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Gene Found for Form of Brittle Bone Disease

Findings could lead to test for couples evaluating risk of having more children

WEDNESDAY, Dec. 27, 2006 (HealthDay News) -- Researchers at the National Institutes of Health (NIH) say they've pinpointed a genetic defect responsible for a form of brittle bone disease.

Most forms of Osteogenesis Imperfecta (OI), a disorder that weakens bones, leads to frequent fractures and can even lead to death in infants, is caused by a defect in the genes that contain information for type I collagen, which is the material that holds bones, tendons, skin and other tissues together. About 10 percent to 15 percent of OI patients do not have a defect in these genes.

To determine what causes these unexplained cases of OI, the researchers examined tissue samples from three OI patients who had died during their first year of life. The cause of the patients' disorder was unknown.

The study, published in the Dec. 28 issue of the New England Journal of Medicine, found that some previously unexplained forms of OI could be attributed to defects in a gene that contains information for cartilage associated protein, or CRTAP. CRTAP is part of a complex of proteins involved in transforming collagen into its final form.

The well-known forms of OI result from a dominant defect -- requiring only one copy of the defective gene to cause the disease. But the NIH researchers found that the form of OI caused by mutations in the CRTAP gene was recessive, requiring two copies of the affected gene -- one from each parent -- to cause OI.

"This discovery provides a basis for counseling families that have lost a child to this previously unexplained form of Osteogenesis Imperfecta," Duane Alexander, director of the National Institute of Child Health and Human Development, said in a prepared statement. "It also offers insight into a crucial step needed in the formation of bone and other tissues," he said.

Joan Marini, lead researcher and chief of NIH's Bone and Extracellular Matrix Branch, estimated that this recessive form of OI occurs in about 2 percent to 3 percent of lethal OI cases.

Couples who have lost a child to OI could be tested for the presence of the recessive CRTAP gene and apprised of their risk of having another child with the disorder. Similarly, the siblings of the children with OI could also be counseled on their likelihood of carrying the defective gene.

More information

The National Institute of Arthritis and Musculoskeletal and Skin Diseases has more about Osteogenesis Imperfecta.

SOURCE: National Institutes of Health/National Institute of Child Health and Human Development, news release, Dec. 27, 2006
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