Xanthine dehydrogenase deficiency with novel sequence variations presenting as rheumatoid arthritis in a 78‐year‐old patient

Summary This report describes the clinical, biochemical and molecular data of a 78‐year‐old patient with xanthine dehydrogenase deficiency presenting as rheumatoid arthritis. Background Xanthinuria type I is a rare disorder of purine metabolism caused by xanthine dehydrogenase (XDH) deficiency; fewer than 150 cases have been described in the literature so far. Methods We describe the clinical history and urine and serum findings of a 78‐year‐old patient with isolated XDH deficiency presenting as rheumatoid arthritis. The diagnosis was confirmed by mutation analysis. Results The patient suffered from arthral symptoms and nephrocalcinosis. Very low concentrations of uric acid were observed in her serum and urine. The allopurinol loading test indicated her xanthinuria to be type I. Analysis of genomic DNA revealed novel heterozygous deletion in exon 8 (g.27073delC, p.214QfsX4) and previously published heterozygous nucleotide missense transition in exon 25 (g.64772‐C>T, p.T910M). Conclusion Hereditary xanthinuria is a rare disorder, but it also needs to be considered in patients not originating from Mediterranean countries or the Near or Middle East. Urate concentration in serum and urine may provide an initial indication of XDH deficiency before high‐performance liquid chromatography (HPLC) analysis is performed. The key to identifying the disorder is a greater awareness of XDH deficiency amongst primary care physicians, nephrologists, and urologists, but also rheumatologists. The diagnosis and therapeutic management requires a multidisciplinary approach.