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. Here, CD55 is linked to paroxysmal nocturnal hemoglobinuria.