Long-read sequencing for diagnosis of genetic myopathies

Genetic myopathies are caused by pathogenic variants in >300 genes across the nuclear and mitochondrial genomes. Although short-read next-generation sequencing (NGS) has revolutionised the diagnosis of genetic disorders, large and/or complex genetic variants, which are over-represented in the genetic myopathies, are not well characterised using this approach. Long-read sequencing (LRS) is a newer genetic testing technology that overcomes many of the limitations of NGS. In particular, LRS provides improved detection of challenging variant types, including short tandem repeat (STR) expansions, copy number variants and structural variants, as well as improved variant phasing and concurrent assessment of epigenetic changes, including DNA methylation. The ability to concurrently detect multiple STR expansions is particularly relevant given the growing number of recently described genetic myopathies associated with STR expansions. LRS will also aid in the identification of new myopathy genes and molecular mechanisms. However, use of LRS technology is currently limited by high cost, low accessibility, the need for specialised DNA extraction procedures, limited availability of LRS bioinformatic tools and pipelines, and the relative lack of healthy control LRS variant databases. Once these barriers are addressed, the implementation of LRS into clinical diagnostic pipelines will undoubtedly streamline the diagnostic algorithm and increase the diagnostic rate for genetic myopathies. In this review, we discuss the utility and critical impact of LRS in this field.