Mutation of the linker region of the polymerase γ-1 (POLG1) gene associated with progressive external ophthalmoplegia and parkinsonism

Objective: To define the molecular basis of the autosomal dominant progressive external ophthalmoplegia and parkinsonism in a large family with a dominantly transmitted multiple mitochondrial DNA deletion disorder. Design: Microsatellite analysis and screening of the progressive external ophthalmoplegia 1 (PEO1), adenine nucleotide translocator 1 (ANT1), and polymerase gamma-1 (POLG1) genes. Results: We identified 3 novel heterozygous POLG1 substitutions in the same family. Autosomal dominant progressive external ophthalmoplegia segregated with 1532G > A in exon 8 and an intronic variant c. 2070 + 158G > A in cis. The one patient with parkinsonism had an additional heterozygous substitution in exon 7 in trans (1389G > T). Both coding region mutations were predicted to alter conserved amino acids in the linker region of polymerase gamma. None of the substitutions were found in 192 ethnically matched control chromosomes, 108 patients with progressive external ophthalmoplegia, nor 140 cases of sporadic idiopathic Parkinson disease. Conclusion: Both autosomal dominant progressive external ophthalmoplegia and parkinsonism can because caused by mutations that directly affect the polymerase domain of polymerase gamma.