Peripheral CHI3L1 expression is associated with APOE ε4 status in early-onset Alzheimer’s disease

Our exploratory findings indicate that peripheral <i>CHI3L1</i> expression may reflect APOE ε4-linked immune activity, with a trend toward higher expression in EOAD and in female ε4 carriers. The observed genotype- and sex-dependent expression patterns indicate preliminary differences in peripheral immune activity that warrant replication in larger cohorts. Peripheral <i>CHI3L1</i> may thus serve as a hypothesis-generating marker of genotype-linked inflammatory phenotypes rather than a validated biomarker.