Miyoshi myopathy and limb girdle muscular dystrophy R2 are the same disease

Metabolic dysregulation contributes to the development of dysferlinopathy

Dysferlin is a transmembrane protein that plays a prominent role in membrane repair of damaged muscle fibers. Accordingly, mutations in the dysferlin gene cause progressive muscular dystrophies, collectively referred to as dysferlinopathies for which no effective treatment exists. Unexpectedly, experimental approaches that successfully restore membrane repair fail to prevent a dystrophic phenotype, suggesting that additional, hitherto unknown dysferlin-dependent functions contribute to the development of the pathology. Our experiments revealed an altered metabolic phenotype in dysferlin-deficient muscles, characterized by (1) mitochondrial abnormalities and elevated death signaling and (2) increased glucose uptake, reduced glycolytic protein levels, and pronounced glycogen accumulation. Strikingly, elevating mitochondrial volume density and muscle glycogen accelerates disease progression; whereas, improvement of mitochondrial function and recruitment of muscle glycogen with exercise ameliorated functional parameters in a mouse model of dysferlinopathy. Collectively, our results not only shed light on a metabolic function of dysferlin but also imply new therapeutic avenues aimed at promoting mitochondrial function and normalizing muscle glycogen to ameliorate dysferlinopathies, complementing efforts that target membrane repair.

Muscle MRI Pattern in Dysferlinopathy and its Correlation with Dysferlin Gait

BACKGROUND AND OBJECTIVES

Magnetic resonance imaging (MRI) in dysferlinopathy has consistently demonstrated a particular pattern of affliction. We aimed to study muscle MRI characteristics of lower limbs in limb girdle muscular dystrophy (LGMD)-R2 phenotypes and correlate them with the gait pattern.

METHODS

Forty genetically and/or biopsy-proven cases of dysferlinopathy underwent muscle MRI of the lower limbs. The pattern and extent of fatty infiltration and edema were recorded. Spearman's correlation analysis was used to find the correlation between muscle involvement and demographics, duration of illness, Muscular Dystrophy Functional Rating Scale (MDFRS), genotype, and gait pattern.

RESULTS

Mean age at onset and duration of illness at evaluation were 21.5 ± 6.3 years and 7.15 ± 4.95 years, respectively. Male: Female of patients was 2:1. Long head of biceps femoris was most severely involved with relative sparing of short head. Specific MRI pattern was noted based on phenotype, though no genotypic correlation was observed. Adductor magnus and semimembranosus were more severely involved in LGMD and proximodistal (PD) forms compared to Miyoshi muscular dystrophy type 1 phenotype. In addition, tibialis posterior and extensor hallucis longus were more severely involved in PD compared to MM and LGMD phenotypes. MDFRS mobility domain and duration of illness correlated with MRI findings. Gait pattern analysis revealed more severe involvement of flexor hallucis longus compared to extensor hallucis longus.

CONCLUSIONS

Muscle involvement differed based on the phenotype. Characteristic great toe extension in PD phenotype showed an imaging correlation with more severe involvement of flexor hallucis longus compared to extensor hallucis longus. Thus, imaging can be a potential biomarker to study the evolution and severity of disease in dysferlinopathy.

Rapid Quantitative Assessment of Muscle Sodium Dynamics After Exercise Using 23Na-MRI in Dysferlinopathy and Healthy Controls

BACKGROUND

Dysferlin plays a key role in cell membrane repair; its absence or malfunction in patients with dysferlin-deficient limb girdle muscular dystrophy leads to muscle fibre death. Muscle magnetic resonance (MR) imaging allows non-invasive and repeatable measurements that can report on pathological changes observed in dysferlinopathy patients (DP). We aimed to demonstrate the feasibility of utilising volume-localised 23Na spectroscopy as a novel approach to characterise muscle Na+ content and biexponential T2* at rest, and dynamically post-exercise, in patients with dysferlinopathy and in matched healthy controls.

METHODS

Adult DP and age and sex matched healthy volunteers (HV) were recruited and scanned on a 3 T clinical MR scanner. Following baseline scans, participants performed physiotherapist-guided isometric dorsiflexion contractions until tibialis anterior (TA) muscle exhaustion. Dynamic volume-localised sodium-23 (23Na)- and proton (1H)-MR scans were acquired serially for 35 min post-exercise. MR data were analysed to determine TA lipid content, change in TA sodium content, biexponential sodium T2* properties and TA water 1H T2.

RESULTS

Ten DP (mean age ± standard deviation [SD]: 38.0 ± 10.8 years; 80% female) and 10 HV (mean age ± SD: 38.9 ± 11.5 years) were scanned. Baseline muscle water 1H T2 and sodium concentration were significantly higher in DP compared to matched controls (1H T2 DP [SD] = 33.8 [2.7] ms, 1H T2 HV = 29.3 [1.1] ms, p < 0.001; [23Na]DP = 36.2 [11.4] mM, [23Na]HV = 19.6 [3.1] mM, p < 0.001). 1H T2 and sodium content in healthy controls showed significant post-exercise elevation with a slower time-to-peak for sodium content compared to 1H T2. 1H T2 and sodium content change post-exercise was highly variable in the DP group. Notably, 23Na dynamics in one DP with normal muscle fat fraction were similar to HV. Biexponential 23Na T2* was measured at baseline in HV (T2*slow = 13.4 [2.3] ms, T2*fast = 2.2 [1.3] ms), and DP (T2*slow = 14.0 [1.5] ms and T2*fast = 1.0 [0.5] m). Equivalent measurements post-exercise revealed an increase in the fraction of the slow-relaxing component in HV (p < 0.05), consistent with oedematous changes.

CONCLUSIONS

Assessment of TA muscle fat fraction, 1H T2, sodium content and sodium T2* relaxation properties revealed differences at baseline and in post-exercise dynamics between patients with dysferlinopathy and matched controls. Post-exercise 23Na recovery dynamics followed a well-defined time course in HV. Heterogeneous alterations in sodium content and MR relaxation properties in DP may reflect altered ion homeostasis associated with chronic muscle damage.

Performance of upper limb entry item to predict forced vital capacity in dysferlin-deficient limb girdle muscular dystrophy

Dysferlin-deficient limb girdle muscular dystrophy (LGMD R2), also referred to as dysferlinopathy, can be associated with respiratory muscle weakness as the disease progresses. Clinical practice guidelines recommend biennial lung function assessments in patients with dysferlinopathy to screen for respiratory impairment. However, lack of universal access to spirometry equipment and trained specialists makes regular monitoring challenging. This study investigated the use of the Performance of Upper Limb (PUL) clinical scale entry item as a low-cost screening tool to identify patients with dysferlinopathy at risk of respiratory impairment. Using data from 193 patients from the Jain Foundation's International Clinical Outcomes Study, modelling identified a significant positive relationship between the PUL entry item and forced vital capacity (FVC). Eighty-eight percent of patients with the lowest PUL entry item score of 1 presented with FVC % predicted values of <60 %, suggestive of respiratory impairment. By contrast, only 10 % of the remainder of the cohort (PUL entry item of 2 or more) had an FVC of <60 %. This relationship also held true when accounting for ambulatory status, age, and sex as possible confounding factors. In summary, our results suggest that the PUL entry item could be implemented in clinical practice to screen for respiratory impairment where spirometry is not readily available.

MRI for the diagnosis of limb girdle muscular dystrophies

PURPOSE OF REVIEW

In the last 30 years, there have many publications describing the pattern of muscle involvement of different neuromuscular diseases leading to an increase in the information available for diagnosis. A high degree of expertise is needed to remember all the patterns described. Some attempts to use artificial intelligence or analysing muscle MRIs have been developed. We review the main patterns of involvement in limb girdle muscular dystrophies (LGMDs) and summarize the strategies for using artificial intelligence tools in this field.

RECENT FINDINGS

The most frequent LGMDs have a widely described pattern of muscle involvement; however, for those rarer diseases, there is still not too much information available. patients. Most of the articles still include only pelvic and lower limbs muscles, which provide an incomplete picture of the diseases. AI tools have efficiently demonstrated to predict diagnosis of a limited number of disease with high accuracy.

SUMMARY

Muscle MRI continues being a useful tool supporting the diagnosis of patients with LGMD and other neuromuscular diseases. However, the huge variety of patterns described makes their use in clinics a complicated task. Artificial intelligence tools are helping in that regard and there are already some accessible machine learning algorithms that can be used by the global medical community.

Clinical description of a homozygous Lys 1169* variant in the DYSF gene associated with autosomal recessive Miyoshi muscular dystrophy type 1: A familial case report

Miyoshi Muscular Dystrophy Type 1 is a rare autosomal recessive myopathy caused by mutations in the dysferlin (DYSF) gene. This disease presents with progressive distal lower limb weakness, such as gastrocnemius and soleus muscles resulting in difficulty standing on tiptoes, walking, and climbing stairs. We describe a family consisting of 6 siblings, 2 affected males, 1 affected female, 1 affected-death female, and 2 unaffected females. The affected members of this family have lived without an appropriate diagnosis for more than 20 years. Our patients have a homozygous nonsense pathogenic variant of the DYSF gene with 0 frequency in the Genome Aggregation Database. Our study shows that genetic testing provides a crucial aid to doctors when the physical examination and the clinical history are insufficient. It also emphasizes that a precise and accurate diagnosis prompts the correct management of a complex case.

Pilot investigations into the mechanistic basis for adverse effects of glucocorticoids in dysferlinopathy

BACKGROUND

Dysferlinopathies are a clinically heterogeneous group of muscular dystrophies caused by gene mutations resulting in deficiency of the membrane-associated protein dysferlin. They manifest post-growth and are characterised by muscle wasting (primarily in the limb and limb-gridle muscles), inflammation, and replacement of myofibres with adipose tissue. The precise pathomechanism for dysferlinopathy is currently unclear; as such there are no treatments currently available. Glucocorticoids (GCs) are widely used to reduce inflammation and treat muscular dystrophies, but when administered to patients with dysferlinopathy, they have unexpected adverse effects, with accelerated loss of muscle strength.

METHODS

To investigate the mechanistic basis for the adverse effects of GCs in dysferlinopathy, the potent GC dexamethasone (Dex) was administered for 4-5 weeks (0.5-0.75 µg/mL in drinking water) to dysferlin-deficient BLA/J and normal wild-type (WT) male mice, sampled at 5 (Study 1) or 10 months (Study 2) of age. A wide range of analyses were conducted. Metabolism- and immune-related gene expression was assessed in psoas muscles at both ages and in quadriceps at 10 months of age. For the 10-month-old mice, quadriceps and psoas muscle histology was assessed. Additionally, we investigated the impact of Dex on the predominantly slow and fast-twitch soleus and extensor digitorum longus (EDL) muscles (respectively) in terms of contractile function, myofibre-type composition, and levels of proteins related to contractile function and metabolism, plus glycogen.

RESULTS

At both ages, many complement-related genes were highly expressed in BLA/J muscles, and WT mice were generally more responsive to Dex than BLA/J. The effects of Dex on BLA/J mice included (i) increased expression of inflammasome-related genes in muscles (at 5 months) and (ii) exacerbated histopathology of quadriceps and psoas muscles at 10 months. A novel observation was pronounced staining for glycogen in many myofibres of the damaged quadriceps muscles, with large pale vacuolated myofibres, suggesting possible myofibre death by oncosis.

CONCLUSION

These pilot studies provide a new focus for further investigation into the adverse effects of GCs on dysferlinopathic muscles.

Nanodysferlins support membrane repair and binding to TRIM72/MG53 but do not localize to t-tubules or stabilize Ca2+ signaling

Mutations in the DYSF gene, encoding the protein dysferlin, lead to several forms of muscular dystrophy. In healthy skeletal muscle, dysferlin concentrates in the transverse tubules and is involved in repairing the sarcolemma and stabilizing Ca2+ signaling after membrane disruption. The DYSF gene encodes 7-8 C2 domains, several Fer and Dysf domains, and a C-terminal transmembrane sequence. Because its coding sequence is too large to package in adeno-associated virus, the full-length sequence is not amenable to current gene delivery methods. Thus, we have examined smaller versions of dysferlin, termed "nanodysferlins," designed to eliminate several C2 domains, specifically C2 domains D, E, and F; B, D, and E; and B, D, E, and F. We also generated a variant by replacing eight amino acids in C2G in the nanodysferlin missing domains D through F. We electroporated dysferlin-null A/J mouse myofibers with Venus fusion constructs of these variants, or as untagged nanodysferlins together with GFP, to mark transfected fibers We found that, although these nanodysferlins failed to concentrate in transverse tubules, three of them supported membrane repair after laser wounding while all four bound the membrane repair protein, TRIM72/MG53, similar to WT dysferlin. By contrast, they failed to suppress Ca2+ waves after myofibers were injured by mild hypoosmotic shock. Our results suggest that the internal C2 domains of dysferlin are required for normal t-tubule localization and Ca2+ signaling and that membrane repair does not require these C2 domains.

Magnetic resonance imaging-based criteria to differentiate dysferlinopathy from other genetic muscle diseases

The identification of disease-characteristic patterns of muscle fatty replacement in magnetic resonance imaging (MRI) is helpful for diagnosing neuromuscular diseases. In the Clinical Outcome Study of Dysferlinopathy, eight diagnostic rules were described based on MRI findings. Our aim is to confirm that they are useful to differentiate dysferlinopathy (DYSF) from other genetic muscle diseases (GMD). The rules were applied to 182 MRIs of dysferlinopathy patients and 1000 MRIs of patients with 10 other GMD. We calculated sensitivity (S), specificity (Sp), positive and negative predictive values (PPV/NPV) and accuracy (Ac) for each rule. Five of the rules were more frequently met by the DYSF group. Patterns observed in patients with FKRP, ANO5 and CAPN3 myopathies were similar to the DYSF pattern, whereas patterns observed in patients with OPMD, laminopathy and dystrophinopathy were clearly different. We built a model using the five criteria more frequently met by DYSF patients that obtained a S 95.9%, Sp 46.1%, Ac 66.8%, PPV 56% and NPV 94% to distinguish dysferlinopathies from other diseases. Our findings support the use of MRI in the diagnosis of dysferlinopathy, but also identify the need to externally validate "disease-specific" MRI-based diagnostic criteria using MRIs of other GMD patients.

Characteristics of the muscle involvement along the disease progression in a large cohort of oculopharyngodistal myopathy compared to oculopharyngeal muscular dystrophy

BACKGROUND AND OBJECTIVES

Oculopharyngodistal myopathy (OPDM) is an autosomal dominant myopathy clinically characterized by distal muscle weakness. Even though the identification of four causative genes, LRP12, GIPC1, NOTCH2NLC and RILPL1, it is unclear whether the myopathy progressed similarly among OPDM subtypes. We aimed to establish diagnostic clues in muscle imaging of OPDM in comparison with clinicopathologically similar oculopharyngeal muscular dystrophy (OPMD).

METHODS

Axial muscle CT and/or T1-weighted MRI data from 54 genetically confirmed patients with OPDM (OPDM_LRP12; n = 43, OPDM_GIPC1; n = 6, OPDM_NOTCH2NLC; n = 5) and 57 with OPMD were evaluated. We scored the degree of fat infiltration in each muscle by modified Mercuri score and performed hierarchical clustering analyses to classify the patients and infer the pattern of involvement on progression.

RESULTS

All OPDM subtypes showed a similar pattern of distribution in the affected muscles; soleus and medial gastrocnemius involved in the early stage, followed by tibialis anterior and extensor digitorum longus. For differentiating OPDM and OPMD, severely affected gluteus medius/minimus and adductor magnus was indicative of OPMD.

DISCUSSION

We identified a diagnostic muscle involvement pattern in OPDM reflecting its natural history. The results of this study will help in the appropriate intervention based on the diagnosis of OPDM, including its stage.

Patterns of Clinical Progression Among Patients With Autosomal Recessive Limb-Girdle Muscular Dystrophy: A Systematic Review

OBJECTIVES

As the clinical course of autosomal recessive limb-girdle muscular dystrophy (LGMDR) is highly variable, this study characterized the frequency of loss of ambulation (LOA) among patients by subtype (LGMDR1, LGMDR2, LGMDR3-6, LGMDR9, LGMDR12) and progression to cardiac and respiratory involvement among those with and without LOA.

METHODS

Systematic literature review.

RESULTS

From 2929 abstracts screened, 418 patients were identified with ambulatory status data (LOA: 265 [63.4%]). Cardiac and/or respiratory function was reported for 142 patients (34.0%; all with LOA). Among these, respiratory involvement was most frequent in LGMDR3-6 (74.1%; mean [SD] age 23.9 [11.0] years) and cardiac in LGMDR9 (73.3%; mean [SD] age 23.7 [17.7] years). Involvement was less common in patients without LOA except in LGMDR9 (71.4% respiratory and 52.4% cardiac).

CONCLUSIONS

This study described the co-occurrence of LOA, cardiac, and respiratory involvement in LGMDR and provides greater understanding of the clinical progression of LGMDR.

Portrait of Dysferlinopathy: Diagnosis and Development of Therapy

Dysferlinopathy is a disease caused by a dysferlin deficiency due to mutations in the DYSF gene. Dysferlin is a membrane protein in the sarcolemma and is involved in different functions, such as membrane repair and vesicle fusion, T-tubule development and maintenance, Ca2+ signalling, and the regulation of various molecules. Miyoshi Myopathy type 1 (MMD1) and Limb-Girdle Muscular Dystrophy 2B/R2 (LGMD2B/LGMDR2) are two possible clinical presentations, yet the same mutations can cause both presentations in the same family. They are therefore grouped under the name dysferlinopathy. Onset is typically during the teenage years or young adulthood and is characterized by a loss of Achilles tendon reflexes and difficulty in standing on tiptoes or climbing stairs, followed by a slow progressive loss of strength in limb muscles. The MRI pattern of patient muscles and their biopsies show various fibre sizes, necrotic and regenerative fibres, and fat and connective tissue accumulation. Recent tools were developed for diagnosis and research, especially to evaluate the evolution of the patient condition and to prevent misdiagnosis caused by similarities with polymyositis and Charcot-Marie-Tooth disease. The specific characteristic of dysferlinopathy is dysferlin deficiency. Recently, mouse models with patient mutations were developed to study genetic approaches to treat dysferlinopathy. The research fields for dysferlinopathy therapy include symptomatic treatments, as well as antisense-mediated exon skipping, myoblast transplantation, and gene editing.

Anoctamin-5 related muscle disease: clinical and genetic findings in a large European cohort

Anoctamin-5 related muscle disease is caused by biallelic pathogenic variants in the anoctamin-5 gene (ANO5) and shows variable clinical phenotypes: limb-girdle muscular dystrophy type 12 (LGMD-R12), distal muscular dystrophy type 3 (MMD3), pseudometabolic myopathy or asymptomatic hyperCKaemia. In this retrospective, observational, multicentre study we gathered a large European cohort of patients with ANO5-related muscle disease to study the clinical and genetic spectrum and genotype-phenotype correlations. We included 234 patients from 212 different families, contributed by 15 centres from 11 European countries. The largest subgroup was LGMD-R12 (52.6%), followed by pseudometabolic myopathy (20.5%), asymptomatic hyperCKaemia (13.7%) and MMD3 (13.2%). In all subgroups, there was a male predominance, except for pseudometabolic myopathy. Median age at symptom onset of all patients was 33 years (range 23-45 years). The most frequent symptoms at onset were myalgia (35.3%) and exercise intolerance (34.1%), while at last clinical evaluation most frequent symptoms and signs were proximal lower limb weakness (56.9%) and atrophy (38.1%), myalgia (45.1%) and atrophy of the medial gastrocnemius muscle (38.4%). Most patients remained ambulatory (79.4%). At last evaluation, 45.9% of patients with LGMD-R12 additionally had distal weakness in the lower limbs and 48.4% of patients with MMD3 also showed proximal lower limb weakness. Age at symptom onset did not differ significantly between males and females. However, males had a higher risk of using walking aids earlier (P = 0.035). No significant association was identified between sportive versus non-sportive lifestyle before symptom onset and age at symptom onset nor any of the motor outcomes. Cardiac and respiratory involvement that would require treatment occurred very rarely. Ninety-nine different pathogenic variants were identified in ANO5 of which 25 were novel. The most frequent variants were c.191dupA (p.Asn64Lysfs*15) (57.7%) and c.2272C>T (p.Arg758Cys) (11.1%). Patients with two loss-of function variants used walking aids at a significantly earlier age (P = 0.037). Patients homozygous for the c.2272C>T variant showed a later use of walking aids compared to patients with other variants (P = 0.043). We conclude that there was no correlation of the clinical phenotype with the specific genetic variants, and that LGMD-R12 and MMD3 predominantly affect males who have a significantly worse motor outcome. Our study provides useful information for clinical follow up of the patients and for the design of clinical trials with novel therapeutic agents.

Utilization of Targeted RNA-Seq for the Resolution of Variant Pathogenicity and Enhancement of Diagnostic Yield in Dysferlinopathy

For inherited diseases, obtaining a definitive diagnosis is critical for proper disease management, family planning, and participation in clinical trials. This can be challenging for dysferlinopathy due to the significant clinical overlap between the 30+ subtypes of limb–girdle muscular dystrophy (LGMD) and the large number of variants of unknown significance (VUSs) that are identified in the dysferlin gene, DYSF. We performed targeted RNA-Seq using a custom gene-panel in 77 individuals with a clinical/genetic suspicion of dysferlinopathy and evaluated all 111 identified DYSF variants according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) guidelines. This evaluation identified 11 novel DYSF variants and allowed for the classification of 87 DYSF variants as pathogenic/likely pathogenic, 8 likely benign, while 16 variants remained VUSs. By the end of the study, 60 of the 77 cases had a definitive diagnosis of dysferlinopathy, which was a 47% increase in diagnostic yield over the rate at study onset. This data shows the ability of RNA-Seq to assist in variant pathogenicity classification and diagnosis of dysferlinopathy and is, therefore, a type of analysis that should be considered when DNA-based genetic analysis is not sufficient to provide a definitive diagnosis.

Myostatin and follistatin as monitoring and prognostic biomarkers in dysferlinopathy

Myostatin is a myokine which acts upon skeletal muscle to inhibit growth and regeneration. Myostatin is endogenously antagonised by follistatin. This study assessed serum myostatin and follistatin concentrations as monitoring or prognostic biomarkers in dysferlinopathy, an autosomal recessively inherited muscular dystrophy. Myostatin was quantified twice with a three-year interval in 76 patients with dysferlinopathy and 38 controls. Follistatin was quantified in 62 of these patients at the same timepoints, and in 31 controls. Correlations with motor function, muscle fat fraction and contractile cross-sectional area were performed. A regression model was used to account for confounding variables. Baseline myostatin, but not follistatin, correlated with baseline function and MRI measures. However, in individual patients, three-year change in myostatin did not correlate with functional or MRI changes. Linear modelling demonstrated that function, serum creatine kinase and C-reactive protein, but not age, were independently related to myostatin concentration. Baseline myostatin concentration predicted loss of ambulation but not rate of change of functional or MRI measures, even when relative inhibition with follistatin was considered. With adjustment for extra-muscular causes of variation, myostatin could form a surrogate measure of functional ability or muscle mass, however myostatin inhibition does not form a promising treatment target in dysferlinopathy.

Minimal expression of dysferlin prevents development of dysferlinopathy in dysferlin exon 40a knockout mice

Dysferlin is a Ca²⁺-activated lipid binding protein implicated in muscle membrane repair. Recessive variants in DYSF result in dysferlinopathy, a progressive muscular dystrophy. We showed previously that calpain cleavage within a motif encoded by alternatively spliced exon 40a releases a 72 kDa C-terminal minidysferlin recruited to injured sarcolemma. Herein we use CRISPR/Cas9 gene editing to knock out murine Dysf exon 40a, to specifically assess its role in membrane repair and development of dysferlinopathy. We created three Dysf exon 40a knockout (40aKO) mouse lines that each express different levels of dysferlin protein ranging from ~ 90%, ~ 50% and ~ 10-20% levels of wild-type. Histopathological analysis of skeletal muscles from all 12-month-old 40aKO lines showed virtual absence of dystrophic features and normal membrane repair capacity for all three 40aKO lines, as compared with dysferlin-null BLAJ mice. Further, lipidomic and proteomic analyses on 18wk old quadriceps show all three 40aKO lines are spared the profound lipidomic/proteomic imbalance that characterises dysferlin-deficient BLAJ muscles. Collective results indicate that membrane repair does not depend upon calpain cleavage within exon 40a and that ~ 10-20% of WT dysferlin protein expression is sufficient to maintain the muscle lipidome, proteome and membrane repair capacity to crucially prevent development of dysferlinopathy.

Distal myopathy

Distal myopathies are a group of genetic, primary muscle diseases. Patients develop progressive weakness and atrophy of the muscles of forearm, hands, lower leg, or feet. Currently, over 20 different forms, presenting a variable age of onset, clinical presentation, disease progression, muscle involvement, and histological findings, are known. Some of them are dominant and some recessive. Different variants in the same gene are often associated with either dominant or recessive forms, although there is a lack of a comprehensive understanding of the genotype-phenotype correlations. This chapter provides a description of the clinicopathologic and genetic aspects of distal myopathies emphasizing known etiologic and pathophysiologic mechanisms.

Water T2 could predict functional decline in patients with dysferlinopathy

BACKGROUND

Water T2 (T2_H2O ) mapping is increasingly being used in muscular dystrophies to assess active muscle damage. It has been suggested as a surrogate outcome measure for clinical trials. Here, we investigated the prognostic utility of T2_H2O to identify changes in muscle function over time in limb girdle muscular dystrophies.

METHODS

Patients with genetically confirmed dysferlinopathy were assessed as part of the Jain Foundation Clinical Outcomes Study in dysferlinopathy. The cohort included 18 patients from two sites, both equipped with 3-tesla magnetic resonance imaging (MRI) systems from the same vendor. T2_H2O value was defined as higher or lower than the median in each muscle bilaterally. The degree of deterioration on four functional tests over 3 years was assessed in a linear model against covariates of high or low T2_H2O at baseline, age, disease duration, and baseline function.

RESULTS

A higher T2_H2O at baseline significantly correlated with a greater decline on functional tests in 21 out of 35 muscles and was never associated with slower decline. Higher baseline T2_H2O in adductor magnus, vastus intermedius, vastus lateralis, and vastus medialis were the most sensitive, being associated bilaterally with greater decline in multiple timed tests. Patients with a higher than median baseline T2_H2O (>40.6 ms) in the right vastus medialis deteriorated 11 points more on the North Star Ambulatory Assessment for Dysferlinopathy and lost an additional 86 m on the 6-min walk than those with a lower T2_H2O (<40.6 ms). Optimum sensitivity and specificity thresholds for predicting decline were 39.0 ms in adductor magnus and vastus intermedius, 40.0 ms in vastus medialis, and 40.5 ms in vastus lateralis from different sites equipped with different MRI systems.

CONCLUSIONS

In dysferlinopathy, T2_H2O did not correlate with current functional ability. However, T2_H2O at baseline was higher in patients who worsened more rapidly on functional tests. This suggests that inter-patient differences in functional decline over time may be, in part, explained by different severities of the active muscle damage, assessed by T2_H2O measure at baseline. Significant challenges remain in standardizing T2_H2O values across sites to allow determining globally applicable thresholds. The results from the present work are encouraging and suggest that T2_H2O could be used to improve prognostication, patient selection, and disease modelling for clinical trials.

Identification of a novel heterozygous DYSF variant in a large family with a dominantly-inherited dysferlinopathy

AIMS

Dysferlinopathy is an autosomal recessive muscular dystrophy, caused by bi-allelic variants in the gene encoding dysferlin (DYSF). Onset typically occurs in the second to third decade and is characterised by slowly progressive skeletal muscle weakness and atrophy of the proximal and/or distal muscles of the four limbs. There are rare cases of symptomatic DYSF variant carriers. Here, we report a large family with a dominantly inherited hyperCKaemia and late-onset muscular dystrophy.

METHODS AND RESULTS

Genetic analysis identified a co-segregating novel DYSF variant [NM_003494.4:c.6207del p.(Tyr2070Metfs*4)]. No secondary variants in DYSF or other dystrophy-related genes were identified on whole genome sequencing and analysis of the proband's DNA. Skeletal muscle involvement was milder and later onset than typical dysferlinopathy presentations; these clinical signs manifested in four individuals, all between the fourth and sixth decades of life. All individuals heterozygous for the c.6207del variant had hyperCKaemia. Histological analysis of skeletal muscle biopsies across three generations showed clear dystrophic signs, including inflammatory infiltrates, regenerating myofibres, increased variability in myofibre size, and internal nuclei. Muscle magnetic resonance imaging revealed fatty replacement of muscle in two individuals. Western blot and immunohistochemical analysis of muscle biopsy demonstrated consistent reduction of dysferlin staining. Allele-specific quantitative PCR analysis of DYSF mRNA from patient muscle found that the variant, localised to the extreme C-terminus of dysferlin, does not activate post-transcriptional mRNA decay.

CONCLUSIONS

We propose that this inheritance pattern may be underappreciated and that other late-onset muscular dystrophy cases with mono-allelic DYSF variants, particularly C-terminal premature truncation variants, may represent dominant forms of disease.

Three-year quantitative magnetic resonance imaging and phosphorus magnetic resonance spectroscopy study in lower limb muscle in dysferlinopathy

BACKGROUND

Natural history studies in neuromuscular disorders are vital to understand the disease evolution and to find sensitive outcome measures. We performed a longitudinal assessment of quantitative magnetic resonance imaging (MRI) and phosphorus magnetic resonance spectroscopy (³¹ P MRS) outcome measures and evaluated their relationship with function in lower limb skeletal muscle of dysferlinopathy patients.

METHODS

Quantitative MRI/³¹ P MRS data were obtained at 3 T in two different sites in 54 patients and 12 controls, at baseline, and three annual follow-up visits. Fat fraction (FF), contractile cross-sectional area (cCSA), and muscle water T₂ in both global leg and thigh segments and individual muscles and ³¹ P MRS indices in the anterior leg compartment were assessed. Analysis included comparisons between patients and controls, assessments of annual changes using a linear mixed model, standardized response means (SRM), and correlations between MRI and ³¹ P MRS markers and functional markers.

RESULTS

Posterior muscles in thigh and leg showed the highest FF values. FF at baseline was highly heterogeneous across patients. In ambulant patients, median annual increases in global thigh and leg segment FF values were 4.1% and 3.0%, respectively (P < 0.001). After 3 years, global thigh and leg FF increases were 9.6% and 8.4%, respectively (P < 0.001). SRM values for global thigh FF were over 0.8 for all years. Vastus lateralis muscle showed the highest SRM values across all time points. cCSA decreased significantly after 3 years with median values of 11.0% and 12.8% in global thigh and global leg, respectively (P < 0.001). Water T₂ values in ambulant patients were significantly increased, as compared with control values (P < 0.001). The highest water T₂ values were found in the anterior part of thigh and leg. Almost all ³¹ P MRS indices were significantly different in patients as compared with controls (P < 0.006), except for pH_w , and remained, similar as to water T₂ , abnormal for the whole study duration. Global thigh water T₂ at baseline was significantly correlated to the change in FF after 3 years (ρ = 0.52, P < 0.001). There was also a significant relationship between the change in functional score and change in FF after 3 years in ambulant patients (ρ = -0.55, P = 0.010).

CONCLUSIONS

This multi-centre study has shown that quantitative MRI/³¹ P MRS measurements in a heterogeneous group of dysferlinopathy patients can measure significant changes over the course of 3 years. These data can be used as reference values in view of future clinical trials in dysferlinopathy or comparisons with quantitative MRI/S data obtained in other limb-girdle muscular dystrophy subtypes.

Comparison of strength testing modalities in dysferlinopathy

INTRODUCTION/AIMS

Dysferlinopathy demonstrates heterogeneity in muscle weakness between patients, which can progress at different rates over time. Changing muscle strength due to disease progression or from an investigational product is associated with changing functional ability. The purpose of this study was to compare three methods of strength testing used in the Clinical Outcome Study (COS) for dysferlinopathy to understand which method and which muscle groups were most sensitive to change over time.

METHODS

Patients were evaluated at each study visit using functional scales, manual muscle testing, and handheld dynamometry (HHD) at all 15 sites. A fixed-frame system (Fixed) was used at a subset of seven sites. Screening and baseline visits were evaluated for reliability. Data over a 1-year period were analyzed to determine sensitivity to change among strength modalities and individual muscle groups.

RESULTS

HHD and Fixed captured significant change across 1 year in summed muscle strength score of four muscle groups (P < .01). Strength summed scores were significantly correlated with functional scales (rho = 0.68-0.92, P < .001). Individual muscle groups, however, showed high levels of variability between visits.

DISCUSSION

Although both HHD and Fixed demonstrate change over 12 months, HHD is a less expensive option that provides data on a continuous scale and may be easier to implement. Due to variability in strength measures, researchers should carefully consider use of strength testing as an outcome and may wish to select functional measures with less variability as clinical trial endpoints.

Update Distale Myopathien

Die Distalen Myopathien umfassen eine Gruppe von genetisch determinierten Muskelerkrankungen bei denen Paresen und eine fortschreitende Atrophie der distalen Muskelgruppen im Vordergrund stehen. Der klinische Phänotyp, der Erkrankungsbeginn, der Vererbungsmodus sowie histologische Veränderungen helfen die einzelnen Formen zu differenzieren. Das klinische und genetische Spektrum ist allerdings heterogen. In den letzten Jahren hat durch die erweiterte genetische Diagnostik die Anzahl der nachgewiesenen Mutationen exponentiell zugenommen. Im folgenden Beitrag werden die Klassifikation, die klinischen Besonderheiten und die relevanten genetischen Aspekte dargestellt.