Co-occurrence of m.1555AG and m.11778GA mitochondrial DNA mutations in two Indian families with strikingly different clinical penetrance of Leber hereditary optic neuropathy

摘要

Background: Mitochondrial DNA (mtDNA) mutations are known to cause Leber hereditary optic neuropathy (LHON). However, the co-occurrence of double pathogenic mutations with different pathological significance in pedigrees is a rare event. Methods: Detailed clinical investigation and complete mtDNA sequencing analysis was performed for two Indian families with LHON. The haplogroup was constructed based on evolutionarily important mtDNA variants. Results: We observed the existence of double pathogenic mutations (m.11778GA and m.1555AG) in two Indian LHON families, who are from different haplogroup backgrounds (M5a and U2e1), with different clinical penetrance of the disease (visual impairment). The m.11778GA mutation in the MT-ND4 gene is associated primarily with LHON; whereas, m.1555AG in the 12S rRNA gene has been reported with aminoglycoside-induced non-syndromic hearing loss. Conclusions: The absence of hearing abnormality and widely varying clinical expression of LHON suggest additional nuclear modifier genes, environmental factors, and population heterogeneity might play an important role in the expression of visual impairment in these families.