The first disorders to be described in association with deficiencies of the GPI-anchor biosynthesis pathway were paroxysmal nocturnal haemoglobinuria (PNH), caused by somatic mutations in PIGA (3), in haemopoietic cells, and inherited GPI deficiency caused by a hypomorphic promoter mutation in PIGM (4). This evidence concerns the gene PIGA and paroxysmal nocturnal hemoglobinuria.