Exome Sequencing Reveals Novel TTN Variants in Saudi Patients with Congenital Titinopathies

Familial childhood onset, slowly progressive myopathy plus cardiomyopathy expands the phenotype related to variants in the TTN gene

This report describes a novel TTN -related phenotype in two brothers, both affected by a childhood onset, very slowly progressive myopathy with cores, associated with dilated cardiomyopathy only in their late disease stages. Clinical exome sequencing documented in both siblings the heterozygous c.2089A>T and c.19426+2T>A variants in TTN. The c.2089A>T, classified in ClinVar as possibly pathogenic, introduces a premature stop codon in exon 14, whereas the c.19426+2T>A affects TTN alternative splicing. The unfeasibility of segregation studies prevented us from establishing the inheritance mode of the muscle disease in this family, although the lack of any reported muscle or heart symptoms in both parents might support an autosomal recessive transmission. In this view, the occurrence of cardiomyopathy in both probands might be related to the c.2089A>T truncating variant in exon 14, and the childhood onset, slowly progressive myopathy to the c.19426+2T>A splicing variant, possibly allowing translation of an almost full length TTN protein.

A Novel Homozygous Founder Variant of RTN4IP1 in Two Consanguineous Saudi Families

The genetic architecture of mitochondrial disease continues to expand and currently exceeds more than 350 disease-causing genes. Bi-allelic variants in RTN4IP1, also known as Optic Atrophy-10 (OPA10), lead to early-onset recessive optic neuropathy, atrophy, and encephalopathy in the afflicted patients. The gene is known to encode a mitochondrial ubiquinol oxidoreductase that interacts with reticulon 4 and is thought to be a mitochondrial antioxidant NADPH oxidoreductase. Here, we describe two unrelated consanguineous families from the northern region of Saudi Arabia harboring a missense variant (RTN4IP1:NM_032730.5; c.475G Collapse

Key Words

• RTN4IP1
• age of variant
• encephalopathy
• founder variant
• in silico pathogenicity prediction
• missense
• optic atrophy
• structural modeling

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MESH Headings

• Antioxidants
• Brain Diseases
• Carrier Proteins/genetics
• Humans
• Mitochondrial Proteins/genetics
• Mutation/genetics
• NADP/genetics
• Optic Atrophy/genetics
• Oxidoreductases/genetics
• Saudi Arabia

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Grants

• MR/W019027/1 Medical Research Council
• MR/S005021/1 Medical Research Council
• Department of Health
• 203105/Z/16/Z Wellcome Trust
• G0800674 Medical Research Council

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Affiliation(s)

Mazhor Aldosary Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Maysoon Alsagob Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia Center of Excellence for Biomedicine, Joint Centers for Excellence Program, King Abdulaziz City for Science and Technology (KACST), Riyadh 11442, Saudi Arabia
Hanan AlQudairy Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Ana C. González-Álvarez Bioscience Program, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia Computational Biology Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
Stefan T. Arold Bioscience Program, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia Computational Biology Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Centre de Biologie Structurale (CBS), INSERM, CNRS, Université de Montpellier, F-34090 Montpellier, France
Mohammad Anas Dababo Department of Pathology and Laboratory Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Omar A. Alharbi Radiology Department, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Rawan Almass Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
AlBandary AlBakheet Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Dalia AlSarar Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
Alya Qari Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Mysoon M. Al-Ansari Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia Department of Molecular Oncology, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Monika Oláhová Welcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
Saif A. Al-Shahrani Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Moeenaldeen AlSayed Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia College of Medicine, Alfaisal University, P.O. Box 50927, Riyadh 11533, Saudi Arabia
Dilek Colak Department of Molecular Oncology, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Robert W. Taylor Welcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK NHS Highly Specialized Service for Rare Mitochondrial Disorders, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne NE1 4LP, UK
Mohammed AlOwain Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Namik Kaya Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia

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Use of animal models to understand titin physiology and pathology

In recent years, increasing attention has been paid to titin (TTN) and its mutations. Heterozygous TTN truncating variants (TTNtv) increase the risk of a cardiomyopathy. At the same time, TTNtv and few missense variants have been identified in patients with mainly recessive skeletal muscle diseases. The pathogenic mechanisms underlying titin‐related diseases are still partly unknown. Similarly, the titin mechanical and functional role in the muscle contraction are far from being exhaustively clarified. In the last few years, several animal models carrying variants in the titin gene have been developed and characterized to study the structural and mechanical properties of specific titin domains or to mimic patients' mutations. This review describes the main animal models so far characterized, including eight mice models and three fish models (Medaka and Zebrafish) and discusses the useful insights provided by a thorough characterization of the cell‐, tissue‐ and organism‐phenotypes in these models.