Current and new next-generation sequencing approaches to study mitochondrial DNA

Mitochondria harbor multiple copies of a maternally inherited nonnuclear genome. Point mutations, deletions, or depletion of the mitochondrial DNA (mtDNA) are associated with various human diseases. mtDNA defects are currently studied using Sanger sequencing, Southern blot, and long and quantitative PCR. However, these technologies are expensive and are limited in speed, throughput, and sensitivity. Recently, next-generation sequencing (NGS) has been used to study mtDNA defects; however, its potential applications still need to be fully validated. We analyzed mtDNA from 16 control samples and 33 affected samples, which were previously investigated by traditional techniques. Different NGS approaches were tested, using classic library preparation based on PCR amplifications and an innovative PCR-free protocol, defining their suitability and utility for: i) generating full accurate mtDNA sequence, ii) assessing heteroplasmy for single point mutations with high accuracy, and iii) detecting break positions and heteroplasmy of single large deletions. This study confirmed that PCR-based library preparations are appropriate for the first two points and showed that a new PCR-free method gave the best results for the third aim. This study tested different approaches and describes an innovative PCR-free protocol, suitable for detection and heteroplasmy quantification of mtDNA single large deletions. NGS may become the method of choice for genetic analysis on mtDNA.