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Precision medicine is a medical approach for prevention, diagnosis and treatment of disease that is targeted or tailored to an individual’s unique genetic makeup. It is in contrast to the common one-size-fits-all approach, where disease treatment and prevention strategies are intended for the average person, with less consideration for the differences between individuals.

But so far, genomics studies on precision medicine have focused mainly on white European populations (78%) and neglect other races and ethnicities, according to an analysis published in the journal Cell. The rest of the individuals included in the studies were Asians (10%), Africans (2%), Hispanics (1%) and less than 1 percent for all other groups.

According to the report, ignoring genomic diversity can mean missing out on information that could benefit everyone.

The genetics of disease range from fairly simple to strangely complex. At one end are Mendelian diseases, where one gene variant essentially guarantees that you’ll have that disease, regardless of your genetic background. Examples are muscular dystrophy or Huntington’s disease.  

At the other end are polygenic diseases which may be caused by many different genes called polygenes, together with environmental factors. Examples are hypertension or coronary artery disease. The lack of diversity in data sets can be particularly problematic for researchers studying polygenic diseases which vastly outnumber Mendelian diseases, making them a top research priority.

A researcher trying to identify the genes involved in a polygenic disease is like someone looking for an unknown number of needles in an enormous haystack.

For example, Sarah Tishkoff, an evolutionary geneticist at the Perelman School of Medicine at the University of Pennsylvania cites a gene that’s strongly associated with non-diabetic kidney disease. This is a rare condition among Europeans, but more common among West Africans because it provides some protection against sleeping sickness. Tishkoff says that if we’d only considered European variation, we’d have missed this example of how disease-causing genes can also be beneficial in some environments.

Aside from the changing genes, the genetic markers that act as signposts can get mixed up and rearranged in different populations, according to the authors. In fact, basic evolutionary theory predicts it.

Homo sapiens appeared in Africa approximately 300,000 to 200,000 years ago and left in small bursts of migration. Africans harbor much more genetic diversity than any other human population.

Every time a small band of humans left Africa, they carried only a small fraction of that diversity with them, and the populations that come from those migrants tend to have bigger chunks of the genome linked together.

A marker that accurately identified a gene that increased the risk of heart disease in Europeans might be miles away, genomically speaking, from that same gene in other populations, making the marker meaningless.

Tishkoff stresses that ignoring genomic diversity means that right now, precision medicine is worse, in some cases, for populations of non-European descent.

Alice Popejoy, a postdoctoral geneticist at Stanford University agrees, though she emphasizes that the genetics of health disparities is only a small part of the problem because “environment matters and widespread systemic and structural racism that exacerbates environmental effects are more important.”

“Funding agencies need to financially encourage studying ethnically diverse populations,” Tishkoff says. She added that it’s also important that researchers who   collect genomic data from diverse populations make an effort to provide participants with their results.