Prevalence and Inheritance of Hip Osteoarthritis in Iceland

Sammanfattning: Hereditary factors are suggested to contribute to osteoarthritis (OA), but their relative importance is uncertain. Moreover, the underlying specific variations at the genome level remain unknown. The prevalence of hip OA in Iceland was assessed by examining colon radiographs and was found to be at least 5-fold higher compared to Sweden and Denmark. The age-standardized incidence of total hip replacement (THR) for primary hip OA in Iceland between 1982 and 1996 was determined and found to be 50 percent higher than in Sweden. A comparison of two methods for estimating hip OA from colon radiographs showed that a simple quantitative method of measuring joint space was more reliable than a qualitative method. The contribution of heritability to hip OA leading to THR was investigated by combining information from two population-wide databases in Iceland: a national register of all THR and a database of all Icelandic genealogy records. A genetic contribution to THR for OA was shown by (a) identifying a large number of familial clusters of THR for OA, and by showing that (b) OA patients descended from fewer founders than matched controls, (c) the kinship coefficient among patients with THR for OA was greater for than matched controls, and (d) the relative risk for siblings of THR for OA patients was 3.1 (2.5, 3.1). Icelandic patients with THR for OA are thus significantly more related to each other than the general Icelandic population. Finally, a genome locus with a lod score of 2.58 was identified on chromosome 16p by a genome wide scan of a large Icelandic family with primary hip OA. These findings support a significant genetic contribution to a common form of OA and encourages the continued search for genes conferring an increased susceptibility to OA.