Osteoporosis Clues Found in Girls’ Genes
Medical scientists based at Childrens Hospital Los Angeles have shown that osteoporosis, a much-dreaded ailment of old age, appears to have roots in early childhood, with some children inheriting genes that increase their risk of brittle bones later in life.
Led by Dr. Vicente Gilsanz, a radiologist at the hospital, and Jesus Sainz, a neurology researcher at the UCLA School of Medicine, the scientists used CT scanners to measure the bone density of 100 healthy girls between 6 and 12 years old. The researchers also analyzed the girls’ blood samples to determine their genetic characteristics.
They found that girls with genes that slightly impair the functioning of Vitamin D, which is crucial to bone growth, had backbones that were as much as 9% less dense than those of the other girls.
The study, appearing today in the New England Journal of Medicine, is the first to link bone density at a very early age with a specific genetic makeup. The work underscores the importance of ensuring that children get enough calcium in their diet to strengthen bones and help prevent osteoporosis, the researchers say. Experts say that a million fractures a year among the elderly are attributed to thinning bones.
Dr. Karl Insogna, director of the Yale University Bone Center, said the study made an “interesting” and “potentially important” contribution to understanding early bone growth in young girls. “It points to one way that we may identify children in the future who need particular” help building up their bones.
Previously, doctors have largely blamed the disease, which primarily strikes women, on poor dietary calcium intake, reduced physical activity and the inexorable thinning of bones after menopause. But the new research suggests that the problem for some women may also be a genetically controlled tendency to build too little bone in the first place.
“The emphasis has been on studying older people with osteoporosis because that is when the disease manifests itself,” said Gilsanz. “This shows that the antecedents of the disease can be seen in young kids.”
In their study, the researchers conducted precise CT scans of leg bones and backbones of girls who had not yet gone through puberty, when bones grow dramatically. All the girls were of Mexican American descent, which narrowed the genetic variation among them, making it easier for the scientists to pinpoint the sought-after genes.
Using a form of DNA analysis known as PCR, they looked at nine forms of a gene that regulates the receptor on cells that interacts with Vitamin D. The nutrient affects bone growth chiefly by regulating the body’s use of calcium.
The researchers found a slight difference in leg bone density associated with the various gene types, but it was the variation in backbone density that most intrigued them. Gilsanz said that it is not known if the girls with the lowest bone densities associated with certain genes will make up for the lack during puberty.
If not, even a small early deficit in bone growth could have big consequences later, Gilsanz said. Older women lose about 1% of their bone mass per year, he said, so a 9% percent shortfall in bone density could translate into developing symptoms of brittle bones sooner than other women.
The researchers are not sure if increased calcium consumption would offset the genetic tendency, but theoretically it might help. Currently, nutrition experts say, most young and teenage girls do not consume enough calcium to maximize bone strength. For them, the recommended dietary allowance for calcium is 1200 milligrams. Eight ounces of skim milk contain about 300 mg. Other rich sources besides dairy products are dark green leafy vegetables (but not spinach), broccoli, beans, peas and tofu.
