Objectives: To examine the hypothesis that mitochondrial DNA may be released extracellularly early in life and induce an “autoimmune” response that may contribute to the pathogenesis of autism.
Methods: We investigated a homogeneous group of young Caucasian children with the same endophenotype. Subjects were diagnosed with autistic disorder using the ADI-R and ADOS-G scales, which have been validated in the Greek population. Anti-mitochondrial antibody Type 2 (AMA-M2) was detected using a commercial EIA Kit. Total DNA was extracted from serum samples using Qiagen DNA Micro extraction kit. Mitochondrial specific DNA for Cytochrome B (mt-CytB) and 7S (mt-7S) was detected and quantified by Real time PCR using Taqman assay. GAPDH DNA was used to exclude any genomic “contamination.” Total DNA was isolated from supernatant fluids of cultured LAD2 cells using the same method.
Results: NT induces release of extracellular mitochondrial DNA (mtDNA) that could act as
“autoimmune” triggers. We further show that serum from young autistic patients contains mtDNA (n=20; cytochrome B, p=0.0002 and 7S, p=0.006), and anti-mitochondrial antibody Type 2 (n=14; p=0.001) as compared to normally developing, unrelated controls (n=12). Extracellular blood mtDNA and other components may characterize an autistic endophenotype and may contribute to its pathogenesis by activating auto-immune responses.
Conclusions: These results suggest that serum mitochondrial components may induce autoimmune responses, as previously reported for TLR9 activation on human peripheral polymorphonuclear leukocytes, and may help with early diagnosis of at least a subgroup of autistic patients.