Researchers report they have identified a genetic defect that causes a rare bone disease in which the body makes too much bone, a finding that may lead to treatments for osteoporosis. According to Dr. Michael Levyn, director of the bone and mineral center at Hopkins University, the new finding will help bone researchers understand why the body loses the ability to make new bone cells as people age.
Later, Levine explained the researchers studied DNA from 15 people who have a condition called progressive osseous heteroplasia or POH. People who have POH form extraskeletal bone, essentially small rice-like bone fragments that grow in various organs in the body. He said DNA from the patients revealed 13 of the 18 shared a GNAS1 mutation -- guanine nucleotide binding protein alpha stimulating activity polypeptide. GNAS1 controls a protein that plays a critical role in way cells function. In the case of POH, the GNAS1 mutation results in a mistaken signal to non-skeletal cells, which results in the creation of bone by the misinformed cells.
Levyn, who also worked with researchers from the University of Pennsylvania School of Medicine, the Royal Children's Hospital in Melbourne, Australia, and the Washington University School of Medicine in St. Louis, said the finding may lead to development of a genetic treatment for POH. But he said the real significance of the research might be the light it sheds on the genetic basis for bone formation. Although about one in 100,000 people have POH, many millions of people will develop osteoporosis, which affects most elderly women and many elderly men.
Up until age 30 healthy people have the ability to grow new bone but after that time the bone building cells, called osteoblasts die off and with those cells goes the ability to make bone. As the mineral content of bone decreases, the bones become fragile and easily break, which leads to the disability associated with osteoporosis.
Currently, osteoporosis treatment is aimed at replacing calcium in bones but there is no approved treatment aimed at growing new bones. Since the GSNA1 mutation is instructing cells to differentiate not into muscle, fat or skin but rather into bone it may provide a model to help researchers understand how they can manipulate cells in people with osteoporosis to grow bone.
Dr. Michael J. Econs, a bone researcher at the University of Indiana, Indianapolis, said Levine's team might be on the right track. "In a very general sense, the more we know about genes that are important in bone formation or born resorbtion or mineralization, the more likely we are to be able to design therapies for various metabolic bone diseases, including osteoporosis." Econs was not involved in the research.
Dr. Craig Langman of Northwestern University Medical School and the kidney and mineral metabolism center at Children's Memorial Hospital, Chicago, agreed the new research might pave the way for development of "designer drugs that really target this mutation."
But Langman cautioned it is premature to suggest this new finding will quickly lead to development of osteoporosis treatments. He predicted that it would have more value in finding ways to "treat this particular genetic disease." The research was funded by a grant from the National Institutes of Health and the Johns Hopkins University School of Medicine's General Clinical Research Center.