Epidemiology of Hereditary Thrombotic Thrombocytopenic Purpura (TTP) in Spain: Preliminary Results of a Study of the Spanish TTP Registry (REPTT)

INTRODUCTION

Hereditary thrombotic thrombocytopenic purpura (hTTP) is an ultra-rare disease, with an unknown incidence around the different countries. Our group has reported an estimate of immune TTP incidence in Spain of 2.67 new cases per million inhabitants and year (Pascual-Izquierdo C. et al. 2021). hTTP is supposed to cause only 5-10% of all annual TTP episodes. It is important to know current epidemiology of hTTP, its disease burden and the needs of treatment in the different scenarios to be able to define improved treatment and preventive strategies, such as recombinant enzyme substitutive therapy or the gene therapy. Our registry aims to study the real epidemiology of the disease in our country with this non-interventional, retrospective, cross-sectional, multi-center study.

METHODS

A nation-wide anonymous survey has been launched via email through the members of the hematology scientific societies in Spain: the “Sociedad Española de Hematología y Hemoterapia” (SEHH), the “Sociedad Española de Transfusión Sanguínea” (SETS) and the “Sociedad Española de Trombosis y Hemostasia” (SETH). As hTTP is supposed to be extremely rare, hospitals having no hTTP patients were encouraged to answer the survey as well. Answers were reviewed case by case. Population coverage of each hospital answering the survey was obtained from official reports of the hospital itself or the health authorities. Basic descriptive statistics (medians, range, frequencies) were performed in Excel software. Fisher exact test was used to compare proportions. This study was funded as an Investigator-Initiated Research grant (nº. IISR-2023-200440) by Takeda Farmaceutica S.A, but the research, data analysis, interpretation and writing were independent from the funder. This study was approved by the Ethics Committee of Hospital Universitari i Politècnic La Fe of Valencia, Spain (2024-0254-1).

RESULTS

A total of 60 answers were received. Seventeen answers were ruled out due to duplicates (n=5), impossibility to identify the hospital (n=7), centers with no direct care to patients (n=4) and centers from other countries (n=1). Forty-two hospitals were accounted throughout the whole geography of Spain (at least one answer from 14 out of the 17 Spanish counties).

The total population coverage of these hospitals was 13,158,179 habitants (27,6% of the total Spanish population). Twenty cases of hTTP patients were reported, diagnosed from 1983 to 2023, and being treated in 11 different hospitals. The calculated prevalence of the disease was of 1.52 cases per million population and the incidence was 0.038 new cases per million inhabitants and year. In other words, that would mean a new patient diagnosed every 26 years per million habitants. We have observed that hTTP patients are usually treated in reference hospitals (all the cases). Only 11 out of 42 (26%) answers received are from hospitals covering <200,000 habitants. We believe that there might be an overestimation of the disease in our study, as reference hospitals are possibly giving coverage to the population of small regional hospitals for this disease. This will be verified in the next step of the study.

The 20 cases reported had a current median age of 37 y. (range 6-67) [only 3 patients <15y, one missing data], and they had been diagnosed at a median age of 10 y. (range 0-61) [10 childhood diagnosis, 8 adulthood diagnosis, 2 missing data]. Eight (40%) patients received periodic treatment in a prophylaxis regimen (50% of children vs. 25% of adults; P= .367), while the remaining 12 patients only on demand.

CONCLUSION

This is the first report on epidemiology of hTTP in our country and confirms the rarity of the disease. On-demand treatment is used for the majority of patients (60%). We are planning to expand the study and collect more precise data of patients in the Spanish TTP Registry.