Incidence, Age, and Gender of Children with Thrombotic Thrombocytopenic Purpura (TTP) Associated with Severe, Acquired ADAMTS13 Deficiency.

TTP associated with severe acquired ADAMTS13 deficiency has been rarely reported among children. Specific aims: [1] To identify all published reports of TTP associated with acquired ADAMTS13 deficiency in children <18 years old and document the age and gender distribution. [2] To document the incidence in the Oklahoma TTP-HUS Registry region of TTP associated with acquired ADAMTS13 deficiency (activity <10%) in children <18 years old.

Systematic literature review using MEDLINE, PubMed, Embase, Cochrane, and CINAHL databases. Comprehensive search terms for TTP, HUS, and children were combined with the term, ADAMTS13. Bibliographies of selected articles were reviewed. Incidence was calculated using person-years of all children < 18 years old in the Registry region (58 counties) over the 16.5 year period (January 1, 1996 to June 30, 2012) using 2000 census data.

The systematic literature search identified 22 publications reporting 53 children with acquired ADAMTS13 deficiency. Their age and gender are presented in the Figure. Two-thirds of children were ages 9–17 years. Among the 18 children ages 0–8 years, 8 (44%) were girls; among the 35 children ages 9–17 years, 24 (69%) were girls. The relative frequency of the older children was greater than younger children (p=0.02). Although there were more girls than boys reported, the difference was not significant (p=0.13). From January 1, 1995 to June 30, 2012, 72 patients with acquired ADAMTS13 deficiency were enrolled in the Oklahoma TTP-HUS Registry; one patient was less than 18 years old. The calculated incidence for the Oklahoma Registry region was 0.10/10⁶ children/year.

The Oklahoma Registry experience documents for the first time the incidence of TTP associated with acquired ADAMTS13 deficiency in children: 0.10/10⁶ children/year, 6% of our previously calculated incidence rate of 1.74/10⁶/year for all patients with TTP and acquired ADAMTS13 deficiency (J Thromb Haemost 2005;3:1432). The age and gender distribution of children in published case reports suggests that TTP associated with acquired ADAMTS13 deficiency in children is not a distinct juvenile disorder, but more likely a continuum of the spectrum of TTP in adults (J Thromb Haemost 2005;3:1432).

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George:Alexion, Inc.: Consultancy; Baxter, Inc.: Consultancy; Amgen, Inc.: Consultancy, PI of clinical trial involving romiplostim, PI of clinical trial involving romiplostim Other, Research Funding. Terrell:Baxter, Inc.: Consultancy; Amgen, Inc.: Consultancy.