Bone Density Gene Discovered

Scientists have discovered a gene that appears to control bone density, opening the way to possible new treatments for crippling osteoporosis.

Researchers from the biotechnology company Chiroscience R&D found the gene in a small group of South Africans suffering from an inherited disease that is the opposite of osteoporosis -- these patients can die because their bones grow too dense and large.

A mutation in the gene appears responsible for making bone grow out of control. Chiroscience hopes to harness the protein this gene produces and turn it into a drug that might increase the bone mass of people with osteoporosis, the disease that makes bones brittle.

Developing a drug, however, takes years -- and osteoporosis experts urged caution Tuesday.

More immediately, doctors who treat Afrikaners, South Africans of Dutch descent who suffer from sclerosteosis, the large-bone disease, hope the discovery will lead to a genetic test to help their patients in planning children.

"What we have found is really the holy grail of bone biology," said Chiroscience researcher Jeffrey Van Ness in announcing at a biotechnology meeting here that the company had successfully mapped the "bone mass gene."

But while this may be the first gene discovered in the complex process of bone building, nobody knows what role it could play in osteoporosis, said Dr. Conrad Johnston of Indiana University, an adviser to the National Osteoporosis Foundation. He cautioned that many genes may play a role in osteoporosis, and that studies of other large-bone diseases have found more bone is not always better -- sometimes it's fracture-prone.

"Certainly if you discover a gene that increases amounts of bone, it is very interesting and should lead to lots of good research," Johnston said. But "whether it will lead to any treatment is highly speculative."

Osteoporosis afflicts 10 million Americans, mostly elderly women. They're at risk of severe injury, such as breaking a hip, along with chronic pain and stooped posture as spinal vertebrae and other bones fracture. The disease costs $14 billion annually in medical bills and lost productivity.

Bone is living tissue: Cells called osteoclasts dissolve worn-out bone while other cells called osteoblasts replace it with new bone. During childhood, new bone builds faster than old bone dissolves. People hit their peak bone mass in their mid-20s.

But as people age, bone removal exceeds new bone formation. When that happens too fast, or when people didn't build up enough strong bone when young, osteoporosis results.

Some treatments, including estrogen and the popular nonhormonal drug Fosamax, can slow bone loss and help restore a little bone. But no drug can reverse osteoporosis by building large amounts of bone.

Sclerosteosis is an incurable rare disease that is the opposite -- bones, even the skull, grow very dense. By middle age, skull pressure often causes incurable headaches, even suden death.

Chiroscience worked with Dr. Peter Beighton of the University of Cape Town to study the genes of a small group of Afrikaners with sclerosteosis. Only a few other people around the world have ever gotten the disease.

Afrikaners who suffer from it inherited a mutated bone mass gene from each parent. Chiroscience pinpointed the problem gene on chromosome 17, mapped it and say they discovered that a single mutation appears to be the culprit.

Beighton said in a statement that creating a genetic sclerosteosis test should be a priority so Afrikaner couples will know if they're at risk. About one in 20,000 are thought to be, and two Afrikaner children are born with sclerosteosis every year.

While acknowledging a test was possible, Chiroscience on Tuesday stressed efforts to try to turn the gene's protein into a drug to help grow bone in osteoporosis patients.

Written By Lauran Neergaard