title: Epilepsy due to mutations in the mitochondrial polymerase gamma (POLG) gene: A clinical and molecular genetic review.
abstract: We performed a systematic review of the clinical, molecular, and biochemical features of polymerase gamma (POLG)-related epilepsy and current evidence on seizure management. Patients were identified from a combined electronic search of articles using Ovid Medline and Scopus databases, published from January 2000 to January 2015. Only patients with a confirmed genetic diagnosis of POLG mutations were considered. Seventy-two articles were included for analysis. We identified 128 pathogenic variants in 372 patients who had POLG-related epilepsy. Among these, 84% of the cases harbored at least one of these pathogenic variants: p.Ala467Thr, p.Trp748Ser, and p.Gly848Ser. A bimodal distribution of disease onset was present in early childhood (<5 years) and adolescence; female patients had a later presentation than male patients (median age 4.00 vs. 1.83 years, p-value = 0.041). Focal-onset seizure including convulsive, myoclonus, and occipital seizures was common at the outset and was refractory to pharmacotherapy. We confirmed that homozygous pathogenic variants located in the linker region of POLG were associated with later age of onset and longer survival compared to compound heterozygous variants. In addition, biochemical and molecular heterogeneities in different tissues were frequently observed. POLG-related epilepsy is clinically heterogeneous, and the prognosis is, in part, influenced by the location of the variants in the gene and the presence of hepatic involvement. Normal muscle and fibroblast studies do no exclude the diagnosis of POLG-related mitochondrial disease and direct sequencing of the POLG gene should be the gold standard when investigating suspected cases.
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Maria-Eleni
authors.initials: ME
authors.lastname: Anagnostou
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Yi Shiau
authors.initials: YS
authors.lastname: Ng
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Taylor
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom. robert.mcfarland@newcastle.ac.uk.
authors.forename: Robert
authors.initials: R
authors.lastname: McFarland
mesh_terms: D017668:Age of Onset; D001921:Brain / Q000000981:diagnostic imaging / Q000473:pathology; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase / Q000235:genetics*; D016206:Databases, Bibliographic / Q000706:statistics & numerical data; D004569:Electroencephalography; D004827:Epilepsy / Q000000981:diagnostic imaging / Q000235:genetics* / Q000401:mortality; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008285:Major Histocompatibility Complex / Q000235:genetics; D008297:Male; D009154:Mutation / Q000235:genetics*; D059906:Neuroimaging
chemical_list: D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; C413027:POLG protein, human
keywords: Mitochondrial disease; Status epilepticus; Stroke-like lesion; Treatment; mtDNA copy number