Elevated plasma GFAP levels in MCI link APOE ε4 allele with impaired gait speed

The presence of at least one copy of the apolipoprotein ε4 allele (APOE ε4) is a known predictor of gait impairment risk among older adults. However, the mechanisms by which APOE ε4 affects gait performance remain unclear. This cross-sectional study aimed to reveal underlying pathological mechanisms linking APOE ε4 carriage to slow gait. This secondary analysis used baseline assessments from the J-MINT multicenter intervention trial, focusing on older adults with mild cognitive impairment. Gait speed was measured at baseline, with slow gait (SG) defined as speeds one standard deviation below the age- and sex-specific mean. APOE phenotype and plasma biomarkers related to Alzheimer's disease (AD), including amyloid-β composite biomarker, phosphorylated Tau 181, neurofilament light, and glial fibrillary acidic protein (GFAP), were also measured. The analysis included 236 non-APOE ε4 carriers and 84 carriers of at least one APOE ε4. APOE ε4 carriers exhibited significantly slower gait speed than non-carriers (1.20 m/s [SD = 0.22] vs 1.26 m/s [SD = 0.23], p = 0.042). Significant interaction between APOE ε4 carriage and SG was observed only in plasma GFAP levels (F_{1, 312} = 7.17, p = 0.008), indicating that individuals with APOE ε4 and SG had significantly higher plasma GFAP levels. Elevated plasma GFAP levels fully mediated the association between APOE ε4 carriage and gait speed (partially standardized indirect effect = -0.059: -0.12 to -0.013]). No other AD-related biomarkers mediated this association. Our results suggest that APOE ε4-related gait changes may reflect AD pathology, as indicated by elevated GFAP levels, and could potentially accelerate dementia symptoms.