Among more than 20 well-characterised seronegative conditions, serositis is a common feature, occurring in disorders such as FMF, TRAPS, and the rarer adenosine deaminase 2 deficiency (DADA2) and NLRP2 spectrum disorders [3,8]. This evidence concerns the gene NLRP2 and hyperinsulinemic hypoglycemia, familial, 4.