Novel POLG mutations and variable clinical phenotypes in 13 Italian patients

Paola Da Pozzo, Elena Cardaioli, Anna Rubegni, Gian Nicola Gallus, Alessandro Malandrini, Alessandra Rufa, Carla Battisti, Maria Alessandra Carluccio, Raffaele Rocchi, Fabio Giannini, Amedeo Bianchi, Michelangelo Mancuso, Gabriele Siciliano, Maria Teresa Dotti, Antonio Federico

POLG gene encodes the catalytic subunit of DNA polymerase gamma, essential for mitochondrial DNA (mtDNA) replication and repair. Mutations in POLG have been linked to a spectrum of clinical phenotypes, resulting in autosomal recessive or dominant mitochondrial diseases. These mutations have been associated with heterogeneous phenotypes, presenting with varying severity and at different ages of onset, ranging from the neonatal period to late adult life. We screened 13 patients for POLG mutations. All patients underwent a complete neurological examination, and in most of cases, muscle biopsy was performed. We detected 15 different variations in 13 unrelated Italian patients. Two mutations were novel and mapped in the pol domain (p.Thr989dup and p.Ala847Thr) of the enzyme. We also report new cases carrying controversial variations previously described as incompletely penetrant or a variant of unknown significance. Our study increases the range of clinical presentations associated with mutations in POLG gene, underlining some peculiar clinical features, such as PEO associated with corneal edema, and epilepsy, severe neuropathy with achalasia. The addition of two new substitutions, including the second report of an in-frame duplication, to the growing list of defects increases the value of POLG genetic diagnosis in a range of neurological presentations.