Severe Plasma Prekallikrein Deficiency: Clinical Characteristics, Novel KLKB1 Mutations, and Estimated Prevalence.

BACKGROUND: Severe plasma prekallikrein (PK) deficiency is an autosomal-recessive defect characterized by isolated aPTT prolongation. To date, no comprehensive methodologically-firm analysis investigated the diagnostic, clinical, and genetic characteristics of PK deficiency, and its prevalence remains unknown. PATIENTS/METHODS: We described new families with PK deficiency, retrieved clinical and laboratory information of cases systematically searched in the (grey) literature, and collected blood of these cases for complementary analyses. The Genome Aggregation Database (gnomAD) and the population-based Gutenberg Health Study served to study the prevalence of mutations and relevant genetic variants. RESULTS: We assembled a cohort of 111 cases from 89 families and performed new genetic analyses in eight families (three unpublished). We identified new KLKB1 mutations, excluded the pathogenicity of some of the previously described ones, and estimated a prevalence of severe PK deficiency of 1/155,668 overall and 1/4,725 among Africans. One individual reported with PK deficiency had, in fact, congenital kininogen deficiency associated with decreased PK activity. One-quarter of individuals had Factor XII clotting activity below the reference range. Four major bleeding events were described in 96 individuals, of which 3 were provoked, for a prevalence of 4% and an annualized rate of 0.1%. The prevalence of cardiovascular events was 15% (6% 65 years) for an annualized rate of 0.4%. CONCLUSIONS: We characterized the genetic background of severe PK deficiency, critically appraised mutations, and provided prevalence estimates. Our data on laboratory characteristics and clinical course of severe PK deficiency may have clinical implications.