Natural history of mitochondrial optic neuropathies

Abstract

Mitochondrial optic neuropathies (MON) may occur as a single organ disease (non‐syndromic MON) or in the context of a multisystem mitochondrial disorder (syndromic MON). By far the most frequent MON are Leber's hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (ADOA). LHON is in most cases caused by mitochondrial DNA (mtDNA) mutations m.11778G>A, m.3460G>A or m.14484T>C, while ADOA is most frequently due to mutations in the OPA1 gene. As therapy trials have been performed, are ongoing or are planned for LHON and ADOA, it is important to know about the natural history of these disorders which may help to design trials or may serve as an external comparator.In LHON, an international observational retrospective registry (REALITY) analysed the visual course and outcome in 44 LHON patients, and found (after an average follow‐up time of 32.5 months) the mean best‐corrected visual acuity (BCVA) to be 1.46 LogMAR in m.11778G>A, 1.52 LogMAR in m.3460G>A, and 0.97 LogMAR in m.14484T>C mutations carriers. In line with previous findings, children below age 12 years at onset had the best visual prognosis. Since 25 of the 44 patients had taken idebenone at some point, this work does not qualify as a natural history study, though.A meta‐analysis of 12 retrospective and 3 prospective studies included data from 695 LHON patients with the m.11778G>A mutation. This meta‐analysis was hampered by the poor and variable definition of recovery among studies, and by the fact that idebenone use could not always be excluded. Main findings were some degree of recovery in 14.4% of patients, and 11.3% in those above age 15 years. Final BCVA of better than 1.0 logMAR was rare.In an own study of 83 LHON patients (73.5% with m.11778G>A mutation), BCVA at last observation was better than 1.0 logMAR in 18.1%, between 1.0 and 1.68 logMAR in 33.7% and worse than 1,68 logMAR (off‐chart) in 48.2%. Spontaneous recovery by at least 0.2 logMAR occurred in 16.3% of patients.In OPA1‐ADOA, a retrospective analysis of data from 64 affected patients showed a mean age at visual failure onset of 7.0 years (range 1.0–16.0 years), and a mean BCVA at last observation of 1.02 LogMAR. Longitudinal data in 43 OPA1 patients with a mean follow‐up duration of 18.0 years showed on average a slow visual decline of 0.032 LogMAR/year, but some patients deteriorated much faster (range 0–0.171 LogMAR/year).In conclusion, currently available data on the natural history of MON are hampered by retrospective analysis, low sample sizes, unsystematic phenotyping, variable definitions of key outcomes (eg, recovery) and often incomplete information on the administration of idebenone or other drugs. Large multicenter studies on natural history are needed but are more and more difficult to perform with the advent and sometimes even approval of disease‐modifying treatments.