Genetic association studies
The volume of genetic association studies has increased from a trickle to a veritable cascade, with DNA-based genotyping, the identification of single-nucleotide polymorphisms (SNP), and the completion of the Human Genome Project.
Abstract
The urge to associate genetic markers with human traits or diseases has been around for centuries. The association of specific hair colors with certain personality types has a long tradition in folklore. The rate-limiting factor has been the availability of measurable genetic markers. When the ABO blood groups were identified as early biological markers under genetic control, they were promptly used for association studies. For example, the association of type O with peptic ulcers was reported nearly 50 years ago.1 (Interestingly, these blood group markers still emerge as associated with personality traits, presumably seeming more “scientific” than hair color.) Then, HLA genotyping stimulated another round of association studies. Although many putative HLA associations could not be reproduced, several were remarkably strong, such as those with ankylosing spondylitis and two of neurologic interest, MS and narcolepsy.2,3⇓ Now, with DNA-based genotyping, the identification of single-nucleotide polymorphisms (SNP), and the completion of the Human Genome Project, the volume of genetic association studies has increased from a trickle to a veritable cascade. The basic idea underlying genetic association studies is both simple and important. Normal phenotype characteristics as well as diseases represent an interplay of environmental factors operating on a genetic background. Many common diseases are said to be complex, meaning they are oligogenic and multifactorial. That is, they are the end result of the complex effects of several or many genes interacting with the …