Acute intermittent porphyria (AIP) is an autosomal dominant disorder characterized by a relatively high frequency of porphobilinogen deaminase (PBGD) gene mutations (1/1700 of newborns) [1,2] but low and incomplete clinical penetrance, encompassing ~1% of PBGD mutation carriers [3,4]. This evidence concerns the gene HMBS and autoimmune pancreatitis.