PIGA and paroxysmal nocturnal hemoglobinuria: Notably, defects in the enzymes of the GPI biosynthetic pathway such as phosphatidylinositol glycan class A (PIGA) and phosphatidylinositol glycan class M (PIGM) cause paroxysmal nocturnal hemoglobinuria (PNH) [1] and autosomal recessive GPI-anchor deficiency [2], respectively.