Functional analysis in serum from atypical Hemolytic Uremic Syndrome patients reveals impaired protection of host cells associated with mutations in factor H.

A subgroup of patients with the most severe form of the Hemolytic Uremic Syndrome (HUS) presents mutations in the complement regulatory protein factor H. The functional analyses of the factor H mutant proteins purified from some of these patients have shown a specific defect in the capacity to control complement activation on cellular surfaces. Here, we show that these factor H-related complement regulatory defects can be detected in the patients' serum with a simple hemolytic assay. Data obtained from HUS patients and control individuals indicate that this assay is a useful tool for the molecular diagnosis of factor H-related HUS.