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D. Michael Hallman, Ph.D.

assistant professor of human genetics, School of Public Health

Genetic changes from adolescence to adulthood may predict disease risk factors

Do the genes we inherit at birth predispose us to develop heart disease?

Do our genes increase or decrease our chances of developing complications from diabetes?

D. Michael Hallman, Ph.D.

D. Michael Hallman, Ph.D.

Do the effects of some genes change as we grow older?

Finding the answers to questions about the genetics of cardiovascular disease and type 2 diabetes is at the core of research by D. Michael Hallman, Ph.D. One project he works on focuses on examining the genetics of cardiovascular disease risk factors, including high cholesterol levels.

“I have a particular interest in genetic factors that affect changes in lipid levels with age, from childhood through adolescence and into adulthood,” Hallman said. “For example, few children have high cholesterol levels, but many adults do. Relatively little is known about possible changes in gene effects with age, as there are few studies that have been able to measure cardiovascular disease risk factors periodically in large groups of individuals as they age from childhood and into adulthood.”

Hallman is working with data collected from two studies, Project HeartBeat! and the Bogalusa Heart Study, that measured the traits related to cardiovascular disease in school-aged children.

Project HeartBeat! involved children, ages 8-18 years, from The Woodlands and Conroe, who were measured up to three times annually over a four-year period.

“We’re measuring variants in selected genes involved in blood pressure or changes in height, weight and body fat, in order to try to identify variants that affect changes in these traits over time,” Hallman explained.

The Bogalusa Heart Study measured cholesterol levels, blood pressure and other cardiovascular disease risk factors in children living in Bogalusa, La., every three years from the 1970s to the 1990s. Eventually, Hallman says, this study developed into a longitudinal study of the changes that occur with age in traits related to cardiovascular disease, with individuals ranging from 5-38 years of age.

“In earlier work on the Bogalusa Heart Study sample, we investigated several genes involved in regulating the levels of cholesterol and other blood lipids, finding one case where the effect of a particular gene in raising high density-lipoprotein cholesterol (the “good” cholesterol) did not appear until adolescence,” Hallman said.

A second project Hallman investigates is the genetics of type 2 diabetes and its complications, particularly diabetic retinopathy, which is a leading cause of blindness in adults. Examining genetic data from Mexican Americans with type 2 diabetes led Hallman to an important finding.

“We have helped establish that genes appear to be more likely to affect the development of severe diabetic retinopathy than milder forms – that is, a tendency to develop more severe diabetic retinopathy may run in families, while almost anyone who has diabetes long enough may develop at least mild retinopathy,” Hallman explained.

Hallman said he hopes his research will lead to a better understanding of the genetic factors that affect cardiovascular disease and complications resulting from type 2 diabetes.

“We know from years of work that there probably aren’t going to be any common genetic variants in the population that have large effects on these conditions at an individual level, though some genetic mutations are common enough in the population to have modest risk-raising effects in large numbers of people,” he said. “I hope my work can contribute to our knowledge of the genetic factors that affect the physiological changes that occur at puberty and with later aging.”