In medicine, apolipoprotein E4 (apolipoprotein ε4) is an apolipoprotein which is "a major and the second most common isoform of apolipoprotein E. In humans, Apo E4 differs from apolipoprotein E3 at only one residue 112 (cysteine is replaced by arginine), and exhibits a lower resistance to denaturation and greater propensity to form folded intermediates. Apo E4 is a risk factor for Alzheimer disease and cardiovascular diseases.
|heading||Prevalence of Alzheimer's disease by age 80 or 85|
|ApoE epsilon4/epsilon4 homozygotes||45%|
|ApoE epsilon3/epsilon4 heterozygotes||27%|
|No apoE epsilon4 alleles||9%|
Testing for apolipoprotein E4
"The disclosure of APOE genotyping results to adult children of patients with Alzheimer's disease did not result in significant short-term psychological risks" according to a randomized controlled trial. 
- Anonymous (2023), Apolipoprotein E4 (English). Medical Subject Headings. U.S. National Library of Medicine.
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- Green RC, Roberts JS, Cupples LA, Relkin NR, Whitehouse PJ, Brown T et al. (2009). "Disclosure of APOE genotype for risk of Alzheimer's disease.". N Engl J Med 361 (3): 245-54. DOI:10.1056/NEJMoa0809578. PMID 19605829. PMC PMC2778270. Research Blogging. Review in: Ann Intern Med. 2009 Nov 17;151(10):JC5-9