METHODS Patients The subjects in this study were patients attending departments of paediatric and adult nephrology and departments of internal medicine in several university hospitals in France and Belgium over a period of 3 years. All participants provided informed consent. The clinical work out was performed in each referring centre. Twenty five patients (15 children and 10 adults) with atypical HUS and no factor H mutation were studied. Six of the patients had a familial variant of HUS (at least two siblings with the disease) and six exhibited persistent mild alternative pathway complement consumption with low C3 levels. Nineteen patients presented a sporadic, atypical form of HUS.

Case reports Patient 1, a 32 year old Caucasian woman (P1), after pregnancy developed acute renal failure, hypertension, and haemolytic anaemia of rapid onset. Renal biopsy disclosed a pattern of thrombotic microangiopathy predominantly in the glomeruli, with few vascular lesions. HUS recurred 2 and 4 months later with partial renal function recovery but