Experts Project Lower Lifelong Organ Damage Risk With Recombinant ADAMTS13 in Rare Blood Clotting Disorder

For patients born with congenital thrombotic thrombocytopenic purpura, or cTTP, the quiet accumulation of microscopic blood clots across a lifetime may matter more than the dramatic acute episodes that define the disease. A new study published in the journal Advances in Therapy has attempted to quantify that hidden, long-term threat, and its conclusions point toward a cautiously optimistic future for people receiving a recently approved recombinant enzyme therapy. Because cTTP is so rare, the researchers could not simply follow large groups of patients for decades. Instead, they turned to a rigorous technique known as structured expert elicitation, asking six experienced UK clinicians to project, with quantified uncertainty, how likely patients on continuous recombinant ADAMTS13 prophylaxis are to develop lasting organ damage.

The biology underlying the concern is well understood. cTTP is caused by inherited deficiency of ADAMTS13, the enzyme that cleaves von Willebrand factor, an adhesive protein central to blood clotting. Without sufficient ADAMTS13 activity, ultra-large von Willebrand factor multimers accumulate in the circulation and sweep platelets into spontaneous microthrombi that lodge in the smallest blood vessels. Autopsy studies have found these platelet-rich clots in nearly every organ, with the brain, heart, kidneys, and digestive tract most heavily affected. Persistently low enzyme activity therefore translates into a slow, cumulative assault on the microvasculature, raising the risk of stroke, myocardial infarction, chronic kidney disease, and ultimately increased mortality, even in patients who never experience a full-blown acute TTP crisis.

Historically, the mainstay of treatment has been plasma-based therapy, in which patients receive infusions of fresh-frozen plasma, solvent or detergent-treated plasma, or plasma-derived factor VIII and von Willebrand factor concentrates that happen to carry functional ADAMTS13. These approaches help, but they are imperfect replacements. Phase 3 trial data show that plasma-based therapy restores mean peak ADAMTS13 activity to only about 19 percent of normal levels, leaving a persistent enzymatic deficit. The treatment burden is also considerable, requiring frequent hospital visits and carrying risks of severe allergic reactions and pathogen transmission. Observational cohorts reflect the consequences: a European and US study of 78 patients found organ damage in 28 percent, most often neurological, renal, and cardiac, while a Japanese cohort of 55 patients reported long-term damage in 29 percent, including renal impairment and cerebral infarction.

Recombinant ADAMTS13, developed as TAK-755 and marketed as Adzynma, changes the equation. As a laboratory-produced version of the missing enzyme, it achieves peak ADAMTS13 activity of roughly 100 percent of normal, a dramatic improvement over the partial restoration offered by plasma infusions. In a phase 3 trial of 48 patients, no acute or subacute TTP events were reported over 12 months of prophylaxis. On the strength of these data, regulators in the United States, the European Union, Japan, and the United Kingdom have approved the therapy, and the 2025 focused update of the International Society on Thrombosis and Haemostasis guidelines now recommends prophylactic recombinant ADAMTS13 over plasma-based therapy to prevent acute episodes in patients in remission. What remained unknown, however, was whether the therapy also protects against the slow accumulation of organ damage over decades.

To address that gap, the research team, led by Amie Padhiar and colleagues, followed the York protocol for structured expert elicitation, developed at the University of York as part of the STEER resources for healthcare decision making. Six UK consultant hematologists, each with at least three years of experience treating cTTP patients and direct experience managing at least one patient on prophylaxis, agreed to participate. That small number is a reflection of the disease itself: cTTP is ultra-rare, and the six clinicians who took part represent the majority of UK specialists with hands-on experience of the condition. Before making any estimates, the experts completed training on subjective probability and common cognitive biases, and received an evidence brief summarizing the phase 3 and 3b recombinant ADAMTS13 trials alongside benchmark data on plasma-based therapy.

The quantities the experts were asked to judge were carefully anchored to real trial populations. For children and adolescents, whose mean age at trial completion was 9.1 years, the panel estimated the cumulative probability of experiencing at least one long-term organ damage event, defined as stroke or transient ischemic attack, myocardial infarction, or chronic kidney disease, by ages 15, 20, and 25 years, corresponding to roughly 6, 11, and 16 years of continued prophylaxis. For adults, whose mean starting age was 38.3 years, the corresponding time points were ages 45 and 55 years. Each expert used the bisection method to identify a median, quartiles, and plausible limits for each quantity, and the individual probability distributions were then combined through unweighted linear opinion pooling using the Sheffield Elicitation Framework tool.

The aggregated projections were striking. For children and adolescents on recombinant ADAMTS13 prophylaxis, the median estimated cumulative risk of organ damage was 3.25 percent by age 15 years, rising to 4.48 percent by age 20 and 5.76 percent by age 25. For adults, the median projected risk was 4.85 percent by age 45 and 7.42 percent by age 55. When set against benchmark estimates derived from regression analysis of a retrospective study by Borogovac and colleagues, in which patients predominantly received on-demand plasma-based treatment, the contrast is substantial: the plasma-based benchmarks stood at 10.3, 17.3, and 24.4 percent at ages 15, 20, and 25 for younger patients, and at 11.4 and 25.5 percent at ages 45 and 55 for adults. Across every age point examined, the expert-elicited risks under recombinant prophylaxis were markedly lower.

The qualitative commentary from the panel helps explain why. Experts consistently attributed the lower projected risk to the higher plasma ADAMTS13 levels achieved with the recombinant therapy, combined with consistent prophylactic coverage rather than reactive, on-demand treatment. They emphasized the importance of early and regular prophylaxis, noting that children tend to be monitored more intensively than adults and that starting therapy in childhood may prevent subclinical damage that would otherwise accumulate before diagnosis. Several experts suggested the benefits of recombinant ADAMTS13 would become more apparent with longer follow-up, particularly for vascular health. Adherence emerged as a critical variable: one expert warned that missed doses could account for residual cases of end-organ damage, and the adolescent-to-adult transition was flagged as a particularly vulnerable period requiring structured adherence support. By age 55, uncertainty widened, reflecting comorbidities, smoking, and the possible late manifestation of subclinical damage sustained earlier in life.

The authors and independent observers alike stress that these numbers are projections, not observations. The credible intervals around the estimates are wide, particularly at older ages, spanning for example from under 1 percent to nearly 30 percent for adults by age 55, and the distributions were consistently right-skewed, with most experts predicting low risks but a few anticipating higher ones. The benchmark comparison is contextual rather than a head-to-head trial, since the Borogovac cohort largely received on-demand therapy that does not reflect current UK practice, and no causal claims about comparative effectiveness can be drawn. The composite endpoint also obscures potential differences between neurological, cardiac, and renal risks. Funding came from Takeda, the therapy’s manufacturer, and several authors are company employees or consultants, factors the paper discloses transparently.

Nevertheless, the study fills a genuine void. For ultra-rare diseases where decades-long prospective trials are logistically impossible, structured expert elicitation offers a transparent, bias-mitigated way to generate the kinds of risk estimates that clinicians, patients, and health technology assessment bodies need today. The findings suggest that sustained recombinant ADAMTS13 prophylaxis may substantially reduce the lifetime burden of organ damage in cTTP, reinforcing the value of early initiation and unwavering adherence. They also chart the path forward: prospective registries with long-term follow-up, organ-specific risk modeling, and validation of these projections against real-world outcomes. Until such data arrive, these expert-derived estimates stand as the best available evidence, and they paint a picture in which a once-devastating inherited disorder may increasingly be managed as a chronic condition with a far gentler long-term trajectory.

Subject of Research: Projected long-term organ damage risk in congenital thrombotic thrombocytopenic purpura patients treated with recombinant ADAMTS13 prophylaxis, estimated through structured expert elicitation

Article Title: Estimating Long-Term Organ Damage Risk in Patients with Congenital Thrombotic Thrombocytopenic Purpura Receiving Recombinant ADAMTS13 Prophylaxis: A Structured Expert Elicitation Study

Article References: Padhiar, A., Burke, C., Puls, M., Berkley, A., Heard, O., Kaur, H., Wolff, H., & Murphy, L. (2026). Estimating Long-Term Organ Damage Risk in Patients with Congenital Thrombotic Thrombocytopenic Purpura Receiving Recombinant ADAMTS13 Prophylaxis: A Structured Expert Elicitation Study. Advances in Therapy. https://doi.org/10.1007/s12325-026-03786-y

Image Credits: AI Generated

DOI: 10.1007/s12325-026-03786-y

Keywords: congenital thrombotic thrombocytopenic purpura, recombinant ADAMTS13, structured expert elicitation, organ damage, plasma-based therapy, von Willebrand factor, stroke, chronic kidney disease, myocardial infarction, prophylaxis, rare disease, health technology assessment