A new paper by Venter and colleagues at his Rockville, Maryland-based institute provides a prime example. Writing in the September issue of Clinical Phamacology & Therapeutics, Venter et al. argue that knowing how genetic differences between ethnicities affect patients’ reactions to certain medications isn’t good enough. To make sure patients get the best healthcare, they say, doctors should be looking at how each person is likely to respond to a particular drug regimen based on his or her unique genetic makeup.

“Even the term ‘Caucasian’ can be deceptive,” the authors noted. “If a self-identified Caucasian originates from a founder population in which certain disease-specific alleles occur at higher frequencies (e.g. Quebec French Canadians or Ashkenazi Jews), his or her doctor may miss an important aspect of the patient’s medical history. One’s ethnicity/race is, at best, a probabilistic guess at one’s true genetic makeup.”

To further emphasize the differences between people within the same ethnic group, the authors compare the publicly available genome sequences of Venter himself and Nobel Prize winner James Watson, focusing on six genes involved in drug metabolism.

One of those genes revealed a substantial difference between the two men. CYP2D6 is involved in the metabolism of various drugs for high blood pressure, heart arrhythmia and depression. Venter’s genotype indicates that like most Europeans he is an “extensive metabolizer” of such drugs; but Watson’s genotype puts him in the “intermediate metabolizer” category, which is more common among Asians.

Using race as a guide, the authors noted, a physician would have no reason to expect Venter and Watson to react differently to drugs that are metabolized by CYP2D6.

Venter and his colleagues conclude by emphasizing the need for personalized health care based on genomic information, adding that the cost to do so is dropping rapidly.

“Given the complex nature of drug responses, it would ultimately better serve all to dissect the relevant factors of a drug response instead of categorically stereotyping a culture with a presumed genetic background.”

Images: Venter photo by Michael Janich; Watson photo courtesy of the National Library of Medicine

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The answer is, very certain. We typically claim that the genotyping technology we use reports the correct call for more than 99.9 percent of the approximately 580,000 single-letter DNA variations we report. Those variations, known as single-nucleotide polymorphisms, or SNPs, are the raw data upon which the 23andMe Personal Genome Service™ is built.

But apparently one of our customers decided to do more than ask. He designed a simple experiment to test the reproducibility of the SNP chips that 23andMe and other companies use to give people access to their genetic data.

Antonio C.B. Oliveira signed himself up for 23andMe and a similar service, then wrote a computer program to compare the genotype calls at the 560,299 SNPs where both companies reported data. He found a grand total of 23 discrepancies, or about 0.004% of the common reported SNPs.

“This error rate seems to me to be quite acceptable,” Oliveira concluded on Longa Vista, a blog he established to share his results.

Oliveira is actually the second customer to conduct such an experiment. When Ann Turner compared two datasets for the same person (not herself) back in January, she discovered 35 discrepancies.

And when Craig Venter and his colleagues published his full genome last October, they also found the discrepancies between their own sequencing results and two different SNP genotyping platforms to be negligible.

We aren’t surprised – these results confirm experiments that 23andMe performed before launching our Personal Genomics Service™ last year. But now 23andMe can say with confidence that independent testing has shown that the Illumina genotyping technology we use is extremely robust.

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