RT Journal Article SR Electronic T1 Late-onset Leber’s hereditary optic neuropathy: the role of environmental factors in hereditary diseases JF BMJ Case Reports JO BMJ Case Reports FD BMJ Publishing Group Ltd SP e227977 DO 10.1136/bcr-2018-227977 VO 12 IS 3 A1 Moura-Coelho, Nuno A1 Pinto Proença, Rita A1 Tavares Ferreira, Joana A1 Cunha, João Paulo YR 2019 UL http://casereports.bmj.com/content/12/3/e227977.abstract AB Leber’s hereditary optic neuropathy (LHON) is an optic neuropathy of mitochondrial inheritance, characterised by incomplete penetrance and variable expressivity. Typically, young male patients present with sequential, severe, rapidly progressive loss of central vision, with characteristic funduscopic findings. However, LHON may present at any age, in both genders, and fundus examination may be normal. Evidence has emerged to support the role of environmental factors in triggering LHON, by disrupting the normal mechanisms of mitochondrial function. We present two clinical cases of LHON of late onset, and provide a literature review on atypical cases of LHON and the role of environmental triggers.