Of this paediatric UK cohort of 10 patients who were initially considered as “mutation negative CAPS”, one patient was found to have a NOD2 mutation and an eventual diagnosis of Blau syndrome; one patient had a germline mutation in NLRP3 that was missed by an historic Sanger sequencing approach that only focused on exons considered to harbour mutation hotspots; and NLRP3 mosaicism was present in 4/10 (40%), confirming the important role of somatic NLRP3 mosaicism some CAPS patients. The gene discussed is NLRP3; the disease is Blau syndrome.