The possibility of a genetic test for DDH was recently reported in a scientific study from Jefferson Medical College in Philadelphia. Before we get too excited about a possible genetic test, it’s important to note that this study involved a family that had multiple cases of hip dysplasia over four generations. Clearly, this is a severe form of DDH that may not represent ordinary DDH even in families where two members have been affected. An example of inheritance of disease is the BRCA gene for breast, ovarian, colon cancer. Most people that get those cancers do not have the BRCA gene, but the ones who do are at much greater risk for more cancer in them or in family members.
Many diseases run in families without any genetic cause because of shared habits such as food choices, exercise, sun exposure, smoking, exposure to environmental chemicals, etc. While the risk of hip is slightly increased when one child or parent has been affected, it is clear that external factors are very important for the vast majority of people with hip dysplasia. For example, it’s known that hip dysplasia is more common in first born children, breech babies, and in babies born in winter months or colder climates. Those types of variations are more often associated with natural processes such as position in the womb, or seasonal variations of sun exposure, clothing, indoor living, or dietary habits that change with the time of year. Hip dysplasia is also more common in cultures that practice traditional swaddling, and programs to teach healthy swaddling have decreased hip dislocations by seven to ten times the amount seen otherwise. External factors play a huge role in the occurrence of hip dysplasia.
It is more likely hip dysplasia is “multi-factorial”. This means that there are probably mild genetic variations that are very common such as increased joint flexibility that allows the hips to become unstable when other factors come into play. There are so many people with joint laxity that a genetic test is unlikely to sort out those who will develop hip dysplasia from the rest of the population.
In the end researchers need to look for both external factors and genetic factors. It may be possible to prevent external factors but genetic influences are currently impossible to prevent. Even if preventive measures are found for the external factors, there will always be a small number of cases that cannot be prevented because of genetics, or other issues that are beyond our control. For those patients it’s important to emphasize early detection and early treatment.
The International Hip Dysplasia Institutes promotes a three-pronged approach to curing hip dysplasia. One prong is to find environmental factors for prevention in the vast majority of cases. The second prong is to encourage genetic tests to identify the few families that are at greater risk for hip dysplasia so those families can benefit from early detection and treatment. The third prong is to develop better methods of treatment for those who need it.
In summary, it is unlikely that a genetic test will be found to identify all patients at risk for hip dysplasia just as it is unlikely that genetic testing will identify everyone who is at risk for cancer, heart attacks, or stomach ulcers. However, the search for genetic factors needs to continue along with the search for external factors that may be preventable.