The pentad of thrombocytopenia, haemolytic anaemia, mild renal dysfunction, 
neurological signs and fever, classically characterizes the syndrome of 
thrombotic thrombocytopenic purpura (TTP). TTP usually occurs in adults but also 
children have been described with this condition. The disorder may take a 
relapsing course, termed chronic relapsing TTP (CRTTP), which although very 
rare, may also begin in childhood. Deficiency of a recently identified enzyme, 
the von Willebrand factor (vWF)-cleaving protease, seems to play a major role in 
the development of TTP. We report on a 3-year-old boy with a dramatic but 
typical clinical course of CRTTP. At the time of diagnosis, neurological 
deficits and multiple cerebral infarctions had already occurred. In plasma, 
vWF-cleaving protease was completely absent, both during acute TTP and in 
remission. There was no protease inhibitor detected. Regular infusions of fresh 
frozen plasma were successfully given for replacement on a prophylactic basis.
CONCLUSION: Assay of von Willebrand factor-cleaving protease helps to diagnose a 
form of thrombotic thrombocytopenic purpura which may be managed by prophylactic 
treatment with fresh frozen plasma.