BACKGROUND: Hereditary transthyretin amyloidosis (ATTRv) is a rare disorder caused by pathogenic TTR gene variants. Glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) are potential biomarkers for astrocyte activation and neuroaxonal damage, respectively. This study investigates serum GFAP (sGFAP) and NfL (sNfL) levels in ATTRv patients, pre-symptomatic subjects, and healthy controls (HCs) to evaluate their utility as biomarkers of disease progression and CNS involvement. METHODS: Our multicenter cross-sectional study included 111 ATTRv patients (56 symptomatic, 55 pre-symptomatic subjects) and 183 HCs. Serum levels of sGFAP and sNfL were measured using ultrasensitive immunoassays. The statistical comparisons were performed using ANCOVA models (age and sex adjusted), with correlations examined between serum biomarkers and disease severity (Neuropathy Impairment Score, NIS). RESULTS: sGFAP levels were elevated in symptomatic (median: 238.35 pg/ml) and pre-symptomatic subjects (median: 105.50 pg/ml) vs. HCs (median: 75.5 pg/ml, p <
0.002). sNfL was elevated only in symptomatic patients (median: 43.68 pg/ml) compared to pre-symptomatic subjects (median: 9.36 pg/ml) and HCs (median: 7.54 pg/ml, p <
0.002). Both biomarkers correlated significantly with NIS, reflecting disease severity. Female HCs had higher sGFAP levels than males (median 88.6 pg/ml vs. 59.8 pg/ml
p 0.011). CONCLUSION: sGFAP and sNfL mark distinct ATTRv stages, with sGFAP indicating early preclinical changes and sNfL correlating with neurological progression. Sex differences in sGFAP levels among HCs suggest that sex should be considered as a covariate in biomarker analyses.