Pathological aspects of membranoproliferative glomerulonephritis (MPGN) and haemolytic uraemic syndrome (HUS) thrombocytic thrombopenic purpura (TTP)

In this paper, epidemiology, pathogenesis and typical morphological aspects of all three types of membranoproliferative glomerulonephritis (MPGN), of the haemolytic uraemic syndrome (HUS) as well as of thrombotic thrombopenic purpura. (TTP) will be reviewed on the light microscopical, immunohistological or immunofluorescence and electron microscopical level. In particular, differences in the pathogenesis of these diseases are discussed. Important recent molecular and genetic insights into the pathogenesis of the three types of MPGN, of typical and atypical HUS and of TTP, i.e. dysregulation of the complement system, distinct molecular defects in C3 and factor H, the major regulatory protein of the alternative pathway of complement activation, and deficiency of a von Willebrand factor (VWF)-cleaving protease, i.e. ADAMTS 13, are highlighted. Finally, particular emphasis will be put on differences in glomerular and vascular morphology in the three types of MPGN and in thrombotic microangiopathy (TMA),which is the characteristic morphological alteration of the kidney in HUS and TTP, respectively.