Plasma NfL, GFAP and pTau181 in patients with Isolated REM Sleep Behaviour Disorder

Study objectives: Idiopathic/isolated REM sleep behaviour disorder (iRBD) is recognized as a prodromal stage of neurodegenerative diseases, particularly of alpha-synucleinopathies. The development of blood-based biomarkers enables the in vivo assessment of neuronal, glial and Alzheimer's disease (AD)-related changes. This study aimed to analyse plasma levels of Neurofilament Light chain (NfL), Glial Fibrillary Acidic Protein (GFAP), and phosphorylated-Tau 181 (pTau181) in iRBD patients compared to healthy controls (HC) and AD patients. Method: In this cross-sectional study, iRBD patients were compared to sex/age-matched HC and AD patients. All participants underwent cognitive and motor assessments. Plasma NfL, GFAP, and pTau181 levels were quantified using SIMOA (Quanterix, Billerica, MA). Analyses of covariance and Spearman correlation coefficients were used for comparisons and correlations. Results: The study included 44 iRBD patients (81.8% males, mean age 71.0 ± 6.4 years), 55 HC (66.3% males, mean age 69.1 ± 5.5 years), and 28 AD patients (82.1% males, mean age of 70.4 ± 6.7 years). iRBD patients showed significantly higher plasma NfL and GFAP levels and similar pTau181 levels compared to HC. Compared to AD patients, iRBD patients had lower levels of GFAP, NfL and pTau181. In iRBD, GFAP and NfL levels were significantly correlated, with no correlations between biomarkers and clinical symptoms. Conclusions: High plasma NfL and GFAP levels in iRBD patients reflect a possible ongoing neurodegenerative process. Normal pTau181 plasma levels in iRBD suggest that AD-related neurodegeneration is not present at this stage. Future studies on plasma markers predicting phenoconversion are crucial for setting neuroprotective interventions in iRBD patients.