Muscle MRI Research Articles

Novel variants, muscle imaging, and myopathological changes in Chinese patients with VCP-related multisystem proteinopathy.

The objective of this research was to study the clinical features, genetic characteristics, muscle imaging, and muscle pathological changes of a cohort of Chinese patients with mutations in the valosin-containing protein (VCP) gene. Nine patients from seven Chinese pedigrees were recruited. Variants were detected by next-generation sequencing and confirmed by Sanger sequencing. Thigh muscle MRIs were performed in five patients. All the patients received muscle biopsies. Seven variants in VCP were identified, and two were novel. All the patients presented with adult-onset muscle weakness. The appearance of "isolated island sign" or "contra-isolated island sign" was observed in four of the five the patients on muscle MRIs. Muscle biopsies demonstrated the combination of neuropathic and myopathic changes in seven patients and muscle dystrophic changes in two patients. Notably, rimmed vacuoles and cytoplasmic VCP and p62-positive protein aggregates were observed in all the patients. Our finding of novel variants expanded the mutational spectrum of the VCP gene. This cohort of Chinese patients with VCP mutations mainly present with inclusion body myopathy with predominant limb-girdle distribution. The characteristic pattern of fatty infiltration, especially the "isolated island" and "contra-isolated island" on muscle MRI, along with rimmed vacuoles in muscle biopsy, provides valuable clues for guiding genetic diagnostic workup.

Quantitative muscle MRI displays clinically relevant myostructural abnormalities in long-term ICU-survivors: a case–control study

BackgroundLong-term data on ICU-survivors reveal persisting sequalae and a reduced quality-of-life even after years. Major complaints are neuromuscular dysfunction due to Intensive care unit acquired weakness (ICUAW). Quantitative MRI (qMRI) protocols can quantify muscle alterations in contrast to standard qualitative MRI-protocols.MethodsUsing qMRI, the aim of this study was to analyse persisting myostructural abnormalities in former ICU patients compared to controls and relate them to clinical assessments. The study was conducted as a cohort/case–control study. Nine former ICU-patients and matched controls were recruited (7 males; 54.8y ± 16.9; controls: 54.3y ± 11.1). MRI scans were performed on a 3T-MRI including a mDTI, T2 mapping and a mDixonquant sequence. Water T2 times, fat-fraction and mean values of the eigenvalue (λ1), mean diffusivity (MD), radial diffusivity (RD) and fractional anisotropy (FA) were obtained for six thigh and seven calf muscles bilaterally. Clinical assessment included strength testing, electrophysiologic studies and a questionnaire on quality-of-life (QoL). Study groups were compared using a multivariate general linear model. qMRI parameters were correlated to clinical assessments and QoL questionnaire using Pearson´s correlation.ResultsqMRI parameters were significantly higher in the patients for fat-fraction (p < 0.001), water T2 time (p < 0.001), FA (p = 0.047), MD (p < 0.001) and RD (p < 0.001). Thighs and calves showed a different pattern with significantly higher water T2 times only in the calves. Correlation analysis showed a significant negative correlation of muscle strength (MRC sum score) with FA and T2-time. The results were related to impairment seen in QoL-questionnaires, clinical testing and electrophysiologic studies.ConclusionqMRI parameters show chronic next to active muscle degeneration in ICU survivors even years after ICU therapy with ongoing clinical relevance. Therefore, qMRI opens new doors to characterize and monitor muscle changes of patients with ICUAW. Further, better understanding on the underlying mechanisms of the persisting complaints could contribute the development of personalized rehabilitation programs.

Radiomics and machine learning applied to STIR sequence for prediction of quantitative parameters in facioscapulohumeral disease.

Quantitative Muscle MRI (qMRI) is a valuable and non-invasive tool to assess disease involvement and progression in neuromuscular disorders being able to detect even subtle changes in muscle pathology. The aim of this study is to evaluate the feasibility of using a conventional short-tau inversion recovery (STIR) sequence to predict fat fraction (FF) and water T2 (wT2) in skeletal muscle introducing a radiomic workflow with standardized feature extraction combined with machine learning algorithms. Twenty-five patients with facioscapulohumeral muscular dystrophy (FSHD) were scanned at calf level using conventional STIR sequence and qMRI techniques. We applied and compared three different radiomics workflows (WF1, WF2, WF3), combined with seven Machine Learning regression algorithms (linear, ridge and lasso regression, tree, random forest, k-nearest neighbor and support vector machine), on conventional STIR images to predict FF and wT2 for six calf muscles. The combination of WF3 and K-nearest neighbor resulted to be the best predictor model of qMRI parameters with a mean absolute error about ± 5 pp for FF and ± 1.8 ms for wT2. This pilot study demonstrated the possibility to predict qMRI parameters in a cohort of FSHD subjects starting from conventional STIR sequence.

LAMA2-Related Muscular Dystrophy: The Importance of Accurate Phenotyping and Brain Imaging in the Diagnosis of LGMD.

We report three siblings from a non-consanguineous family presenting with contractural limb-girdle phenotype with intrafamilial variability. Muscle MRI showed posterior thigh and quadriceps involvement with a sandwich-like sign. Whole-exome sequencing identified two compound heterozygous missense TTN variants and one heterozygous LAMA2 variant. Brain MRI performed because of concentration difficulties in one of the siblings evidenced white-matter abnormalities, subsequently found in the others. The genetic analysis was re-oriented, revealing a novel pathogenic intronic LAMA2 variant which confirmed the LAMA2-RD diagnosis. This work highlights the importance of a thorough clinical phenotyping and the importance of brain imaging, in order to orientate and interpret the genetic analysis.

Unique Clinical, Radiological and Histopathological Characteristics of a Southeast Asian Cohort of Patients with Limb-Girdle Muscular Dystrophy 2G/LGMD-R7-Telethonin-Related.

We describe a cohort of five patients with limb-girdle muscular dystrophy (LGMD) 2G/LGMD-R7 in a South-east Asian cohort. LGMD2G/LGMD-R7-telethonin-related is caused by mutations in the TCAP gene that encodes for telethonin. We identified consecutive patients with LGMD2G/LGMD-R7-telethonin-related, diagnosed at the National Neuroscience Institute (NNI) and National University Hospital (NUH) between January 2000 and June 2021. At onset, three patients presented with proximal lower limb weakness, one patient presented with Achilles tendon contractures, and one patient presented with delayed gross motor milestones. At last follow up, three patients had a limb girdle pattern of muscle weakness and two had a facioscapular humeral pattern of weakness. Whole body muscle MRI performed for one patient with a facioscapular-humeral pattern of weakness showed a pattern of muscle atrophy similar to facioscapular-humeral dystrophy. One patient had histological features consistent with myofibrillar myopathy; electron microscopy confirmed the disruption of myofibrillar architecture. One patients also had reduced staining to telethonin antibody on immunohistochemistry. We report the unique clinical and histological features of a Southeast Asian cohort of five patients with LGMD2G/LGMD-R7-telethonin-related muscular dystrophy and further expand its clinical and histopathological spectrum.

Contribution of muscle MRI for diagnosis of myopathy

Inherited myopathies are a group of disease, which, although distinct from a genetic and prognostic point of view, can lead to non-specific clinical pictures due to phenotypic overlap. Acquired immuno-mediated myopathies may also pose the problem of clinically accurate etiological orientation. The assessment of fatty infiltration and pathological increase in water volume of the muscle contingent on whole-body muscle MRI is becoming increasingly important in aiding the initial diagnosis of inherited and acquired myopathies. MRI helps orientating the clinical diagnostic hypotheses thanks to the patterns of muscle involved (more or less specific according to the entities), which led to the development of decision-making algorithms proposed in the literature. The aim of this article is to specify the proper MRI protocol for the evaluation of myopathies and the basis of the interpretation and to provide a summary of the most frequently inherited and acquired myopathies described in the literature.

Correlation between whole body muscle MRI and functional measures in paediatric patients with facioscapulohumeral muscular dystrophy

Symptoms and severity of facioscapulohumeral muscular dystrophy (FSHD) can vary greatly, even within the same family. Clinical trial readiness requires accurate and reliable methods of assessing disease stage and progression. MRI has not previously been assessed as a disease biomarker in paediatric FSHD. Eleven patients with FSHD1 underwent whole body muscle MRI. Pre-selected muscles were analysed by a paediatric radiologist using the semi-quantitative Mercuri/Kim method. Within each domain (oedema, fat replacement, atrophy) scores for each muscle were then summated to give each participant three cumulative domain scores. The same participants had functional measures scored: FSHD-CSS (Ricci), FSHD-CS (Lamperti), FSHD-COM, PUL2.0, MFM-32, 6MWT, myometry and manual muscle testing. Pearson coefficient was calculated to determine strength of correlation. The scores for atrophy and fat replacement showed strong correlation with functional outcome measures, particularly FSHD-CSS, FSHD-CS and FSHD-COM. In contrast, muscle oedema correlated poorly with all functional outcome measures, with no relationship seen to the 6MWT. This study of eleven children suggests that semi-quantitative visual Mercuri score utilising fat replacement or atrophy on whole body muscle MRI correlates strongly with disease-specific functional measures and may be a useful measure of disease severity in paediatric FSHD.

Disease specific determinants of cardiopulmonary fitness in systemic sclerosis

ObjectivesWe aimed to quantify the burden of exercise intolerance in systemic sclerosis (SSc) and explore the disease features that contribute to impaired exercise capacity (measured as peak oxygen uptake, peak VO2) to provide novel mechanistic insights into the causes of physical disability in SSc. MethodsThirty-three SSc patients with no history of cardiac disease and no active myositis underwent cardiac and skeletal muscle MRI, transthoracic echocardiography, pulmonary function tests and cardiopulmonary exercise testing (CPET). CPET results were compared to an age-, sex-, and weight-matched controls with no overt cardiopulmonary disease. Native T1 and T2-mapping sequences were used to quantify diffuse fibroinflammatory myocardial disease and qualitative assessment of skeletal muscle oedema was performed. The associations between parameters of cardiorespiratory function and skeletal muscle abnormalities and peak VO2 were evaluated with linear regression analysis. ResultsExercise capacity was markedly impaired in SSc and significantly reduced when compared to control subjects (percent predicted peak VO2: 70% vs 98%, p < 0⋅01). Diffuse myocardial fibroinflammatory disease (p < 0⋅01) and skeletal muscle oedema (p = 0⋅01) were significantly associated with reduced exercise capacity. There was no association between impaired exercise capacity and left ventricular ejection fraction. ConclusionSSc is associated with marked functional impairment that is not explained by commonly used parameters of cardiac function such as left ventricular ejection fraction. Rather, only more sensitive measures of organ involvement are associated with impaired exercise tolerance. Our results show diffuse interstitial changes of the myocardium and skeletal muscle affect oxygen uptake and are important contributors to functional limitation in SSc.

Quantitative muscle MRI captures early muscle degeneration in calpainopathy

To evaluate differences in qMRI parameters of muscle diffusion tensor imaging (mDTI), fat-fraction (FF) and water T2 time in leg muscles of calpainopathy patients (LGMD R1/D4) compared to healthy controls, to correlate those findings to clinical parameters and to evaluate if qMRI parameters show muscle degeneration in not-yet fatty infiltrated muscles. We evaluated eight thigh and seven calf muscles of 19 calpainopathy patients and 19 healthy matched controls. MRI scans were performed on a 3T MRI including a mDTI, T2 mapping and mDixonquant sequence. Clinical assessment was done with manual muscle testing, patient questionnaires (ACTIVLIM, NSS) as well as gait analysis. Average FF was significantly different in all muscles compared to controls (p < 0.001). In muscles with less than 8% FF a significant increase of FA (p < 0.005) and decrease of RD (p < 0.004) was found in high-risk muscles of calpainopathy patients. Water T2 times were increased within the low- and intermediate-risk muscles (p ≤ 0.045) but not in high-risk muscles (p = 0.062). Clinical assessments correlated significantly with qMRI values: QMFM vs. FF: r = − 0.881, p < 0.001; QMFM versus FA: r = − 0.747, p < 0.001; QMFM versus MD: r = 0.942, p < 0.001. A good correlation of FF and diffusion metrics to clinical assessments was found. Diffusion metrics and T2 values are promising candidates to serve as sensitive early and non-invasive methods to capture early muscle degeneration in non-fat-infiltrated muscles in calpainopathies.

Muscle MRI in immune-mediated necrotizing myopathy (IMNM): implications for clinical management and treatment strategies

ObjectivesImmune-mediated necrotizing myopathy (IMNM) is the most severe idiopathic inflammatory myopathy (IIM) and early aggressive poly-immunotherapy is often required to reduce long-term disability. The aim of this study is to investigate muscle MRI in IMNM as outcome measure for disease activity, severity, progression, response to treatment, and to better characterize the pattern of muscle involvement.MethodsThis is a retrospective, observational, cross-sectional, and longitudinal study including 22 IMNM patients, divided into three groups based on timing of first MRI and if performed before or under treatment. T1 score and percentage of STIR positive muscles (STIR%) were considered and analyzed also in relation to demographic, clinical and laboratory characteristics.ResultsSTIR% was higher in untreated patients and in those who performed MRI earlier (p = 0.001). Pelvic girdle and thighs were in general more affected than legs. T1 score was higher in patients with MRI performed later in disease course (p = 0.004) with a prevalent involvement of the lumbar paraspinal muscles, gluteus medius and minimus, adductor magnus and hamstrings. 22% of STIR positive muscles showed fat replacement progression at second MRI. Higher STIR% at baseline correlated with higher risk of fat replacement at follow-up (p = 0.003); higher T1 score correlated with clinical disability at follow-up, with late treatment start and delayed treatment with IVIG (p = 0.03).InterpretationMuscle MRI is a sensitive biomarker for monitoring disease activity and therapy response, especially when performed early in disease course and before treatment start, and could represent a supportive outcome measure and early prognostic index in IMNM.

Highly asymmetrical distribution of muscle wasting correlates to the heteroplasmy in a patient carrying a large-scale mitochondrial DNA deletion: a novel pathophysiological mechanism for explaining asymmetry in mitochondrial myopathies

Mitochondrial diseases are a heterogeneous group of pathologies, caused by missense mutations, sporadic large-scale deletions of mitochondrial DNA (mtDNA) or mutations of nuclear maintenance genes. We report the case of a patient in whom extended muscle pathology, biochemical and genetic mtDNA analyses have proven to be essential to elucidate a unique asymmetrical myopathic presentation. From the age of 34 years on, the patient has presented with oculomotor disorders, right facial peripheral palsy and predominantly left upper limb muscle weakness and atrophy. By contrast, he displayed no motor weakness on the right hemi-body, and no sensory symptoms, cerebellar syndrome, hypoacusis, or parkinsonism. Cardiac function was normal. CK levels were elevated (671 UI/L). Electroneuromyography (ENMG) and muscle MRI showed diffuse myogenic alterations, more pronounced on the left side muscles. Biopsy of the left deltoid muscle showed multiple mitochondrial defects, whereas in the right deltoid, mitochondrial defects were much less marked. Extended mitochondrial biochemical and molecular workup revealed a unique mtDNA deletion, with a 63.4% heteroplasmy load in the left deltoid, versus 8.1% in the right one. This case demonstrates that, in mitochondrial myopathies, heteroplasmy levels may drastically vary for the same type of muscle, rising the hypothesis of a new pathophysiological mechanism explaining asymmetry in hereditary myopathies.

Segmentation of shoulder muscle MRI using a new Region and Edge based Deep Auto-Encoder

Automatic segmentation of shoulder muscle MRI is challenging due to the high variation in muscle size, shape, texture, and spatial position of tears. Manual segmentation of tear and muscle portion is hard, time-consuming, and subjective to pathological expertise. This work proposes a new Region and Edge-based Deep Auto-Encoder (RE-DAE) for shoulder muscle MRI segmentation. The proposed RE-DAE harmoniously employs average and max-pooling operations in the Convolutional encoder and decoder blocks. The DAE’s region and edge-based segmentation encourage the network to extract homogenous and anatomical information, respectively. These two concepts, systematically combined in a DAE, generate a discriminative and sparse hybrid feature space (exploiting both region homogeneity and boundaries). Moreover, the concept of static attention is exploited in the proposed RE-DAE that helps effectively learn the tear region. The performances of the proposed RE-DAE architectures have been tested using a 3D MRI shoulder muscle dataset using the hold-out cross-validation technique. The MRI data has been collected from the Korea University Anam Hospital, Seoul, South Korea. Experimental comparisons have been conducted by employing innovative custom-made and existing pre-trained CNN architectures using transfer learning and fine-tuning. Objective evaluation on the muscle datasets using the proposed SA-RE-DAE showed a dice similarity of 85.58% and 87.07%, an accuracy of 81.57% and 95.58% for tear and muscle regions, respectively. The high visual quality and the objective result suggest that the proposed SA-RE-DAE can correctly segment tear and muscle regions in shoulder muscle MRI for better clinical decisions.

PET-MRI in idiopathic inflammatory myositis: a comparative study of clinical and immunological markers with imaging findings

BackgroundWe sought to determine the utility of PET-MRI in diagnosing Idiopathic Inflammatory Myositis (IIM), and look for association between FDG uptake and clinical, pathological and laboratory parameters.MethodsA retrospective, observational study was conducted on IIM patients having positive serum autoantibodies and who underwent PET-MRI (3-Tesla SIEMENS Biograph MR scanner) between 2017 and 2021. Thirty patients who underwent PET-MRI to detect systemic metastasis without muscle involvement formed the control group.ResultsIn the IIM cohort, female: male sex ratio was 1.73, mean age at diagnosis was 40.33 years, and the mean duration of illness was 7 months. 33.33% of patients had severe limb weakness. Mi2B (43.33%), Mi2A (43.33%), PL-7(10%), PL-12(6.67%), SRP (16.67%), Tif1gamma (3.33%), NxP2 (3.33%), Ro-52(40%), PM-Scl, U1-RNP, ANA (26.67%) were the serum autoantibodies identified. Using SUV max Ratio to quantify FDG uptake, PET-MRI showed a sensitivity of 100% with 93.3% specificity in diagnosing IIM.FDG uptake was maximum in proximal lower limb region followed by proximal upper limb. Multivariate regression analysis showed that the severity of muscle weakness, serum Mi2B antibody positivity and serum creatinine kinase levels had a significant positive correlation with FDG uptake (value of 0.005, 0.043, 0.042, respectively for whole-body FDG uptake). FDG uptake also showed good correlation with histopathological features and muscle MRI, but there was no significant association with treatment response. Three female patients in our cohort had primary malignancy involving the breast, uterus, and cervix.ConclusionsPET-MRI is a promising diagnostic modality for IIM. PET-MRI reflects the severity of muscle inflammation, showing good association with various clinical/laboratory parameters, histopathology, and muscle MRI. Parameters associated with severe muscle inflammation in PET-MRI—clinical severity of muscle weakness, Mi2B positivity, and serum creatine kinase levels—may be used as clinical/laboratory markers of disease severity in IIM. PET-MRI has the added advantage of detection of systemic malignancy.

Nemaline Myopathy in Brazilian Patients: Molecular and Clinical Characterization.

Nemaline myopathy (NM), a structural congenital myopathy, presents a significant clinical and genetic heterogeneity. Here, we compiled molecular and clinical data of 30 Brazilian patients from 25 unrelated families. Next-generation sequencing was able to genetically classify all patients: sixteen families (64%) with mutation in NEB, five (20%) in ACTA1, two (8%) in KLHL40, and one in TPM2 (4%) and TPM3 (4%). In the NEB-related families, 25 different variants, 11 of them novel, were identified; splice site (10/25) and frame shift (9/25) mutations were the most common. Mutation c.24579 G>C was recurrent in three unrelated patients from the same region, suggesting a common ancestor. Clinically, the “typical” form was the more frequent and caused by mutations in the different NM genes. Phenotypic heterogeneity was observed among patients with mutations in the same gene. Respiratory involvement was very common and often out of proportion with limb weakness. Muscle MRI patterns showed variability within the forms and genes, which was related to the severity of the weakness. Considering the high frequency of NEB mutations and the complexity of this gene, NGS tools should be combined with CNV identification, especially in patients with a likely non-identified second mutation.

Hoffman myopathy and hypothyroidism.

Learning point for clinicians: Hypothyroidism should be included in the differential diagnosis of any patient with muscle weakness and hypertrophy, since it is reversible on therapy. A strong index of clinical suspicion, coupled with relevant laboratory investigations and judicial use of muscle MRI can aid in early diagnosis, without the need for biopsy.

Quantitative vs qualitative muscle MRI: Imaging biomarker in patients with Oculopharyngeal Muscular Dystrophy (OPMD)

Oculopharyngeal muscular dystrophy (OPMD) is a genetic muscle disease causing ptosis, severe swallowing difficulties and progressive limb weakness, although atypical presentations may be difficult to diagnose. Sensitive biomarkers of disease progression in OPMD are needed to enable more effective clinical trials. This study was designed to test the feasibility of using MRI to aid OPMD diagnosis and monitor OPMD progression. Twenty-five subjects with Dixon whole-body muscle MRI were enrolled: 10 patients with genetically confirmed OPMD, 10 patients with non-OPMD muscular dystrophies, and 5 controls. Using the MRI Dixon technique, muscle fat replacement was evaluated in the tongue, serratus anterior, lumbar paraspinal, adductor magnus, and soleus muscles using quantitative and semi-quantitative rating methods. Changes were compared with muscle strength testing, dysphagia severity, use of gait aids, and presence of dysarthria. Quantitative MRI scores of muscle fat replacement in the tongue could differentiate OPMD from other muscular dystrophies and from controls. Moreover, fat fraction in the tongue correlated with clinical severity of dysphagia. This study provides preliminary support for the use of Dixon-based quantitative MRI images as outcome measures for monitoring disease progression in clinical trials and provides rationale for future prospective studies aimed at methodological refinement and covariate identification.

VP.46 Dermatomyositis-specific autoantibodies and muscle MRI findings

To date, 5 dermatomyositis specific autoantibodies (DMSAs) have been identified. Recent studies have revealed that each DM subtype according to the positive DMSA has clinical and pathological characteristic features, which naturally raises a question whether each DM subtype has unique features also on muscle MRI. We studied muscle MRI of 125 patients who had one of the 5 DMSAs and were pathologically diagnosed with DM by sarcoplasmic MxA expression at our center from January 2009 to November 2021. A total of proximal 12 leg and 8 arm muscles were evaluated in the axial plane, in addition to fascia and subcutaneous fat (SF). For skeletal muscle, the intensity (faint or strong), distribution (diffuse, patchy, or peripheral), percent area of affected (none, below 50%, more than 50%), and the texture (honeycomb pattern, homogeneous, or heterogeneous) of high signal intensity (HSI) within each muscle were evaluated. We graded the scores 0-3 according to the percent area of HSI in fascia and the scores 0-2 according to the HSI in SF. Among 125 patients, 79 were women, 32 were children (< 18years), and the median age were 54 years. Of these patients, 42 had anti-TIF1-γ, 16 anti-Mi-2, 16 anti-MDA5, 44 anti-NXP2, and 7 anti-SAE antibodies, respectively. Anti-TIF1-γ DM was associated with peripheral distribution of HSI (97.6% vs non- TIF1-γ DM 77.1%; p < 0.01). Anti-NXP2 DM was associated with diffuse distribution of HSI (97.7% vs 76.5%; p < 0.01) and high fascia score (p < 0.05). Anti-MDA5 DM was reversely associated with diffuse distribution of HSI (31.3% vs 91.7%; p < 0.001) and honeycomb pattern (62.5% vs 99.1%; p < 0.001), while it tended to have patchy distribution of HSI (56.3% vs 31.2%; p = 0.057). All DM patients had at least one HSI area in fascia. Each DM subtype according to positive DMSA seems to have characteristic MRI features, except for anti-SAE DM whose sample number was too small in this study. Fascial edema is common among DM patients.

P.15 Symptomatic DMD carrier as a differential diagnosis in patients presenting asymmetrical limb weakness

Duchenne/Becker muscular dystrophy (DMD) is one of the most common myopathies, characterized by an X-linked recessive disease. Asymmetrical limb weakness is rarely present in patients with muscle diseases such as ANO5-related myopathy, facioscapulohumeral muscular dystrophy, and sporadic inclusion body myositis. We report two cases of symptomatic DMD carriers presenting with asymmetrical limb weakness. A 50-year-old woman visited the department of neurology presenting with slowly progressive weakness of the limbs since childhood. A neurological examination revealed a weakness of the right arm and both legs, which were graded 4 as MRC system. Muscle MRI showed asymmetric fatty infiltration of the limbs, markedly affected by right biceps brachii, latissimus dorsi, and gastrocnemius. Immunohistochemistry (IHC) of the C-terminal region of the dystrophin gene presented several scattered stain-negative fibers. Genetic analysis revealed c.6703delG (p.Ser2235Ilefs*12, NM_004006.2) mimicking single exon 46 deletion in MLPA. A 29-year-old female presented with an elevated level of serum creatine kinase without subjective weakness. Neurologic examination showed the subtle motor weakness of the right arm, graded 4+. Muscle MRI revealed high T1 signal change on the right biceps femoris, which was not affected clinically, in addition to right biceps brachii and latissimus dorsi. IHC showed dystrophic changes and a mosaic pattern of dystrophin expression. The diagnosis was confirmed by MLPA, revealing heterozygous deletion of exon 44 in the DMD gene. Asymmetrical limb weakness can be a remark for the diagnosis of symptomatic DMD carrier. Furthermore, muscle MRI is more sensitive in detecting pathologic changes than routine neurologic examination. And single-base point mutation can mimick the exon deletion in MLPA, which needs sequencing analysis in a case of single exon deletion in DMD. Therefore, a multidisciplinary approach is mandatory for final diagnosis and a better understanding of symptomatic DMD carriers.

P.01 A KLHL40 3′UTR splice-altering variant causes milder NEM8

Nemaline myopathy 8 (NEM8) is typically a severe autosomal recessive disorder associated with variants in the kelch-like family member 40 gene (KLHL40). To date, only protein-altering pathogenic variants in <i>KLHL40</i> have been implicated in NEM8. Common features include fetal akinesia/hypokinesia, fractures, contractures, dysphagia, respiratory failure, and neonatal death. Here, we describe a 26-year-old man with relatively mild NEM8. He presented with hypotonia and bilateral femur fractures at birth, later developing bilateral Achilles' contractures, scoliosis, and elbow and knee contractures. He had walking difficulties throughout his childhood and became wheelchair bound from age 13 after prolonged immobilization. Muscle MRI at age 13 indicated prominent fat replacement in his pelvic girdle, posterior compartments of thighs, vastus intermedius and legs. Muscle biopsy revealed nemaline bodies and intranuclear rods. RNA sequencing and western blotting of patient skeletal muscle indicated significant reduction in <i>KLHL40</i> mRNA and protein respectively. Using gene panel screening, exome sequencing and RNA sequencing, we identified compound heterozygous variants in <i>KLHL40</i>; a truncating 10.9 kb deletion in trans with a likely pathogenic variant (c.*152G>T) in the 3' untranslated region (UTR). Computational tools SpliceAI and Introme predicted the c.*152G>T variant created a cryptic donor splice site. RNA sequencing and in vitro analyses indicated that the c.*152G>T variant induces multiple de novo splicing events. Nonsense mediated decay of <i>KLHL40</i> mRNA, provoked by introduction of 3' UTR introns, likely explains the loss of both mRNA and protein expression in the patient. Our analysis of 3' UTR variants in ClinVar suggests that SNPs that introduce aberrant 3'UTR splicing may be under recognised in Mendelian disease. We encourage consideration of this mechanism during disease gene screening.

P.207 Muscle magnetic resonance imaging in Myotonic dystrophy type 1: Longitudinal study for 5 years

Myotonic dystrophy type 1 is the most common genetic muscle disease in adults, caused by increased expansion of CTG repeats in the DMPK gene. It is characterized by progressive distal dominant muscle weakness and myotonia. The aim of this study was to evaluate objective longitudinal changes in the muscle magnetic resonance imaging in DM1 patients over five years. Eighteen genetically diagnosed DM1 patients were enrolled at baseline. The mean age was 44.86±9.83, mean CTG repeat length was 465±328.86 and a disease duration of 18.29±9.43 years. The baseline motor function such as medical research council sum score, Muscular impairment rating scale and 6-minute walk test were evaluated at the baseline and after 5 years of follow up. The pulmonary function and serum creatine kinase levels were also evaluated. The muscle magnetic resonance imaging was performed at baseline and after 5 years. The individual muscles were semi-quantitatively graded using five-point Mercuri scores. The thirteen upper muscle groups and twenty one lower limb muscles were evaluated. The lower muscle groups including gluteus muscles. The fatty infiltrative changes progressed after 5 years of follow up, with significant score changes were most prominently observed in lower limb muscles including gastrocnemius, soleus, tibialis anterior, gastrocnemius and tensor fascia latae muscles. Among upper limb muscles, latissimus dorsi showed most significant fatty infiltrative changes, followed by serratus and rhomboid muscles. Bases on the longitudinal follow up of the muscle MRI, DM1 showed significant deterioration in the lower limb muscles, with prominent changes in the crural muscles. This is the first longitudinal muscle MRI study and more studies are warranted to understand muscle degeneration in DM1.