Specialists in arthritic disease are often asked if OA is an inherited disease. People with OA are concerned about the possibility of their siblings developing the same problem or about their chances of “passing” the disease to their children.
Studies of large populations of patients have demonstrated that OA does, indeed, have a major genetic component. Researchers have found that a pattern of heritability exists among joint sites. That is, if a parent has OA of the hip, there is a higher likelihood of his or her child having OA of the hip. Similar patterns have been identified for knee and spine OA. Unfortunately, the results across many studies are not always consistent. These discrepancies may arise because different investigators perform these studies a little differently. For example, they may use different populations of patients (older, younger, different ethnicities, and so on), different definitions of disease, and different ways of interpreting physical exams and x-rays. This complicates the task of understanding the complex genetics underlying OA.
Advances in DNA mapping have led arthritis specialists to examine the genetic makeup of individuals with OA to see if it differs from the genetic makeup of people without OA. Researchers in Asia have already identified variations in a gene responsible for the development of cartilage that is associated with a higher risk of hip and knee OA in Japanese and Chinese patients. This gene, which is called GDF5, was found to be more common in patients with OA than in a similar-size group of people without OA. These findings do not imply that GDF5 is the only gene that affects OA, however. The variations of the incidence of disease in populations affected, in the distribution of joints affected, and the inheritance pattern of this disease suggest that more than one gene may be involved and that other environmental factors may influence the onset and progression of OA.
To get a better understanding of the genetics of OA, an international research network has launched the largest study ever in an attempt to discover the source of the genetic susceptibility for OA. Scientists in the United States and the United Kingdom are studying families of people with OA. After taking detailed histories of patients, their family history of OA, and their risk factors for OA, these researchers will perform a complete physical exam of each patient, including x-rays of the hand, hip, knee, and lower spine. Next, blood samples will be taken for DNA testing. The researchers will then analyze the DNA samples and x-rays and chart the family tree in an attempt to identify the genes involved. If this study succeeds in pinpointing the gene or group of genes that cause OA, doctors may be able to identify those patients who are at risk for OA early and help them modify their lifestyles to slow the onset and reduce the symptoms of the disease. In the future, perhaps an effective treatment or a cure can be found with more modern genetic techniques.
Today, however, you should inform your doctor of any family history of OA. This information should include how the affected family members are related to you, which joints were affected, and how they were treated. For example, did that family member use a cane, take any specific medications, or have a joint replacement? This information will give your physician a better idea of your own risk for developing OA, including which joints may be affected and which risk factors you might be able to modify so as to reduce the impact of this disease.