The hyper IgD syndrome (HIDS) is an inflammatory disease caused by mevalonate kinase deficiency. There is no cure, and available treatments of HIDS febrile episodes have shown limited clinical efficacy. The development of effective interventions for HIDS is limited by our poor understanding of the disease. The goal of the study is to better characterize the inflammatory response during HIDS episodes and to determine the relationship between this response and blood and urine markers of mevalonate kinase deficiency. This knowledge will help us learn more about the cause of the disease and should lead to the identification of new disease biomarkers that can be used to evaluate clinical efficacy in future therapeutic trials.