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I am more than the spitting image of my DNA

January 18, 2015

In October 2014, direct-to-consumer genetic testing became available in Canada. If you have two hundred-dollar bills to rub together, a laboratory will crack the lid of your genetic code and let your genome out of its bottle. You are then granted three genomic wishes.

  1. A prediction of the likelihood of certain diseases
  2. A prediction of personal response to certain drugs (pharmacogenomics) and,
  3. Information about your ancestry

This service is at the frontier of personalized medicine; using genetic data to tailor treatment to the individual. It is a health industry shift from reactive to proactive care.

Deciphering your DNA code has never been simpler. After ordering a DNA collection kit online, you must register it and provide a sputum sample before sending the kit back. Email updates allow you to track the progress of your sample. Results are usually processed in 4-6 weeks and are reported in the following categories:

  • Genetic risk for disease
  • Response to certain drugs
  • Profile of inherited conditions
  • Physical attributes, and
  • Ancestry

A 2011 study cast doubt on the accuracy of genetic predictions. One of the authors said, “The current state of science is that most of the diseases and traits that are tested … cannot be predicted with great accuracy.”

This statement needs to be clarified because genomics is not haruspicy. It is founded on a solid scientific foundation. I know that the DNA in my sputum holds more predictive value than inspecting the entrails of several other laboratory investigations. But I am much more than the spitting image of my DNA. Genetic predisposition to a disease is a far throw from the phenotypical expression of that disease. Non-medical people may overestimate the genetic contribution and undervalue the complexity of environmental factors.

No test is perfect and there will always be false positives and false negatives. The presence of genetic predisposition is not fatalistic; while its absence provides no comfort for the worried well. There are certain conditions that cannot presently be averted (e.g. Alzheimer’s disease). Knowing that you are at higher risk to develop the unpreventable may do nothing but create psychological anguish. In the end, much of the data offers little advantage over a good old-fashioned family history. Of course, “most people will be at low risk for most diseases.”

There can be value in screening couples planning to have a baby (dedicated genetic services exist for this purpose), but screening asymptomatic patients will not improve quality (or quantity) of life for all disease.

There may be usefulness in lifestyle recommendations based on personalized data but I remain skeptical. Everyone is aware of the benefits of exercise, maintaining a normal weight, and following a healthy diet. Everyone knows that smoking, excessive alcohol intake, and a sedentary lifestyle are deadly habits. Does this knowledge consistently drive healthy behavioral change? No, it does not.

The “hereditary horoscope” is far more promising in the field of pharmacogenomics. Without “genotype-guided dosing”, clinicians tend to routinely start drugs at low doses and then increase them slowly. So it doesn’t really matter whether an individual is a fast or slow metabolizer, the drug is titrated according to clinical response. Warfarin, for example, is meticulously monitored and the dosage is frequently adjusted. Nevertheless, predicting which patient will fail to respond or develop side-effects on a particular drug can guide personalized drug selection. This area of research is a sandbox of discovery for academics and drug developers. (23andMe and Pfizer have recently confirmed working together).

Marketing genetic data directly to the consumer is not without controversy. The data must be interpreted in the context of usefulness. Drug response results might encourage certain patients to self-manage or stop using prescribed medication. Errors and violations of privacy can cause unnecessary harm.

If a patient’s genetic data is integrated into his/her electronic medical record, this may be shared with health insurers and employers.

“Currently there are no protections for Canadians against discrimination based on their genetics – life insurance companies and employers may request an individual’s genetic information or may ask whether an individual has had a genetic test.”

As for ancestry information, this works well if you are interested in climbing the family tree, spearheading a scandalous exposé, or open to meeting a distant cousin.

I am excited about the future of medicine.

I will gladly review results of patients who decide to undergo DNA testing but, at this point in time, I think that direct-to-consumer DNA testing complicates–rather than complements–the task of the family doctor. It raises far more questions than it answers.


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