It has been suggested that a vWF High Molecular Weight Multi-mers (HMWM) decrease or a PAA were involved in the pathogenesis of HUS. We have studied 8 children (6 girls,_2 boys; 7 months-8_1/2 years old) with HUS : plasma creatinine /μmol/l; mean(range)/=306 (105-524), hemoglobin (g/100ml)-7(6.3-7.8), schistocytes (%)=8(1-18), platelets (x103/mm3)-57(10-115). The vWF was studied quantitatively (antigen ; vWF RAg assay) and qualitatively (multimeric pattern : immunoblotting and autoradiography).

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... PAA studied by incubating the patient's platelet poor plasma (RPR) with washed normal platelets (aggregometer, % light transmission) and confirmed by Thromboxane B2 (TXB2) assay and [14C] Serotonine release study. The PAA was characterized by studying the in vitro effect of several platelet aggregation inhibitors, Immunoglobulins (Igs) and Fresh Frozen Plasma (FFP) on the platelet aggregation.An increase of vWF RAg (%) was observed in 6 cases : mean:330, and possibly related with renal failure. A vWF HMWM decrease was found in 3 patients : 2/3 with associated infection(E.Coli, Pneumococcus), 1/3 with severe hemolysis. Two of these 3 patients had a favourable renal outcome and 1 a severe course (chronic hemodialysis, Arterial Thrombotic MicroAngiopathy at renal histology).An important PAA was evidenced only in 1 patient : post bone-marrow graft HUS during neuroblastoma(NB),arterial hypertension and chronic renal failure. This PAA was Ca++, TXB2 and cAMP dependent; it was moderately inhibited in vitro by Igs and FFP, but persisted after 5 days of Igs infusion (0.3g/Kg/day). Treatment with aspirin and dipyridamole (10mg/Kg/day each) suppressed the patient platelet auto-aggregation although the PAA persisted (follow up:10months). The PAA did not seem to be related with the NB (absence of GD2 ganglioside, specific marker of NB); it could be related with anti platelet antibodies. The coexistence of the two abnormalities could not be demonstrated in our patients.In conclusion, a vWF HMWM decrease was found in 3 out of 8 children patients with HUS. Its presence was not correlated with the severity of the disease. We could demonstrate the presence of PAA during childhood HUS in only 1 post bone-marrow graft case. The PAA characterization is useful for therapeutic decisions and contributes to a better pathogenetic understanding.