Abstract
BACKGROUND: Globally, the World Health Organization ranks major depressive disorder (MDD) as the leading cause of disability. However, MDD molecular etiology is still poorly understood. AIM: To explore the possible association between mitochondrial ND6 T14502C mutation and MDD. METHODS: Clinical data were collected from two pedigrees, and detailed mitochondrial genomes were obtained for the two proband members. The assessment of the resulting variants included an evaluation of their evolutionary conservation, allelic frequencies, as well as their structural and functional consequences. Detailed mitochondrial whole genome analysis, phylogenetic, and haplotype analysis were performed on the probands. RESULTS: Herein, we reported the clinical, genetic, and molecular profiling of two Chinese families afflicted with MDD. These Chinese families exhibited not only a range of onset and severity ages in their depression but also extremely low penetrances to MDD. Sequence analyses of mitochondrial genomes from these pedigrees have resulted in the identification of a homoplasmic T14502C (I58V) mutation. The polymorphism is located at a highly conserved isoleucine at position 58 of ND6 and distinct mitochondrial DNA (mtDNA) polymorphisms originating from haplogroups M10 and H2. CONCLUSION: Identifying the T14502C mutation in two individuals with no genetic relation who exhibit symptoms of depression provides compelling evidence that this mutation may be implicated in MDD development. Nonetheless, the two Chinese pedigrees that carried the T14502C mutation did not exhibit any functionally significant mutations in their mtDNA. Therefore, the phenotypic expression of the T14502C mutation related to MDD may be influenced by the nuclear modifier gene(s) or environmental factors.