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.
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).
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.
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.