Porphobilinogen Deaminase (HMBS) is a member of the HMBS family. PBGD is the third enzyme of the heme biosynthetic pathway and catalyzes the head to tail condensation of four porphobilinogen molecules into the linear hydroxymethylbilane. HMBS is involved in the production of heme, which is important for all of the body's organs, although it is most abundant in the blood, bone marrow, and liver. In addition, Heme is an essential component of iron-containing proteins called hemoproteins, including hemoglobin. Defects in PBGD are the cause of acute intermittent porphyria.