AIP is caused by defects in the hydroxymethylbilane synthase (HMBS) gene, resulting in a selected accumulation of heme precursors like 5-aminolevulinic acid (ALA) and porphobilinogen (PBG) in the heme biosynthesis pathway, which are associated with acute attacks of the disease (Puy et al., 2010). The gene discussed is HMBS; the disease is autoimmune pancreatitis.