Primary osteoarthritis of the hip: a genetic disease caused by European genetic variants.

Primary osteoarthritis of the hip is a separate phenotype that occurs at a rate of 3% to 6% in the populations of the world with European ancestry. In all non-European populations, there is a consistent rarity of primary osteoarthritis that suggests a different etiology for these few patients. Family, sibling, and twin studies prove primary osteoarthritis to be a genetic disease with a 50% heritability caused by European genetic variants. The genetic basis is reinforced by the lower rate of primary osteoarthritis in American minorities consistent with their degree of European gene admixture. Whether the mechanism of degeneration of primary osteoarthritis may be secondary through a morphologic deformity, such as femoroacetabular impingement, remains unknown. The virtual absence of the disease in non-Europeans indicates that the European gene component is necessary for the expression of this separate phenotype of osteoarthritis.