The global epidemiology of acquired factor X deficiency.

Objectives: To summarize available data and contribute to a broader understanding of the global incidence and prevalence of acquired factor X deficiency.

Methods: A comprehensive review of English-language publications from PubMed and Embase was conducted. The majority of publications on acquired factor X deficiency were associated with light-chain (AL) amyloidosis. Therefore, this review is structured to assess publications reporting on (1) acquired factor X deficiency associated with AL amyloidosis or (2) acquired factor X deficiency associated with other causes.

Results: The literature includes case reports, case-series, and limited population-based reports of the epidemiology of acquired factor X deficiency. Though no definitive global incidence or prevalence estimates for AL-amyloidosis-associated acquired factor X deficiency were identified, the finding that roughly 6-14% of patients with AL amyloidosis have factor X activity levels below 45-50% of normal highlights the rarity of acquired factor X deficiency associated with AL-amyloidosis. Indeed, AL amyloidosis itself is a rare disorder with an estimated annual incidence of ∼10 cases per million population. Only case reports were available to inform the epidemiology of acquired factor X deficiency not associated with AL amyloidosis. We identified 35 cases from 29 papers published from around the globe. At least 25 of those patients experienced a bleeding event, with factor X activity levels ranging from <1% to 39%.

Conclusion: More population-based data are needed to understand the epidemiology of acquired factor X deficiency; however, the limited data seem to indicate this condition is quite rare. The variation across papers in thresholds used to define deficiency highlights the need for a standardized definition to better inform drug development, resource allocation, and regulatory decision-making.