October 23, 2000
Volume XXXIII, No. 36

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2000 Distinguished Scholar is longtime diabetes detective

Dr. Michael Stern, a research "detective" who has helped define antecedents of type 2 diabetes, is the Presidential Distinguished Scholar for 2000. Professor of medicine and chief of the Division of Clinical Epidemiology, he spoke at the 2000-2001 Academic Convocation.

Dr. Stern reflected on the many outstanding colleagues he has worked with over the years. "I am here merely as their representative," he told the audience. Three of those collaborators, Dr. Steve Haffner, Dr. Helen Hazuda and Sharon Fowler, joined the Division of Clinical Epidemiology shortly after it was established in 1976.

Dr. Stern has used epidemiological techniques to try to discover the reason for the strong tendency toward type 2 diabetes in Mexican Americans. Few studies had been conducted on the topic by the end of the 1970s. "Now there are many," he said, "but I believe that ours was one of the first and probably the longest running, since it is entering its 21st year."

S.A. Heart Study

The Western lifestyle, marked by increased caloric intake and decreased physical activity, is thought to be driving the modern epidemic of obesity, diabetes and cardiovascular disease. Dr. Stern and his colleagues hypothesized that increasing levels of education and affluence in developed societies such as the United States would result in a slowing or even a reversal of this epidemic.

Through the San Antonio Heart Study, they conducted random samples of populations in three types of neighborhoods—low-income, exclusively Mexican American barrios; middle-income neighborhoods; and upper-income, suburban neighborhoods. "The idea behind our sampling design was that the three neighborhood types would reflect increasing levels of affluence and educational attainment, and, in the case of Mexican Americans, increasing acculturation to mainstream U.S. society," Dr. Stern said.

The study team surveyed more than 3,300 Mexican Americans and more than 1,850 non-Hispanics. Eight years later, the scientists recorded outcomes of study participants, indeed finding that the incidence of type 2 diabetes in the study groups decreased as socioeconomic status increased. In each of the neighborhood types, incidence of type 2 diabetes was higher in Mexican Americans than in non-Hispanics.

Behavioral changes

Dr. Stern’s team devised behavioral scales to understand how sociocultural change could lead to a change in disease rate.

The team’s further studies showed that incidence of type 2 diabetes among Mexicans living in Mexico City is lower than among San Antonio Mexican Americans of comparable socioeconomic status. The group theorizes that the Western lifestyle’s poor diet and exercise traits have not become as ingrained in the Mexico City residents.

Genetic hypothesis

Dr. Stern also discussed the "Genetic Admixture Hypothesis," a scenario to explain why Mexican Americans are more susceptible to type 2 diabetes than are non-Hispanics.

The hypothesis holds that:

  • Native Americans for many centuries adapted to food scarcity, leading to accumulation of diabetes susceptibility genes.

  • Sudden availability of caloric abundance has permitted expression of these diabetes susceptibility genes.

  • Mexican Americans have Native American ancestry, with an influx of diabetes susceptibility genes from this ancestral gene pool.

To test the hypothesis, Dr. Stern and his colleagues, including faculty from the Southwest Foundation for Biomedical Research, conducted the San Antonio Family Diabetes Study. The scientists began with 32 diabetic Mexican Americans and enrolled first-, second- and third-degree relatives of these individuals.

The group examined 417 genetic markers in diabetic and non-diabetic participants at the start of the study and five years later. In the diabetics, the scientists found a linkage between genes on human chromosome 6 and diminished effectiveness of insulin, a protein that controls blood sugar level in the body. "We have identified a large number of interesting linkages," Dr. Stern said.

The group has strong evidence for a linkage of diabetes to a region on chromosome 10. "We recently received funding to find the actual gene," Dr. Stern said.