AIP is an autosomal dominant disorder caused by a deficient activity of hydroxymethylbilane synthase (HMBS) (EC 4.3.1.8; OMIM: 609806), also referred to as porphobilinogen deaminase, producing a markedly increase in the urinary excretion of 5‐aminolevulinic acid (ALA) and porphobilinogen (PBG). Here, HMBS is linked to autoimmune pancreatitis.