Association of mutations in hemochromatosis genes with clinical severity of calcium pyrophosphate arthritis

Aims: To study factors associated with the development of calcium pyrophosphate (CPP) arthritis and the severity phenotype. Methods: Transversal case-control study. Cases had to be confirmed by both X-ray chondrocalcinosis and CPP crystals in synovial fluid. Controls had neither chondrocalcinosis nor CPP crystals in synovial fluid. Patients and controls with hemochromatosis or primary hyperparathyroidism were not included. Mutations of hemochromatosis genes (HFE), magnesium (Mg), calcium (Ca), phosphate, iron (Fe), transferrin saturation, ferritin, parathyroid hormone (PTH), and calcifediol levels were studied. Results: Three hundred patients and 300 sex and age matched controls were compared. Lower serum Mg (sMg) and higher ferritin levels were found among patients. Hypomagnesemia (HypoMg) and HFE mutations were more frequent among patients. Involvement of over one joint was observed in 199 (66.4%) patients whereas persistent joint inflammation was retrieved in 154 (51.4%) of the patients. Initial analysis showed that the frequency of polyarticular and inflammatory phenotypes seemed to be progressively overrepresented in patients with HFE mutations. Further bivariate and multivariate analysis adjusted for the time from onset disclosed that the presence of genotypes with C282Y mutations was associated with polyarticular disease (hazard risk 3.501, 95% confidence interval 1.862–6.581, P < 0.001). Although C282Y mutations also seemed to be associated with inflammatory patterns, the association did not reach statistical significance (P = 0.173). Conclusions: Low sMg and high ferritin levels are associated with CPP arthritis (CPPA). In patients without hemochromatosis, HFE mutations, and specifically C282Y mutations seem to associate with the polyarticular disease phenotype, and plausibly with the chronic inflammatory phenotype.