Significant associations between NfL values and time to diagnosis were observed in incident ALS (β regression coefficient: −0.49, p < 0.001) and AD (β: −0.19, p < 0.001), with a trend in atypical parkinsonism (β: −0.37, p = 0.06), In contrast, GFAP showed a progressive increase only in AD, peaking in the 5 years before diagnosis and showing significant association with time to diagnosis (β: −0.21, p < 0.001) while remaining flat in PD, APD, and ALS. This evidence concerns the gene NEFL and Parkinson disease.