New insights into postrenal transplant hemolytic uremic syndrome

After renal transplantation, hemolytic uremic syndrome (HUS) may occur either as a recurrent or de novo form. Over the past decade, much effort has been devoted to elucidating the pathogenesis of atypical HUS (aHUS). Approximately 60-70% patients with aHUS have mutations in regulatory factors of the complement system or antibodies against complement factor H. The risk of post-transplant recurrence of aHUS depends on the genetic abnormality involved, and ranges from 15% to 20% in patients with mutations in the gene that encodes membrane cofactor protein and from 50% to 100% in patients with mutations in the genes that encode circulating regulators of complement. Given the poor outcomes associated with recurrence, isolated renal transplantation had been contraindicated in patients at high risk of aHUS recurrence. However, emerging therapies, including pre-emptive plasma therapy and anti-C5 component monoclonal antibody (eculizumab) treatment have provided promising results and should further limit indications for the risky procedure of combined liver-kidney transplantation. Studies from the past 2 years have demonstrated genetic abnormalities in complement regulators in 30% of renal transplant recipients who experienced de novo HUS after renal transplantation. This finding suggests that the burden of endothelial injury in a post-transplantation setting may trigger de novo HUS in the presence of mild genetic susceptibility to HUS.