Higher baseline GFAP, NfL, and P-tau concentrations were associated with lower MMSE scores in DLB, and GFAP and NfL were associated with a faster cognitive decline (GFAP: annual change of −2.11 MMSE points, 95% CI −2.88 to −1.35 MMSE points, p < 0.001; NfL: annual change of −2.13 MMSE points, 95% CI −2.97 to −1.29 MMSE points, p < 0.001). The gene discussed is NEFL; the disease is Lewy body dementia.