Clinical,Imaging,Pathological And Molecular Biological Features Of RR-LSM

Background and Objective:Riboflavin responsive lipid storage myopathy(RR-LSM)is the most common type of lipid storage myopathy in China,which mostly belongs to multiple acyl—CoA dehydrogenation deficiency type III.Riboflavin responsive lipid storage myopathy is a treatable metabolic myopathy disease.The phenotypes and symptoms in riboflavin responsive lipid storage myopathy were heterogeneous and variable,which created a challenge to diagnose and treatment.Therefore,this study analyzed the clinical data,imaging characteristics,pathological characteristics and genetic features of RR-LSM patients to explore its mutational spectrum and phenotype.I hope this study can offer some help for clinical diagnosis.Materials and methods:The main subjects of research were obtained from the Neurology Department of The First Affiliated Hospital of Zhengzhou University.They were RR-LSM patients who admitted to our hospital for diagnose.The medical histories(including family history)were carefully collected.Physical examination,neurological examination,and a series of laboratory tests and examinations(including muscle biopsy)were performed.Genomic DNA was extracted from peripheral blood samples of patients and their parents.The genetic test was performed using targeted next generation sequencing.Sanger sequencing was used to confirm the identical variants of the proband and parents.Research use the single-nucleotide polymorphism(dbSNP)database and the 1000 Genomes Project to check frequency in the general population of the identified variants.In order to exclude the possibility that the variants represent polymorphisms,200 healthy controls of Chinese origin examined identical genomic fragments for the presence of the mutations.Mutation Taster predict the possible protein functional changes caused by the mutations.SPSS statistical software version 22.0 was used to analyze data.Results:Clinical features:most patients showed progressed exercise intolerance and weakness in proximal limbs.One patient developed skin damage which completely relieved after treatment.This is first reported riboflavin responsive lipid storage myopathy patients caused by ETFDH mutation can present with skin damage.Muscle MRI:the typical characteristic of muscle MRI imaging is edema in affected muscles.Semitendinosus and semimembranosus are often affected.In addition,the abnormal signal can disappear after treatment.Muscle pathology:typical pathologic findings of RR-LSM patients were developed:hematoxylin-eosin staining(HE)revealed vacuoles in muscle fibers.The Oil Red O staining(ORO)showed lipid droplets accumulation.Genetic testing:all patients who underwent genetic testing had heterozygous mutations in the ETFDH gene.The four mutation sites:c.684±1G>T、c.1204A>T、c.122T>C and c.970G>T were not reported before.c.1204A>T and c.970G>T were absent in 200 healthy Chinese controls,1000 genomes database,and ExAC database.The two mutations are predicted to be disease-causing by Mutationtaster.Treatment and prognosis:17 patients were followed for a period of two years,all cases were significantly improved after treatment with drugs like riboflavin,L-carnitine,coenzyme Q10,while 5 cases relapsed,but the symptoms improved again after drug treatment.Conclusion:First,riboflavin responsive lipid storage myopathy is a heterogeneous group disorders which mainly progressed exercise intolerance and weakness in proximal limbs.The heterogeneous clinical features can cause misdiagnosis.The study reports a patient with RR-LSM presenting with skin damage caused by ETFDH mutation which is a novel type of skin damage responsive to riboflavin.It has yet not been reported in patients with RR-LSM.This expands the known phenotype of RR-LSM.Second,the muscle MRI images of riboflavin responsive lipid storage myopathy patients mainly presented with edema.Abnormal signal disappeared after the remission of clinical symptoms,this indicated that MRI could be used to evaluate efficacy and prognosis.Third,typical pathologic findings of RR-LSM patients were:hematoxylin-eosin staining(HE)revealed vacuoles in muscle fibers and the Oil Red O staining(ORO)showed lipid droplets accumulation.Fourth,ETFDH gene mutation is the most common cause of riboflavin responsive lipid storage myopathy in our study.Four pathogenic mutations of ETFDH which have not been reported before were identified:c.684+1G>T、c.1204A>T、c.122T>C and c.970G>T.These expands the known mutational spectrum of ETFDH gene.Fifth,RR-LSM is a treatable genetic disorder,early definitive diagnosis and treatment can significantly improve the quality of life.