ADAMTS13 (C9orf8) is a gene at 9q34 which codes for A disintegrin and metalloproteinase with thrombospondin motifs 13, the von Willebrand factor-cleaving protease. As the name suggests, its normal function is to cleave membrane-bound vWF multimers into smaller units. Uncleaved vWF multimers act as nidus of platelet aggregation.
Mutations affecting its proteolytic function have been associated with the formation of platelet microthrombi in the small blood vessels, as in congenital thrombotic thrombocytopenic purpura (Schulman-Upshaw syndrome). Schulman-Upshaw syndrome is autosomal recessive with neonatal onset of haemolytic anaemia with erythrocyte fragmentation, thrombocytopenia, and neurological and renal dysfunction. It can be treated by fresh plasma.
Mutations making one of the two copies of the gene dysfunctional have been associated with some variants of atypical haemolytic-uraemic syndrome.