Recurrent Lobar Hemorrhages and Multiple Cortical Superficial Siderosis in a Patient of Alzheimer's Disease With Homozygous APOE ε2 Allele Presenting Hypobetalipoproteinemia and Pathological Findings of <sup>18</sup>F-THK5351 Positron Emission Tomography: A Case Report. The gene discussed is APOE; the disease is Alzheimer disease.