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

Evidence-based Guideline: Diagnosis and Treatment of Limb-Girdle and Distal Dystrophies

Report of the Guideline Development Subcommittee of the American Academy of Neurology and the Practice Issues Review Panel of the American Association of Neuromuscular & Electrodiagnostic Medicine

Pushpa Narayanaswami, MBBS, DM, FAAN¹; Michael Weiss, MD, FAAN²; Duygu Selcen, MD³; William David, MD, PhD⁴; Elizabeth Raynor, MD¹; Gregory Carter, MD⁵; Matthew Wicklund, MD, FAAN⁶; Richard J. Barohn, MD, FAAN⁷; Erik Ensrud, MD^8,10; Robert C. Griggs, MD, FAAN⁹; Gary Gronseth, MD, FAAN⁷; Anthony A. Amato, MD, FAAN¹⁰
(1) Department of Neurology, Beth Israel Deaconess Medical Center/Harvard Medical School, Boston, MA

(2) Department of Neurology, University of Washington Medical Center, Seattle, WA

(3) Department of Neurology, Mayo Clinic, Rochester, MN

(4) Department of Neurology, Massachusetts General Hospital, Boston, MA/Harvard Medical School, Boston, MA

(5) St Luke's Rehabilitation Institute, Spokane, WA

(6) Department of Neurology, Penn State Hershey Medical Center, Hershey, PA

(7) Department of Neurology, University of Kansas Medical Center, Kansas City, KS

(8) Neuromuscular Center, Boston VA Medical Center, Boston, MA

(9) Department of Neurology, University of Rochester Medical Center, Rochester, NY

(10) Department of Neurology, Brigham and Women’s Hospital, Boston, MA/Harvard Medical School, Boston, MA

Correspondence to

American Academy of Neurology:

[e-mail]
Approved by the AAN Guideline Development Subcommittee on July 13, 2013; by the AAN Practice Committee on February 3, 2014; by the AANEM Board of Directors on July 10, 2014; and by the AANI Board of Directors on July 7, 2014.
STUDY FUNDING

Funding for this publication was made possible (in part) by grant DD10-1012 from the Centers for Disease Control and Prevention. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention. The remaining funding was provided by the American Academy of Neurology.

This guideline was endorsed by the American Academy of Physical Medicine and Rehabilitation on April 17, 2014; by the Child Neurology Society on July 11, 2014; by the Jain Foundation on March 14, 2013; and by the Muscular Dystrophy Foundation on August 27, 2014.
AUTHOR CONTRIBUTIONS

Pushpa Narayanaswami: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content, study supervision.

Michael Weiss: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Duygu Selcen: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

William David: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Elizabeth Raynor: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Gregory Carter: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Matthew Wicklund: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Richard J. Barohn: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Erik Ensrud: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Robert C. Griggs: study concept and design.

Gary Gronseth: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content.

Anthony A. Amato: study concept and design, acquisition of data, analysis or interpretation of data, drafting/revising the manuscript, critical revision of the manuscript for important intellectual content, study supervision.

DISCLOSURE
Dr. Narayanaswami has received honoraria from the American Academy of Neurology (AAN) and the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM).
Dr. Weiss has served as a speaker for the AAN, AANEM, American Academy of Physical Medicine & Rehabilitation (AAPM&R), Athena Diagnostics, Nufactor, Walgreens, and Grifols Inc.; serves on speakers’ bureaus for Athena Diagnostics and Walgreens; has consulted for Genzyme Corporation, CSL Behring, Questcor Pharmaceuticals, and Washington State Labor and Industries; and has received research funding support from the ALS Therapy Alliance and Northeast ALS Consortium.
Dr. Selcen has served as an editorial board member for Neuromuscular Disorders and has received funding for research from the National Institutes of Health (NIH).
Dr. David reports no relevant disclosures.
Dr. Raynor reports no relevant disclosures.
Dr. Carter has served as the senior associate editor for Muscle & Nerve, has received honoraria from the AANEM and the Canadian Association of Physical Medicine and Rehabilitation, has received funding for research from the National Institutes on Aging and the National Institute on Disability and Rehabilitation Research, and has testified on a case regarding the use of marijuana in pain.
Dr. Wicklund has served on a scientific advisory board for Sarepta Therapeutics, has served on a speakers’ bureau for Genzyme, has received grant funding from Eli Lilly, and has collaborated on research without compensation with Athena Diagnostics..
Dr. Barohn has served as a consultant or on a scientific advisory board for Genzyme, Grifols, MedImmune, and Novartis; has received honoraria from Alexion, Isis, Baxter, Sarepta, and CSL Behring; and has received funding for research from the US Food and Drug Administration (FDA) and the NIH.  
Dr. Ensrud reports no relevant disclosures.
Dr. Gronseth serves as an editorial advisory board member of Neurology Now, is an associate editor of Neurology, and receives honoraria from the AAN.
Dr. Griggs consults for PTC Therapeutics (Chair of DSMB), Novartis (DSMB), Marathon Pharmaceuticals, Taro Pharmaceuticals, and Viromed (DSMB); receives funding from the NIH, the Italian Telethon (DSMB Chair), the Muscular Dystrophy Association, the Parent Project for Muscular Dystrophy, and the AAN; and receives royalties from Elsevier (for Cecil Essentials and Cecil Textbook of Medicine).
Dr. Amato has served as a consultant or on scientific advisory boards for MedImmune, Amgen, Biogen, DART, and Baxter; serves as an associate editor for Neurology and Muscle & Nerve; has received royalties from publishing from Neuromuscular Disorders; has received honoraria from the AAN and AANEM; and has received funding for research from Amgen, MedImmune, Novartis, the FDA, and the NIH.

ABBREVIATIONS

AAN = American Academy of Neurology

AD = autosomal dominant

AE = adverse event

ALS = amyotophic lateral sclerosis

AR = autosomal recessive

BMD = Becker muscular dystrophy

CDC = Centers for Disease Control and Prevention

CHF = congestive heart failure

CI = confidence interval

CK = creatine kinase

CMD = congenital muscular dystrophy

CMT = Charcot-Marie-Tooth syndrome

CyA = cyclosporine A

DMD = Duchenne muscular dystrophy

EDB = extensor digitorum brevis

EDMD = Emery-Dreifuss muscular dystrophy

EF = ejection fraction

EM = electron microscopy

fALS = familial amyotophic lateral sclerosis

FCMD = Fukuyama congenital muscular dystrophy

FVC = forced vital capacity

GH = growth hormone

hIBM = hereditary inclusion body myopathy

hIBMPFD = hereditary inclusion body myopathy with Paget disease and frontotemporal dementia

HMERF = hereditary myopathy with early respiratory failure

LDM = Laing distal myopathy

LGMD = limb-girdle muscular dystrophyLVEF = left ventricular ejection fraction

MEB = muscle-eye-brain disease

MFM = myofibrillar myopathy

MM3= Miyoshi myopathy type III

MR = mental retardation

PDB = Paget disease of bone

PIRCs = percussion-induced rapid contractions

RAE = right atrial enlargement

ULN = upper limit of normal

VO₂ max = maximal oxygen uptake

Wmax = maximal workload

WWS = Walker-Warburg syndrome

ABSTRACT

Objective: To review the current evidence and make practice recommendations regarding the diagnosis and treatment of limb-girdle muscular dystrophies (LGMDs).

Methods: Systematic review and practice recommendation development using the American Academy of Neurology guideline development process.

Results: Most LGMDs are rare, with estimated prevalences ranging from 0.07 per 100,000 to 0.43 per 100,000. The frequency of some muscular dystrophies varies based on the ethnic background of the population studied. Some LGMD subtypes have distinguishing features, including pattern of muscle involvement, cardiac abnormalities, extramuscular involvement and muscle biopsy findings. The few published therapeutic trials were not designed to establish clinical efficacy of any treatment.

Principal Recommendations: For patients with suspected muscular dystrophy, clinicians should use a clinical approach to guide genetic diagnosis based on clinical phenotype, inheritance pattern, and associated manifestations (Level B). Clinicians should refer newly diagnosed patients with an LGMD subtype and high risk of cardiac complications for cardiology evaluation even if they are asymptomatic from a cardiac standpoint (Level B). In LGMD patients with a known high risk of respiratory failure, clinicians should obtain periodic pulmonary function testing (Level B). Clinicians should refer patients with muscular dystrophy to a clinic that has access to multiple specialties designed specifically to care for patients with neuromuscular disorders (Level B). Clinicians should not offer patients with LGMD gene therapy, myoblast transplantation, neutralizing antibody to myostatin, or growth hormone outside of a research study designed to determine efficacy and safety of the treatment (Level R).

INTRODUCTION

Limb-girdle muscular dystrophies (LGMDs) are a group of myopathies characterized by predominantly proximal muscle weakness (pelvic and shoulder girdles).^e1 Initially described as a clinical phenotype, they are now recognized as a heterogeneous group of myopathies that vary in severity and may affect persons at all ages from childhood through adulthood. In 1995, the LGMDs were classified into 2 main groups depending on the inheritance pattern: LGMD1, autosomal dominant, and LGMD2, autosomal recessive. Overlaid on this numeric division is a letter designating the order of discovery for each chromosomal locus (e.g., LGMD1A implying autosomal dominant LGMD type A; LGMD2D implying autosomal recessive LGMD type D).^e2,e3 With advances in molecular genetics that identify new genetic defects associated with the LGMD phenotype, this list of disorders continues to grow. Unfortunately, the literature is conflicting as to the appropriate terminology for different disorders. For example, prior to genetic discovery, and even after, various reports refer to some of these disorders as congenital myopathies, myofibrillar myopathies, hereditary inclusion body myopathies (hIBMs), distal myopathies/dystrophies, or LGMD.^e4 Table e-1 delineates the most recent classification of what is considered “muscular dystrophies” in adults that were included in this review.

The LGMDs are rare disorders with a combined minimum prevalence of 2.27/100,000.^e5 Given the wide variation in phenotypic expression of the LGMDs, establishing a clinical diagnosis is a challenge. Importantly, some of these disorders are associated with potentially serious cardiac and respiratory complications. In the evaluation of a patient with LGMD, the ideal approach is to utilize the person’s clinical presentation and narrow down the possible genotype to a few disorders. This will help both to predict the long-term prognosis and to plan further evaluation, such as muscle biopsy or blood tests to confirm the genetic defect and tests of cardiorespiratory function. With increasingly accurate molecular diagnosis, knowledge regarding the genotype/phenotype correlations, although far from complete, is slowly advancing. Although there is some literature discussing the clinical approach to LGMDs,^e6 no systematic reviews of the literature or practice guidelines are available for clinicians who evaluate these disorders. This evidence-based guideline reviews the current evidence regarding the diagnosis and treatment of LGMDs.

We have classified the LGMDs by their molecular diagnosis and also discuss non–limb-girdle adult-onset myopathies that are genotypically identical to the LGMDs, such as Miyoshi distal myopathy, which is allelic to LGMD2B. In addition, other hereditary myopathies that overlap and may indeed be considered forms of LGMD (e.g., hIBMs, myofibrillar myopathies, Emery-Dreifuss muscular dystrophy [EDMD], Becker muscular dystrophy [BMD], manifesting carriers of dystrophin mutations) are included. We also review the distal myopathies. Hence, this review encompasses 3 major phenotypic dystrophies: limb-girdle weakness, humeroperoneal weakness as in EDMD, and distal weakness as in the distal myopathies. We use the terms LGMD and muscular dystrophy interchangeably to refer to the disorders reviewed in this guideline. Duchenne dystrophy, congenital muscular dystrophy, myotonic dystrophy, and facioscapulohumeral dystrophy are not included in this guideline, as they will be discussed in forthcoming guidelines. This guideline seeks to answer the following clinical questions:

1. In a population of patients with suspected muscular dystrophy, what proportion of patients has a genetic defect confirming LGMD/distal myopathy/distal muscular dystrophy/BMD?

2. In patients with muscular dystrophy, what is the association between specific features and subtypes of these disorders, in particular ethnicity; age at onset; scapular winging; weakness, atrophy, hypertrophy, or MRI changes in the facial muscles, calf, gastrocnemius, quadriceps, hip adductors, hip abductors, and tibialis anterior; cardiac dysfunction (arrhythmias, congestive heart failure, reduced/abnormal ejection fraction [EF], dilated cardiomyopathy, hypertrophic cardiomyopathy); respiratory dysfunction (abnormal/reduced forced vital capacity [FVC]); dysphagia; dysarthria; hoarse voice; contractures; and cognitive dysfunction? In patients with LGMD, what is the association between the degree of creatine kinase (CK) elevations and specific subtypes of these disorders, in particular CK normal, <10-fold elevation, and >10-fold elevation?

3. In patients with LGMD or distal muscular dystrophy, what is the association between specific muscle biopsy features and subtypes of these disorders, in particular rimmed vacuoles, inflammation, and inclusions?

4. How often do patients with muscular dystrophy and its specific subtypes have significant respiratory abnormalities (FVC < 50% predicted), cardiac abnormalities (EF < 50%, evidence of hypertrophic cardiomyopathy or generalized wall motion abnormality, arrhythmias, conduction defects), or bone loss (osteoporosis or bone mineral density 2.5 SD below peak bone mass, osteopenia or bone mass of 1.0–2.5 SD below peak bone mass)?

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?
DESCRIPTION OF THE ANALYTIC PROCESS

In July 2010, the American Academy of Neurology (AAN) Guideline Development Subcommittee and the American Association of Neuromuscular & Electrodiagnostic Medicine Practice Issues Review Panel (appendices e-1e-3) formed a panel of neurologists, other physicians with relevant expertise, methodologists, and patient advocates. The MEDLINE, EMBASE, and Cochrane databases were searched from 1987 onward for relevant peer-reviewed articles in humans and in English only (appendix e-4 provides the full search strategy and terms). Through an initial search conducted in 2011 and an updated search conducted in 2013, a total of 3,246 abstracts were identified. Of those, 1,335 articles were selected for full-text review. Two panel members, working independently of each other, reviewed each of the 1,335 articles and selected 699 for final review and classification. Each final article was reviewed by 2 panel members who rated it according to the AAN 2011 criteria for classification of articles (appendix e-5), using the scheme appropriate to the clinical question. The AAN population screening evidence scheme was used for questions 1–4, and the therapeutic scheme for question 5. Where differences in article ratings occurred, a third panel member determined the ultimate rating. Recommendations were developed by a modified Delphi process, and ratings of the recommendations (appendix e-6) were linked to the strength of the evidence as per the 2011 guideline development process.^e7 The recommendations are made by first assigning a confidence level to the evidence relative to each outcome that is deemed important. The confidence level depends on the class of studies available. The level of confidence is high if there are 2 Class I studies and very low if there are less than 2 Class III studies. Second, transparently discussed deductive principles and inferences are used to refine the level of recommendation. For instance, a Level B recommendation may be made if deductive inferences are convincing (>80% of the panel accepts them) as long as the confidence in the evidence is at least low (2 Class III studies).

Articles with descriptions of at least 3 patients were considered for inclusion. In instances of the initial description of a disorder, rare disorders, or rare manifestations of a disorder, we included studies with fewer than 3 patients. Studies were excluded if they reported group outcomes for more than one disorder and individual disorders could not be identified within the group. Genetic testing was necessary for confirmation of all diagnoses except BMD or manifest carriers of Duchenne muscular dystrophy (DMD), for which we accepted muscle biopsy immunohistochemistry/Western blot confirmation. Most often, the initial article describing the disorder did not have the gene defect identified, and therefore the article was not classified. However, these cross-referenced articles were reviewed in conjunction with the subsequent articles delineating the gene defect to obtain details of the clinical phenotype. For all questions, we classified the evidence by specific diseases: LGMD types 1A–E and 2A–P (autosomal dominant and recessive, respectively, where the gene/protein defects are known), distal myopathies, myofibrillar myopathies, EDMD, and hIBM. Because some LGMD gene defects may cause different phenotypes, the different disorders that are associated with the same gene defect are discussed together. It is also known that some protein defects can cause more severe phenotypes presenting early in childhood with congenital muscular dystrophy with or without brain involvement. We briefly state this when applicable but do not describe these phenotypes, as they will be addressed in forthcoming guidelines. We recognize that this classification is inherently artificial, because the phenotypes may merge with time. See page 174 of this document for an index of the diseases reviewed in this guideline and the pages on which they are discussed. Table e-1 and appendices e-1 through e-6 are available herein; figures e-1 and e-2 and table e-2 are available on the Neurology^® Web site at Neurology.org.
ANALYSIS OF EVIDENCE

Clinical Question 1: In a population of patients with suspected muscular dystrophy, what proportion of patients has a genetic defect confirming LGMD/distal myopathy/distal muscular dystrophy/BMD?

No articles were available for disorders due to genetic defects in DNAJB6, TRIM32, FHL1, MYH7, filamin C, VCP, matrin-3, selenoprotein, cavin, nebulin, nesprin, KLHL9, and Welander distal myopathies.

LGMD1A (myotilin). This is discussed below in the section on myofibrillar myopathies.
LGMD1B (lamin A/C, also causes autosomal dominant [AD]-EDMD). One Class I^e5 and 9 Class III studies^e8-e16 were reviewed. In a Class I population study of 1,105 patients with various genetic disorders of muscle, the frequency of LGMD1B/AD-EDMD was 8.8% (95% confidence interval [CI] 2.1–15.6), translating to a population prevalence of 0.2/100,000 (95% CI 0–0.4).^e5 In the 9 Class III studies, the frequency of laminopathy among patients with LGMD ranged from 0.9-4%. However, when looking at patients with idiopathic cardiomyopathy, mutations in lamin A/C were found in 8%–39% of cases.
LGMD1C (caveolin-3). Three Class III studies^e11,e13,e17 were reviewed. Caveolin-3 mutations were identified in 1.3%-2.6% of patients in these series.
LGMD1E (desmin). This is discussed below in the section on myofibrillar myopathies.
LGMD2A (calpain-3). There were 2 Class I studies^e5,e18 and 19 Class III studies.^{e11,e13,e17,e19-e34} Calpainopathies have been reported in patients of many ethnic backgrounds and from 6 continents. In a Class I study, the overall prevalence of calpainopathy among various genetic disorders of muscle was 0.6/100,000 (95% CI 0.3–0.9) and the prevalence among all LGMD cases was 18/68 or 26.5% (95% CI 16–37).^e5 In the other Class I study of 84 Italian patients with an unknown muscular dystrophy, 39 patients (46.4%) had calpainopathy and the prevalance was calculated to be 9.47 per million.^e18

In the 19 Class III studies, calpain-3 mutations accounted for 6%–57% of the LGMD, with the majority of series reporting 18.5%-35% of LGMD being calpainopathies. LGMD2A appeared to be the most common LGMD subtype in many published series in the Netherlands, England, Italy, Bulgaria, Spain, France, Turkey, Brazil, and Japan, and constituted 28.4% of known LGMD cases in northern Italy,^e17 26.5% in northern England,^e5 and 21% in the Netherlands.^e34

LGMD2B (dysferlin). One Class I study^e5 and 11 Class III studies^{e10,e11,e13,e17,e19,e20,e23,e24,e28,e35,e36} were reviewed. Two studies describe the same cohort,^e20,e24 with additional patients studied over time; therefore, the studies are reviewed together. A Class I study^e5 found the prevalence of dysferlin mutations to be 0.13/100,000. The total group was composed of 1,105 patients with various hereditary muscle diseases, of which LGMDs overall constituted 6.15% (68 cases). Dysferlinopathies comprised 4/68 (5.9%, 95% CI 0.3–11.5) LGMD cases. The 11 Class III studies reported a frequency of dysferlinopathy ranging from 0.6%–33% of the LGMDs.
LGMD2C (γ-sarcoglycan). Two Class I^e5,e37 and 16 Class III^{e10,e11,e13,e17,e19,e23,e24,e38-e46} studies were reviewed. A Class I study^e5 found the overall prevalence of γ-sarcoglycanopathy to be 1.3 per 1 million (0.13/100,000; 95% CI 0–0.3), forming 5.9% (95% CI 0.3–11.5) of the 1,105 patients with genetic muscle diseases. Another Class I study evaluated the genetic–epidemiologic aspects of primary sarcoglycanopathies in a geographic area in northeast Italy between 1982 and 1996.^e37 Muscle biopsies consistent with dystrophy and normal dystrophin were included in the analysis. Thirteen of 204 patients had a gene defect in one of the sarcoglycans. Four of the 13 were found to have γ-sarcoglycan gene defects (2 unrelated, 2 siblings) (4/204, 2%). The LGMD2C prevalence was 1.72 per 1 million.

The frequency of γ-sarcoglycanopathy in the 16 Class III studies ranged from 1.3%–13.2%. In those cases selected for abnormal expression of the sarcoglycans on immunohistochemistry, γ-sarcoglycan mutations were felt to be responsible in 7%–21%.

LGMD2D (α-sarcoglycan). Two Class I^e5,e37 and 14 Class III^{e10,e13,e17,e23,e24,e38-e40,e43-e48} studies were reviewed. One Class I study^e5 found the prevalence of α-sarcoglycanopathy to be 0.07 (95% CI 0–0.2) per 100,000. Another Class I study from Italy reported 7/204 (3.4%) patients as having α-sarcoglycan mutations. The prevalence of LGMD2C was 3.02 per million.^e37 The 14 Class III studies reported α-sarcoglycan mutations to be responsible for 3.3%–15% of LGMDs. Of those with reduced expression of sarcoglycans on immunohistochemistry staining, 34%–40% were deemed to be LGMD2D.
LGMD2E (ß-sarcoglycan). Two Class I^e5,e37 and 13 Class III^{e10,e11,e13,e17,e20,e23,e24,e38-e40,e43,e45,e46} studies were reviewed. One Class I study^e5 found the prevalence of β-sarcoglycanopathies to be 0.07/100,000. β-Sarcoglycanopathies comprised 2.9% of the total group of genetic muscle diseases (1,105), of which LGMD formed 6.15% (68 cases). Another Class I study evaluated the genetic–epidemiologic aspects of sarcoglycanopathies in a geographic area in northeast Italy.^e37 Two unrelated patients (2/204, 1%) were found to have β-sarcoglycan mutations; the prevalence of LGMD2E was 0.86/1000000.^e37 The 13 Class III studies reported β-sarcoglycan mutations to be responsible for 0%–23% of LGMDs, with most reporting about 4%. Of those with reduced expression of sarcoglycans on immunohistochemistry staining, 15%–43% were deemed to be LGMD2E.
LGMD2F (δ-sarcoglycan). Two Class I^e5,e37 and 12 Class III^{e10,e13,e17,e23,e24,e40,e43-e46,e49,e50} studies were reviewed. Neither Class I study reported δ-sarcoglycan mutations. The 12 Class III studies reported δ-sarcoglycan mutations to be responsible in 0%–14% of LGMDs, and approximately 8% of those cases had reduced sarcoglycan expression on immunohistochemistry.
LGMD2G (telethonin). Two Class III studies were reviewed.^e23,e51 In one Class III study of 63 unrelated patients with myofibrillar myopathy diagnosed by demonstration of myofibrillar degradation products and ectopic expression of multiple proteins on muscle biopsy, no mutations in the gene for telethonin were found.^e51 In another Class III study of 140 patients with LGMD from 40 families, telethonin mutations were shown in 6 patients (4.2%) in one family (2.5%).^e23
LGMD2I (FKRP). One Class I study,^e5 one Class II study,^e52 and 12 Class III studies^{e10,e11,e13,e17,e28,e32,e46,e53-e57} were reviewed. The Class I study^e5 found the prevalence of autosomal recessive FKRP mutations to be 0.43/100,000 (95% CI 0.2–0.7). Mutations involving FKRP were demonstrated in 19.1% (95% CI 9.8–28.5) of all genetic muscle diseases (1,105), 68 (6.15%) of which were LGMD. LGMD2I formed 19% of the LGMD group. In the Class II study, 2.0% (2/102) of consecutive unrelated German patients with persistent hyperCKemia were asymptomatic or minimally symptomatic (myalgia or fatigue), and 5.1% (5/98) of consecutive unrelated patients with LGMD2 had mutations in the FKRP gene.^e52 The 12 Class III studies found mutations in the FKRP gene in 4%–30% of LGMD.
LGMD2J (titin). One Class III study of 25 families and 25 sporadic cases of mainly distal myopathies revealed mutations in the titin gene in 4/25 (16%) families but in none of the sporadic cases.^e58
LGMD2K (POMT1). One Class III study of 92 patients with evidence of dystroglycanopathy based on muscle biopsy but negative genetic testing for FKRP mutations demonstrated that 8 patients (8.7%) had mutations in the POMT1 gene.^e59 These included the following phenotypes and distributions: Walker-Warburg syndrome (WWS) (1/8), muscle-eye-brain disease/Fukuyama congenital muscular dystrophy (MEB/FCMD) (1/8), congenital muscular dystrophy with intellectual disability (mental retardation) (CMD-MR) (3/8), and LGMD with intellectual disability (mental retardation) (LGMD-MR) (3/8).
LGMD2L (anoctamin-5). Two Class III studies were identified.^e60,e61 In one Class III study of 64 British and German patients from 59 families with either a limb-girdle or Miyoshi myopathy phenotype without dysferlin mutations, 20 patients (31.3%) from 15 (25.4%) families had a mutation in the anoctamin-5 gene.^e60 In another Class III study of 101 Finnish patients with undetermined LGMD, calf distal myopathy, or CK elevations more than 2,000 IU/L, 25 patients (24.8%) were identified with anoctamin-5 gene mutations.^e61
LGMD2M (fukutin). One Class III study of 92 patients with evidence of dystroglycanopathy based on muscle biopsy but negative genetic testing for FKRP mutations demonstrated that 6 patients (6.5%) had mutations in the fukutin gene.^e59 These included the following phenotypes and distributions: WWS (1/6), MEB/FCMD (1/6), CMD without intellectual disability (mental retardation) (CMD-noMR) (1/6), and LGMD without intellectual disability (mental retardation) (LGMD-noMR) (3/6).
LGMD2N (POMT2). One Class III study of 92 patients with evidence of dystroglycanopathy based on muscle biopsy but negative genetic testing for FKRP mutations demonstrated that 9 patients (9.7%) had mutations in the POMT2 gene.^e59 These included the following phenotypes and distributions: MEB/FCMD (6/9), CMD with cerebellar ataxia (2/9), and LGMD-MR (1/9).
LGMD2O (POMGNT1). One Class III study of 92 patients with evidence of dystroglycanopathy based on muscle biopsy but negative genetic testing for FKRP mutations demonstrated that 7 patients (7.6%) had mutations in the POMGNT1 gene.^e59 Six of the 7 patients had MEB/FCMD and 1 had LGMD-noMR.
BMD. Five Class I^e5,e62-e65 and 5 Class III^e10,e66-e69 studies were reviewed. One Class I study identified 79 patients with BMD residing in the Northern Health Region of England by searching the clinical and muscle biopsy records.^e62 The minimum prevalence was estimated to be 2.38/100,000. A Class I epidemiologic study in the territory of Northwest Tuscany, central Italy, estimated the incidence of BMD to be 2.42 x 10^-5 male live births.^e63 Thirty-one percent of patients with LGMD (32/103) from 29 families were found to be affected by BMD. Another Class I study examined the prevalence of BMD in a geographically isolated area of Okinawa, Japan.^e64 The prevalence was estimated to be 1.82 x 10^-5 in the male population. The incidence of BMD in the period from 1957–1985 was 3.21 x 10^-5 live-born males. However, this study may underestimate the prevalence and incidence because patients with BMD were diagnosed only on the basis of immunohistochemical analysis of muscle biopsies; Western blots were not performed. In another Class I study, 109 of 1,105 (9.9%, 95% CI 8.1–11.6) patients with inherited muscle diseases carried the diagnosis of BMD, with an estimated prevalence of 7.29/100,000 males (95% CI 5.9–8.7).^e5 The last Class I study analyzed 3,048 muscle biopsies processed by the National Institute of Neuroscience in Tokyo and identified 41 patients as having LGMD.^e65 Among those, 5 patients (12%) had BMD. Population prevalence was not provided. The 5 Class III studies reported the frequency of BMD to be 1.6%–55.6% of patients presenting with limb-girdle weakness.
Duchenne/Becker manifesting carriers. Four studies, 2 Class I^e5,e65 and 2 Class III,^e67,e70 were reviewed. One Class I study^e5 found the prevalence of Duchenne/Becker manifest carriers to be 13/1,105 (1.2%) (95% CI 0.5–1.8), corresponding to a population prevalence of 0.43/100,000 (95% CI 0.2–0.7). In one Class I study of 3,048 Japanese patients with a diagnosis of LGMD based on clinical and histopathologic criteria, only 2 women had evidence of dystrophinopathy on immunohistochemistry.^e65 In one of the Class III studies, in which 201 biopsies were reanalyzed using dystrophin immunoblot, 1/4 females with unclassified congenital myopathies (25%), 1/20 females with unclassified myopathies (5%), and 5/9 females (56%) with hyperCKemia were diagnosed as being manifest dystrophinopathy carriers.^e67 The other Class III study retrospectively looked at 169 Israeli families with members affected by progressive muscular dystrophy. Molecular analysis was performed on 106 DMD and 5 BMD families, with 81 available probands. The investigators were able to exclude a diagnosis of DMD/BMD on the basis of clinical symptoms and signs (49 families), or normal dystrophin on biopsy and/or the absence of linkage to chromosome X by analysis of restriction fragment length polymorphism–derived haplotypes (11 families).^e70
Emerin. Two Class III studies were reviewed.^e10,e13 In one study of 550 patients with the clinical diagnosis of childhood or adult LGMD, distoproximal myopathy, or hyperCKemia, emerin mutations were seen in 2/550 (0.4%). There were 346 patients with LGMD, for a frequency of 0.6% of all LGMD.^e13 Another study found 2 of 370 patients with muscular dystrophy to have genetically confirmed X-linked EDMD, for a frequency of 0.54% of patients referred with a diagnosis of LGMD.^e10
Transmembrane protein 43 (TMEM43) encoding LUMA/EDMD5. A Class III study of 41 patients with the EDMD phenotype identified 2 patients with the heterozygous missense mutations p.Glu85Lys and p.Ile91Val in TMEM43.^e71
Myofilbrillar myopathies. The term myofibrillar myopathy (MFM) refers to a group of myopathies characterized by the following specific histologic features: (1) amorphous, hyaline, or granular material in the muscle fibers on trichrome-stained sections; (2) decreased oxidative enzyme activity in many abnormal fiber regions; (3) congophilia of the hyaline structures; (4) small rimmed vacuoles; and (5) myofibrillar degeneration on electron microscopy (EM).^e51 The disorder is genetically heterogeneous. In this section we discuss all MFMs with identified genetic defects.
Myotilin (also LGMD1A). One Class I study^e5 and 3 Class III studies^e8-e10 were reviewed. In a Class I population study of patients with muscular dystrophy in northern England, 1,105 cases registered and followed by the neuromuscular team at the Institute of Human Genetics, Newcastle University were studied. Diagnoses were obtained in 836 patients (75.7%). The combined prevalence of inherited myopathies was 37/100,000. LGMD comprised the fifth major category, with 68/1,105 cases, or 6.15%. No cases of LGMD1A were identified. However, 2 patients diagnosed with MFM had a mutation in the myotilin gene. This corresponds to a frequency of 0.18% (95% CI 0–0.4) of the clinic population, for a point prevalence in the population of 0.07 (95% CI 0–0.2) per 100,000.^e5 In a Class III study, 6/57 (10.5%) families with MFM were found to carry myotilin mutations.^e9 A large multicenter Class III study enrolled 370 patients with LGMD from 337 families. Genotype analysis was directed by the phenotype and muscle biopsy protein abnormalities. Of 297 patients, one was found to have myotilinopathy, for a frequency of <1%. However, because only 179/297 patients had undergone mutation analysis at the time of publication, it is possible that this number is an underestimate.^e10 In another Class III study, 44 families with LGMD1, 14 with LGMD2, 24 with facioscapulohumeral dystrophy, 2 with scapuloperoneal dystrophy, and 2 with unclassified autosomal dominant dystrophies were screened for myotilin gene mutations. A myotilin gene mutation was found in one Argentinian family, for a frequency of 1/58 families with LGMD (1.7%).^e8
Desmin (also LGMD1E). One Class I study^e5 and one Class III study^e51 were reviewed. The Class I study reported the prevalence of desminopathy to be 0.17/100,000 (95% CI 0–0.3).^e5 In the Class III study, desminopathy was seen in 4/63 (6.3%) unrelated patients with MFM.^e51
αB-Crystallin. One Class III study was reviewed.^e51 Two of 63 patients (3%) with MFM were found to carry a mutation in CRYAB.
Z-band alternatively spliced PDZ motif-containing protein (ZASP) (also known as Markesbery-Griggs distal myopathy). One Class III study was reviewed.^e72 Among 54 unrelated MFM patients without mutations in desmin, αB-crystallin, or myotilin, 11 patients (20.3%) were found to carry a mutation in LDB3, the gene that encodes ZASP.

BCL2-associated athanogene 3 (BAG3). One Class III study was reviewed.^e73 Among 53 unrelated MFM patients without mutations in desmin, αB-crystallin, myotilin, ZASP, or filamin C, 3 patients (5.6%) were found to carry a mutation in BAG3.
Autosomal recessive hIBM/Nonaka myopathy. Glucosamine (UDP-N-acetyl)-2-epimerase/N-acetylmannosamine kinase (GNE) quadriceps-sparing myopathy. Two Class III studies were reviewed.^e10,e74 A large multicenter Class III study enrolled 370 patients with LGMD from 337 families. Genotype analysis was directed by the phenotype and muscle biopsy protein abnormalities. One of 297 patients was found to have a mutation in the GNE gene, for a frequency of <1%. However, because only 179/297 patients had undergone mutation analysis at the time of publication, it is possible that this number is an underestimate.^e10 In another Class III study, 92 of 1,000 (9.2%) Persian Jewish volunteers in Israel demonstrated heterozygous mutations in the GNE gene and therefore carrier status for hIBM.^e74