Relative Risk

Glenys Thomson, Department of Integrative Biology, University of California, Berkeley, California, USA

Copyright © 1998 Elsevier Ltd. All Rights Reserved.

A genetic marker association with a disease is demonstrated if a statistically significant difference is found in marker allele (or genotype) frequencies between ethnically matched unrelated patients and a group of unrelated control individuals. ABO blood group associations with certain diseases are well established, however the associations so far are consistently weak. In contrast, many strong associations of the HLA system with disease have been found. Association studies are increasingly relevant for mapping purposes in all disease studies. Association data have been used as a follow-up to linkage studies to further localize the disease-predisposing gene in a number of monogenic traits, and also to detect the role of candidate genes in complex diseases. To perform an association study between a disease and, say, a particular HLA antigen, or other genetic marker, a 2 x 2 table of antigen presence or absence versus disease presence or absence is set up as follows. Traditionally, the class antigen presence includes individuals who are homozygote and heterozygote for the marker allele, or HLA antigen, but also see below.

Marker allele



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