Abstract

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system with genetics and environmental determinants. Studies focused on the neurogenetics of MS showed that mitochondrial DNA (mtDNA) mutations that can ultimately lead to mitochondrial dysfunction, alter brain energy metabolism and cause neurodegeneration. We analyzed the whole mitochondrial genome using next-generation sequencing (NGS) from 47 Saudi individuals, 23 patients with relapsing-remitting MS and 24 healthy controls to identify mtDNA disease-related mutations/variants. A large number of variants were detected in the D-loop and coding genes of mtDNA. While distinct unique variants were only present in patients or only occur in controls, a number of common variants were shared among the two groups. The prevalence of some common variants differed significantly between patients and controls, thus could be implicated in susceptibility to MS. Of the unique variants only present in the patients, 34 were missense mutations, located in different mtDNA-encoded genes. Seven of these mutations were not previously reported in MS, and predicted to be deleterious with considerable impacts on the functions and structures of encoded-proteins and may play a role in the pathogenesis of MS. These include two heteroplasmic mutations namely 10237T>C in MT-ND3 gene and 15884G>C in MT-CYB gene; and three homoplasmic mutations namely 9288A>G in MT-CO3 gene, 14484T>C in MT-ND6 gene, 15431G>A in MT-CYB gene, 8490T>C in MT-ATP8 gene and 5437C>T in MT-ND2 gene. Notably some patients harboured multiple mutations while other patients carried the same mutations. This study is the first to sequence the entire mitochondrial genome in MS patients in an Arab population. Our results expanded the mutational spectrum of mtDNA variants in MS and highlighted the efficiency of NGS in population-specific mtDNA variant discovery. Further investigations in a larger cohort are warranted to confirm the role of mtDNA MS.

Highlights

  • Multiple sclerosis (MS) is a progressive inflammatory, immune-mediated disease of the central nervous system characterized by demyelination, axonal loss and neurodegeneration [1]

  • Out of a large number of variants, we found distinct unique variants that were only present in the patients or only occur in the controls

  • We found a number of common variants and the prevalence of some of them differed significantly between patients and controls

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Summary

Introduction

Multiple sclerosis (MS) is a progressive inflammatory, immune-mediated disease of the central nervous system characterized by demyelination, axonal loss and neurodegeneration [1]. MS is the most disabling neurological condition of young adults [2] and more commonly occurs in females than in males [3]. MS can be categorized based on the phase and severity of disease progression into: clinically isolated syndrome (CIS), relapsing-remitting MS (RRMS), secondary progressive MS (SPMS), and primary progressive MS (PPMS). 85% of MS patients present with RRMS, which is marked by alternate periods of acute demyelination (relapses) and periods of neurological recovery and stability (remissions). After a period of 15–20 years, most patients with RRMS progress into a SPMS with worsened neurological function and signified by few or no acute relapses [7]

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