Leberís Hereditary Optic Neuropathy (LHON) is a rare hereditary disease, transmitted maternally and caused by mitochondrial DNA point mutations in genes encoding MT‑ND1, MT‑ND4, MT‑ND4L and MT‑ND6 subunits of complex I of the mitochondrial respiratory chain. It is characterized by bilateral visual impairment and is most often observed in young males. The purpose of this paper is the assessment of the clinical symptomatology and the genetic investigation in Bulgarian patients with LHON. Based on clinical evaluation and genetic studies, LHON was diagnosed in 12 patients Ė 9 men and 3 women, aged 7 Ė 41 y. A complete neuro-ophthalmological study and molecular-genetic examination was performed. Seven patients from two unrelated families had a family history of LHON, and the remaining 5 patients were sporadic cases. The visual acuity in the patients varied between 0.01 and 0.6 and the most common perimetric finding was the bilateral central/cecocentral scotoma. In 2 out of 3 patients, studied at the acute stage of the disease, optic disc hyperemia and peripapillary retinal vessels tortuosity were identified ophthalmoscopically, and in the other 9 patients, studied after the acute stage, a picture of bilateral optic atrophy was established. The genetic study revealed the following gene mutations causing the disease: MTND4*LHON11778A, p. R340H in 3 patients, MTND1*LHON3460A, p. A52T in 2, MTND1*LHON3635A, p. S110N in a family with 4 affected individuals; MTND4*LHON11778A, p. R340H and MTND6*LHON14484C, p. M64V in a family with 3 affected members. Beside the common mutations, a rare for the European population mutation MTND1*LHON3635A, p. S110N was found in a family of 4 affected individuals. Another family represents interest, with 3 members with a digenic inheritance of MTND4*LHON11778A, p. R340H and MTND6*LHON14484C, p. M64V.
Key words: Leberís Hereditary Optic Neuropathy, neuroophthalmologic examination, genetic investigation