Genetic variations underlying Alzheimer's disease: evidence from genome-wide association studies and beyond

With the advent of genome-wide association studies (GWAS) and next-generation sequencing, more than 20 risk loci that affect Alzheimer's disease have been identified. These loci are estimated to explain about 28% of the heritability of liability, 30% of familial risk, and over 50% of sibling recurrence risk of developing Alzheimer's disease. These estimates are high in comparison with those for other complex diseases for which more risk loci have been discovered, such as type 2 diabetes, which is mostly a result of the strong effect of APOE epsilon 4 and to a lesser extent the rare variant TREM2 p.Arg47His. The search for functionally relevant genetic variants in risk loci detected in GWAS has revealed that the genetic variations underlying Alzheimer's disease include common variants affecting expression and splicing, a functional intragenic copy number variation, and rare pathogenic variants in risk loci, some of which might lead to familial Alzheimer's disease. An understanding of the contribution of these variants to the development of Alzheimer's disease has several clinical implications, including enhancing diagnostic accuracy and providing targets for the development of novel treatments.