy in Italy. The prevalence of LGMD2A was estimated at 9.47 per million inhabitants in northeastern Italy. Two founder mutations were identified (500delA, 114240.0009; R490Q, 114240.0010).

Todorova et al. (2007) identified mutations in the CAPN3 gene in 20 (42%) of 48 unrelated Bulgarian patients with muscular dystrophy. Three novel and 6 recurrent mutations were identified. Forty percent of the patients were homozygous for the 500delA mutation, and 70% carried it on at least 1 allele.

By high-throughput denaturing HPLC, Piluso et al. (2005) scanned the CAPN3 gene in 530 individuals with different grades of symptoms consistent with LGMD. They found 141 LGMD2A patients carrying 82 different CAPN3 mutations, of which 45 were novel. Females had a more favorable course than males. In 94% of the most severely affected LGMD2A patients, the defect was also discovered in the second allele. CAPN3 mutations were found in 35.1% of patients with classic LGMD phenotypes, 18.4% of atypical patients, and 12.6% of patients with high serum creatine kinase levels. Piluso et al. (2005) broadened the spectrum of LGMD2A phenotypes and set the carrier frequency at 1:103.

Among 46 European patients suspected to have LGMD2A based on Western blot results, Duno et al. (2008) found that 16 patients had mutations in the CAPN3 gene identified by both direct genomic sequencing and cDNA analysis. Both mutant alleles were demonstrated in 10 patients. A total of 16 mutations were identified, including 5 novel mutations. Only 3 of the genetically confirmed LGMD2A patients were of Danish origin, indicating a 5- to 6-fold lower prevalence in Denmark compared to other European countries.

Reviews

Nigro (2003) provided a review of the molecular bases of autosomal recessive LGMD.

Population Genetics

Pfaendler (1950) reported an affected Swiss pedigree which was studied further by Touraine (1955). Jackson and Carey (1961) found the same type of autosomal recessive muscular dystrophy in the descendants of Swiss immigrants in an Amish isolate in Indiana. Moser et al. (1966) found autosomal recessive muscular dystrophy to be 4 times more frequent in the Canton of Berne than in other countries studied. He mapped the places of origin of the parents of cases within the canton, which proved to be the same area as those from which the Amish family names were derived.

Urtasun et al. (1998) reported the highest prevalence rate of LGMD described to that time in Guipuzcoa, a small mountainous Basque province in northern Spain: 69 per million. Genetic studies demonstrated that 38 cases corresponded to LGMD2A due to calpain-3 gene mutations. Only 1 patient with alpha-sarcoglycanopathy was found, and in 12 patients the genetic defect was not identified. The particular calpain-3 mutation predominant in Basques (exon 22, 2362AG-to-TCATCT; 114240.0006) had only rarely been found in the rest of the world. The clinical characteristics of the patients with calpain-3 gene mutations were quite homogeneous and different from the other groups, allowing for a precise clinical diagnosis. Disease onset was between ages 8 and 15 years, occurring in the pelvic girdle in most cases, and patients became wheelchair-bound between 11 and 28 years after onset. No pseudohypertrophy of calves or contractures were observed.

Canki-Klain et al. (2004) found that 550delA (114240.0009) was the most common mutation among Croatian patients with LGMD2A, with a prevalence of 76% of mutant CAPN3 alleles. The detection of 4 healthy 550delA heterozygous individuals yielded a frequency of 1 in 133 (0.75%) in the general Croatian population. All 4 carriers originated from an island and mountain region near the Adriatic, indicating a probable founder effect.

Fanin et al. (2005) determined that the prevalence of LGMD2A in northeastern Italy was 9.47 per million. Two founder mutations in the CAPN3 gene, 550delA and R490Q (114240.0010), were identified. Todorova et al. (2007) identified mutations in the CAPN3 gene in 20 (42%) of 48 unrelated Bulgarian patients with muscular dystrophy. Forty percent of the patients were homozygous for the 500delA mutation, and 70% carried it on at least 1 allele.

Van der Kooi et al. (2007) found that LGMD2A was the most common form of LGMD in the Netherlands, accounting for 21% (14 of 67) of all families with LGMD studied.

Guglieri et al. (2008) found that LGMD2A was the most common form of LGMD in Italy, present in 28.4% of 155 Italian probands.

Duno et al. (2008) found that LGMD2A was uncommon in patients of Danish origin, with an approximately 5- to 6-fold lower prevalence in Denmark compared to other European countries.

Vissing et al. (2016) stated that LGMD2A is the most common limb-girdle muscular dystrophy form worldwide.

Animal Model

Tagawa et al. (2000) created transgenic mice that expressed an inactive mutant of Capn3, in which the active site cys129 is replaced by ser (C129S). Transgenic mice expressing mutant C129S mRNA showed significantly decreased grip strength. Sections of soleus and extensor digitorum longus (EDL) muscles of the aged transgenic mice showed increased numbers of lobulated and split fibers, respectively, which are often observed in limb-girdle muscular dystrophy muscles. Centrally placed nuclei were also frequently found in the EDL muscle of the transgenic mice, whereas wildtype mice of the same age had almost none. More mutant protein was produced in aged transgenic mice muscles, and the protein showed significantly less autolytic degradation activity than that in wildtype mice. The authors hypothesized that accumulation of the mutant protein caused these myopathy phenotypes.

Kramerova et al. (2004) generated Capn3-knockout (C3KO) mice. The mice were atrophic, with small foci of muscular necrosis. Myogenic cells fused normally in vitro, but lacked well-organized sarcomeres, as visualized by electron microscopy. Titin (188840) distribution was normal in longitudinal sections from the C3KO mice; however, electron microscopy of muscle fibers showed misaligned A-bands. In vitro studies revealed that calpain-3 can bind and cleave titin and that some mutations that are pathogenic in human muscular dystrophy result in reduced affinity of calpain-3 for titin. Kramerova et al. (2004) suggested a role for calpain-3 in myofibrillogenesis and sarcomere remodeling.

Kramerova et al. (2005) showed that the rates of atrophy and growth were decreased in C3KO mouse muscles under conditions promoting sarcomere remodeling. In wildtype mice, ubiquitinated proteins accumulated during muscle reloading, possibly reflecting removal of atrophy-specific and damaged proteins. The increase in ubiquitination correlated with an increase in calpain-3 expression. There was upregulation of heat shock proteins in C3KO muscles following challenge with a physiologic condition that required highly increased protein degradation. Old C3KO mice showed evidence of insoluble protein aggregate formation in skeletal muscles. Kramerova et al. (2005) suggested that accumulation of aged and damaged proteins may lead to cellular toxicity and a cell stress response in C3KO muscles, and that these characteristics may be pathologic features of LGMD2A.

History

By an ingenious mathematical analysis, Morton (1960) concluded that homozygosity at either of 2 loci may result in limb-girdle muscular dystrophy and that about 1.6% of the normal population is heterozygous for a limb-girdle muscular dystrophy gene.

Rudman et al. (1972) concluded that patients with limb-girdle dystrophy are at least 7 times more sensitive to growth hormone than the normal population.

Using probes on human chromosome 6q flanking the dystrophin-related sequence, Passos-Bueno et al. (1991) performed linkage analysis in 226 persons from 19 Brazilian families with autosomal recessive LGMD. They excluded linkage of LGMD to both MYB (6q22-q23) and ESR (6q24-q27) at theta = 0.10, as well as to TCP1 (6q25-q27) at theta = 0.05, and concluded that the dystrophin-homologous sequence on chromosome 6q was not the gene responsible for LGMD.