Profiling mitochondrial DNA indices across whole blood, plasma, and CSF in amyotrophic lateral sclerosis

Recent studies increasingly implicate mitochondrial DNA (mtDNA) alterations in neurodegenerative diseases, but findings across studies remain inconsistent. We aimed to characterize mtDNA indices across whole blood, plasma and CSF compartments and evaluate their clinical relevance.

We enrolled two study cohorts: (1) a whole blood cohort of 102 ALS patients; and (2) a plasma and cerebrospinal fluid (CSF) cohort including 132 ALS patients and 62 non-neurodegenerative controls. The D-loop and COX3 regions were selected as representative mtDNA fragments, while B2M was used as a nuclear reference. Quantification was performed using SYBR Green-based quantitative PCR.

In whole blood, higher D-loop/COX3 ratios were associated with better functional status and longer survival. In the cell-free compartments, CSF ccf-mtDNA markers (D-loop and COX3) were significantly higher in ALS than in controls, whereas plasma abundance showed no significant group difference. Within ALS, higher ccf-mtDNA indices tended to correlate with greater disease severity and more rapid functional decline. In addition, higher plasma and CSF D-loop/COX3 ratios showed marginal trends toward association with faster disease progression.

This study systematically characterizes mtDNA alterations in whole blood, plasma and CSF samples of ALS, offering new insights into mtDNA involvement in neurodegeneration.