Functional Evaluation of Factor H genetic and Acquired Abnormalities: Application for Atypical Hemolytic Uremic Syndrome (aHUS)

The atypical hemolytic uremic syndrome (aHUS) is a paradigm of a disease, caused by overactivation of the alternative complement pathway secondary to a not well-understood trigger event. About 60 % of the patients present genetic or acquired abnormalities in the proteins of the alternative complement pathway. In 40 % of the cases the affected protein is the complement regulator Factor H (FH)—30 % due to mutations and 10 % because of anti-FH autoantibodies. Here we describe the detailed protocol for a rapid test to analyse the functional defect associated with genetic or acquired FH-related abnormalities. It can be applied for the characterization of the underlying complement defect in aHUS, based on spontaneous lysis of non-sensitized sheep erythrocytes in contact with patients’ plasma or serum.