OPA1 mutations and mitochondrial DNA haplotypes in autosomal dominant optic atrophy

Autosomal dominant optic atrophy is a form of blindness, due in part to mutations affecting the mitochondrial-targeted OPA1 gene product. Both OPA1-positive and OPA1-negative families exhibit variable expressivity and incomplete penetrance. The purpose of this study was therefore to determine if the background mtDNA genotype acts as a genetic modifier for the expression of this disease. Methods: To find novel pathogenic OPA1 mutations, we performed complete OPA1 gene exon sequencing in 30 patients. To assess the possibility that mitochondrial DNA haplotype acts as a genetic modifier, we determined the mitochondrial DNA haplotype in 29 Caucasian OPA1-positive and OPA1-negative patients. Deviations in haplotype distribution between patient and control groups were determined by statistical means. Results: Seven new pathogenic OPA1 mutations were found. Most were detected in the mitochondrial targeting N-terminus or in the coiled-coil domain at the C-terminus. Mitochondrial DNA haplotype analysis indicated that the European haplogroup distribution was different between Caucasian patients and controls. Further, haplogroup J was three-fold over-represented in OPA1-negative patients. Conclusions: Overall, our results support haploinsufficiency as a genetic mechanism in OPA1-positive cases and also suggest that mtDNA genetic background may influence disease expression in a subset of cases. Genet Med 2006:8(4):217-225.