Now, researchers at the University of North Carolina at Chapel Hill have shown for the first time that the same thing is true in blacks. They also found average levels of the protein to be higher in blacks, -- both patients and others -- than in whites and higher among white men than among white women.
"These discoveries are likely to be important in the search for better ways to predict who is at strong risk of developing osteoarthritis, who had it already and whose illness is most likely to progress," said Dr. Joanne M. Jordan, associate professor of medicine and orthopaedics at the UNC School of Medicine. "No one had ever studied African-Americans in this way before."
Just knowing how much of the protein, which is considered an emerging "biomarker" of the illness, is naturally present in the different races and sexes could become a major tool for determining when the illness occurs and when it advances, said Jordan, also adjunct professor of epidemiology at the UNC School of Public Health. "We must take these differences into account. An African-American person, for example, could be falsely considered at high risk because of elevated COMP when in fact COMP levels are just higher in blacks normally."
A report on the new findings appears in the March issue of Arthritis & Rheumatism, a medical journal. Other authors are Dr. Jordan Renner and doctoral students Gheorghe Luta and Anca Dragomir of UNC and Thomas Stabler and Dr. Virginia B. Kraus of Duke University. Others are Dr. Vlad Vilim of the Institute of Rheumatology in Prague, Czech Republic, Dr. Marc C. Hochberg of the University of Maryland and Dr. Charles G. Helmick of the Centers for Disease Control and Prevention in Atlanta.
More than 750 men and women of both races participated in the study, which involved measuring COMP levels in volunteers with no X-ray evidence of osteoarthritis. Some of the differences recorded may stem from differences in joint size and total body cartilage content.
The National Institute of Arthritis, Musculoskeletal and Skin Diseases and several pharmaceutical companies have begun a public-private consortium, called the Osteoarthritis Initiative, to find biomarkers of osteoarthritis that could help evaluate osteoarthritis progression, Jordan said.
"Currently, to be able to market an osteoarthritis drug that actually modifies the disease and not just treats symptoms, it takes a clinical trial of at least two to three years," she said. "Because we do not have any good way to measure progression of osteoarthritis, the goal of the Osteoarthritis Initiative is to identify biomarkers that could shorten this time by giving us better indicators of progression."
COMP, short for cartilage oligometic matrix protein, a glycoprotein compound that includes carbohydrates, promises to be a strong indicator, the physician said.
Osteoarthritis, the most common form of arthritis, afflicts almost a million North Carolinians and more than 21 million people nationally, including many adults over age 65, the physician said. Some estimates suggest that as many as 70 million Americans will suffer from some form of arthritis within the next 20 years as baby boomers age.
Jordan leads the Centers for Disease Control and Prevention and National Institutes of Health-funded Johnston County Osteoarthritis Project. That unique research involves more than 3,000 volunteers and is the largest study ever done of arthritis in both black and white rural communities.
Earlier work she and colleagues did showed, among other things, that significantly more people may have legs of slightly unequal length than doctors previously believed. They also discovered that COMP increases markedly in the blood of people with hip or knee osteoarthritis even before X-rays reveal joint damage.
They further found that COMP levels correspond closely with pain that patients with undiagnosed osteoarthritis report to doctors. People with five or more years of hip or knee pain, for example, showed about 33 percent more of the protein in their blood than people reporting no pain, Jordan said.
"The best things people can do to minimize knee and hip osteoarthritis are to avoid activities that put heavy physical demands on joints and especially to lose any excess weight," she said. "Also, evidence suggests it's important to keep thigh and other leg muscles strong through non-stressful exercise."
The National Institute of Arthritis, Musculoskeletal and Skin Diseases recently awarded Jordan as principal investigator and colleagues $4 million grant to establish a new center for multidisciplinary clinical research on arthritis. Experts from rheumatology, nutrition, epidemiology, health behavior, biostatistics, nephrology, psychology, nursing, orthopaedics, family medicine and other areas will be involved.
Note: Jordan can be reached at (919) 966-0559.
Contact: David Williamson, (919) 962-8596
Journal
Arthritis & Rheumatism