Author Affiliations: Division of Genomic Medicine, Department of Medicine, and Institute for Human Genetics, University of California, San Francisco.
Genetics researchers have been grappling for decades with the problem of how to identify the genetic variants contributing to disease traits with complex inheritance. In common diseases such as type 2 diabetes, cardiovascular disease, and late-onset Alzheimer disease (LOAD), a contribution by genetic variants can be inferred because these diseases are “familial”; ie, the more genetically related a relative is to the affected person, the more frequently the relative is also affected. Yet these disorders do not demonstrate patterns that conform to the simple mendelian patterns of inheritance and therefore are unlikely to be caused by variants of large effect in a single gene that is being passed on in a family. Instead, smaller contributions from variants in many different genes, acting together along with shared environmental influences, are thought responsible for the observed familiality.
Nussbaum RL. Genome-Wide Association Studies, Alzheimer Disease, and Understudied Populations. JAMA. 2013;309(14):1527-1528. doi:10.1001/jama.2013.3507