Mitochondrial D-Loop Region Methylation Is Not Altered in Children with Autism Spectrum Disorder

Background/Objectives: Although the etiopathogenesis of autism spectrum disorder (ASD) remains incompletely elucidated, current evidence supports a multifactorial model involving genetic and environmental factors that interact to induce a heterogeneous range of symptoms. In recent years, epigenetic mechanisms, particularly DNA methylation, have been recognized as key contributors to ASD pathophysiology. Alterations in mitochondrial DNA (mtDNA) methylation are also emerging as relevant contributors in several human conditions. The mitochondrial D-loop, a non-coding control region essential for mtDNA replication and transcription, is considered a hotspot for epigenetic regulation and its methylation levels have been found altered in various diseases, such as cancer, metabolic disorders, and neurological illness. However, to date, no studies have investigated mtDNA methylation changes in ASD. Methods: We analyzed the average methylation levels of a fragment containing ten CpG sites within the D-loop region and the mtDNA copy number in peripheral blood samples from 49 children with ASD and 50 neurotypically developing (NT) controls using Methylation-Sensitive High-Resolution Melting and quantitative PCR. Results: No significant differences in D-loop methylation levels were observed between ASD and NT children. Similarly, the mtDNA copy number did not differ between the two groups. No significant correlations were found between D-loop methylation or mtDNA copy number and either ASD severity or age. Conclusions: This is the first study investigating mtDNA methylation in ASD. Our results indicate that methylation of the D-loop region and the mtDNA copy number are not altered in ASD children. Further studies including larger cohorts and extended mtDNA regions are warranted to confirm and expand these findings.