In a recent article (1), Chapman et al described a genetic linkage of primary hip osteoarthritis (OA) with restricted areas on chromosome 11q. This is an elegant study, which may well provide important new insights into hip OA. Nonetheless, I would like to raise concerns about their choice of patients for this study.
Their cohort, as described previously (2), was ascertained by identifying siblings of patients in the UK who had undergone total hip replacement for primary hip OA. The authors went to considerable lengths to make sure that primary OA was the reason for the joint damage. There are, however, at least two other factors that may need to be taken into account. First, by choosing patients who underwent total hip replacement, they are, by definition, choosing patients with advanced disease. There is some evidence to suggest that a different set of factors may be involved in the incidence and progression of knee OA (3,4). If this is the case for hip OA as well, then a study of this sort may identify genes involved in disease progression rather than disease initiation, although it would be impossible to differentiate between the two without investigating other groups of patients.
Another important consideration is health services utilization. Not everyone in the UK with advanced OA undergoes joint replacement surgery. Some patients with advanced OA suffer relatively little, others do not seek help in spite of severe symptoms, and others refuse surgery for one reason or another (such as comorbidity or obesity) (5,6). It is possible, therefore, that the genes identified in this study will be markers of some factor that predisposes persons with hip OA to require joint replacement surgery, rather than being markers of disease.