Platelet-activating factor acetylhydrolase IB subunit alpha is an enzyme that in humans is encoded by the PAFAH1B1 gene. The protein is often referred to as Lis1 and plays an important role in regulating the motor protein Dynein. PAFAH1B1 was identified as encoding a gene that when mutated or lost caused the lissencephaly associated with Miller–Dieker syndrome. PAFAH1B1 encodes the non-catalytic alpha subunit of the intracellular Ib isoform of platelet-activating factor acetylhydrolase, a heterotrimeric enzyme that specifically catalyzes the removal of the acetyl group at the SN-2 position of platelet-activating factor (identified as 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine). Two other isoforms of intracellular platelet-activating factor acetylhydrolase exist: one composed of multiple subunits, the other, a single subunit. In addition, a single-subunit isoform of this enzyme is found in serum.