The prevalence of hereditary thrombotic thrombocytopenic purpura (hTTP) is considerably higher than current estimates, according to findings published in Blood Advances. Flora Peyvandi, MD, PhD, and colleagues aimed to provide a more accurate estimate of the prevalence of hTTP using available exome and genome sequencing data for 807,162 patients. Accounting for all 758 pathogenic variants identified, as well as 140 variants reported previously, the researchers estimated a global hTTP prevalence of 40 and 23 cases/10 6, respectively. Among the 140 previously reported variants, the highest estimated prevalence was in East Asians (42/10 6). Estimated prevalences in other populations included Finnish (32/10 6), non-Finnish Europeans (28/10 6), Admixed Americans (19/106), Africans/African Americans (6/10 6), and South Asians (4/10 6). The lowest prevalences were seen for Middle Eastern (1/10 6) and Ashkenazi Jewish (0.7/10 6) populations. hTTP prevalence is substantially higher than the currently estimated prevalence based on diagnosed patients,” Dr. Peyvandi and colleagues wrote.