Upshaw–Schulman syndrome, or hereditary thrombotic thrombocytopenic purpura (HTTP), is a congenital TTP characterized by a persistent and severe ADAMTS13 deficiency (<10%) caused by homozygous or compound heterozygous pathogenic mutations in the ADAMTS13 gene [73]. Here, ADAMTS13 is linked to congenital thrombotic thrombocytopenic purpura.