A study of twins conducted by Stanford University School of Medicine investigators shows that our environment, more than our heredity, plays the starring role in determining the state of our immune system, the body’s primary defense against disease. This is especially true as we age, the study indicates.
Much has been made of the role genes play in human health. Stunning advances in gene-sequencing technologies, in concert with their plummeting costs, have turned many scientists’ attention to minute variations in the genome — the entire toolbox of genes carried in virtually every cell in the body — in the hope of predicting people’s future health. Such studies have revealed a genetic contribution to health outcomes. But, with some notable exceptions, very few individual genetic variants contribute much to particular health conditions. “The idea in some circles has been that if you sequence someone’s genome, you can tell what diseases they’re going have 50 years later,” said Mark Davis, PhD, professor of microbiology and director of Stanford’s Institute for Immunity, Transplantation and Infection. But while genomic variation clearly plays a key role in some diseases, he said, the immune system has to be tremendously adaptable in order to cope with unpredictable episodes of infection, injury and tumor formation. “The immune system has to think on its feet,” said Davis, senior author of the new study, which will be published Jan. 15 in Cell. Lead authorship is shared by former Stanford postdoctoral scholars Petter Brodin, MD, PhD, and Vladimir Jojic, PhD.
Examining differences in the levels and activity states of these components within pairs of monozygotic and dizygotic twins, the Stanford scientists found that in three-quarters of the measurements, nonheritable influences — such as previous microbial or toxic exposures, vaccinations, diet and dental hygiene — trumped heritable ones when it came to accounting for differences within a pair of twins. This environmental dominance was more pronounced in older identical twins (age 60 and up) than in younger twins (under age 20).