[Incomplete hemolytic uremic syndrome associated with partial factor H deficiency]

Hemolytic uremic syndrome (HUS) consists of the association of hemolytic anemia, thrombocytopenia and renal failure. Most cases are related to toxins (verotoxins) produced by Escherichia coli 0157:H7 and generally have good renal prognosis. Atypical forms can occur, with a less favorable prognosis, and can be due to mutations in the gene codifying factor H, a protein that regulates activation of the alternative complement pathway, among other causes. Factor H deficiency produces continuous complement activation, causing injury to capillary endothelial cells. We report a case of incomplete (absence of thrombocytopenia and uremia), atypical HUS in which hypocomplementemia secondary to partial factor H deficiency was detected, with favorable outcome. Prior to symptom onset, the patient had a Campylobacter infection, precipitating the symptoms. Genetic analysis showed a heterozygous mutation (C846T) located in the SCR4 domain, generating an amino acid change in the factor H molecule (Pro240Leu). This mutation may have been the cause of the partial factor H deficiency and the patient's symptoms on admission.