Gene-association studies can be used for studying rare diseases.
Gene-disease association studies are not however without disadvantages.
In a study looking at the association between apolipoprotein E gene variants and Alzheimer’s disease, Farrer and colleagues* found that there was a strong association between the genetic variant epsilon4 (APOE4), and the development of Alzheimer’s disease. In fact the risk was higher in those individuals who had inherited two copies of the variant, compared with one copy, and lowest for individuals who had inherited two different variants.
*Farrer LA, Cupples LA, van Duijn CM, Kurz A, Zimmer R, Müller U, Green RC, Clarke V, Shoffner J, Wallace DC, et al. Apolipoprotein E genotype in patients with Alzheimer's disease: implications for the risk of dementia among relatives. Ann Neurol. 1995 Nov;38(5):797-808.
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