Muscular Dystrophy, Limb-Girdle, Autosomal Dominant 1
A number sign (#) is used with this entry because of evidence that autosomal dominant limb-girdle muscular dystrophy-1 (LGMDD1), previously LGMD1E, is caused by heterozygous mutation in the DNAJB6 gene (611332) on chromosome 7q36.
DescriptionAutosomal dominant limb-girdle muscular dystrophy is characterized by proximal and/or distal muscle weakness and atrophy. The age at onset is variable and can range from the first to the sixth decade, although later onset is less common. Most patients present with proximal muscle weakness that progresses to distal involvement, but some can present with distal impairment. The severity is variable: patients with a more severe phenotype can lose ambulation after several decades and have facial weakness with bulbar and respiratory involvement. Muscle biopsy shows dystrophic changes with protein aggregates, myofibrillar degeneration, and rimmed vacuoles (summary by Ruggieri et al., 2015).
Genetic Heterogeneity of Autosomal Dominant Limb-Girdle Muscular Dystrophy
Other forms of autosomal dominant LGMD include LGMDD2 (608423), previously LGMD1F, caused by mutation in the TNPO3 gene (610032) on chromosome 7q32; LGMDD3 (609115), previously LGMD1G, caused by mutation in the HNRNPDL gene (607137) on chromosome 4q21; and LGMDD4 (618129), previously LGMD1I, caused by mutation in the CAPN3 gene (114240) on chromosome 15q15.
For a discussion of autosomal recessive LGMD, see 253600.
NomenclatureAt 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.'
Several autosomal domianant forms of LGMD were reclassified: LGMD1A was reclassified as myofibrillar myopathy (MFM3; 609200); LGMD1B was reclassified as Emery-Dreifuss muscular dystrophy (EDMD2; 181350); and LGMD1C was reclassified as rippling muscle disease (RMD2; 606072).
A form previously designated LGMD1H (613530), which maps to chromosome 3p25-p23, was not renamed or reclassified.
The symbol LGMD1D was formerly used for a disorder later found to be the same as desmin-related myopathy (MFM1; 601419). According to the report of the 105th ENMC workshop, the form of limb-girdle muscular dystrophy mapping to chromosome 7q was designated 'LGMD1E' (Bushby and Beckmann, 2003). OMIM had earlier designated the form on 7q as LGMD1D but later used the symbol for a form of LGMD and dilated cardiomyopathy thought to map to chromosome 6q in 1 family; the disorder in that family was later found to map to 2q35 and a causative mutation was identified in the desmin gene (DES; see 125660.0008).
Clinical FeaturesSchneiderman et al. (1969) reported a large 4-generation family with slowly progressive autosomal dominant limb-girdle muscular dystrophy. Symptom onset generally occurred during the third decade, with muscular weakness affecting both the upper and lower limbs, although most affected individuals recalled being slow and clumsy as children. Most retained ambulation, but 2 were bedridden in their seventies and eighties. None had facial involvement. Skeletal muscle biopsy showed dystrophic changes, including variation in fiber size, rounded fibers, vacuoles, and small basophilic fibers with vesicular nuclei. Electron microscopy showed focal degeneration and destruction of myofibrils, lamellar bodies, and dense granular lysosome-like structures. The Pelger-Huet anomaly (PHA; 169400) also segregated within this family, and linkage with muscular dystrophy was suggested. The recombination fraction was about 0.25, but the lod score was only 0.35. (The Pelger-Huet anomaly was later found to be caused by mutation in the lamin B receptor gene (LBR; 600024) on chromosome 1q42.)
Using the diagnostic classification for LGMD outlined by Speer et al. (1992), Speer et al. (1995) described 2 families with autosomal dominant LGMD. One of the families had previously been reported by Schneiderman et al. (1969) (family 1701). Individuals were considered affected when they had progressive proximal leg weakness with or without proximal arm weakness, absent ankle deep-tendon reflexes, and elevated creatine kinase values. The diagnostic evaluation of at least 1 affected member per family documented a myopathic process. Three of 15 members of family 1701 had moderately severe dysphagia.
Servidei et al. (1999) studied a large Italian family in which 10 individuals over 3 generations were affected by a progressive neuromyopathy. The disease was characterized by onset from the late teens to early fifties with distal leg weakness and atrophy, development of generalized muscle weakness with distal-to-proximal progression sparing facial and ocular muscles, dysphonia and dysphagia, pes cavus and areflexia, variable clinical expression ranging from subclinical myopathy to severely disabling weakness, and mixed neurogenic and myopathic abnormalities on electromyography. Morphologic, immunocytochemical, and ultrastructural studies were performed in muscle biopsies from 3 affected patients. All muscle biopsies showed variation of fiber size, panesterase-positive angular fibers, mild to severe fibrosis, and numerous rimmed vacuoles. Electron microscopy failed to demonstrate the nuclear or cytoplasmic filamentous inclusions specific to inclusion body myopathies--see, e.g., inclusion body myositis (IBM; 147421) and Nonaka myopathy (NM; 605820)--and, accordingly, immunohistochemistry did not show any positivity with SMI-31 antibodies detecting hyperphosphorylated tau.
Ruggieri et al. (2015) provided follow-up of the family reported by Servidei et al. (1999). Eight family members, including 7 males and 1 female, were clearly affected with an inexorably progressive myopathy. Five patients were alive at the time of the report, and ranged in age from 22 to 79 years. Muscle weakness and atrophy tended to begin distally, with progression to proximal muscles as well as facial and bulbar muscles, but sparing extraocular muscles. Features included dysarthria, dysphagia, dysphonia, and dyspnea. All had upper and lower limb involvement, and facial weakness was present in 3 of the 5. Foot dorsiflexor weakness was the only sign in the youngest patient, age 22 years. Two patients had lost ambulation. MRI of 2 older patients showed fatty infiltration of muscles of the proximal and distal lower limbs. EMG showed a myogenic pattern, and muscle biopsy showed dystrophic changes with rimmed vacuoles. Ruggieri et al. (2015) noted the predominance of affected males, and postulated a sex effect.
Sandell et al. (2010) reported a large 4-generation Finnish family with autosomal dominant LGMD. The age at onset ranged from 20 to 60 years, and all except 1 presented with difficulty climbing stairs; 1 patient presented with a slow running speed. All patients showed more severe involvement of the pelvic girdle than the shoulder girdle, resulting in a waddling gait, and 3 of 8 had no shoulder girdle signs at ages 69, 45, and 43 years. All were ambulatory except an 80-year-old patient. Some patients had mild calf hypertrophy. None had contractures, dysphagia, dysarthria, respiratory problems, or cardiac involvement. Most patients had increased serum creatine kinase and myopathic EMG. Muscle biopsies showed myopathic changes, such as fiber size variation, atrophic fibers, mild to moderate fibrosis, adipose tissue, rimmed vacuoles, and internal nuclei. Some biopsies showed cytoplasmic protein inclusions, and electron microscopy showed myofibrillar disintegration with filamentous inclusions and Z disc streaming.
Hackman et al. (2011) reported 4 additional Finnish families with adult-onset, slowly progressive autosomal dominant LGMD. The phenotype was homogeneous, with onset of muscle weakness in the pelvic girdle between the fourth and sixth decade, later involvement of the shoulder girdle, and marked walking difficulties by the eighth decade. Muscle biopsies showed myopathic and/or dystrophic features as well as myofibrillar disintegration and tubulofilamentous inclusions close to autophagic vacuoles. Some patients had mild calf hypertrophy, and none had cardiac or respiratory involvement. One patient had dysarthria and 2 had dysphagia.
Harms et al. (2012) reported 2 unrelated families with LGMD1E. The first was a Caucasian family in which 5 individuals had onset of limb-girdle weakness beginning in the fourth decade. The disorder was manifest as difficulty in climbing stairs or getting up from the floor. In 2 patients, the quadriceps muscles were less affected than the hamstrings. None had cardiac, pulmonary, or bulbar involvement. The disorder was slowly progressive, but a wheelchair was required after about 20 years. Skeletal muscle biopsy from 3 patients showed a chronic myopathy with rimmed vacuoles, variation in fiber size, and internal nuclei. Immunostaining showed TDP43 (605078)- and DNAJB6-positive accumulations in multiple fibers; some inclusions were around and within the vacuoles. Serum creatine kinase was increased, and EMG showed clear myopathic changes. Three affected individuals from an African American family had a distal-predominant myopathy with onset between 18 and 35 years. Weakness began in the lower limbs, often manifest as tripping, but progressed to include the hands and proximal legs with loss of ambulation after about 20 to 40 years. There was no cardiac or pulmonary involvement.
Couthouis et al. (2014) reported an American family with autosomal dominant LGMD. Two patients were reported in detail. The proband developed progressive proximal muscle weakness of the lower limbs shortly after high school, necessitating the use of a cane in his late thirties and a wheelchair in his fifties. He also had upper limb weakness and spinal stenosis. Physical examination showed weakness of the shoulder and hip muscles as well as weakness of the intrinsic hand muscles and deep finger flexors. He had mild dyspnea and sleep-disordered breathing, but cardiac examination was normal. Skeletal muscle biopsy showed marked variation in fiber size, scattered fibers with rimmed vacuoles, and angular atrophic fibers characteristic of neurogenic atrophy. The patient's son reported slow running in childhood and proximal muscle weakness that became apparent in his teenage years. Physical examination at age 28 showed proximal greater than distal muscle weakness and atrophy that affected the lower more than the upper extremities. Cardiac examination was normal.
Ruggieri et al. (2015) reported 4 unrelated patients with sporadic occurrence of LGMD1E. Three had a more severe phenotype, with onset between 6 and 16 years of progressive severe muscle weakness affecting the proximal and distal muscles of the upper and lower limbs and resulting in loss of ambulation between 30 and 40 years of age. Some patients had contractures and mild respiratory involvement. Most had onset of weakness in the proximal muscles, but 1 had onset in the distal muscles. None had facial muscle weakness or bulbar signs. Muscle biopsies showed dystrophic features, with internal nuclei, extreme variability of fiber diameters, necrosis, regeneration, and fatty replacement. The most common finding was sarcoplasmic vacuoles with a basophilic rim. Immunolocalization showed DNAJB6 staining on the rim of nuclei, in the cytoplasm of fibers, and on the surface and cytoplasmic inclusion of vacuolated fibers. TDP43 and p62 (SQSTM1; 601530) colocalized in sarcoplasmic inclusions and vacuoles with variable intracellular distribution.
Early Reports of Limb-Girdle Muscular Dystrophy
Bacon and Smith (1971) reported a late-onset familial muscular dystrophy with features of a limb-girdle type. De Coster et al. (1974) described a family with late-onset limb-girdle muscular dystrophy in 9 males of 6 sibships in 3 generations. Changes in type II muscle fibers were described. They thought it was different from other reported dystrophies. Henson et al. (1967) and Heyck and Laudahn (1969) described a dominant limb-girdle muscular dystrophy limited to females.
Espir and Matthews (1973) described 2 brothers with what they referred to as 'quadriceps myopathy.' All 3 daughters of one of them had mild involvement. Patients presented in adulthood with severe aching in the thigh muscles followed by proximal lower limb weakness. Clinically the thighs showed islands of hypertrophy in wasted quadriceps muscles and knee reflexes were absent. In late stages, prominent areas of hypertrophy projecting from patches of atrophy gave the quadriceps a strikingly unusual appearance. The disorder showed a relatively benign course with late involvement of pelvic girdle and hand muscles. The authors found no reports of precisely similar cases.
Clinical ManagementDaniele et al. (2007) provided a review of therapeutic strategies in various forms of LGMD, including ongoing studies in gene therapy.
InheritanceThe transmission pattern of LGMD1E in the families reported by Speer et al. (1995) was consistent with autosomal dominant inheritance.
MappingSpeer et al. (1999) reported the identification of a new locus for autosomal dominant limb-girdle muscular dystrophy on chromosome 7q. Two of 5 families demonstrated evidence in favor of linkage to that region; 1 of the families had been reported by Schneiderman et al. (1969) (family 1701) and another by Speer et al. (1995) (family 1047). The maximum 2-point lod scores were 2.63 at D7S3058 and 3.76 at D7S427, respectively. Flanking markers placed the novel LGMD1 locus between D7S2423 and D7S427, with multipoint analysis slightly favoring the 9-cM interval spanned by D7S2546 and D7S2423. Three of 5 families, including one reported by Chutkow et al. (1986) (family 383), appeared to be unlinked to this new locus on chromosome 7, thus establishing further heterogeneity within the LGMD1 diagnostic classification.
By genomewide linkage analysis of a Finnish family with autosomal dominant adult-onset LGMD, Sandell et al. (2010) found linkage to a 6.4-Mb region on chromosome 7q36 (lod score of 3.76 with D7S1823) that overlapped with the region identified by Speer et al. (1999).
In 4 additional Finnish families with adult-onset slowly progressive autosomal dominant LGMD, Hackman et al. (2011) refined the LGMD1E locus to a 3.4-Mb region between D7S3037 and the telomere on 7q36.
Genetic Heterogeneity
Chutkow et al. (1986) reported a kindred with a slowly progressive limb-girdle muscular dystrophy inherited in an autosomal dominant pattern. The family had immigrated to the U.S. from the Palermo region of Sicily. Onset was anywhere from the second to sixth decade, with hip girdle involvement preceding shoulder girdle involvement. Facial muscles were not affected. Creatine kinase was elevated in most, and muscle biopsy showed atrophy, fatty replacements, fiber splitting, fibrosis, and autophagic vacuoles. In the family reported by Chutkow et al. (1986), Speer et al. (1999) excluded linkage to chromosome 7q36.
Molecular GeneticsIn affected members of a Caucasian family with autosomal dominant limb-girdle muscular dystrophy, type 1E, Harms et al. (2012) identified a heterozygous mutation in the DNAJB6 gene (F93L; 611332.0001). The mutation was identified by whole-genome exome capture followed by next-generation sequencing. Sequencing of the DNAJB6 gene in 13 additional probands with a similar disorder revealed a second mutation (P96R; 611332.0002) in affected members of an African American family with an autosomal dominant myopathy. DNAJB6 is a member of the HSP40/DNAJ family of molecular cochaperones that protects client proteins from irreversible aggregation during protein synthesis or during times of cellular stress.
Sarparanta et al. (2012) identified 4 different heterozygous mutations in the DNAJB6 gene (611332.0001, 611332.0003-611332.0005) in affected members of 9 families with LGMD1E. Five of the families were of Finnish origin (Sandell et al., 2010 and Hackman et al., 2011) and carried the same mutation (611332.0003). Two additional families had previously been reported by Speer et al. (1995, 1999). Electron microscopy of patient muscle showed Z-disc myofibrillar disintegration and autophagic rimmed vacuoles. DNAJB6 was detected in protein accumulations together with its known ligands MLF1 (601402) and HSPA8 (600816). However, DNAJB6 appeared more in the periphery of the protein accumulations, in contrast to more pronounced colocalization seen in myotilinopathies. Three of the mutations resulted in a phe93-to-leu (F93L) substitution in a highly conserved residue. In vitro functional expression studies showed that the mutations increased the half-life of DNAJB6, extended this effect to the wildtype protein, and reduced the protective antiaggregation effect of DNAJB6. The mutations showed a dominant toxic effect mediated specifically by the cytoplasmic isoform of DNAJB6. The compromised antiaggregation function may lead to impaired protein quality control and accumulation of other proteins. DNAJB6 was found to interact with members of the chaperone-assisted selective autophagy (CASA) complex, including a myofibrillar myopathy (MFM6; 612954)-related protein BAG3 (603883). The findings indicated that LGMD1E is mediated by defective chaperone function, resulting in insufficient maintenance of sarcomeric structures or defective clearance of misfolded sarcomeric proteins.
In affected members of an American family with LGMD1E, Couthouis et al. (2014) identified a heterozygous F89I mutation in the DNAJB6 gene (611332.0005). Couthouis et al. (2014) stated that this was the same mutation identified by Sarparanta et al. (2012). Haplotype analysis determined that the mutation arose independently in the 2 families, suggesting that it may be a mutation hotspot.
In affected members of a large family with LGMD1E, originally reported by Servidei et al. (1999), Ruggieri et al. (2015) identified a heterozygous missense mutation in the DNAJB6 gene (F100V; 611332.0006). The mutation, which was found by a combination of linkage analysis and exome sequencing, segregated with the disorder in the family. Direct Sanger sequencing of the DNAJB6 gene in 63 patients with sporadic occurrence of a similar disorder identified 4 with de novo heterozygous mutations (611332.0003; 611332.0007-611332.0009), thus accounting for 6.4% of the cohort. All the mutations affected the conserved G/F domain, although direct functional studies were not performed. There was some evidence for a genotype/phenotype correlation: proximal G/F mutations were associated with proximal myopathy, whereas distal G/F mutations were associated with distal-onset myopathy. The mutations were predicted to affect the G/F-J interaction in different ways.
Animal ModelBengoechea et al. (2015) found that transgenic mice expressing the LGMD1E-associated DNAJB6 F93L mutation (611332.0001) in the Dnajb6b isoform had early lethality due to profound muscle weakness, whereas mice with the mutation in the Dnajb6a isoform were unaffected after 1 year. Muscle biopsy of affected mice showed localization of mutant Dnajb6b in the Z-disc, myofibrillar disorganization, desmin and keratin inclusions, and abnormal sarcoplasmic protein aggregations of RNA-binding proteins.
HistoryBy genomewide linkage analysis with 292 microsatellite markers in an Italian family with vacuolar neuromyopathy, Servidei et al. (1999) originally found evidence for linkage of the disease to chromosome 19p13. The maximum 2-point lod score was 2.23 at marker D19S894. By haplotype analysis using a set of 11 novel microsatellite markers isolated from the critical region, Sangiuolo et al. (2000) narrowed the disease locus to an interval of 250 kb. However, Ruggieri et al. (2015) used linkage analysis and exome sequencing in the family reported by Servidei et al. (1999) to identify a mutation in the DNAJB6 gene on chromosome 7q36 (see MOLECULAR GENETICS), thus indicating that the original linkage to 19p13 was incorrect.