As children transform into adults some of the genes involved in controlling their blood pressure change as well, according to a study of more than 500 pairs of twins.
The study of black and white identical and fraternal twins showed that changes in gene expression between ages 14 and 18 accounted for up to one third of the blood pressure variation that occurred by age 18, says Dr. Harold Snieder, genetic epidemiologist at the Medical College of Georgia.
The findings are being presented March 4 in Denver during the 64th Annual Scientific Conference of the American Psychosomatic Society.
"We know this is a period of great change, between 14 and 18 years of age, as children are growing, hormones are raging and the stability of adulthood has not yet been reached," says Dr. Snieder. Those factors prompted him and his colleagues to look at what happens to blood pressure and related hemodynamics - such as heart rate and how much blood the heart pumps with each beat - near the beginning and end of the biologically tumultuous times.
Researchers left much-discussed obesity out of this equation, focusing instead on genes and environmental factors directly influencing blood pressure and hemodynamics. The huge twin cohort and some complex mathematical modeling made it possible to quantify the role of genetics.
They found genetics played a moderate to high role, explaining between 25 and 64 percent of the individual differences in blood pressure and hemodynamics, Dr. Snieder says. Genes also played a major role - between 60 and 100 percent - in the consistency they saw in the measures over the four-year period.
Most surprisingly, he says, was the emergence of novel genetic influences that accounted for up to a third of the total variation at age 18.
"A substantial part of the individual differences between the twins were due to new genetic effects between this period of age 14 and 18," says Dr. Snieder. "There are new genes being switched on that are involved in blood pressure and factors underlying blood pressure. I think that is the most interesting finding: the large amount of new genes that come into play."
Even though the genes responsible for blood pressure regulation remain unknown, it's widely believed - and some previous studies in adult twins have shown - that the genes are consistent over a lifetime, Dr. Snieder says.
"The next step is following these kids for a long period of time to see whether the genetic effects stabilize or, after another three or four years, there is another large jump in new genetic effect," he says. Despite conventional thinking, this scientist who focuses on genetics, was not totally surprised to see the novel genes show up during puberty - although the amount of change surprised him - but suspects gene expression may be consistent from that point onward.
"We need to know what the genes are to develop new medications and treatments and this shows that at different ages there appear to be different genes," says Dr. Snieder, who already is working to identify some genes that may influence unhealthy increases in blood pressure that occur over time.
A second finding that bears further study is that the importance of non-shared environmental influences became more important in the black twins over the four-year period, says Dr. Snieder.
Non-shared influences could mean one twin starts riding a bike to school while the other continues taking a bus or even that they start going to different schools. Environmental factors are wide-ranging - including diet, physical activity, socioeconomic issues and stress - and difficult to accurately measure, Dr. Snieder says.
However, if factors negatively influencing blood pressure in blacks can be identified, it could contribute to solving health disparities such as blacks tending to have higher rates of hypertension that start at a younger age, he says.
Toni Baker
tbakermcg.edu
Medical College of Georgia
mcg.edu