Since 2017, more than 250 analyses performed at the Molecular Genetics Laboratory of the Timone Enfant Hospital have yielded negative results in patients with rare genetic muscle diseases. The researchers hypothesise that some of these misdiagnosed patients carry pathogenic RNA (transcript) disrupting variants that were not identified by DNA sequencing. In fact, DNA sequencing analyses can be negative despite the presence of a pathogenic variant that disrupts RNA splicing or expression, causing a genetic disease. For this reason, RNA sequencing can provide a diagnosis in patients who have not been diagnosed by DNA sequencing, thus putting an end to diagnostic wandering. Thus, as a descriptive prevalence study, the objectives are first to determine the rate of positive diagnoses made by the RNAseq approach in patients with muscle diseases that have not yet been diagnosed, and then to identify the genomic characteristics of the pathogenic variants identified in patients by RNAseq analysis, in order to facilitate the identification of this type of variant in future patients.
50 patients will be included in this study during 2 years.
patients with rare genetic muscle diseases who have benefited from high-throughput sequencing analysis (panel of 200 genes defined by the FILNEMUS Rare Neuromuscular Disease Network) carried out at the Molecular Genetics Laboratory, Medical Genetics Department, Timone Enfant Hospital since 2017.
this genetic analysis did not identify pathogenic variants explaining the patient's phenotype This criterion is necessary in order to include only patients in diagnostic error.
a muscle biopsy of the patient is available in the Biological Resources Centre (CRB) at the AP-HM.
Patients with no muscle biopsy available in the CRB.
Patients with an established molecular diagnosis.
Patients for whom RNA extraction from a muscle biopsy sample did not yield RNA of sufficient quality (INR >7) will be excluded from the study. A maximum of two extraction attempts will be performed.
Single group
ARN extraction from muscle biopsies
Other interventionThere will be no visits from participants, so we will be using samples already in the Biological Resources Centre (CRB). RNA will be extracted from muscle biopsies taken as part of the treatment. RNAseq libraries will be sequenced by the Genomics and Bioinformatics Platform (GBiM) at Marseille Medical Genetics (MMG, U1251, AMU). Sequencing will be performed in paired-end (2\*100 bp) on Illumina's Novaseq 6000 system (50 million clusters per sample, 100 M paired-end reads) and then analysed by bioinformatics.
rate of positive diagnoses using the RNAseq approach
to determine the rate of positive diagnoses made using the RNAseq approach in patients with muscle diseases who have not yet been diagnosed. A patient is considered to be in diagnostic limbo if DNA sequencing of 200 genes responsible for muscle diseases has not identified pathogenic variants responsible for the patient's phenotype. Investigators are going to use transcriptomic analysis (RNA sequencing) in combination with innovative bioinformatics tools to identify variants with a deleterious effect at RNA level in patients with undiagnosed muscle diseases. This will make it possible to establish a molecular diagnosis and put an end to misdiagnosis in many patients.
Identification of genomic characteristics
identify the genomic characteristics of pathogenic variants identified by the RNAseq approach. This analysis could potentially uncover certain characteristics that are specific to this type of variant, making it possible to suggest their presence in other undiagnosed patients in the future.
Click on the lead sponsor to view all of their trials.
