Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare thrombotic microangiopathy characterized by severe congenital ADAMTS13 deficiency and recurring acute episodes causing morbidity and premature death. Information on the annual incidence and severity of acute episodes in hTTP patients is largely lacking. This study reports prospective data of 87 patients from the Hereditary TTP Registry (ClinicalTrials.gov NCT01257269) for survival, frequency and severity of acute episodes from enrollment until December 2019. The 87 patients, followed for median 4.2 years (range 0.01-15), had a median age at overt disease onset and at clinical diagnosis of 4.6 years and of 18 years (range 0.0-70 for both), respectively. Forty-three patients received regular plasma prophylaxis, while 22 did not, and treatment changed over time or was unknown in the remaining 22. Forty-three patients experienced 131 acute episodes of which 91 (69%) occurred in patients on regular prophylaxis. This resulted in an annual incidence of acute episodes of 0.36 (95%CI 0.29-0.44) with and of 0.41 (95%CI 0.30-0.56) without regular plasma treatment. More than one third of acute episodes (n=51) were documented in children <10 years of age at enrollment and were often triggered by infections. Their annual incidence of acute episodes was significantly higher than in patients >40 years of age (1.18 [95% CI 0.88-1.55] vs. 0.14 [95% CI 0.08-0.23]). Prophylactic plasma infusion regimens used were insufficient to prevent acute episodes in many patients. Such regimens are burdensome, caregivers, patients and their guardians are reluctant to start regular plasma infusions, from which particularly children would benefit.
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