Abstract: Solving challenging Titinopathy cases via multi-omics and iPSCs
Yanmin Zhang1, Ling Xu1, Carsten G. Bönnemann3, Sophelia Chan#2, Asif Javed#1 1School of Biomedical Sciences, LKS faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. 2Department of Paediatrics and Adolescent Medicine, School of Clinical Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. 3Neuromuscular and Neurogenetic Disorders of Childhood Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. Titinopathy, or skeletal muscle dystrophy due to autosomal recessive mutations in Titin (TTN) poses a diagnostic challenge due to significant variability in disease manifestation and incomplete knowledge of the role of different parts of the gene in normal muscle function. Many apparently healthy individuals harbor rare putative deleterious variants in TTN. This confounds interpretation of TTN variants in cardiac and neuromuscular disease patients. In this study, we investigated six titinopathy patients from four unrelated families with diverse disease manifestation. In each case, a confirmed diagnosis was reached by co-analyzing familial DNA and proband muscle-biopsy based RNA sequencing data. In three out of four families, one of the pathogenic variants is located in metatranscript-only exons. Comparison with in-house and public muscle transcriptomics datasets brought credence to the outlying isoform usage in each family. These patients present commonality in aberrant isoform usage and shared functional changes in muscle transcriptome, highlighting the importance of metatranscript-only exons. However, the regulatory mechanisms underlying the aberrant isoform expression remain unclear. Therefore, we established patient-derived induced pluripotent stem cells (iPSCs) for these metatranscript-exon only titinopathy patients and gender-matched control donors. This provides us opportunity to examine the mechanical abnormalities in skeletal tissue and gain insights into the regulatory processes of titin isoform switching in metatranscript-exon only titinopathy patients.
