Especially in children under 2 years of age, there are rare conditions such as congenital TTP (caused by variants in the gene ADAMTS13), cobalamin metabolic disturbances (caused by variants in the gene MMAHC, C cobalamin defects or MTA, G cobalamin defects79), and coagulation disorders that must be ruled out before the diagnosis of aHUS77. Here, ADAMTS13 is linked to thrombotic thrombocytopenic purpura.