Race and Diabetes

It’s another one of those, “Everyone knows that…” facts. For forty years we have all been taught that some ethnic groups are at higher risk of developing insulin resistance and type 2 diabetes mellitus. So now “everyone knows that” African Americans, Native Americans and people from the Indian sub-continent are all genetically predisposed to these medical maladies.

Now it looks as if “everyone” might have been wrong.

James Neel first proposed the theory of the “thrifty genotype” in 1962. He suggested that cycles of feast and famine early in human history created a gene that helps the body use scarce nutrients – a gene that leads to obesity and diabetes in sedentary modern populations with ready and continuous access to food.

Several months ago I pointed out some of the problems with the thrifty genotype theory, and why many of us have become more convinced about the concept of the “thrifty phenotype.” I have many friends, colleagues and former trainees who have dedicated themselves to hunting for diabetes genes. As early as the mid-1980s I was worried that they were going to vanish down a rabbit hole.

It seemed illogical that a gene or genes could “explain” an illness that was, until recently, very rare. It would have to be a gene that was somehow switched on and off by diet or some other environmental factors. It is certainly possible but seemed implausible, given that there are dozens of genes designed to control food intake and metabolism. But my friends the gene jockeys had the louder voice, and it was good for them to see what they could find. Now, twenty years later, more than 250 genes have been studied as possible causes of type 2 diabetes, but together these genes explain less than 1 percent of diabetes prevalence worldwide.

There is an interesting piece of research published in the journal Perspectives in Biology and Medicine by a team of researchers from the United States and Australia, that supports what I was saying. The study was co-authored by UC Irvine anthropologist Michael Montoya, an anthropologist at the University of California at Irvine, together with an epidemiologist and population geneticist. Together they analyzed existing genetic studies published across a variety of disciplines. The team found no evidence to support the thrifty genotype theory.

They also found that in most existing studies of the suspected genes that contribute to diabetes in ethnic minorities, researchers had failed to control for the potential impact of social and environmental factors. If those factors are taken into account, other factors – such as poverty, housing segregation or poor diet – were stronger indicators of diabetes than genes.

As Montoya said,

“Our study challenges the presumption that Native American, Mexican American, African American, Australian Aborigine, or other indigenous groups are genetically prone to diabetes because the evidence demonstrates that higher rates of diabetes across population groups can be explained by non-genetic factors alone. Our study shows that by focusing on genes, researchers miss the more significant and alterable environmental causes of diabetes.”

One of Montoya’s co-authors, Stephanie Malia Fullerton, a population geneticist and bioethicist at the University of Washington added,

“When it comes to diabetes, we’re finding that genes are no more important for ethnic minorities than for anyone else.”

This new critique of genetic and ethnic studies will need to be replicated, and it is a little bit of a surprise that such important work was published in Perspectives rather than one of the journals dedicated to epidemiology.

I have no inside knowledge about why the study was published where it was. But it often happens that it can be very difficult to get new research published if it contradicts the mainstream. There have been examples of experts squashing data that contradicts their own, but it is uncommon. Most of the time the difficulty in getting revolutionary new data published is not because of some conspiracy, but because any kind of evidence, particularly if it is radically different, attracts the most concentrated scrutiny by independent reviewers.

If this new data analysis is confirmed, it is going to mean a radical re-think about the ways in which we screen, manage and advise people from different ethnic groups.

It also confirms something that I’ve said a hundred times: Biology is Not Destiny.