Evidence-based Guideline: Diagnosis and Treatment of Limb-Girdle Muscular Dystrophy

Conclusion

In patients with LGMD and distal muscular dystrophy, a combination of clinical, radiologic, and laboratory features are useful in directing genetic diagnosis (multiple Class I–III studies). Single features that are pathgnomonic of a disorder are seen only rarely (see figures 1–5 in the summary article published in print and figures e-1 and e-2 and table e-2, available as online data supplements).

Clinical Question 5: Are there effective therapies (medications, gene therapy, exercise, complementary and alternative therapies, orthopedic interventions, surgery) for muscular dystrophies that improve muscle strength, slow the rate of strength decline, preserve ambulation and overall function, delay time to tracheostomy ventilation, maintain healthy EF, slow cardiac mortality, preserve quality of life and activities of daily living, and delay overall mortality?

There were 12 studies (2 Class I,^e493,e494 4 Class II,^e495-e498 and 6 Class III^{e246,e344,e462,e465,e499,e500}) evaluating treatments for disorders described below. No articles were identified for the other disorders discussed in this guideline.

In a Class II randomized, double-blind, placebo-controlled trial,^e498 adeno-associated virus (AAV) gene transfer to the extensor digitorum brevis (EDB) muscle was performed in 6 patients with LGMD2D (α-sarcoglycanopathy) on one side. Saline was injected into the opposite EDB as a control. α-Sarcoglycan gene expression increased 4- to 5-fold in 3 subjects (at 6 weeks in 2 subjects and at 12 weeks in the third subject); restoration of the α-sarcoglycan complex was also noted.^e498 Three subjects were followed for an additional 3 months and reported on in a subsequent Class I study.^e494 Persistent α-sarcoglycan gene expression was noted at 6 months in 2/3 subjects. One patient failing gene transfer demonstrated an early rise in neutralizing antibody titers and T-cell immunity to AAV. No adverse effects (AEs) were reported.^e494

A Class III study^e500 of 3 patients with LGMD2C who received the highest of 3 escalating doses of AAV-vector expressed human γ-sarcoglycan genes (4.5 x 10¹⁰ copies) into the extensor digitorum communis found increased γ-sarcoglycan expression (4.5%–10% positively stained fibers on muscle biopsy) 30 days after injection. One patient had detected γ-sarcoglycan by Western blot as well. Muscle strength was stable over 6 months of follow-up. MRI of the forearm before and 15 days postinjection did not reveal changes. Inflammatory markers did not change and no inflammation was noted on repeat biopsy.

Conclusion. AAV gene therapy into the EDB muscle of patients with LGMD2D probably increases the expression of α-sarcoglycan gene and restores the protein complex for up to 6 months postinjection without significant AEs (one Class I and one Class II study). Data are insufficient to determine the effect of AAV-vector expressed γ-sarcoglycan genes in patients with LGMD2C (one Class III study).
Clinical context. These are small proof-of-concept studies. Despite increased expression of the target protein in these few patients, the clinical relevance of gene therapy is yet to be determined. Other considerations include the number of injection sites and frequency of injection.
A Class I phase 1/2 randomized, double-blind, placebo-controlled trial evaluated the safety and tolerability of a neutralizing antibody to myostatin (MYO-029), which is an endogenous inhibitor of muscle growth.^e493 Four dosing cohorts of 36 patients each (total 116 subjects: 36 BMD; 38 LGMD2A, 2B, 2C, 2D, 2E, and 2I; 42 facioscapulohumeral dystrophy) were included in the trial. The dosing cohorts were 1 mg/kg, 3 mg/kg, 10 mg/kg, and 30 mg/kg intravenously every 2 weeks for 6 months, for a total of 13 doses. Subjects were followed for 3 months after the last dose. MYO-029 was found to be safe and well tolerated. One hundred four of 116 subjects (89%) reported AEs. The only AE that was significantly more common in the treatment group was accidental injury (8/27 [27.6%] in the placebo group and 13/27 [48%], 11/27 [41%], and 4/27 [15%] in the 1, 3, and 10 mg/kg cohorts, respectively, p = 0.026). The major AE was cutaneous hypersensitivity, seen in 4/27 patients (15%) in the 10 mg/kg group and 2/6 patients (33%) in the 30 mg/kg cohort. Rash and urticaria were noted in 12 subjects in all (2/29 [7%] in the placebo group, 3/27 [11%] in the 1 mg/kg group, 1/27 [3.7%] in the 3 mg/kg group, 4/27 [15%] in the 10 mg/kg group, and 2/6 [33%] in the 30 mg/kg group). Seven subjects (6%) had serious AEs (2/29 patients [6.9%] in the placebo group, 2/27 [7.4%] in the 3 mg/kg group [one patient with dementia and one with depression followed by suicide attempt], and 3/27 [11.1%] in the 10 mg/kg cohort [one case of diplopia and unconfirmed aseptic meningitis, one case of diarrhea, and one case of chest pain]). No deaths were reported. The 30 mg/kg cohort was discontinued due to cutaneous hypersensitivity. No improvement was noted in muscle strength, but a trend toward increase in lean body muscle mass using dual-energy x-ray absorptiometry was noted in the 3 mg/kg group (placebo -0.07 ± 0.7, 3 mg/kg 2.4 ± 0.7, p = 0.05). The study was not powered to assess efficacy.^e493
Conclusion. Neutralizing antibody to myostatin (MYO-029) is probably safe and tolerable in patients with BMD and LGMD2A–E and 2I at doses of 1 and 3 mg/kg, although a few serious side effects were noted which require further research. Cutaneous hypersensitivity is noted at 10 and 30 mg/kg doses. There are no data regarding long-term safety. There is probably a trend toward increase in lean body muscle mass, but the study was not powered to assess efficacy (one Class I study).
A 12-month randomized, double-blind, placebo-controlled Class II study^e495 evaluated the efficacy of prednisolone 0.35 mg/kg/day for 6 months with crossover to placebo for 6 months in 4 boys with BMD. Isometric muscle strength at 3 months increased by 139% with prednisolone (p < 0.001, corrected for multiple outcomes) but was nonsignificant at 6 months. Three of the 4 patients showed stable or improved muscle strength on prednisolone. Two of the 4 patients improved or stabilized on placebo and 1/4 deteriorated on placebo. The difference was nonsignificant by χ² test. Although improvements were noted in ankle and wrist dorsiflexors and elbow extensors at 3 months and in knee flexors and neck extensors at 3 and 6 months, these differences were nonsignificant when the authors corrected for multiple outcomes. The study was underpowered to detect a significant improvement or to exclude benefit in other outcomes.^e495
Conclusion. On the basis of one Class II study, prednisolone 0.35 g/kg/day is probably effective to improve isometric muscle strength in patients with BMD after 3 months of treatment.
A Class III study^e496 evaluated myoblast transplantation into the tibialis anterior in 3 males with BMD compared with saline injections into the opposite tibialis anterior. Patients were pretreated with cyclosporine A (CyA) for 2 months prior to transplantation and continued it for a year posttransplantation. Force generation in the tibialis anterior was measured bilaterally at baseline, after 2 months of CyA, after myoblast implantation, and after discontinuation of CyA. CyA alone produced a significant bilateral increase in muscle force pretransplantation in one patient, and another patient had significant bilateral increase in tibialis anterior force on CyA posttransplantation, but because the increase was bilateral it was felt to be unlikely to be due to the transplant. None of the biopsies showed dystrophin level changes that could be considered therapeutic.^e496
Conclusion. On the basis of one Class III study, data are inadequate to support or refute the use of myoblast transfer in BMD.
A randomized double-blind Class III study^e497 evaluated the effects of self-injected subcutaneous growth hormone (GH) 0.07 mg/kg/week for 3 months in 10 patients with BMD. The cardiomyopathic index (echocardiogram QT:PQ ratio) did not change significantly. The complexity of ventricular premature beats as assessed by the Lown classification system decreased from 4A to 1A in 1/6 patients treated with GH and from 4B to 4A in 1/4 patients treated with placebo. In patients treated with GH, left ventricular mass assessed by echocardiogram increased by 42 g (baseline 150 ± 14, 6 weeks 163 ± 27, 12 weeks 173 ± 27, p < 0.05) and reduced nonsignificantly in controls. Relative wall thickness also increased by 12% (baseline 0.23 ± 0.01, 6 and 12 weeks 0.05 ± 0.01, p < 0.05), and end-systolic wall stress dropped by 13% in patients treated with GH (baseline 168 ± 19, 6 weeks 149 ± 14, 12 weeks 146 ± 15, p < 0.05) without change in controls. Plasma levels of brain natriuretic peptide, which were elevated when compared with normal values, decreased by 40% in the active treatment group, whereas no significant changes were detected in the placebo group (GH baseline ± SE 190 ± 60 ng/mL, 12 weeks 114 ± 50, p < 0.05; placebo baseline 205 ± 45, 12 weeks 210 ± 55). Timed functional tests and pulmonary function did not change significantly between groups over 12 weeks. No AEs were noted.^e497
Conclusion. Data are inadequate to support or refute the use of subcutaneous GH injections to improve cardiac and pulmonary function in patients with BMD (one Class III study).
A Class III study^e499 evaluated a hand training program consisting of 3 weekly sessions of resistance and stretching exercises (2 self-training, one guided by an occupational therapist) in 12 patients with Welander distal myopathy. There was a one-grade increase in right hand strength on manual muscle testing in 7/12 patients and a 2-grade increase in 1/12. There was also an increase in peak pre–/post–pinch grip as measured by Grippit in 11/12. Range of motion measured with a finger goniometer increased from -470 degrees in the right hand and -790 in the left hand to -260 and -510 degrees, respectively. Self-reported performance of activities of daily living improved in multiple domains. When corrected for multiple outcomes, none of these changes was significant. Mean pre–/post–pinch grip scores, grip strength measured with Grippit, and life satisfaction score changes were also nonsignificant.^e499
Conclusion. On the basis of one Class III study, data are insufficient to support or refute the benefit of a hand exercise program in Welander distal myopathy.
Another Class III study^e246 evaluated the effect of endurance training in 9 ambulatory patients with LGMD2I and 9 healthy, sedentary, age-matched controls. The home training program consisted of 30-minute stationary bicycle ergometer exercise sessions at a heart rate corresponding to 65% of maximal oxygen uptake (VO₂ max) for 12 weeks. The number of sessions increased progressively for the first 4 weeks to 5 times a week in the last 8 weeks. In the patients, VO₂ max and maximal workload (Wmax) increased by 21% and 27%, respectively, at 12 weeks (p < 0.0005). These parameters also increased in the control group, but there was no difference in the absolute increase between groups. Plasma lactate and heart rate did not change before and after training. Self-reported improvement was noted in physical endurance (8/9 patients), leg muscle strength (7/9), and walking distance (6/9). Capillary density increased on the 5 tested muscle biopsies (mean ± SE before: 209 ± 19 mm², after: 255 ± 30 mm², p = 0.05). CK levels and mean muscle type II fiber area showed a trend toward increase in 5/9 patients with LGMD2I tested at 12 weeks (CK levels before: 661 ± 154, after: 1,068 ± 298, p = 0.08; type II fiber area before: 7,604 ± 735 mm², after: 8,982 ± 1,204 mm², p = 0.09). There were no AEs.^e246
Conclusion. Data are insufficient to support or refute the benefit of endurance training for 12 weeks to improve VO₂ max, Wmax, and patient-reported outcomes of leg strength, physical endurance, and walking distance in patients with LGMD2I (one Class III study).
A Class III study by the same authors evaluated endurance training in 11 men with BMD and 7 healthy sedentary men.^e344 The exercise protocol was similar to that of the previous study.^e246 Six patients continued the protocol 3 times weekly for 12 months. At 12 weeks VO₂ max and Wmax improved by 47% and 80%, respectively (p < 0.005), which was 3–4 times higher than the changes in controls. Plasma lactate levels and heart rate were not significantly different. A significant increase in muscle strength of the hip abductors and foot dorsiflexors and plantarflexors was also noted; this was maintained at 12 months (increase in strength [Newtons, mean ± SE]: hip abductors 22 ± 7%, foot dorsiflexors 13 ± 6%, foot plantarflexors 20 ± 4%, p < 0.05). At 12 months there was a 40% increase in quadriceps strength as well (hip abduction 13 ± 7%, hip flexion 14 ± 8%, knee extension 40 ± 15%, foot dorsiflexion 25 ± 5%, foot plantarflexion 21 ± 5%, p < 0.05). In one patient LVEF increased from 35% to 50% at 12 months. LVEF did not change in any of the other patients. A “majority” of patients with BMD reported improvement in physical endurance, leg muscle strength, and walking distance after 12 weeks of training. CK levels, lean body mass, and body fat percentage did not change. No changes were noted in muscle fiber diameter or capillary density. In the 6 patients who continued the endurance program for 12 months, the improvement in VO₂ max, Wmax, and muscle strength was sustained but did not improve further. In 1/3 patients tested, cardiac EF increased from 35% to 50% at 12 months.^e344
Conclusion. Data are insufficient to determine the effect of 12 weeks of endurance training for improving VO₂ max, Wmax, muscle strength, and patient-reported outcomes of physical endurance, leg muscle strength, and walking distance in patients with BMD (one Class III study).
Two Class III studies^e462,e465 evaluated the effects of exercise on hIBM3 secondary to a defect in the MYH2 gene. In the first study,^e462 8 patients participated in an 8-week home exercise program for 30 minutes/day, 5 days a week on a stationary bicycle. No improvements were seen in any of the outcomes after correction for multiple outcomes. The same authors studied 6 patients from the same families after a similar exercise protocol.^e465 Maximal workload increased in all patients (statistical data not provided), and expression of MYH IIx and increase in MYH types I and IIa were noted on postexercise biopsies of the vastus lateralis compared to pre-exercise biopsies (p < 0.05). There was no change in muscle strength of the knee extensors and flexors.
Conclusion. Data are inadequate to assess the effect of endurance training on maximum workload, muscle strength, or change in the expression of myosin isoforms on muscle biopsy in hIBM3 (2 conflicting Class III studies).
RECOMMENDATIONS FOR THE DIAGNOSIS, EVALUATION, AND MANAGEMENT OF LIMB-GIRDLE AND DISTAL MUSCULAR DYSTROPHIES

The recommendations below encompass 3 major areas: diagnosis, evaluation, and management of muscular dystrophies, including limb-girdle, humeroperoneal, and distal muscular dystrophies. Each recommendation is preceded by clinical context that outlines the evidence, general principles of care, and evidence from related disorders that drive the recommendations.

Key:

EVID: Statements supported directly by the systematically reviewed evidence.

PRIN: An accepted axiom or principle.

RELA: Statements supported by strong evidence not included in the systematic review.

INFER: An inference from one or more of the other statements.
Note: Given the relative paucity of literature directly relevant to LGMDs for some of the clinical questions, some of the recommendations below are based in part on evidence from other neuromuscular disorders, primarily amyotrophic lateral sclerosis (ALS).
Overall management

Clinical context. Our systematic review has highlighted the medical complexity of caring for patients with muscular dystrophy (EVID). Such patients may develop cardiac, pulmonary, nutritional, and musculoskeletal complications that require the assistance of cardiologists, pulmonologists, orthopedists, physiatrists, physical therapists, occupational therapists, nutritionists, orthotists, and speech pathologists, in addition to neurologists (INFER). In addition, myopathies with a limb-girdle, humeroperoneal, or distal pattern of weakness may be challenging to diagnose (INFER). A specific diagnosis provides patients with “closure,” assists genetic counseling, and directs monitoring for complications and optimal management (PRIN).

Recommendation.

A00. Clinicians should refer patients with suspected muscular dystrophy to neuromuscular centers to optimize the diagnostic evaluation and subsequent management (Level B).

Diagnosis of muscular dystrophies (see also table e-2 and figures 1–5, e-1, and e-2)

Clinical context. Our evidence-based review found that muscular dystrophies have some characteristic features, including a predilection for certain ethnicities, type of inheritance (autosomal dominant, recessive, or X-linked), patterns of weakness (limb-girdle, humeroperoneal, or distal), hypertrophy or atrophy of specific muscle groups, and ancillary characteristics such as scapular winging, level of serum CK, particular EMG abnormalities (e.g., myotonic discharges), cardiac and respiratory involvement, and characteristic features on muscle biopsy (e.g., rimmed vacuoles, myofibrillar myopathy, reducing bodies). Very few features were pathognomonic of a specific disorder; for example, a history of PDB, frontotemporal dementia, or motor neuron disease is pathognomonic of hIBMPFD due to mutations in the gene for VCP. Similarly, the likelihood of genetic diagnosis for the dystroglycanopathies (LGMD2K, LGMD2M, LGMD2N, LGMD2O, and LGMD2P) increases in the presence of abnormalities on brain MRI and abnormal α-dystroglycan immunostaining on muscle biopsy. In most of the other muscular dystrophies reviewed, a constellation of features narrows the differential diagnosis to a few disorders (EVID). The predisposition of certain ethnicities to specific disorders was noted (EVID). However, many disorders are described in several ethnic groups, making it difficult to use ethnicity alone to arrive at a diagnosis. Therefore, in conjunction with specific clinical patterns, certain ethnicities may help to narrow the differential diagnosis and direct confirmatory testing in a proportion of patients (INFER). The limb-girdle and distal muscular dystrophies are presumed to have genetic origins because no plausible environmental cause has been identified. Sporadic cases may be due to autosomal dominant, recessive, or X-linked inheritance (PRIN).
The accurate diagnosis of the muscular dystrophies is important for patients, their families, and for efficient and cost-effective use of medical resources (INFER). Knowing the specific type of muscular dystrophy assists in defining the long-term prognosis, since some dystrophies are more rapidly progressive, involve the cardiorespiratory systems more frequently, or are associated with other disorders (EVID). The identification of these dystrophies through genetic testing will not only inform long-term prognosis but will also assist in directing care more efficiently (e.g., more frequent cardiorespiratory monitoring and prophylactic treatments such as pacer/defibrillator placement for those disorders known to be associated with cardiac involvement) (INFER). Precise identification of the disorder also eliminates the need for repeated testing for an acquired, treatable disorder such as an inflammatory myopathy, because some dystrophies can have inflammation on muscle biopsy, making diagnosis difficult on the basis of routine biopsy findings alone (INFER). In addition, the temptation to try immunosuppressive agents repeatedly, looking for a therapeutic response, is not unusual when there is no diagnosis and the patient is worsening (INFER). This exposes patients to potentially serious side effects of immunosuppressive medications (PRIN). Patients on immunosuppressants need to be monitored at regular intervals, adding logistical difficulties to a population that may have significantly impaired mobility (INFER). Health care costs are also increased by repeated investigations, immunosuppressive treatments, and laboratory monitoring (PRIN). Although establishing a genetic diagnosis is expensive on the front end, the costs of continued investigation for other causes and the risks and expenses associated with empiric trials of immunosuppressants make a strong case for establishing a genetic diagnosis, which often provides patients a sense of “closure” (INFER). Establishing a genetic diagnosis is crucial for genetic counseling of families to inform decision making about having children and for screening of offspring based on the genetics of the disorder (PRIN). Treatment of cardiomyopathy, arrhythmias, and ventilatory failure prolongs life and improves quality of life in patients with other neuromuscular diseases (RELA).^{e43,e501-e505} The recommendations below also discuss the overall differential diagnosis of LGMD syndromes, including Pompe disease (acid α-glucosidase deficiency) and the collagen VI disorders, Ullrich and Bethlem myopathy, which may mimic LGMD or EDMD, respectively. These disorders were not formally reviewed in the evidence since they are not included under LGMD, but they should be considered in the differential diagnosis of LGMD and EDMD.
Recommendations.

A0. For patients with suspected muscular dystrophy, clinicians should use a clinical approach to diagnosis based on the clinical phenotype, including the pattern of muscle involvement, inheritance pattern, age at onset, and associated manifestations (e.g., early contractures, cardiac or respiratory involvement) (Level B).

Limb-girdle pattern of weakness (see figures 35).

A1. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal dominant inheritance, cardiomyopathy, respiratory involvement, EMG with myotonic or “pseudomyotonic” discharges (the latter characterized by runs of decrescendo positive sharp wave discharges without the typical waxing and waning of amplitudes and frequencies seen in myotonic discharges), ankle dorsiflexor weakness (foot drop), and muscle biopsy (if performed) showing features of myofibrillar myopathy, clinicians should perform genetic testing for mutations in the genes for desmin (LGMD1E), myotilin (LGMD1A), DNAJB6 (LGMD1D), ZASP, filamin C, αB-crystallin, and titin (Level B).

A2. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal dominant inheritance, rippling muscles, and percussion-induced rapid contractions, clinicians should perform genetic testing for mutations in the caveolin-3 gene (LGMD1C) (Level B).
A3. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal dominant inheritance, early humeroperoneal weakness, contractures (neck, elbows, knee, ankle), and cardiomyopathy, clinicians should perform genetic testing for mutations in the lamin A/C gene (LGMD1B or AD-EDMD) (Level B).
A4. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal dominant inheritance, distal weakness, myotonic discharges on EMG, past or family history of Paget disease, frontotemporal dementia, or motor neuron disease, clinicians should perform genetic testing for mutations in VCP (hIBMPFD) (Level B).
A5. In patients with limb-girdle weakness and suspected muscular dystrophy who either do not have clinical features to suggest a specific form of dystrophy or in whom initial genetic testing is not informative, clinicians should perform muscle biopsy in order to delineate characteristic features that direct further genetic testing (such as immunohistochemistry/immunoblotting for various sarcolemmal proteins, calpain-3, or features of myofibrillar myopathy; see figures 35) or to exclude an alternative diagnosis (e.g., a metabolic myopathy, mitochondrial myopathy, congenital myopathy, or inflammatory myopathy) (Level B).
A6. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance, scapular winging but no calf hypertrophy, and normal cardiorespiratory function, clinicians should perform initial genetic testing for mutations in calpain-3 (LGMD2A). Patients of English, French, Spanish, Italian, Portuguese, or Brazilian descent may have a higher pretest probability of this disorder (Level B).
A7. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance and calf atrophy and weakness (i.e., inability to stand on toes), clinicians should perform genetic testing for mutations in anoctamin-5 (LGMD2L) or dysferlin (LGMD2B). If the onset of symptoms is in the teens or early 20s or the patient is from Asia, clinicians should assess for dysferlin mutations first and, if negative, test for anoctamin-5 mutations. If the onset of symptoms is in the 30s or later or the patient is of English or northern European ancestry, clinicians should assess for anoctamin-5 mutations first and, if negative, test for dysferlin mutations (Level B).
A8. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance and muscle biopsy immunohistochemistry showing reduction in α-, β-, γ-, or δ-sarcoglycans, clinicians should perform genetic testing for mutations in the sarcoglycan genes (LGMD2C–2F) (Level B).
A9. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance who are of Hutterite descent, clinicians should perform genetic testing for mutations in TRIM32 (LGMD2H) (Level B).
A10. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance, scapular winging, calf hypertrophy, and early cardiorespiratory involvement, clinicians should perform initial genetic testing for mutations in FKRP (LGMD2I). Patients of northern European descent may have a higher pretest probability of this disorder (Level B).
A11. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance and mental retardation, clinicians should screen for mutations in genes that cause primary or secondary deficiency of α-dystroglycan (LGMD2K, LGMD2M, LGMD2N, LGMD2O, and LGMD2P) (Level B).
A12. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance and epidermolysis bullosa or pyloric atresia, clinicians should perform genetic testing for mutations in plectin (Level B).
A13. In male patients with limb-girdle weakness and suspected muscular dystrophy with probable X-linked inheritance, clinicians should perform genetic testing for mutations in the dystrophin gene (Duchenne or Becker muscular dystrophy) (Level B).
A14. In patients with limb-girdle weakness and suspected muscular dystrophy with probable autosomal recessive inheritance and no other specific clinical features or in whom muscle biopsy does not inform genetic testing, clinicians should perform dried blood spot test for α-glucosidase (acid maltase) deficiency or Pompe disease (Level B).
A15. In female patients with limb-girdle weakness and suspected muscular dystrophy with probable X-linked inheritance, clinicians should perform genetic testing for dystrophin mutations or perform a muscle biopsy and immunostain for dystrophin to assess for a mosaic pattern of staining. If abnormal immunostaining is present, clinicians should confirm the diagnosis of manifesting carrier of dystrophinopathy with genetic testing for mutations in the dystrophin gene (Level B).
Humeroperoneal weakness (figure e-1).

B1. In patients with humeroperoneal weakness and suspected muscular dystrophy with probable autosomal dominant inheritance, early cardiac involvement, and no joint laxity, clinicians should perform genetic testing for mutations in the lamin A/C gene (AD-EDMD, LGMD1B). If the inheritance pattern is probably X-linked, clinicians should perform genetic testing for mutations in the emerin gene (XR-EDMD) (Level B).

B2. In patients with humeroperoneal weakness and suspected muscular dystrophy with early cardiac involvement and no joint laxity who do not possess mutations in the lamin A/C or emerin gene, clinicians should perform muscle biopsy to delineate characteristic abnormalities that direct further genetic testing (see figure e-1 for muscle biopsy features that direct genetic testing) (Level B).
B3. In patients with humeroperoneal weakness and suspected muscular dystrophy with probable autosomal dominant inheritance, joint laxity, protuberant calcaneus, and no cardiac involvement, clinicians should perform genetic testing for mutations in the collagen VI gene (Bethlem myopathy). If the inheritance pattern is probably autosomal recessive with congenital onset, clinicians should perform genetic testing for mutations in the collagen VI gene (Ullrich myopathy) (Level B).
Distal muscular dystrophy (figure e-2).

C1. In patients with late adult onset of index finger and wrist extensor weakness followed by atrophy and weakness of hand muscles and muscle biopsy showing rimmed vacuoles, clinicians should make a diagnosis of Welander distal myopathy. Patients of Swedish or Finnish descent may have a higher pretest probability of this disorder. Clinicians should confirm the diagnosis with genetic testing for Welander myopathy when testing becomes commercially available (Level B).

C2. In patients with suspected distal muscular dystrophy and probable autosomal recessive inheritance with early onset of calf weakness, clinicians should perform genetic testing for mutations in the anoctamin-5 and dysferlin genes. If the patient is of northern European descent, clinicians should perform initial genetic testing for mutations in the anoctamin-5 gene (LGMD2L) and, if negative, perform genetic testing for mutations in the dysferlin gene (LGMD2B). If the patient is from eastern Asia (Japan, China, Korea), clinicians should perform initial genetic testing for mutations in the dysferlin gene (LGMD2B, Miyoshi myopathy) and, if negative, perform genetic testing for mutations in the anoctamin-5 gene (LGMD2L) (Level B).
C3. In patients with suspected distal muscular dystrophy and probable autosomal recessive inheritance with early onset (<30 years of age) of progressive foot drop who are of Japanese or Middle Eastern Jewish descent, clinicians should perform initial genetic testing for GNE mutations (AR-hIBM) (Level B).
C4. In patients with suspected distal muscular dystrophy without the clinical features in C2 or C3 above, clinicians should perform a muscle biopsy to direct further genetic testing (see figure e-2 for biopsy and clinical features that direct genetic testing) (Level B).
Other diagnostic considerations.

D1. In patients with muscular dystrophy who have proximal as well as distal weakness, clinicians should use specific clinical features (e.g., rippling muscles, cardiomyopathy, atrophy of specific muscle groups, irritability on EMG) and biopsy features (MFM, reduction of emerin immunostaining, presence of rimmed vacuoles) to guide genetic testing, which may include mutations in the genes causing the various forms of MFM (see section on MFM), LGMD2B (dysferlin), LGMD2L (anoctamin-5), LGMD2J (titin), LGMD1C (caveolin-3), and EDMD (emerin and lamin A/C) (Level B).

D2. In patients with suspected muscular dystrophy in whom initial genetic testing, muscle biopsy, and dried blood spot test for Pompe disease do not provide a diagnosis, clinicians may obtain genetic consultation or perform parallel sequencing of targeted exomes, whole-exome sequencing, whole-genome screening, or next-generation sequencing to identify the genetic abnormality (Level C).