Further studies are also needed to determine whether there are differences in the total particle numbers and particle size distributions in MCI and AD patients by the APOE genotype and to determine the HDL function and size in the other APOE genotypes (i.e., APOE3E2, APOE4E4, APOE4E2, and APOE2E2). The gene discussed is APOE; the disease is Alzheimer disease.