Transcriptomic Analysis to Put an End to Misdiagnosis in Patients With Rare Muscle Diseases

Transcriptomic Analysis to Put an End to Misdiagnosis in Patients With Rare Muscle Diseases

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.

Inclusion Criteria:

• 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 criterion is necessary to limit the analysis to patients with muscular diseases among all the patients analysed by the Molecular Genetics Laboratory.

• 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.

Exclusion Criteria:

• 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.