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In genetic epidemiology, a genome-wide association study (GWAS) is an examination of genetic variation across the human genome, designed to identify genetic associations with observable traits, such as blood pressure or weight, or why some people get a disease or condition.
The completion of the Human Genome Project in 2003 made it possible to find the genetic contributions to common diseases and analyze whole-genome samples for genetic variations that contribute to their onset.
These studies require two groups of participants: people with the disease and similar people without. After obtaining samples from each participant, the set of markers such as SNPs are scanned into computers. The computers survey each participant's genome for markers of genetic variation.
If genetic variations are more frequent in people with the disease, the variations are said to be "associated" with the disease. The associated genetic variations are then considered pointers to the region of the human genome where the disease-causing problem resides.
Why are these a good idea?
Humans differ in genetic makeup by only 0.1%, but that small part of the genome contains the key differences that can determine a person’s susceptibility to disease. GWA Studies allow researchers to identify factors in many areas, including asthma, cancer, diabetes, heart disease and mental illness research and clinical care.
What are the challenges?
As people have migrated and married over generations, it has become more difficult to limit studies to biological data; for example, people with tuberculosis moving to Colorado might lead to conclusions that Colorado people are biologically inclined to Tuberculosis if correction for population stratification is not properly factored in.
What is an example of a successful GWA Study?
In 2005 it was learned through GWA Studies that age-related macular degeneration is associated with variation in the gene for complement factor H, which produces a protein that regulates inflammation.
In 2007 the Wellcome Trust Case-Control Consortium (WTCCC) carried out genome-wide association studies for the diseases coronary heart disease, type 1 diabetes, type 2 diabetes, rheumatoid arthritis, Crohn's disease, bipolar disorder and hypertension. This study was successful in uncovering many new disease genes underlying these diseases.