History of Genetic Testing
The Human Genome Project, an initiative to catalog human DNA, was first funded by Congress in 1988. Scientists from the government and private corporations worked together to rapidly identify genes and figure out the body function they were responsible for. The initial discoveries were focused on rare disease, and the available genetic tests over the last thirty years were primarily for rare genetic disorders.
One of the examples that has been in the news recently is for Hereditary Breast and Ovarian Cancer Syndrome (HBOC) (A Brief History of the Human Genome Project, 2012; Genetics and Health Resources, 2015). Celebrities Angelina Jolie (Blumm, 2015) and Christina Applegate (Corcoran, 2013) have both been diagnosed with this disorder, which is caused by a variant in the BRCA1 or BRCA2 genes.
About 1 in 500 individuals in the population carry a BRCA1 or BRCA2 variant, but it is more common in those with Ashkenazi Jewish ancestry, where up to 1 in 40 people may have a BRCA1 or BRCA2 mutation (Hereditary Breast & Ovarian Cancer Program HBOC Fact Sheet, 2013).
Today the promise of the Human Genome Project is starting to come to fruition, and a broad group of genetic tests to better individualize medical treatments and assist in lifestyle choices are available.
The National Institutes of Health maintains a voluntary registry of all genetic tests globally, and to date there are listings for over 27,000 tests representing 5,700 conditions and 3,800 genes through more than 600 labs (“The Genetic Test Registry”(n.d.) Retrieved from http://www.ncbi.nlm.nih.gov/gtr/).
As you recall from Part I, genetic variants called single nucleotide polymorphisms (SNPs) are common and interact with the environment, including lifestyle factors, to influence the risk of common disorders (What are single nucleotide polymorphisms (SNPs)? 2015, retrieved from http://ghr.nlm.nih.gov/handbook/genomicresearch/snp).
Because SNPs are common, scientists must study them in large, ethnically diverse populations and repeat their studies several times before drawing any conclusions. These studies are called Genome Wide Association Studies (GWAS) (Panagiotou, 2011). GWAS research examines people who have a disease or trait of interest, and compares their SNPs to people who don’t have the disease.
Usually millions of SNPs are compared at once. Researchers calculate out several important statistics the four most important things to consider are study design, the P-value, the odds ratio, and clinical utility (Panagiotou, 2011; Bush, 2012).
Study Design The size and design of a study must take into account how common a disease or trait is, and how many people are estimated to carry the genetic variant of interest.
When you are working with a very rare disease, it is appropriate to design your studies around a small number of people with the rare disease to find the genetic change that causes it. It is a different story when you are researching a disease or trait that a lot of people have.
For example, many individuals experience osteoarthritis, a disorder that impacts the cartilage in the joints and causes pain and other dysfunction. The lifetime risk is thought to be as high as 1 in 4. Early GWAS studies failed to find any strong genetic associations, and it was reasoned that the first researchers were not using a consistent definition of osteoarthritis.
Later researchers used a specific definition for osteoarthritis that focused on the joint-space width seen on X-ray, and strong genetic associations began to emerge (Amoaka, 2014).
Finally, study design must include replication. If a positive association is found, the study must be replicated using a completely new set of study subjects to see if the association holds (Bush, 2012).