Nicoletti and colleagues [16] analyzed these associations in terms of GMV, finding no association between APOE4 and whole brain GMV in PD patients with and without dementia, while Chung and colleagues [17] investigated whether PD APOE4 carriers and PD patients with an APOE3/APOE3 genotype who did not differ in cognitive function showed differences in regional GMVs. Here, APOE is linked to Parkinson disease.