In addition autoimmune forms, with acquired, de-novo generated inhibitors in the form of autoantibodies exist for both disorders, affecting ADAMTS13 in TTP or the central complement inhibitor factor H in HUS.
Genomic aberrations affecting the genes encoding factor H (FH) and the five FH-related proteins (FHRs) have been described in patients with atypical hemolytic uremic syndrome (aHUS), a rare condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, and ARF.
TTP is confirmed by severe ADAMTS13 deficiency (which can be undertaken in real time) and CM-HUS by an abnormality in complement regulators, confirmed by mutational analysis (in 60% to 70% of cases) or the presence of Factor H antibodies (which may not be available for weeks or months).
TTP and CM HUS are rare disorders, and their diagnosis may be missed, no less because features at presentation may be misdiagnosed as a pregnancy-related TMA, such as hypertension, proteinuria, fetal growth restriction, or in utero fetal death.