CD59 and paroxysmal nocturnal hemoglobinuria: Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired haematopoietic stem cell disorder.1 It is rare in children and results from a somatic mutation in the glycophosphatidylinositol (GPI) glycan A gene on the short arm of the X chromosome.1,2,3 The GPI glycan A gene encodes GPI-anchored markers, including CD55 and CD59, which protect cells from complement-mediated attack.4,5 Although the condition is classically described as presenting with nocturnal haemoglobinuria, this finding is not generally common and is particularly rare in children.4,6