TIME: Almanac 1995

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<text id=94TT0101> <title> Jan. 31, 1994: Why The Bones Break </title> <history> TIME--The Weekly Newsmagazine--1994 Jan. 31, 1994 California:State of Shock </history> <article> <source>Time Magazine</source> <hdr> MEDICINE, Page 97 Why The Bones Break </hdr> <body> A single gene seems to heighten the risk of developing osteoporosis, perhaps by hampering vitamin D uptake By Anastasia Toufexis--Reported by Graeme O'Neill/Sydney and Alice Park/New York Among emblems of old age, a woman's curved spine is one of the most powerful and haunting, at once both metaphor and augury. It conjures up the crush of life's passage. More terrible, it often heralds life's end. For the humped back is often the most visible sign of osteoporosis, a progressive disease that leaves bones thin and brittle. Even so simple a motion as walking or sitting can collapse vertebrae and fracture wrists and hips. Those who suffer such breaks rarely recover their mobility. Many wind up in nursing homes. One-quarter die within six months of a hip fracture. The sight of an elderly person with a stoop sets people to wondering, "Will that happen to me?" Up to now, there has been no way to answer that question. Though osteoporosis afflicts about 25 million Americans, most of them women, the disease offers no early symptoms. Usually it is not diagnosed until after age 50, when a victim suffers a fracture. But that may soon change. Last week a team of Australian scientists reported that they have identified a single gene that appears to put people at very high risk of developing osteoporosis. The genetic studies are still preliminary, but if confirmed, they could lead to a simple screening test that would alert vulnerable people at a young age, early enough for them to take steps that could help ward off the disease. Says Dr. John Eisman, who led the groundbreaking research at the Garvan Institute of Medical Research in Sydney: "I envision a woman going in for a blood test, which will become as routine as a cholesterol check, to assess her bone density and risk for osteoporosis." In a report to Nature, the researchers announced that they have found two versions of a specific gene that are associated with varying bone density. One type, which they dubbed "b," is linked with stronger skeletons, and the other, labeled "B," with weaker ones. The gene itself directs construction of receptors (docking sites within the cell) for a form of vitamin D that plays a crucial role in bone formation. Once vitamin D locks in, the receptors act as a sort of control tower, switching on and off other genes that regulate calcium absorption and the constant renewal of bone. Until about age 35, the body synthesizes new skeletal tissue faster than it dies. Then the balance reverses, with bone being lost faster than it is replaced. In osteoporosis, that normal wasting away reaches such a hazardous level that bones become fragile. They lose their usual spongelike appearance and are more like porous lace. While both men and women experience bone loss, women are much more susceptible to osteoporosis. Bone deteriorates faster after menopause, probably in part because of a sharp drop in levels of the hormone estrogen. According to the new research, the risk of osteoporosis depends heavily on which versions of the vitamin D receptor gene an individual inherits. Since each parent contributes a copy, a person's genetic endowment can be bb, Bb or BB. The most severe threat occurs, says molecular biologist Nigel Morrison, of the Australian team, "when you inherit a double whammy of the low-bone-density form of the gene. Then you're at risk of having osteoporosis by age 65." Examining 311 women, the scientists discovered that those with the BB combination had spines fragile enough to fracture by about 18 years after menopause. Bb women reached this fracture threshold four years later, and those carrying bb genes not until 29 years after menopause. Like so many genetic discoveries these days, the new findings are likely to be a mixed blessing. A screening test could identify people at high risk of osteoporosis even at birth. That knowledge would provide relief for some parents and their offspring--and certain worry for others. But researchers stress that having the B form of the vitamin D receptor gene does not doom people to a severe case of the disease. In fact, bone density is determined about 75% by heredity and 25% by environmental factors. As a hedge against later bone erosion, children identified as vulnerable to osteoporosis will be urged to build up their bone density by increasing their calcium intake and exercising with weights. Those at high risk will also be strongly advised to shun cigarettes and alcohol, which speed up bone loss, and perhaps take vitamin D supplements and estrogen-replacement pills after menopause. Eventually, researchers hope to develop new drugs that stimulate bone formation. "The whole business of genetic testing is clouded by things we can't control," observes Morrison. "What's good is that, here, we can do something about the threat." </body> </article> </text>