PURPOSE: Leber hereditary optic neuropathy (LHON) is regarded as the most common 
mitochondrial disease. We have previously reported comprehensive 
population-based epidemiological data on common mitochondrial DNA (mtDNA) 
mutations including m.3243A>G, m.8344A>G and large-scale mtDNA deletions in 
Northern Finland. Our aim was to investigate the prevalence of primary LHON 
mutations and mutations in the four mtDNA genes considered hot spots for LHON in 
the same population.
METHODS: The study population consisted of 42 adult patients with an 
aetiologically undefined bilateral optic atrophy. The major LHON mutations 
m.3460G>A, m.11778G>A and m.14484T>C were analysed by restriction fragment 
length polymorphism (RFLP), and MTND1, MTND6 and MTATP6 genes were sequenced. 
MTND5 gene was analysed by conformation-sensitive gel electrophoresis (CSGE).
RESULTS: No major LHON mutations were found in the population of the province of 
Northern Ostrobothnia giving the prevalence of these mutations 0-1.36:100 000 
(95% CI). However, two main mutations were found elsewhere in Northern Finland, 
homoplasmic m.11778G>A from Kainuu and heteroplasmic m.3460G>A from Central 
Ostrobothnia. Furthermore, tobacco-alcohol amblyopia was diagnosed in five 
patients in the study population and one of them had m.11778G>A.
CONCLUSION: The prevalence of the three major LHON mutations is lower in 
Northern Finland than elsewhere in Finland or in Western Europe. As LHON and 
tobacco-alcohol amblyopia have a similar phenotype, we recommend analysing the 
known LHON-associated mutations before setting tobacco-alcohol amblyopia 
diagnosis.