This study is a multi-country retrospective and cross-sectional observational study of affected LHON subjects, based on retrospective subjects' medical chart abstractions and cross-sectional administration of patient-reported outcomes (PROs).

The purpose of this study is to understand the evolution of visual functional and structural changes and other associated symptoms in patients with LHON. The relation between genetic, lifestyle and/or environmental factors and the LHON disease will be described, and a better understanding of the natural history of LHON disease and the healthcare associated to with the disease will be sought.

In addition, we would also like to understand the economic burden for patients and their families with LHON resulting from direct and indirect costs they may have because of their disease.

Inclusion Criteria:

• Subjects who have a confirmed and genotyped diagnosis of LHON;
• Subjects with visual function outcomes data including at least 2 visual function assessments between 1 year and 3 years (+/- 4 weeks) after vision loss;
• Subjects who are willing and able to provide written informed consent if required as per local regulations;
• For LHON subjects under the age of 18 years, permission from a legal guardian to participate in the study;

Exclusion Criteria:

• Subjects who received any investigational drug, or participated in any LHON-related interventional clinical trial during the observational period;
• Subjects without medical charts data available.

The study will recruit at least 50 affected LHON subjects (both adult and pediatric) from global clinical sites at the following countries, but not limited to: Spain, Italy, France, United Kingdom, and the United States. Efforts will be done to maintain the population of at least 50 affected LHON subjects.

Recruitment efforts of recruiting approximately 75% of eligible subjects with 11778/ND4 mutation and 30% of eligible subjects under the age of 18 at the time of index date, wherever possible, will be done at the study level.