A National French consensus on gene lists for the diagnosis of myopathies using next-generation sequencing

International audienceNext-generation sequencing (NGS) gene-panel-based analyses constitute diagnosis strategies which are adapted to the genetic heterogeneity within the field of myopathies, including more than 200 implicated genes to date. Nonetheless, important inter-laboratory diversity of gene panels exists at national and international levels, complicating the exchange of data and the visibility of the diagnostic offers available for referring neurologists. To address this issue, we here describe the initiative of the genetic diagnosis section of the French National Network for Rare Neuromuscular Diseases (Filière Nationale des Maladies Rares Neuromusculaires, FILNEMUS), which led to set up a consensual nationwide diagnostic strategy among the nine French genetic diagnosis laboratories using NGS for myopathies. The strategy is based on the determination of 13 clinical and/or histological entry-diagnosis groups, and consists for each group either in a successive NGS analysis of a "core gene list" followed in case of a negative result by the analysis of an "exhaustive gene list", or in the NGS analysis of a "unique exhaustive gene list"

Identification of mutations in TMEM5 and ISPD as a cause of severe cobblestone lissencephaly.

International audienceCobblestone lissencephaly is a peculiar brain malformation with characteristic radiological anomalies. It is defined as cortical dysplasia that results when neuroglial overmigration into the arachnoid space forms an extracortical layer that produces agyria and/or a "cobblestone" brain surface and ventricular enlargement. Cobblestone lissencephaly is pathognomonic of a continuum of autosomal-recessive diseases characterized by cerebral, ocular, and muscular deficits. These include Walker-Warburg syndrome, muscle-eye-brain disease, and Fukuyama muscular dystrophy. Mutations in POMT1, POMT2, POMGNT1, LARGE, FKTN, and FKRP identified these diseases as alpha-dystroglycanopathies. Our exhaustive screening of these six genes, in a cohort of 90 fetal cases, led to the identification of a mutation in only 53% of the families, suggesting that other genes might also be involved. We therefore decided to perform a genome-wide study in two multiplex families. This allowed us to identify two additional genes: TMEM5 and ISPD. Because TMEM has a glycosyltransferase domain and ISPD has an isoprenoid synthase domain characteristic of nucleotide diP-sugar transferases, these two proteins are thought to be involved in the glycosylation of dystroglycan. Further screening of 40 families with cobblestone lissencephaly identified nonsense and frameshift mutations in another four unrelated cases for each gene, increasing the mutational rate to 64% in our cohort. All these cases displayed a severe phenotype of cobblestone lissencephaly A. TMEM5 mutations were frequently associated with gonadal dysgenesis and neural tube defects, and ISPD mutations were frequently associated with brain vascular anomalies