For the purposes of this review article, we use the classification proposed by Goodship et al. [11], which divides TMA into the following forms: thrombotic thrombocytopenic purpura (TTP) resulting from an inherited or acquired deficiency of ADAMTS13; typical hemolitic uremic syndrome caused by Shiga toxin-producing Escherichia coli (STEC-HUS); all other forms grouped under the common term atypical HUS (aHUS). The gene discussed is ADAMTS13; the disease is atypical hemolytic-uremic syndrome.