Mitochondrial DNA variants in normal skins: Insights into prevalent pathogenic variants and quality control...

Mitochondrial genome diversity in normal tissues remains poorly understood due to 100 to 1000 copies of mitochondrial DNA in a cell. This study analyzed mitochondrial DNA variants in two distant sites of normal skin tissues from 119 breast surgery cases using deep sequencing. We identified 1337 variants across the mitochondrial genome (59.1 % in coding region). Intriguingly variants were categorized two groups, homoplasmic (81.1 %) or low heteroplasmy rate group (14.1 %). Even MITOMAP pathogenic variants, two out of eight were homoplasmic, common in several patients, and found in both skin sites of the same individual, while six heteroplasmic pathogenic variants were identified in a single patient with < 5 % heteroplasmy rates, half only detected in a single skin site with < 2 % rates. Pathogenic mutations predicted by AlphaMissense were significantly less common in the homoplasmic group (30/1085) but more common in the heteroplasmic group (216/431). Significant increases of mitochondrial copy number were also repeatedly detected in cases with pathogenic variants. This study provides new insights into the diversity of mitochondrial genome and the complexity of mitochondrial homeostasis in normal skin tissue, including the possibility of evading pathogenic mutations through quality control surveillance and the restoration of mitochondrial function due to increase in copy number.