Analysis of mitochondrial D-loop region methylation and copy number in peripheral blood DNA of Down syndrome individuals including newborns with and without congenital heart defects

Down syndrome (DS) is the most common chromosomal disorder associated with intellectual disability and is characterized by multiple clinical features affecting the neurological, musculoskeletal, and cardiovascular systems. Among these, congenital heart defects (CHD) occur in nearly half of individuals with DS. While the role of nuclear epigenetics in DS has been well characterized, particularly concerning clinical outcomes, mitochondrial epigenetic changes have yet to be thoroughly investigated. Recent evidence suggests that alterations in the methylation pattern of mitochondrial DNA (mtDNA), especially in the regulatory D-loop region, may play a role in various human diseases, including cardiovascular and neurological conditions. This study aimed to investigate D-loop methylation and mtDNA copy number in DS. Peripheral blood DNA samples were collected from 59 individuals with DS and 59 age- and sex-matched controls, ranging in age from newborns to 55 years. Additionally, comparisons were made between DS newborns with CHD (DS-CHD) and without CHD (DS-nonCHD). No significant differences were found in D-loop methylation pattern or mtDNA amount between DS and controls. Similarly, no differences were observed between DS-CHD, DS-nonCHD, and control neonates. Age showed no significant correlation with either biomarker, and only a slight, non-significant increase in mtDNA copy number was observed in males. In conclusion, despite the known mitochondrial dysfunction in DS, particularly in CHD cases, our results suggest that such dysfunction is not associated with changes in D-loop methylation or mtDNA copy number. Further research with larger cohorts is needed to clarify these findings.