INTRODUCTION: Autosomal dominant optic atrophy (ADOA) is considered as the most common form of hereditary optic neuropathy. Although genetic linkage studies point to the OPA1 locus on chromosome 3q28-q29 as by far the most common gene locus, previous screening studies-based on sequencing of the coding exons-detected OPA1 mutations in only 32-70% of ADOA patients. We therefore hypothesised that larger deletions or duplications that remained undetected in previous screening approaches may substantially contribute to the prevalence of OPA1 mutations in ADOA. METHODS: 42 independent ADOA patients were analysed for the presence of genomic rearrangements in OPA1 by means of multiplex ligation probe amplification (MLPA). Deletions or duplications were confirmed either by long distance polymerase chain reaction (PCR) and breakpoint sequencing or loss of heterozygosity analyses with flanking microsatellite markers. Patients underwent ophthalmological examination including visual acuity, colour vision testings, perimetry and funduscopy. RESULTS: We identified genomic rearrangements in 8 of 42 patients, including single exon deletions of exon 9 and exon 24, respectively, a deletion of exons 1-5, two different deletions of the complete OPA1 gene as well as a duplication of the exons 7-9, with the latter being present in three unrelated families. Patients' phenotypes were highly variable, similar to patients with point mutation in OPA1. DISCUSSION: Our findings show that gross genomic aberrations at the OPA1 gene locus are frequent in ADOA and substantially contribute to the spectrum and prevalence of OPA1 mutations in ADOA patients. They further strengthen the hypothesis that haploinsufficiency is a major pathomechanism in OPA1 associated ADOA.
INTRODUCTION:Autosomal dominant optic atrophy (ADOA) is considered as the most common form of hereditary optic neuropathy. Although genetic linkage studies point to the OPA1 locus on chromosome 3q28-q29 as by far the most common gene locus, previous screening studies-based on sequencing of the coding exons-detected OPA1 mutations in only 32-70% of ADOA patients. We therefore hypothesised that larger deletions or duplications that remained undetected in previous screening approaches may substantially contribute to the prevalence of OPA1 mutations in ADOA. METHODS: 42 independent ADOA patients were analysed for the presence of genomic rearrangements in OPA1 by means of multiplex ligation probe amplification (MLPA). Deletions or duplications were confirmed either by long distance polymerase chain reaction (PCR) and breakpoint sequencing or loss of heterozygosity analyses with flanking microsatellite markers. Patients underwent ophthalmological examination including visual acuity, colour vision testings, perimetry and funduscopy. RESULTS: We identified genomic rearrangements in 8 of 42 patients, including single exon deletions of exon 9 and exon 24, respectively, a deletion of exons 1-5, two different deletions of the complete OPA1 gene as well as a duplication of the exons 7-9, with the latter being present in three unrelated families. Patients' phenotypes were highly variable, similar to patients with point mutation in OPA1. DISCUSSION: Our findings show that gross genomic aberrations at the OPA1 gene locus are frequent in ADOA and substantially contribute to the spectrum and prevalence of OPA1 mutations in ADOA patients. They further strengthen the hypothesis that haploinsufficiency is a major pathomechanism in OPA1 associated ADOA.
Authors: Gitte J Almind; Karen Grønskov; Dan Milea; Michael Larsen; Karen Brøndum-Nielsen; Jakob Ek Journal: BMC Med Genet Date: 2011-04-04 Impact factor: 2.103