Two emerging phenotypes of atypical inclusion body myositis: illustrative cases

OBJECTIVES: Sporadic inclusion body myositis (IBM) is the most common acquired myopathy in those aged above 50. It is classically heralded by weakness in the long finger flexors and quadriceps. The aim of this article is to describe five atypical cases of IBM, outlining two potential emerging clinical subsets of the disease. METHODS: We reviewed relevant clinical documentation and pertinent investigations for five patients with IBM. RESULTS: The first phenotype we describe is young-onset IBM in two patients who had symptoms since their early thirties. The literature supports that IBM can rarely present in this age range or younger. We describe a second phenotype in three middle-aged women who developed early bilateral facial weakness at presentation in tandem with dysphagia and bulbar impairment followed by respiratory failure requiring non-invasive ventilation (NIV). Within this group, two patients were noted to have macroglossia, another possible rare feature of IBM. CONCLUSIONS: Despite the classical phenotype described within the literature IBM can present in a heterogenous fashion. It is important to recognise IBM in younger patients and investigate for specific associations. The described pattern of facial diplegia, severe dysphagia, bulbar dysfunction and respiratory failure in female IBM patients requires further characterisation. Patients with this clinical pattern may require more complex and supportive management. Macroglossia is a potentially under recognised feature of IBM. The presence of macroglossia in IBM warrants further study, as its presence may lead to unnecessary investigations and delay diagnosis

Misdiagnosis is an important factor for diagnostic delay in McArdle disease

Diagnosis of McArdle disease is frequently delayed by many years following the first presentation of symptoms to a health professional. The aim of this study was to investigate the importance of misdiagnosis in delaying diagnosis of McArdle disease. The frequency of misdiagnosis, duration of diagnostic delay, categories of misdiagnoses and inappropriate medical interventions were assessed in 50 genetically confirmed patients. The results demonstrated a high frequency of misdiagnosis (90%, n = 45/50) most commonly during childhood years (67%; n = 30/45) compared with teenage years and adulthood (teenage: n = 7/45; adult n = 5/45; not known n = 3/45). The correct diagnosis of McArdle disease was rarely made before adulthood (median age of diagnosis 33 years). Thirty-one patients (62%) reported having received more than one misdiagnosis; the most common were “growing pains” (40%, n = 20) and “laziness/being unfit” (46%, n = 23). A psychiatric/psychological misdiagnosis was significantly more common in females than males (females 6/20; males 1/30; p < 0.01). Of the 45 patients who were misdiagnosed, 21 (47%) received incorrect management. This study shows that most patients with McArdle disease received an incorrect explanation of their symptoms providing evidence that misdiagnosis plays an important part in delaying implementation of appropriate medical advice and management to this group of patients.The authors would like to thank Mr Andrew Wakelin for his great and inspiring work. The authors would also like to thank AGSD-UK, CAPES Foundation, Muscular Dystrophy Campaign and the Euromac Registry for their support

Mutations in GDP-mannose pyrophosphorylase b cause congenital and limb-girdle muscular dystrophies associated with hypoglycosylation of α-dystroglycan

Congenital muscular dystrophies with hypoglycosylation of α-dystroglycan (α-DG) are a heterogeneous group of disorders often associated with brain and eye defects in addition to muscular dystrophy. Causative variants in 14 genes thought to be involved in the glycosylation of α-DG have been identified thus far. Allelic mutations in these genes might also cause milder limb-girdle muscular dystrophy phenotypes. Using a combination of exome and Sanger sequencing in eight unrelated individuals, we present evidence that mutations in guanosine diphosphate mannose (GDP-mannose) pyrophosphorylase B (GMPPB) can result in muscular dystrophy variants with hypoglycosylated α-DG. GMPPB catalyzes the formation of GDP-mannose from GTP and mannose-1-phosphate. GDP-mannose is required for O-mannosylation of proteins, including α-DG, and it is the substrate of cytosolic mannosyltransferases. We found reduced α-DG glycosylation in the muscle biopsies of affected individuals and in available fibroblasts. Overexpression of wild-type GMPPB in fibroblasts from an affected individual partially restored glycosylation of α-DG. Whereas wild-type GMPPB localized to the cytoplasm, five of the identified missense mutations caused formation of aggregates in the cytoplasm or near membrane protrusions. Additionally, knockdown of the GMPPB ortholog in zebrafish caused structural muscle defects with decreased motility, eye abnormalities, and reduced glycosylation of α-DG. Together, these data indicate that GMPPB mutations are responsible for congenital and limb-girdle muscular dystrophies with hypoglycosylation of α-DG. © 2013 The American Society of Human Genetics.Funding for UK10K was provided by the Wellcome Trust under award WT091310

Heart rate and perceived muscle pain responses to a functional walking test in McArdle disease

The aim of this study was to assess a 12-min self-paced walking test in patients with McArdle disease. Twenty patients (44.7 ±11 years; 11 female) performed the walking test where walking speed, distance walked, heart rate (HR) and perceived muscle pain (Borg CR10 scale) were measured. Median (interquartile range) distance walked was 890 m (470–935). From 1 to 6 min, median walking speed decreased (from 75.0 to 71.4 m∙min–1) while muscle pain and %HR reserve increased (from 0.3 to 3.0 and 37% to 48%, respectively). From 7 to 12 min, walking speed increased to 74.2 m∙min–1, muscle pain decreased to 1.6 and %HR reserve remained between 45% and 48%. To make relative comparisons, HR and muscle pain were divided by walking speed and expressed as ratios. These ratios rose significantly between 1 and 6 min (HR:walking speed P = .001 and pain:walking speed P < .001) and similarly decreased between 6 and 11 min (P = .002 and P = .001, respectively). Peak ratios of HR:walking speed and pain:walking speed were inversely correlated to distance walked: rs (HR) = −.82 (P < .0001) and rs (pain) = −.55 (P = .012). Largest peak ratios were found in patients who walked < 650 m. A 12-min walking test can be used to assess exercise capacity and detect the second wind in McArdle disease

236th ENMC International Workshop Bone protective therapy in Duchenne muscular dystrophy: Determining the feasibility and standards of clinical trials Hoofddorp, The Netherlands, 1–3 June 2018

On 1–3 June 2018, the 236th European Neuromuscular Centre workshop was held in Hoofddorp, The Netherlands, to discuss the issue of bone protective therapies in Duchenne muscular dystrophy (DMD), in particular, the feasibility of developing clinical trials. Twenty-six delegates, that included 19 experts in the neuromuscular and bone clinical and research fields, three representatives from patient organizations, two adults with DMD and two representatives from industry, attended this workshop

McARDLE DISEASE: P.115 Natural history of McArdle disease in a cohort of 220 patients

McArdle disease is caused by recessive mutations in the gene encoding muscle glycogen phosphorylase (MGP) which results in enzyme deficiency. The condition is considered to cause a 'pure' muscle phenotype with symptoms including: exercise intolerance, inability to perform isometric activities. Known associated complications include: hyperuricaemia and gout, acute rhabdomyolysis with myoglobinuria leading to compartment syndrome and acute renal failure. We retrospectively assessed case records of 220 patients with genetically confirmed McArdle disease from 2011-2019 and will report data relating to genotype, phenotype (including frequency of known associated complications) and functional capacity based upon a 12 minute walking test. We will also report results of prospective screening for other 'unexpected' co-morbidities in our cohort including the frequency of cardiovascular disease, thyroid disease and pattern retinal dystrophy. We also assessed the frequency of other systemic disorders. Our data suggest that MGP deficiency is not such a benign condition and may be associated with systemic issues beyond the skeletal muscles. The role of MGP in both skeletal and non-skeletal muscle tissues may give a clue as to the underlying pathogenesis of these co-morbidities. Prospective regular monitoring of these patients may be worthwhile.Sin financiación3.115 JCR (2019) Q3, 76/204 Clinical Neurology1.177 SJR (2019) Q1, 85/378 Neurology (clinical)No data IDR 2019UE

Creation and implementation of a European registry for patients with McArdle disease and other muscle glycogenoses (EUROMAC registry)

International patient registries are of particular importance for rare disorders, as they may contribute to overcome the lack of knowledge derived from low number of patients and limited awareness of these diseases, and help to learn more about their geographical or population-based specificities, which is relevant for research purposes and for promoting better standards of care and diagnosis. Our objective was to create and implement a European registry for patients with McArdle disease and other muscle glycogenoses (EUROMAC) and to disseminate the knowledge of these disorders. Teams from nine different countries (United Kingdom, Spain, Italy, France, Germany, Denmark, Greece, Turkey and USA) created a consortium that developed the first European registry dedicated to rare muscle glycogenoses. A work plan was implemented to design the database and platform that constitute the registry, by choosing clinical, genetics and molecular variables of interest, based on experience gained from previous national registries for similar metabolic disorders. Among dissemination activities, several teaching events were organized in different countries, especially those where the consortium considered the awareness of these diseases needs to be promoted among health professionals and patients. EUROMAC represents a step forward in the knowledge of those disorders to which it is dedicated, and will have relevant clinical outcomes at the diagnostic, epidemiological, clinical and research leve

EUROMAC: Disease registry for McArdle disease and other pure muscle glycogenolytic disorders presenting with exercise intolerance

4.055 JCR (2014) Q1, 27/192 Clinical neurology, 61/252 NeurosciencesUE

P.357 - The EUROMAC registry for rare glycogen storage diseases: preliminary report

Sin financiación2.487 JCR (2017) Q2, 108/197 Clinical Neurology, 170/261 Neurosciences1.337 SJR (2017) Q1, 81/378 Neurology (clinical), 30/308 Pediatrics, Perinatology and Child Health; Q2, 36/103 Genetics (clinical), 47/167 NeurologyNo data IDR 2017UE