Changes in serum cartilage marker levels indicate altered cartilage metabolism in families with the osteoarthritis-related type II collagen gene COL2A1 mutation

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Abstract
Objective The Arg519–Cys mutation in type II collagen results in severe, precocious familial osteoarthritis (OA) in 100% of carriers within the first 3 decades of life. The carrier population provided a well‐defined patient population for the study of serum markers of familial OA with respect to pathogenesis, diagnosis, and prognosis. Methods Serum was obtained from 31 mutation‐positive individuals and 16 mutation‐negative individuals. OA severity was determined by clinical and radiologic assessments. Levels of serum cartilage oligomeric matrix protein (COMP), keratan sulfate (KS) epitope, the 846 epitope of aggrecan, and the C propeptide of type II collagen (CPII) were measured and were correlated with the radiologic findings. Results COMP and KS levels, both of which have been suggested to be indicative of disturbed cartilage turnover, were significantly elevated in mutation‐positive individuals and in the individuals with OA regardless of mutation status. There was no statistically significant difference between mutation‐positive, mutation‐negative, OA‐positive, and OA‐negative individuals with respect to serum concentrations of epitope 846 or CPII, both of which are putative markers of cartilage repair. Conclusion Study of the macromolecular constituents of cartilage released into serum in subjects with familial OA revealed altered metabolism in OA, as demonstrated by elevated COMP and KS levels. Other constituents, the 846 epitope and CPII, were not altered, indicating dissociation of cartilage anabolism and breakdown. Future sequential studies will provide an opportunity to define biochemical changes as familial OA develops and to monitor therapeutic responses.