Professor Hanington's Speaking of Science: The Science of '23 and Me'
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Professor Hanington's Speaking of Science: The Science of '23 and Me'

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DNA molecule

DNA molecule

It may barely be December, but the holiday ads for genetic tests are already in full swing.

Direct-to-consumer genetic testing companies (GTC) are really good at advertising with their slogans. “Welcome to you” and “Find your tribe” suggest that sequencing of your genome will reveal some deep hidden secrets within or help you find some group of people to which you belong on a deep level.

While there are over 32 GTCs globally, they all operate on the same overriding assumption that people can somehow be collected into distinct groups of geographic origin or health status based on the information within the genome. But is this assumption true, and what information do genetic companies use to reach these final conclusions?

The completion of the Human Genome Project in April 2003 marked the successful end of the world’s largest collaborative biological project to date in which scientists determined the sequence of all nucleotides present in the human structure. This was an enormous feat with tremendous medical potential because the human genome is in essence the blueprint from which your body is built and continues to function throughout your life.

It is made up of the material deoxyribonucleic acid, commonly referred to as DNA. This material is simple, being composed of four base units called nucleotides: adenine, thymine, cytosine, and guanine, with abbreviations A, T, C, and G. The precise way in which these nucleotides are strung together determines what type of living thing is created; humans, mushrooms, even the tree outside your window.

The goal of the Human Genome Project was to determine, letter for letter, what combination makes up a human. If you know what a healthy genome looks like, you can then sequence a patient and see if they match. If they don’t, you may have just identified the cause of a genetic disorder.

Although this sounds straightforward there is a problem with this technique. The human genome is unbelievably enormous. Your genetic code contains 6.4 billion individual base pairs (The A, T, C, and Gs) and if it were printed, it would fill 5,000 books stacked over 200 feet high.

The Human Genome Project took 13 years to complete and cost nearly $3 billion. Even with vastly improved sequencing technology, reading out every nucleotide of every customer’s DNA just isn’t feasible for a genetic testing company. So what do these companies do? They use a shortcut.

One of the surprising results to come from the Human Genome Project and sequencing of other genomes that followed is that humans are remarkably similar to each other, more so than many other species. This means it is actually easier and faster to map the differences in the human genome than the similarities.

Single nucleotide polymorphisms, or SNPs, are differences of a single nucleotide (one A, T, G, or C) from person to person within a population. They are very common — around 4 to 5 million per individual genome and therefore quickly became a diagnostic tool or proxy used as a marker for the system. Find the location of a disease variant, locate a SNP nearby, and then all you have to do is find the SNP in your patients to locate the variant easily.

Looking at specific SNPs is what many genetic companies do to “sequence your genome.” This type of test is referred to as a “whole-genome analysis” (WGA) as opposed to whole genome sequencing (WGS) in which all are actually determined.

While SNPs can be used to locate genes associated with disease, it is also important to stress that most commercially available genetic tests examine as little as 1% of the human genome, and only indirectly through SNPs. This makes the chance of missing a disease-causing variant or incorrectly identifying a healthy variant as a risk worryingly high.

In 2013, after a longstanding dialogue with 23andMe, the FDA demanded the genetic testing company stop offering its tests over concerns of consequences to public health over potentially inaccurate results. After this, 23andMe gradually regained approval for a number of tests, although it should be noted that an independent study by The University of Southampton into the company this year suggested that consumers not make any health decisions based on these tests, which often focus on “breadth over detail” when looking for variants associated with cancers or other health complications.

Despite these warnings, the fact that direct-to-consumer genetic testing companies bypass a physician or other scientifically literate third party means patients may choose to make what decisions they will given their genetic testing results. Consumers may not only be concerned or distressed by health results, but also undergo life-changing preventive surgery in the wake of obtaining them. The most famous example perhaps was Angelina Jolie, who had a double mastectomy after receiving a positive result for the breast cancer mutation, even though this finding in no way guaranteed she would develop breast cancer or benefit from preventive surgery.

Another emerging concern in genetic testing relates to ownership of the body. The majority of customers for 23andMe sign a “Research Consent Document” which allows them to access and sell your genetic information to third party companies. Such “DNA banking” is quickly becoming a lucrative business but it is unclear what third parties will be able to do with obtained data. It is not hard to imagine companies increasing fees for individuals with a history of family illness or who have specific genetic markers.

Overall, the booming business of direct-to-consumer genetic testing raises many concerns. Not only is the accuracy of these tests in doubt but exactly what personal information consumers are giving away when they opt in for genetic testing is unclear.

Hannah Margolis is an Undergraduate Researcher at Ragusa Lab, Dartmouth College. She can be reached at:


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