MRI in sarcoglycanopathies: a large international cohort study

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.

Analysis of muscle magnetic resonance imaging of a large cohort of patient with VCP-mediated disease reveals characteristic features useful for diagnosis

BACKGROUND

The diagnosis of patients with mutations in the VCP gene can be complicated due to their broad phenotypic spectrum including myopathy, motor neuron disease and peripheral neuropathy. Muscle MRI guides the diagnosis in neuromuscular diseases (NMDs); however, comprehensive muscle MRI features for VCP patients have not been reported so far.

METHODS

We collected muscle MRIs of 80 of the 255 patients who participated in the "VCP International Study" and reviewed the T1-weighted (T1w) and short tau inversion recovery (STIR) sequences. We identified a series of potential diagnostic MRI based characteristics useful for the diagnosis of VCP disease and validated them in 1089 MRIs from patients with other genetically confirmed NMDs.

RESULTS

Fat replacement of at least one muscle was identified in all symptomatic patients. The most common finding was the existence of patchy areas of fat replacement. Although there was a wide variability of muscles affected, we observed a common pattern characterized by the involvement of periscapular, paraspinal, gluteal and quadriceps muscles. STIR signal was enhanced in 67% of the patients, either in the muscle itself or in the surrounding fascia. We identified 10 diagnostic characteristics based on the pattern identified that allowed us to distinguish VCP disease from other neuromuscular diseases with high accuracy.

CONCLUSIONS

Patients with mutations in the VCP gene had common features on muscle MRI that are helpful for diagnosis purposes, including the presence of patchy fat replacement and a prominent involvement of the periscapular, paraspinal, abdominal and thigh muscles.

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.

Nanoparticles systemically biodistribute to regenerating skeletal muscle in DMD

Skeletal muscle disease severity can often progress asymmetrically across muscle groups and heterogeneously within tissues. An example is Duchenne Muscular Dystrophy (DMD) in which lack of dystrophin results in devastating skeletal muscle wasting in some muscles whereas others are spared or undergo hypertrophy. An efficient, non-invasive approach to identify sites of asymmetry and degenerative lesions could enable better patient monitoring and therapeutic targeting of disease. In this study, we utilized a versatile intravenously injectable mesoporous silica nanoparticle (MSNP) based nanocarrier system to explore mechanisms of biodistribution in skeletal muscle of mdx mouse models of DMD including wildtype, dystrophic, and severely dystrophic mice. Moreover, MSNPs could be imaged in live mice and whole muscle tissues enabling investigation of how biodistribution is altered by different types of muscle pathology such as inflammation or fibrosis. We found MSNPs were tenfold more likely to aggregate within select mdx muscles relative to wild type, such as gastrocnemius and quadriceps. This was accompanied by decreased biodistribution in off-target organs. We found the greatest factor affecting preferential delivery was the regenerative state of the dystrophic skeletal muscle with the highest MSNP abundance coinciding with the regions showing the highest level of embryonic myosin staining and intramuscular macrophage uptake. To demonstrate, muscle regeneration regulated MSNP distribution, we experimentally induced regeneration using barium chloride which resulted in a threefold increase of intravenously injected MSNPs to sites of regeneration 7 days after injury. These discoveries provide the first evidence that nanoparticles have selective biodistribution to skeletal muscle in DMD to areas of active regeneration and that nanoparticles could enable diagnostic and selective drug delivery in DMD skeletal muscle.

Differential histological features and myogenic protein levels in distinct muscles of d-sarcoglycan null muscular dystrophy mouse model

Skeletal muscle (SkM) comprises slow and fast-twitch fibers, which differ in molecular composition, function, and systemic energy consumption. In addition, muscular dystrophies (DM), a group of diverse hereditary diseases, present different patterns of muscle involvement, progression, and severity, suggesting that the regeneration-degeneration process may differ depending on the muscle type. Therefore, the study aimed to explore the expression of proteins involved in the repair process in different muscles at an early stage of muscular dystrophy in the δ-sarcoglycan null mice (Sgcd-null), a limb-girdle muscular dystrophy 2 F model. Hematoxylin & Eosin (H&E) Staining showed a high number of central nuclei in soleus (Sol), tibialis (Ta), gastrocnemius (Gas), and extensor digitorum longus (Edl) from four months Sgcd-null mice. However, fibrosis, determined by trichrome of Gomori modified staining, was only observed in Sgcd-null Sol. In addition, the number of Type I and II fibers variated differentially in the Sgcd-null muscles vs. wild-type muscles. Besides, the protein expression level of β-catenin, myomaker, MyoD, and myogenin also presented different expression levels in all the Sgcd-null muscles studied. In summary, our study reveals that muscles with different metabolic characteristics showed distinct expression patterns of proteins involved in the muscle regeneration process. These results could be relevant in designing therapies for genetic and acquired myopathy.

Muscle MRI patterns for limb girdle muscle dystrophies: systematic review

Limb girdle muscle dystrophies (LGMDs) are a group of inherited neuromuscular disorders comprising more than 20 genes. There have been increasing efforts to characterize this group with Muscle MRI. However, due to the complexity and similarities, the interpretation of the MRI patterns is usually done by experts in the field. Here, we proposed a step-by-step image interpretation of Muscle MRI in LGDM by evaluating the variability of muscle pattern involvement reported in the literature. A systematic review with an open start date to November 2022 was conducted to describe all LGMDs' muscle MRI patterns. Eighty-eight studies were included in the final review. Data were found to describe muscle MRI patterns for 15 out of 17 LGMDs types. Although the diagnosis of LGMDs is challenging despite the advanced genetic testing and other diagnostic modalities, muscle MRI is shown to help in the diagnosis of LGMDs. To further increase the yield for muscle MRI in the neuromuscular field, larger cohorts of patients need to be conducted.

Long-term clinical and MRI follow-up in two POMT2-related limb girdle muscular dystrophy (LGMDR14) patients

INTRODUCTION

POMT2-related limb girdle muscular dystrophy (LGMDR14) is a rare muscular dystrophy caused by mutations in the POMT2 gene. Thus far only 26 LGMDR14 subjects have been reported and no longitudinal natural history data are available.

CASE REPORT

We describe two LGMDR14 patients followed for 20 years since infancy. Both patients presented a childhood-onset, slowly progressive pelvic girdle muscular weakness leading to loss of ambulation in the second decade in one patient, and cognitive impairment without detectable brain structural abnormalities. Glutei, paraspinal, and adductor muscles were the primarily involved muscles at MRI.

DISCUSSION

This report provides natural history data on LGMDR14 subjects, with a focus on longitudinal muscle MRI. We also reviewed the LGMDR14 literature data, providing information on the LGMDR14 disease progression. Considering the high prevalence of cognitive impairment in LGMDR14 patients, a reliable application of functional outcome measures can be challenging, therefore a muscle MRI follow-up to assess disease evolution is recommended.

Progression to Loss of Ambulation Among Patients with Autosomal Recessive Limb-girdle Muscular Dystrophy: A Systematic Review

Background

The impact of age at autosomal recessive limb girdle muscular dystrophy (LGMDR) onset on progression to loss of ambulation (LOA) has not been well established, particularly by subtype.

Objectives:

To describe the characteristics of patients with adult-, late childhood-, and early childhood-onset LGMDR by subtype and characterize the frequency and timing of LOA.

Methods:

A systematic review was conducted in MEDLINE, Embase and the Cochrane library. Frequency and timing of LOA in patients with LGMDR1, LGMDR2/Miyoshi myopathy (MM), LGMDR3-6, LGMDR9, and LGMDR12 were synthesized from published data.

Results:

In 195 studies, 695 (43.4%) patients had adult-, 532 (33.2%) had late childhood-, and 376 (23.5%) had early childhood-onset of disease across subtypes among those with a reported age at onset (n = 1,603); distribution of age at onset varied between subtypes. Among patients with LOA (n = 228), adult-onset disease was uncommon in LGMDR3-6 (14%) and frequent in LGMDR2/MM (42%); LGMDR3-6 cases with LOA primarily had early childhood-onset (74%). Mean (standard deviation [SD]) time to LOA varied between subtypes and was shortest for patients with early childhood-onset LGMDR9 (12.0 [4.9] years, n = 19) and LGMDR3-6 (12.3 [10.7], n = 56) and longest for those with late childhood-onset LGMDR2/MM (21.4 [11.5], n = 36).

Conclusions:

This review illustrated that patients with early childhood-onset disease tend to have faster progression to LOA than those with late childhood- or adult-onset disease, particularly in LGMDR9. These findings provide a greater understanding of progression to LOA by LGMDR subtype, which may help inform clinical trial design and provide a basis for natural history studies.

Ambulatory Duchenne muscular dystrophy children: cross-sectional correlation between function, quantitative muscle ultrasound and MRI

Duchenne muscular dystrophy (DMD) is a progressive genetic muscle disease. Quantitative muscle ultrasound (US), muscle MRI, and functional tools are important to delineate characteristics of muscle involvement. We aimed to establish correlations between clinical/functional and above-named imaging tools respecting their diagnostic and prognostic role in DMD children. A cross-sectional retrospective study of 27 steroid-naive, ambulant male children/adolescents with genetically-confirmed DMD (mean age, 8.8 ± 3.3 years). Functional performance was assessed using motor function measure (MFM) which assess standing/transfer (D1), proximal (D2) and distal (D3) motor function, and six-minute walk test (6MWT). Imaging evaluation included quantitative muscle MRI which measured muscle fat content in a specific location of right rectus femoris by mDixon sequence. Quantitative muscle US measured right rectus femoris muscle brightness in standardized US image as an indicator of muscle fat content. We found a highly significant positive correlation between the mean MFM total score and 6MWT (R = 0.537, p = 0.007), and a highly significant negative correlation between fat content by muscle US and MFM total score (R = -0.603, p = 0.006) and its D1 subscore (R =-0.712, p = 0.001), and a significant negative correlation between fat content by US and 6MWT (R = -0.529, p = 0.02), and a significant positive correlation between muscle fat content by mDixon MRI and patient's age (R = 0.617, p = 0.01). Quantitative muscle US correlates significantly with clinical/functional assessment tools as MFM and 6MWT, and augments their role in disease-tracking of DMD. Quantitative muscle US has the potential to act as a substitute to functional assessment tools.

Current and Future Approaches to Classify VUSs in LGMD-Related Genes

Next-generation sequencing (NGS) has revealed large numbers of genetic variants in LGMD-related genes, with most of them classified as variants of uncertain significance (VUSs). VUSs are genetic changes with unknown pathological impact and present a major challenge in genetic test interpretation and disease diagnosis. Understanding the phenotypic consequences of VUSs can provide clinical guidance regarding LGMD risk and therapy. In this review, we provide a brief overview of the subtypes of LGMD, disease diagnosis, current classification systems for investigating VUSs, and a potential deep mutational scanning approach to classify VUSs in LGMD-related genes.

First Identification of Rare Exonic and Deep Intronic Splice-Altering Variants in Patients With Beta-Sarcoglycanopathy

BACKGROUND

The precise genetic diagnosis of a sarcoglycanopathy or dystrophinopathy is sometimes extremely challenging, as pathogenic non-coding variants and/or complex structural variants do exist in DMD or sarcoglycan genes. This study aimed to determine the genetic diagnosis of three patients from two unrelated families with a suspected sarcoglycanopathy or dystrophinopathy based on their clinical, radiological, and pathological features, for whom routine genomic detection approaches failed to yield a definite genetic diagnosis.

METHODS

Muscle-derived reverse transcription-polymerase chain reaction analysis and/or TA cloning of DMD, SGCA, SGCB, SGCD, and SGCG mRNA were performed to identify aberrant transcripts. Genomic Sanger sequencing around the aberrant transcripts was performed to detect possible splice-altering variants. Bioinformatic and segregation studies of the detected genomic variants were performed in both families.

RESULTS

In patients F1-II1 and F1-II2, we identified two novel pathogenic compound heterozygous variants in SGCB. One is a deep intronic splice-altering variant (DISV), c.243 + 1558C > T in intron 2 causing the activation of an 87-base pair (bp) pseudoexon, and the other one is a non-canonical splicing site variant, c.243 + 6T > A leading to the partial intron inclusion of 10-bp sequence. A novel DISV, c.243 + 1576C > G causing a 106-bp pseudoexon activation, and a nonsense variant in SGCB were identified in compound heterozygous state in patient F2-II1. Unexpectedly, the predicted nonsense variant, c.334C > T in exon 3, created a new donor splice site in exon 3 that was stronger than the natural one, resulting in a 97-bp deletion of exon 3 (r.333_429del).

CONCLUSION

This is the first identification of rare exonic and DISVs in the SGCB gene.

Muscle MRI in Myotonic Dystrophy type 1 (DM1): refining muscle involvement and implications for clinical trials

BACKGROUND

Only few studies reported muscle imaging data on small cohorts of patients with Myotonic dystrophy type 1 (DM1). We aimed to investigate the muscle involvement in a large cohort of patients, to refine the pattern of muscle involvement, to better understand the pathophysiological mechanisms of muscle weakness and to identify potential imaging biomarkers for disease activity and severity.

METHODS

134 DM1 patients underwent a cross-sectional muscle MRI study. STIR and T1- sequences in lower and upper body were analysed. Fat replacement, muscle atrophy and STIR positivity were evaluated using three different scales. Correlations between MRI scores, clinical features and genetic background were investigated.

RESULTS

The most frequent pattern of muscle involvement in T1 consisted of fat replacement of the tongue, sternocleidomastoideus, paraspinalis, gluteus minimus, distal quadriceps and gastrocnemius medialis. Degree of fat replacement at MRI correlated with clinical severity and disease duration, but not with CTG expansion. Fat replacement was also detected in milder/asymptomatic patients. More than 80% of patients had STIR positive signal in muscles. Most DM1 patients also showed a variable degree of muscle atrophy regardless MRI signs of fat replacement. A subset of patients (20%) showed a "marbled" muscle appearance.

CONCLUSIONS

muscle MRI is a sensitive biomarker of disease severity also for the milder spectrum of disease. STIR hyperintensty seems to precede fat replacement in T1. Beyond fat replacement, STIR positivity, muscle atrophy and "marbled" appearance suggest further mechanisms of muscle wasting and weakness in DM1, representing additional outcome measures and therapeutical targets for forthcoming clinical trials.

Two decades of advances in muscle imaging in children: from pattern recognition of muscle diseases to quantification and machine learning approaches

Muscle imaging has progressively gained popularity in the neuromuscular field. Together with detailed clinical examination and muscle biopsy, it has become one of the main tools for deep phenotyping and orientation of etiological diagnosis. Even in the current era of powerful new generation sequencing, muscle MRI has arisen as a tool for prioritization of certain genetic entities, supporting the pathogenicity of variants of unknown significance and facilitating diagnosis in cases with an initially inconclusive genetic study. Although the utility of muscle imaging is increasingly clear, it has not reached its full potential in clinical practice. Pattern recognition is known for a number of diseases and will certainly be enhanced by the use of machine learning approaches. For instance, MRI heatmap representations might be confronted with molecular results by obtaining a probabilistic diagnosis based in each disease "MRI fingerprints". Muscle ultrasound as a screening tool and quantified techniques such as Dixon MRI seem still underdeveloped. In this paper, we aim to appraise the advances in recent years in pediatric muscle imaging and try to define areas of uncertainty and potential advances that might become standardized to be widely used in the future.

Muscle magnetic resonance imaging in patients with LAMA2-related muscular dystrophy

LAMA2-related muscular dystrophy (LAMA2-MD) is classified into congenital muscular dystrophy type 1A (MDC1A) and autosomal recessive limb-girdle muscular dystrophy-23 (LGMDR23). The purpose of this study was to identify the involvement pattern of thigh muscles of LAMA2-MD patients on magnetic resonance imaging. Fourteen MDC1A and 3 LGMDR23 patients were included, with 21 known and 8 novel LAMA2 disease-causing variants. In LAMA2-MD, the gluteus maximus, anterior (quadriceps femoris) and posterior (adductor magnus and biceps femoris) thigh muscles were extensively and severely affected with fatty infiltration, with relatively sparing of the adductor longus. The pattern of muscle involvement was similar between MDC1A and LGMDR23, but more severe in MDC1A, as well as in LAMA2-MD patients without ambulation. The rather peculiar pattern of the adductor magnus and long head of the biceps femoris first and severely affected in the mid-thigh level was found in LGMDR23. Strong correlation between fatty infiltration and age as well as disease duration was observed for the adductor longus in MDC1A. Edema and atrophy selectively involved in some muscles. The pattern of fatty infiltration on thigh muscle MRI of LAMA2-MD could provide important information for the diagnosis, differential diagnosis and assessment of clinical severity.

Distinct and Recognisable Muscle MRI Pattern in a Series of Adults Harbouring an Identical GMPPB Gene Mutation

BACKGROUND AND PURPOSE

Mutations in the GMPPB gene affect glycosylation of α-dystroglycan, leading to varied clinical phenotypes. We attempted to delineate the muscle MR imaging spectrum of GMPPB-related Congenital Myasthenic syndrome (CMS) in a single-center cohort study.

OBJECTIVE

To identify the distinct patterns of muscle involvement in GMPPB gene mutations.

METHODS

We analyzed the muscle MR images of 7 genetically proven cases of GMPPB dystroglycanopathy belonging to three families and studied the potential qualitative imaging pattern to aid in clinico -radiological diagnosis in neuromuscular practice. All individuals underwent muscle MRI (T1, T2, STIR/PD Fat sat. sequences in 1.5 T machine) of the lower limbs. Qualitative assessment and scoring were done for muscle changes using Mercuri staging for fibro-fatty replacement on T1 sequence and Borsato score for myoedema on STIR sequence.

RESULTS

All patients were of South Indian origin and presented as slowly progressive childhood to adult-onset fatigable limb-girdle muscle weakness, elevated creatine kinase level, and positive decrement response in proximal muscles. Muscle biopsy revealed features of dystrophy. All patients demonstrated identical homozygous mutation c.1000G >  A in the GMPPB gene. MRI demonstrated early and severe involvement of paraspinal muscles, gluteus minimus, and relatively less severe involvement of the short head of the biceps femoris. A distinct proximo-distal gradient of affliction was identified in the glutei, vasti, tibialis anterior and peronei. Also, a postero-anterior gradient was observed in the gracilis muscle.

CONCLUSION

Hitherto unreported, the distinctive MR imaging pattern described here, coupled with relatively slowly progressive symptoms of fatigable limb-girdle weakness, would facilitate an early diagnosis of the milder form of GMPPB- dystroglycanopathy associated with homozygous GMPPB gene mutation.

Diagnostic interest of whole-body MRI in early- and late-onset LAMA2 muscular dystrophies: a large international cohort

BACKGROUND

LAMA2-related muscular dystrophy (LAMA2-RD) encompasses a group of recessive muscular dystrophies caused by mutations in the LAMA2 gene, which codes for the alpha-2 chain of laminin-211 (merosin). Diagnosis is straightforward in the classic congenital presentation with no ambulation and complete merosin deficiency in muscle biopsy, but is far more difficult in milder ambulant individuals with partial merosin deficiency.

OBJECTIVE

To investigate the diagnostic utility of muscle imaging in LAMA2-RD using whole-body magnetic resonance imaging (WBMRI).

RESULTS

27 patients (2-62 years, 21-80% with acquisition of walking ability and 6 never ambulant) were included in an international collaborative study. All carried two pathogenic mutations, mostly private missense changes. An intronic variant (c.909 + 7A > G) was identified in all the Chilean cases. Three patients (two ambulant) showed intellectual disability, epilepsy, and brain structural abnormalities. WBMRI T1w sequences or T2 fat-saturated images (Dixon) revealed abnormal muscle fat replacement predominantly in subscapularis, lumbar paraspinals, gluteus minimus and medius, posterior thigh (adductor magnus, biceps femoris, hamstrings) and soleus. This involvement pattern was consistent for both ambulant and non-ambulant patients. The degree of replacement was predominantly correlated to the disease duration, rather than to the onset or the clinical severity. A "COL6-like sandwich sign" was observed in several muscles in ambulant adults, but different involvement of subscapularis, gluteus minimus, and medius changes allowed distinguishing LAMA2-RD from collagenopathies. The thigh muscles seem to be the best ones to assess disease progression.

CONCLUSION

WBMRI in LAMA2-RD shows a homogeneous pattern of brain and muscle imaging, representing a supportive diagnostic tool.

Diagnostic magnetic resonance imaging biomarkers for facioscapulohumeral muscular dystrophy identified by machine learning

BACKGROUND

The diagnosis of facioscapulohumeral muscular dystrophy (FSHD) can be challenging in patients not displaying the classical phenotype or with atypical clinical features. Despite the identification by magnetic resonance imaging (MRI) of selective patterns of muscle involvement, their specificity and added diagnostic value are unknown.

METHODS

We aimed to identify the radiological features more useful to distinguish FSHD from other myopathies and test the diagnostic accuracy of MRI. A retrospective cohort of 295 patients (187 FSHD, 108 non-FSHD) studied by upper and lower-limb muscle MRI was analyzed. Scans were evaluated for the presence of 15 radiological features. A random forest machine learning algorithm was used to identify the most relevant for FSHD diagnosis. Different patterns were created by their combination and diagnostic accuracy of each of them was tested.

RESULTS

The combination of trapezius involvement and bilateral subscapularis muscle sparing achieved the best diagnostic accuracy (0.89, 95% Confidence Interval [0.85-0.92]) with 0.90 [0.85-0.94] sensitivity and 0.88 [0.80-0.93] specificity. This pattern correctly identified 91% atypical FSHD patients of our cohort. The combination of trapezius involvement, bilateral subscapularis and iliopsoas sparing and asymmetric involvement of upper and lower-limb muscles was pathognomonic for FSHD, yielding a specificity of 0.99 [0.95-1.00].

CONCLUSIONS

We identified MRI patterns that showed a high diagnostic power in promptly discriminating FSHD from other muscle disorders, with comparable performance irrespective of typical or atypical clinical features. Upper girdle in addition to lower-limb muscle imaging should be extensively implemented in the diagnostic workup to support or exclude a diagnosis of FSHD.

Unmet needs and evolving treatment for limb girdle muscular dystrophies

Limb-girdle muscular dystrophies (LGMDs) represent a major group of muscle disorders. Treatment is sorely needed and currently expanding based on safety and efficacy adopting principles of single-dosing gene therapy for monogenic autosomal recessive disorders. Gene therapy has made in-roads for LGMD and this review describes progress that has been achieved for these conditions. This review first provides a background on the definition and classification of LGMDs. The major effort focuses on progress in LGMD gene therapy, from experimental studies to clinical trials. The disorders discussed include the LGMDs where the most work has been done including calpainopathies (LGMD2A/R1), dysferlinopathies (LGMD2B/R2) and sarcoglycanopathies (LGMD2C/R5, LGMD2D/R3, LGMD2E/R4). Early success in clinical trials provides a template to move the field forward and potentially apply emerging technology like CRISPR/Cas9 that may enhance the scope and efficacy of gene therapy applied to patient care.

Sarcoglycanopathies: an update

Sarcoglycanopathies are the most severe forms of autosomal recessive limb-girdle muscular dystrophies (LGMDs), constituting about 10-25% of LGMDs. The clinical phenotype is variable, but onset is usually in the first decade of life. Patients present muscle hypertrophy, elevated CK, variable muscle weaknesses, and progressive loss of ambulation. Four subtypes are known: LGMDR3, LGMDR4, LGMDR5 and LGMDR6, caused, respectively, by mutations in the SGCA, SGCB,SGCG and SGCD genes. Their four coded proteins, α-SG, ß-SG, λ-SG and δ-SG are part of the dystrophin-glycoprotein complex (DGC) present in muscle sarcolemma, which acts as a linker between the cytoskeleton of the muscle fiber and the extracellular matrix, providing mechanical support to the sarcolemma during myofiber contraction. Many different mutations have already been identified in all the sarcoglycan genes, with a predominance of some mutations in different populations. The diagnosis is currently based on the molecular screening for these mutations. Therapeutic approaches include the strategy of gene replacement mediated by a vector derived from adeno-associated virus (AAV). Pre-clinical studies have shown detectable levels of SG proteins in the muscle, and some improvement in the phenotype, in animal models. Therapeutic trials in humans are ongoing.

Muscle involvement assessed by quantitative magnetic resonance imaging in patients with anoctamin 5 deficiency

OBJECTIVE

Using magnetic resonance imaging (MRI) and stationary dynamometry, the aim was to investigate the muscle affection in paraspinal muscles and lower extremities and compare the muscle affection in men and women with anoctamin 5 (ANO5) deficiency.

METHODS

Seventeen patients (seven women) with pathogenic ANO5-mutations were included. Quantitative muscle fat fraction of back and leg muscles were assessed by Dixon MRI. Muscle strength was assessed by stationary dynamometer. Results were compared with 11 matched, healthy controls.

RESULTS

Muscle involvement pattern in men with ANO5-deficiency is characterized by a severe fat replacement of hamstrings, adductor and gastrocnemius muscles, while paraspinal muscles are only mildly affected, while preserved gracilis and sartorius muscles were hypertrophied. Women with ANO5-myopathy, of the same age as male patients, were very mildly affected, showing muscle affection and strength resembling that found in healthy persons, with the exception of the gluteus minimus and medius and gastrocnemii muscles that were significantly replaced by fat. Although individual muscles showed clear asymmetric involvement in a few muscle groups, the overall muscle involvement was symmetric.

CONCLUSIONS

Patients with ANO5-deficiency have relatively preserved paraspinal muscles on imaging and only mild reduction of trunk extension strength in men only. Our study quantifies the large difference in muscle affection in lower extremity between women and men with ANO5-deficiency. The clinical notion is that affection may be very asymmetric in ANO5-deficiency, but the present study shows that while this may be true for a few muscles, the general impression is that muscle affection is very symmetric.

MR imaging of inherited myopathies: a review and proposal of imaging algorithms

PURPOSE OF REVIEW

The aims of this review are to discuss the imaging modalities used to assess muscle changes in myopathies, to provide an overview of the inherited myopathies focusing on their patterns of muscle involvement in magnetic resonance imaging (MR), and to propose up-to-date imaging-based diagnostic algorithms that can help in the diagnostic workup.

CONCLUSION

Familiarization with the most common and specific patterns of muscular involvement in inherited myopathies is very important for radiologists and neurologists, as imaging plays a significant role in diagnosis and follow-up of these patients.

KEY POINTS

• Imaging is an increasingly important tool for diagnosis and follow-up in the setting of inherited myopathies. • Knowledge of the most common imaging patterns of muscle involvement in inherited myopathies is valuable for both radiologists and neurologists. • In this review, we present imaging-based algorithms that can help in the diagnostic workup of myopathies.

Muscle Diversity, Heterogeneity, and Gradients: Learning from Sarcoglycanopathies

Skeletal muscle, the most abundant tissue in the body, is heterogeneous. This heterogeneity forms the basis of muscle diversity, which is reflected in the specialized functions of muscles in different parts of the body. However, these different parts are not always clearly delimitated, and this often gives rise to gradients within the same muscle and even across the body. During the last decade, several studies on muscular disorders both in mice and in humans have observed particular distribution patterns of muscle weakness during disease, indicating that the same mutation can affect muscles differently. Moreover, these phenotypical differences reveal gradients of severity, existing alongside other architectural gradients. These two factors are especially prominent in sarcoglycanopathies. Nevertheless, very little is known about the mechanism(s) driving the phenotypic diversity of the muscles affected by these diseases. Here, we will review the available literature on sarcoglycanopathies, focusing on phenotypic differences among affected muscles and gradients, characterization techniques, molecular signatures, and cell population heterogeneity, highlighting the possibilities opened up by new technologies. This review aims to revive research interest in the diverse disease phenotype affecting different muscles, in order to pave the way for new therapeutic interventions.

The value of qualitative muscle MRI in the diagnostic procedures of myopathies: a biopsy-controlled study in 191 patients

Background and aims

The role of muscle magnetic resonance imaging (MRI) in the diagnostic procedures of myopathies is still controversially discussed. The current study was designed to analyze the status of qualitative muscle MRI, electromyography (EMG), and muscle biopsy in different cases of clinically suspected myopathy.

Methods

A total of 191 patients (male: n = 112, female: n = 79) with suspected myopathy who all received muscle MRI, EMG, and muscle biopsy for diagnostic reasons were studied, with the same location of biopsy and muscle MRI (either upper or lower extremities or paravertebral muscles). Muscle MRIs were analyzed using standard rating protocols by two different raters independently.

Results

Diagnostic findings according to biopsy results and genetic testing were as follow: non-inflammatory myopathy: n = 65, inflammatory myopathy (myositis): n = 51, neurogenic: n = 18, unspecific: n = 23, and normal: n = 34. The majority of patients showed myopathic changes in the EMG. Edema, atrophy, muscle fatty replacement, and contrast medium enhancement (CM uptake) in MRI were observed across all final diagnostic groups. Only 30% of patients from the myositis group (n = 15) showed CM uptake.

Discussion and conclusion

The study provides guidance in the definition of the impact of muscle MRI in suspected myopathy: despite being an important diagnostic tool, qualitative MRI findings could not distinguish different types of neuromuscular diagnostic groups in comparison with the gold standard histopathologic diagnosis and/or genetic testing. The results suggest that neither muscle edema nor gadolinium enhancement are able to secure a diagnosis of myositis. The current results do not support qualitative MRI as aiding in the diagnostic distinction of various myopathies. Quantitative muscle MRI is, however, useful in the diagnostic procedure of a suspected neuromuscular disease, especially with regard to assessing progression of a chronic myopathy by quantification of the degree of atrophy and fatty replacement and in exploring patterns of muscle group involvements in certain genetic myopathies.

[Sarcoglycanopathies: state of the art and therapeutic perspectives]

Sarcoglycanopathies are the third most common cause of autosomal recessive limb girdle muscular dystrophies (LGMD). They are the result of a deficiency in one of the sarcoglycans a, b, g, or d. The usual clinical presentation is that of a symmetrical involvement of the muscles of the pelvic and scapular girdles as well as of the trunk, associated with more or less severe cardio-respiratory impairment and a marked increase of serum CK levels. The first symptoms appear during the first decade, the loss of ambulation occurring often during the second decade. Lesions observed on the muscle biopsy are dystrophic. This is associated with a decrease or an absence of immunostaining of the sarcoglycan corresponding to the mutated gene and, to a lesser degree, of the other three sarcoglycans. Many mutations have been reported in the four incriminated genes and some of them are prevalent in certain populations. To date, there is no curative treatment, which does not prevent the development of many clinical trials, especially in gene therapy.

Clinical correlations and long-term follow-up in 100 patients with sarcoglycanopathies

BACKGROUND AND PURPOSE

To describe a large series of patients with α, β, and γ sarcoglycanopathies (LGMD-R3, R4, and R5) and study phenotypic correlations and disease progression.

METHODS

A multicentric retrospective study in four centers in the Paris area collecting neuromuscular, respiratory, cardiac, histologic, and genetic data. The primary outcome of progression was age of loss of ambulation (LoA); disease severity was established according to LoA before or after 18 years of age. Time-to-event analysis was performed.

RESULTS

One hundred patients (54 γ-SG; 41 α-SG; 5 β-SG) from 80 families were included. The γ-SG patients had earlier disease onset than α-SG patients (5.5 vs. 8 years; p = 0.022) and β-SG patients (24.4 years). Axial muscle weakness and joint contractures were frequent and exercise intolerance was observed. At mean follow-up of 22.9 years, 65.3% of patients were wheelchair-bound (66.7% α-SG, 67.3% γ-SG, 40% β-SG). Dilated cardiomyopathy occurred in all sarcoglycanopathy subtypes, especially in γ-SG patients (p = 0.01). Thirty patients were ventilated and six died. Absent sarcoglycan protein expression on muscle biopsy and younger age at onset were associated with earlier time to LoA (p = 0.021 and p = 0.002). Age at onset was an independent predictor of both severity and time to LoA (p = 0.0004 and p = 0.009). The α-SG patients showed genetic heterogeneity, whereas >90% of γ-SG patients carried the homozygous c.525delT frameshift variant. Five new mutations were identified.

CONCLUSIONS

This large multicentric series delineates the clinical spectrum of patients with sarcoglycanopathies. Age at disease onset is an independent predictor of severity of disease and LoA, and should be taken into account in future clinical trials.

Skeletal muscle magnetic resonance imaging in Pompe disease

Pompe disease is characterized by a deficiency of acid alpha-glucosidase that results in muscle weakness and a variable degree of disability. There is an approved therapy based on enzymatic replacement that has modified disease progression. Several reports describing muscle magnetic resonance imaging (MRI) features of Pompe patients have been published. Most of the studies have focused on late-onset Pompe disease (LOPD) and identified a characteristic pattern of muscle involvement useful for the diagnosis. In addition, quantitative MRI studies have shown a progressive increase in fat in skeletal muscles of LOPD over time and they are increasingly considered a good tool to monitor progression of the disease. The studies performed in infantile-onset Pompe disease patients have shown less consistent changes. Other more sophisticated muscle MRI sequences, such as diffusion tensor imaging or glycogen spectroscopy, have also been used in Pompe patients and have shown promising results.

MRI in Neuromuscular Diseases: An Emerging Diagnostic Tool and Biomarker for Prognosis and Efficacy

There is an unmet need to identify biomarkers sensitive to change in rare, slowly progressive neuromuscular diseases. Quantitative magnetic resonance imaging (MRI) of muscle may offer this opportunity, as it is noninvasive and can be carried out almost independent of patient cooperation and disease severity. Muscle fat content correlates with muscle function in neuromuscular diseases, and changes in fat content precede changes in function, which suggests that muscle MRI is a strong biomarker candidate to predict prognosis and treatment efficacy. In this paper, we review the evidence suggesting that muscle MRI may be an important biomarker for diagnosis and to monitor change in disease severity. ANN NEUROL 2020;88:669-681.

Deep phenotyping of facioscapulohumeral muscular dystrophy type 2 by magnetic resonance imaging

BACKGROUND AND PURPOSE

The aim was to define the radiological picture of facioscapulohumeral muscular dystrophy 2 (FSHD2) in comparison with FSHD1 and to explore correlations between imaging and clinical/molecular data.

METHODS

Upper girdle and/or lower limb muscle magnetic resonance imaging scans of 34 molecularly confirmed FSHD2 patients from nine European neuromuscular centres were analysed. T1-weighted and short-tau inversion recovery (STIR) sequences were used to evaluate the global pattern and to assess the extent of fatty replacement and muscle oedema.

RESULTS

The most frequently affected muscles were obliquus and transversus abdominis, semimembranosus, soleus and gluteus minimus in the lower limbs; trapezius, serratus anterior, latissimus dorsi and pectoralis major in the upper girdle. Iliopsoas, popliteus, obturator internus and tibialis posterior in the lower limbs and subscapularis, spinati, sternocleidomastoid and levator scapulae in the upper girdle were the most spared. Asymmetry and STIR hyperintensities were consistent features. The pattern of muscle involvement was similar to that of FSHD1, and the combined involvement of trapezius, abdominal and hamstring muscles, together with complete sparing of iliopsoas and subscapularis, was detected in 91% of patients. Peculiar differences were identified in a rostro-caudal gradient, a predominant involvement of lower limb muscles compared to the upper girdle, and in the higher percentage of STIR hyperintensities in FSHD2.

CONCLUSION

This multicentre study defines the pattern of muscle involvement in FSHD2, providing useful information for diagnostics and clinical trial design. Both similarities and differences between FSHD1 and FSHD2 were detected, which is also relevant to better understand the pathogenic mechanisms underlying the FSHD-related disease spectrum.

Permanent muscle weakness in hypokalemic periodic paralysis

OBJECTIVE

To map the phenotypic spectrum in 55 individuals with mutations in CACNA1S known to cause hypokalemic periodic paralysis (HypoPP) using medical history, muscle strength testing, and muscle MRI.

METHODS

Adults with a mutation in CACNA1S known to cause HypoPP were included. Medical history was obtained. Muscle strength and MRI assessments were performed.

RESULTS

Fifty-five persons were included. Three patients presented with permanent muscle weakness and never attacks of paralysis. Seventeen patients presented with a mixed phenotype of periodic paralysis and permanent weakness. Thirty-one patients presented with the classical phenotype of periodic attacks of paralysis and no permanent weakness. Four participants were asymptomatic. Different phenotypes were present in 9 of 18 families. All patients with permanent weakness had abnormal replacement of muscle by fat on MRI. In addition, 20 of 35 participants with no permanent weakness had abnormal fat replacement of muscle on MRI. The most severely affected muscles were the paraspinal muscles, psoas, iliacus, the posterior muscles of the thigh and gastrocnemius, and soleus of the calf. Age was associated with permanent weakness and correlated with severity of weakness and fat replacement of muscle on MRI.

CONCLUSIONS

Our results show that phenotype in individuals with HypoPP-causing mutations in CACNA1S varies from asymptomatic to periodic paralysis with or without permanent muscle weakness or permanent weakness as sole presenting picture. Variable phenotypes are found within families. Muscle MRI reveals fat replacement in patients with no permanent muscle weakness, suggesting a convergence of phenotype towards a fixed myopathy with aging.

The Limb-Girdle Muscular Dystrophies

PURPOSE OF REVIEW

As a group, the limb-girdle muscular dystrophies (LGMDs) are the fourth most prevalent genetic muscle disease, yet they are still not well known or understood. This article defines and describes LGMDs, delineates a diagnostic strategy, and discusses treatment of the LGMDs.

RECENT FINDINGS

In 2018, the definition of the LGMDs was further refined, and a new nomenclature was proposed. Diagnosis of the LGMDs was long guided by the distinctive clinical characteristics of each particular subtype but now integrates use of genetics-with next-generation sequencing panels, exomes, and full genome analysis-early in the diagnostic assessment. Appreciation of the phenotypic diversity of each LGMD subtype continues to expand. This emphasizes the need for precision genetic diagnostics to better understand each subtype and formulate appropriate management for individual patients. Of significant relevance, the explosion of research into therapeutic options accentuates the need for accurate diagnosis, comprehensive disease characterization, and description of the natural histories of the LGMDs to move the field forward and to mitigate disease impact on patients with LGMD.

SUMMARY

The LGMDs are genetic muscle diseases that superficially appear similar to one another but have important differences in rates of progression and concomitant comorbidities. Definitive diagnoses are crucial to guide management and treatment now and in the future. As targeted treatments emerge, it will be important for clinicians to understand the nomenclature, diagnosis, clinical manifestations, and treatments of the LGMDs.

Lower limb muscle magnetic resonance imaging in Chinese patients with myotonic dystrophy type 1

Objectives: Muscle magnetic resonance imaging (MRI) is a reliable noninvasion tool for detecting muscle abnormalities of myopathies. This study aimed to investigate the MRI features of lower limb muscles in Chinese patients with myotonic dystrophy type 1 (DM1) and to evaluate the correlation between clinical factors and muscle MRI.Methods: We retrospectively reviewed the medical records and lower limb muscle MRI in 24 Chinese DM1 patients. Muscular Impairment Rating Scale (MIRS) was used to assess the clinical muscular impairment. Modified Mercuri's scale was used to assess the degree of fatty infiltration. Spearman rank correlation test was used to analyze the relationship between fatty degeneration score with age, age of onset, disease duration, MIRS grading and creatinine kinase (CK) level.Results: Fatty infiltration was found in 22 of 24 DM1 patients and 8 patients were asymmetrically affected. The medial gastrocnemius was the most affected muscle, followed by soleus and tibialis anterior muscles in lower legs. At thigh level, the anterior compartment was usually the most affected region with the rectus femoris relatively spared. 79.2% of DM1 patients had edema in lower limb muscles. The total mean score of fatty infiltration correlated with MIRS grading, age and disease duration but did not correlate with the age of onset or CK level.Conclusion: Here, we found fatty infiltration present in most Chinese DM1 patients with a selective involvement pattern. There is a correlation between the total mean score of fatty infiltration and MIRS grading, age and disease duration.

Very late-onset limb-girdle muscular dystrophy type 2D: A milder form with a normal muscle biopsy

Sarcoglycanopathies are a genetically heterogeneous group of autosomal recessive limb-girdle muscular dystrophies (LGMD) caused by mutations in sarcoglycan genes. We report a Portuguese patient with a very late-onset LGMD phenotype, whose muscle biopsy and immunostaining, in particular for α-sarcoglycan, were unrevealing. Muscle MRI showed a predominant, bilateral and symmetric involvement of the tight muscles and also, to a lesser extent, of the posterior compartment of lower legs muscles. Next generation sequencing (NGS) revealed a known homozygous c.850C > T (p.Arg284Cys) mutation in SGCA gene. Milder forms of α-sarcoglycanopathies could be a challenging diagnosis; particularly if muscle histopathology and α-sarcoglycan immunohistochemistry are unhelpful. NGS plays a crucial role not only for aiding in the establishment of a definite diagnosis, but also for expanding clinical presentations.

Value of muscle magnetic resonance imaging in the differential diagnosis of muscular dystrophies related to the dystrophin-glycoprotein complex

BACKGROUND

Dystrophin-glycoprotein complex (DGC)-related muscular dystrophies may present similar clinical and pathological features as well as undetectable mutations thus being sometimes difficult to distinguish. We investigated the value of muscle magnetic resonance imaging (MRI) in the differential diagnosis of DGC-related muscular dystrophies and reported the largest series of Chinese patients with sarcoglycanopathies studied by muscle MRI.

RESULTS

Fifty-five patients with DGC-related muscular dystrophies, including 22 with confirmed sarcoglycanopathies, 11 with limb-girdle muscular dystrophy 2I (LGMD2I, FKRP-associated dystroglycanopathy), and 22 with dystrophinopathies underwent extensive clinical evaluation, muscle biopsies, genetic analysis, and muscle MRI examinations. Hierarchical clustering of patients according to the clinical characteristics showed that patients did not cluster according to the genotypes. No statistically significant differences were observed between sarcoglycanopathies and LGMD2I in terms of thigh muscle involvement. The concentric fatty infiltration pattern was observed not only in different sarcoglycanopathies (14/22) but also in LGMD2I (9/11). The trefoil with single fruit sign was observed in most patients with dystrophinopathies (21/22), and a few patients with sarcoglycanopathies (4/22) or LGMD2I (2/11). Hierarchical clustering showed that most patients with sarcoglycanopathies or LGMD2I can be distinguished from dystrophinopathies based on the concentric fatty infiltration pattern and trefoil with single fruit sign at the thigh level on muscle MRI.

CONCLUSIONS

Muscle MRI at the thigh level potentially allows distinction of sarcoglycanopathies or FKRP-associated dystroglycanopathy from dystrophinopathies.

European muscle MRI study in limb girdle muscular dystrophy type R1/2A (LGMDR1/LGMD2A)

BACKGROUND

Limb girdle muscular dystrophy type R1/2A (LGMDR1/LGMD2A) is a progressive myopathy caused by deficiency of calpain 3, a calcium-dependent cysteine protease of skeletal muscle, and it represents the most frequent type of LGMD worldwide. In the last few years, muscle magnetic resonance imaging (MRI) has been proposed as a tool for identifying patterns of muscular involvement in genetic disorders and as a biomarker of disease progression in muscle diseases. In this study, 57 molecularly confirmed LGMDR1 patients from a European cohort (age range 7-78 years) underwent muscle MRI and a global evaluation of functional status (Gardner-Medwin and Walton score and ability to raise the arms).

RESULTS

We confirmed a specific pattern of fatty substitution involving predominantly the hip adductors and hamstrings in lower limbs. Spine extensors were more severely affected than spine rotators, in agreement with higher incidence of lordosis than scoliosis in LGMDR1. Hierarchical clustering of lower limb MRI scores showed that involvement of anterior thigh muscles discriminates between classes of disease progression. Severity of muscle fatty substitution was significantly correlated with CAPN3 mutations: in particular, patients with no or one "null" alleles showed a milder involvement, compared to patients with two null alleles (i.e., predicting absence of calpain-3 protein). Expectedly, fat infiltration scores strongly correlated with functional measures. The "pseudocollagen" sign (central areas of sparing in some muscle) was associated with longer and more severe disease course.

CONCLUSIONS

We conclude that skeletal muscle MRI represents a useful tool in the diagnostic workup and clinical management of LGMDR1.

Clinicogenetic lessons from 370 patients with autosomal recessive limb-girdle muscular dystrophy

Limb-girdle muscular dystrophies (LGMD) are a group of genetically heterogeneous disorders characterized by predominantly proximal muscle weakness. We aimed to characterize epidemiological, clinical and molecular data of patients with autosomal recessive LGMD2/LGMD-R in Brazil. A multicenter historical cohort study was performed at 13 centers, in which index cases and their affected relatives' data from consecutive families with genetic or pathological diagnosis of LGMD2/LGMD-R were reviewed from July 2017 to August 2018. Survival curves to major handicap for LGMD2A/LGMD-R1-calpain3-related, LGMD2B/LGMD-R2-dysferlin-related and sarcoglycanopathies were built and progressions according to sex and genotype were estimated. In 370 patients (305 families) with LGMD2/LGMD-R, most frequent subtypes were LGMD2A/LGMD-R1-calpain3-related and LGMD2B/LGMD-R2-dysferlin-related, each representing around 30% of families. Sarcoglycanopathies were the most frequent childhood-onset subtype, representing 21% of families. Five percent of families had LGMD2G/LGMD-R7-telethonin-related, an ultra-rare subtype worldwide. Females with LGMD2B/LGMD-R2-dysferlin-related had less severe progression to handicap than males and LGMD2A/LGMD-R1-calpain3-related patients with truncating variants had earlier disease onset and more severe progression to handicap than patients without truncating variants. We have provided paramount epidemiological data of LGMD2/LGMD-R in Brazil that might help on differential diagnosis, better patient care and guiding future collaborative clinical trials and natural history studies in the field.

Identification of thiostrepton as a pharmacological approach to rescue misfolded alpha-sarcoglycan mutant proteins from degradation

Limb-girdle muscular dystrophy type 2D (LGMD2D) is characterized by a progressive proximal muscle weakness. LGMD2D is caused by mutations in the gene encoding α-sarcoglycan (α-SG), a dystrophin-associated glycoprotein that plays a key role in the maintenance of sarcolemma integrity in striated muscles. We report here on the development of a new in vitro high-throughput screening assay that allows the monitoring of the proper localization of the most prevalent mutant form of α-SG (R77C substitution). Using this assay, we screened a library of 2560 FDA-approved drugs and bioactive compounds and identified thiostrepton, a cyclic antibiotic, as a potential drug to repurpose for LGMD2D treatment. Characterization of the thiostrepton effect revealed a positive impact on R77C-α-SG and other missense mutant protein localization (R34H, I124T, V247M) in fibroblasts overexpressing these proteins. Finally, further investigations of the molecular mechanisms of action of the compound revealed an inhibition of the chymotrypsin-like activity of the proteasome 24 h after thiostrepton treatment and a synergistic effect with bortezomib, an FDA-approved proteasome inhibitor. This study reports on the first in vitro model for LGMD2D that is compatible with high-throughput screening and proposes a new therapeutic option for LGMD2D caused by missense mutations of α-SG.

Muscle MRI in a large cohort of patients with oculopharyngeal muscular dystrophy

BACKGROUND AND OBJECTIVE

Oculopharyngeal muscular dystrophy (OPMD) is a genetic disorder caused by an abnormal expansion of GCN triplets within the PABPN1 gene. Previous descriptions have focused on lower limb muscles in small cohorts of patients with OPMD, but larger imaging studies have not been performed. Previous imaging studies have been too small to be able to correlate imaging findings to genetic and clinical data.

METHODS

We present cross-sectional, T1-weighted muscle MRI and CT-scan data from 168 patients with genetically confirmed OPMD. We have analysed the pattern of muscle involvement in the disease using hierarchical analysis and presented it as heatmaps. Results of the scans were correlated with genetic and clinical data.

RESULTS

Fatty replacement was identified in 96.7% of all symptomatic patients. The tongue, the adductor magnus and the soleus were the most commonly affected muscles. Muscle pathology on MRI correlated positively with disease duration and functional impairment.

CONCLUSIONS

We have described a pattern that can be considered characteristic of OPMD. An early combination of fat replacement in the tongue, adductor magnus and soleus can be helpful for differential diagnosis. The findings suggest the natural history of the disease from a radiological point of view. The information generated by this study is of high diagnostic value and important for clinical trial development.

Identification of a novel SGCA missense mutation in a case of limb-girdle muscular dystrophy 2D with the absence of four sarcoglycan proteins

Limb‐girdle muscular dystrophy 2D (LGMD2D) is caused by mutations in the α‐sarcoglycan gene (SGCA). Due to lack of specificity, it is impossible to identify LGMD2D only by clinical symptoms and conventional immunohistochemical staining. The loss of any protein (α‐, β‐, γ‐, δ‐sarcoglycan) that represent sarcoglycanopathy may cause reduction or absence of the other three proteins. Here, we report a patient with a complete loss of all the four proteins. Next generation sequencing (NGS) results showed a missense mutation (C.218 C > T) and a partial heterozygous deletion containing exons 7 and 8 of SGCA, which led to the final diagnosis of the patient. The discovery of this new mutation could broaden the spectrum of SGCA mutations, which may be associated with putative LGMD2D, especially when all the four proteins are completely missing.

Clinical and genetic spectrum of sarcoglycanopathies in a large cohort of Chinese patients

Background

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophy (LGMD2C, LGMD2D, LGMD2E, and LGMD2F) that are caused, respectively, by mutations in the SGCG, SGCA, SGCB, and SGCD genes. Knowledge about the clinical and genetic features of sarcoglycanopathies in Chinese patients is limited. The aims of this study were to investigate in detail the clinical manifestations, sarcoglycan expression, and gene mutations in Chinese patients with sarcoglycanopathies and to identify possible correlations between them.

Results

Of 3638 patients for suspected neuromuscular diseases (1733 with inherited myopathies, 1557 with acquired myopathies, and 348 unknown), 756 patients had next-generation sequencing (NGS) diagnostic panel. Twenty-five patients with sarcoglycanopathies (11.5%) were identified from 218 confirmed LGMDs, comprising 18 with LGMD2D, 6 with LGMD2E, and one with LGMD2C. One patient with LGMD2D also had Charcot-Marie-Tooth 1A. The clinical phenotypes of the patients with LGMD2D or LGMD2E were markedly heterogeneous. Muscle biopsy showed a dystrophic pattern in 19 patients and mild myopathic changes in 6. The percentage of correct prediction of genotype based on expression of sarcoglycan was 36.0% (4 LGMD2D, 4 LGMD2E, and one LGMD2C). There was a statistically significant positive correlation between reduction of α-sarcoglycan level and disease severity in LGMD2D. Thirty-five mutations were identified in SGCA, SGCB, SGCG, and PMP22, 16 of which were novel. Exon 3 of SGCA was a hotspot region for mutations in LGMD2D. The missense mutation c.662G > A (p.R221H) was the most common mutation in SGCA. Missense mutations in both alleles of SGCA were associated with a relative benign disease course. No obvious clinical, sarcoglycan expression, and genetic correlation was found in LGMD2E.

Conclusions

This study expands the clinical and genetic spectrum of sarcoglycanopathies in Chinese patients and provides evidence that disease severity of LGMD2D may be predicted by α-sarcoglycan expression and SGCA mutation.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1021-9) contains supplementary material, which is available to authorized users.

Advances in Quantitative Imaging of Genetic and Acquired Myopathies: Clinical Applications and Perspectives

In the last years, magnetic resonance imaging (MRI) has become fundamental for the diagnosis and monitoring of myopathies given its ability to show the severity and distribution of pathology, to identify specific patterns of damage distribution and to properly interpret a number of genetic variants. The advances in MR techniques and post-processing software solutions have greatly expanded the potential to assess pathological changes in muscle diseases, and more specifically of myopathies; a number of features can be studied and quantified, ranging from composition, architecture, mechanical properties, perfusion, and function, leading to what is known as quantitative MRI (qMRI). Such techniques can effectively provide a variety of information beyond what can be seen and assessed by conventional MR imaging; their development and application in clinical practice can play an important role in the diagnostic process and in assessing disease course and treatment response. In this review, we briefly discuss the current role of muscle MRI in diagnosing muscle diseases and describe in detail the potential and perspectives of the application of advanced qMRI techniques in this field.

Untangling the complexity of limb-girdle muscular dystrophies

The limb-girdle muscular dystrophies (LGMDs) are a group of genetically heterogeneous, autosomal inherited muscular dystrophies with a childhood to adult onset, manifesting with hip- and shoulder-girdle muscle weakness. When the term LGMD was first conceptualized in 1954, it was thought to be a single entity. Currently, there are 8 autosomal dominant (LGMD1A-1H) and 26 autosomal recessive (LGMD2A-2Z) variants according to the Online Mendelian Inheritance in Man database. In addition, there are other genetically identified muscular dystrophies with an LGMD phenotype not yet classified as LGMD. This highlights the entanglement of LGMDs, which represents an area in continuous expansion. Herein we aim to simplify the complexity of LGMDs by subgrouping them on the basis of the underlying defective protein and impaired function. Muscle Nerve 58: 167-177, 2018.