Cerebrospinal fluid biomarkers in E200K genetic Creutzfeldt-Jakob disease: a national study from an endemic Slovak cohort.

BACKGROUND: Genetic Creutzfeldt-Jakob disease (gCJD) is a rare inherited prion disorder caused by pathogenic variants in the PRNP gene. Slovakia represents one of the major endemic regions worldwide, with most genetic cases linked to the E200K variant. Reliable cerebrospinal fluid (CSF) biomarkers remain important for diagnosis and surveillance in this setting. METHODS: We analyzed CSF samples from 77 consecutive symptomatic patients with genetically confirmed E200K gCJD referred to the National Reference Centre for Prion Diseases in Slovakia between 2020 and 2024. Total tau (T-tau) concentrations were measured by ELISA and 14-3-3 protein was detected by Western blot as part of the routine diagnostic evaluation throughout the study period. Real-time quaking-induced conversion (RT-QuIC) was introduced in 2023 and was performed prospectively thereafter, while archived frozen CSF samples collected earlier were analyzed retrospectively. Diagnostic sensitivity was evaluated overall and according to the PRNP codon 129 genotype. RESULTS: RT-QuIC showed the highest sensitivity (75/77; 97.4%), followed by T-tau (64/77; 83.1%) and 14-3-3 protein (42/77; 54.5%). RT-QuIC was positive in all methionine/valine heterozygotes (30/30; 100%) and in 45 of 47 methionine homozygotes (95.7%) (p = 0.518). In contrast, T-tau and 14-3-3 protein demonstrated significantly higher sensitivity in methionine homozygotes than in heterozygotes (both p < 0.0001). CONCLUSION: RT-QuIC showed the highest diagnostic sensitivity among the evaluated CSF biomarkers in this endemic cohort. Conventional biomarkers showed marked dependence on PRNP codon 129 genotype and may provide complementary diagnostic value.