Abstract
Behavioral variant frontotemporal dementia (bvFTD) and primary psychiatric disorders (PPD) have symptomatic overlap that leads to diagnostic challenges. Cell-free DNA (cfDNA) tests have revolutionized prenatal non-invasive testing and cancer diagnostics. This study investigated the diagnostic potential of brain-derived cfDNA in plasma to differentiate sporadic bvFTD from PPD subjects. Targeted bisulfite sequencing was conducted to quantify glial and neuronal cfDNA levels in plasma samples from 179 bvFTD and 102 PPD subjects of the multi-center DIPPA-FTD study. No significant differences were observed in the absolute levels of glial or neuronal cfDNA between the groups. However, the neuronal-to-glial cfDNA ratio (NGR) was significantly higher in PPD cases (p = 0.0002), suggesting a relative increase in neuronal cfDNA in PPD compared to bvFTD. Diagnostic performance analysis revealed that neuronal cfDNA and NGR achieved an area under the curve (AUC) of 0.74, with a sensitivity of 90% but a specificity of 44% in distinguishing bvFTD from PPD. While increased serum levels of neurofilament light (NfL) and glial fibrillary acidic protein (GFAP) have been shown to effectively differentiate bvFTD from PPD, the addition of brain-derived cfDNA did not provide any incremental diagnostic benefit over these established biomarkers.