Biomarking MELAS with neurofilament light chain and circulating cell free mitochondrial DNA.

Mitochondrial diseases are genetic disorders caused either by nuclear or mitochondrial DNA (mtDNA) alterations and characterized by high genetic and phenotypic variability. The common mtDNA m.3243 A > G variant in the MT-TL1 gene leads to clinical manifestations ranging from the classical MELAS (myopathy, encephalopathy, lactic acidosis and stroke-like episodes) syndrome to milder phenotypes such as MIDD (maternally inherited diabetes and deafness) or a spectrum of clinical features of intermediate severity defined as MELAS-Spectrum. The heterogeneous disease course makes the identification of biomarkers for monitoring disease progression challenging, particularly if we consider the occurrence of stroke-like episodes (SLEs), which remain unpredictable events. Here, we assessed two biomarkers, neurofilament light chain (NF-L) and circulating cell free-mtDNA (ccf-mtDNA), in a cross-sectional study in MELAS patients, including both patients in the interictal period and during SLEs, and MELAS-Spectrum patients. Both biomarkers were significantly elevated in MELAS patients during SLEs, compared to the other patients. In addition, we found significant correlation between NF-L and m.3243 A > G blood heteroplasmy in MELAS patients, as well as between NF-L and clinical severity in the whole patients cohort. Despite the limitations derived from the small sample size and the cross-sectional sample collection, our study confirms the value of NF-L and ccf-mtDNA as biomarkers efficiently hallmarking SLEs, highlighting their potential use to monitor the progression of MELAS.