HMBS and acute intermittent porphyria: Acute intermittent porphyria (AIP) is a rare autosomal dominant disorder caused by the deficient activity of hydroxymethylbilane synthase (HMBS), which is also referred as porphobilinogen deaminase (PBGD), the third enzyme in the pathway of heme biosynthetic (Gill et al., 2009; Chen et al., 2018).