MT-ND4 and Leber hereditary optic neuropathy: The high proportion of male patients (male:female ratio, 8:1) is in agreement with that found in a previous study (92.1%) by Hotta et al14 and is higher than the male:female ratio reported in other countries (3.4:1 in Finland, 5.4:1 in Netherlands, 3.3:1 in England, 3.7: 1 in Denmark, and 6:1 in Serbia).1, 9, 10, 11, 12 Interestingly, this proportion is also higher than that (68.1%) reported for Japanese patients with LHON in 1973 by Imachi et al,13 indicating that penetrance of female carriers may have decreased over the years and that environmental factors may regulate LHON expression.