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Updated: Jan 11, 2026
Genotyping Single Nucleotide Polymorphisms in the Mitochondrial Genome by Pyrosequencing
Published on: February 10, 2023
Characterization of Novel POLG Mutations in Mitochondrial Encephalomyopathy: Pathogenic Validation and Comprehensive
Fanjing Zhou1, Jiang Chen1, Tingzheng Zhang1
1Department of Neurology, Nanjing Drum Tower Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, China.
Introduction/Aims:
Mitochondrial encephalomyopathies are multisystem disorders caused by defects in mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). Sensory ataxic neuropathy, dysarthria, and ophthalmoparesis (SANDO) syndrome is a rare manifestation, often associated with POLG mutations. This study identifies a novel POLG mutation in a SANDO patient, validates its pathogenicity, and analyzes the molecular genetics of 61 reported POLG-SANDO cases.
Methods:
After obtaining informed consent, the proband underwent neurological examination, electromyography, muscle/nerve biopsies (histochemical/ultrastructural analyses), and genetic testing (whole-exome sequencing, mtDNA analysis). Pathogenicity of identified POLG variants was assessed in Cas9-mediated primary neuronal models expressing mutant proteins by measuring reactive oxygen species (ROS) levels and mtDNA copy number (qRT-PCR, ND1/APP ratio). Literature searches (PubMed, CNKI, Wanfang, and ClinVar) identified reported POLG mutations and clinical features in SANDO.
Results:
Clinical and biopsy findings confirmed SANDO syndrome. Genetic analysis revealed compound heterozygous POLG mutations: a novel c.3297G>C (p.W1099C) and a known c.1774C>T (p.L592F). Neurons expressing either mutant exhibited elevated ROS levels (p < 0.05) and reduced mtDNA copy number compared with controls. Literature synthesis identified over 30 SANDO-associated POLG mutations, with p.A467T (31.2%) and p.W748S (22.1%) being the most frequent. The mean age of onset was 31.6 years.
Conclusions:
We identify a novel pathogenic POLG variant (p.W1099C) causing mitochondrial dysfunction via impaired mtDNA maintenance, expanding the SANDO genetic spectrum. Functional studies confirmed both mutations induce mitochondrial dysfunction (elevated ROS and decreased mtDNA Copy Number), validating their pathogenicity. The compiled mutation profile aids diagnosis of this phenotypically heterogeneous, frequently misdiagnosed disorder.
