Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver disorders and has been linked to oxidative stress. Therefore, it can be hypothesized that NAFLD may be associated with genes encoding proteins involved in the base-excision repair (BER) pathway. Moreover, mitochondrial dysfunction plays a significant role in the development of NAFLD. In light of these observations, we suggested that fatty liver may be associated with genes that encode proteins responsible for mitochondrial DNA (mtDNA) degradation. This study evaluates single-nucleotide polymorphisms (SNPs) within the EXOG, ENDOG, POLG, FEN1, PARP1, and XRCC1 genes in 99 patients and 104 controls. SNP genotyping was performed using TaqMan probes and the findings were presented as odds ratios with corresponding 95% confidence intervals. Each of the eight investigated SNPs was found to modulate the risk of NAFLD occurrence. The analysis revealed that the studied haplotypes of EXOG and XRCC1 significantly affected the frequency of NAFLD in patients. The findings allow us to assume that there is a link between FEN1, PARP1, XRCC1, POLG, EXOG, and ENDOG and liver steatosis. We believe that the impaired repair and degradation of damaged mtDNA may have a significant impact on the development of NAFLD.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a multifactorial metabolic disorder that is strongly associated with mitochondrial dysfunction and oxidative stress, which may potentially compromise the integrity of mitochondrial DNA (mtDNA). However, the role of the base excision repair (BER) pathway—the main mechanism responsible for repairing oxidative lesions in mitochondria—and maintaining mtDNA stability in MASLD remains poorly understood. Here, we analyzed total mRNA expression levels of key BER components in whole-blood samples, along with mitochondrial protein levels of the selected components. Additionally, we assessed the mtDNA copy number and the damage of mtDNA and nuclear DNA in peripheral leukocytes from MASLD patients and healthy controls. We found that MASLD patients differed from controls in mtDNA and nuclear DNA damage, mtDNA copy number, and selected BER-related markers. However, because the MASLD and control groups also differed substantially in age and BMI, these molecular differences should be interpreted as potentially being associated with age- and BMI-related metabolic status rather than attributable to MASLD alone. While several BER-related genes were downregulated at the mRNA level, the corresponding mitochondrial protein levels were not consistently decreased in MASLD (ProteomeXchange: PXD075974), indicating a discordance between transcriptional and protein-level regulation. These results suggest that altered mitochondrial BER and mtDNA instability in peripheral leukocytes may reflect the combined influence of MASLD, aging, obesity, and broader metabolic dysfunction.