Alzheimer's disease is a neurodegenerative disease that affects memory, cognitive and non-cognitive functions. Studies show that most cases of Alzheimer's disease occur in people aged 60 or older; meanwhile, 80% of these cases are due to genetics. The risk of having Alzheimer's disease varies by age and ethnicity. That said, some older adults contract this disease late in life, in their 90s. The gene that is usually responsible for Alzheimer's disease (AD) is apolipoprotein E (APOE gene) which is named after the protein encoding Apolipoproteins. It is located on chromosome 19 and has three major alleles on the gene that appears to be responsible for this disease. They are: ε2, containing cysteine ​​in position 112 and arginine in position 158 of the gene, ε3 containing cysteine ​​in both positions 112 and 158, and ε4 containing arginine in both positions 112 and 158 of the gene. The APOE ε4 allele is the most prevalent allele of the disease. The APOE ε4 allele is the most prevalent allele of the disease. The function of this gene is to regulate the metabolism of cholesterol and triglycerides. This shows that it is not just a coincidence that high cholesterol and diabetes lead to late-onset Alzheimer's. The APOE ε4 allele was tested and found to be dangerous in 1993. Since then, many more studies have been completed on this allele and it has been recognized as the primary cause of Alzheimer's disease. Once all of the human genotype was known after using the allele The Human Genome Project was created, a microarray system used to study over 80% of the Caucasian genome for association signals called the 500K GeneChip from Affymetrix. This microarray kit was used to confirm that by using a single nuc...... center of paper ......sion at high density, the results point researchers in the right direction, demonstrating that Alzheimer's late-onset is closely related to this APOE locus, particularly the ε4 allele. Further studies may also show that this allele will likely contribute to other diseases as well. With the use of ultra-high-density genome, further associations will be made regarding the link between late-onset Alzheimer's and the APOE locus. Works Cited Coon, Keith D. Ph.D.; Amanda J. Myers, Ph.D.; David W. Craig, Ph.D.; Jennifer A. Webster, Bachelor of Arts; John V. Pearson, Bachelor of Science; Diane Hu Lince, Ph.D.; Victoria L. Zismann, MS; Thomas G. Beach, MD; Doris Leung, MD "A high-density genome-wide association study reveals that APOE is the major susceptibility gene for late-onset sporadic Alzheimer's disease." Post-Graduate Doctors Press. J Clin Psychiatry 68:4, April 2007: 613-618. (Press)