Detection and Differential Diagnosis of Prekallikrein Deficiency: Genetic Study of New Families and Systematic Review of the Literature
Authors: Barco Stefano , Sollfrank Stefanie , Trinchero Alice , Tomao Luigi , Zieger Barbara , Kremer Hovinga Johanna A. , Conti Laura , Adenäuer Anke , Miloni Erwin , Lackner Karl J. , Rossmann Heidi , Lammle Bernhard 
Published: October 2019

Abstract
Introduction. Prekallikrein (PK) and high-molecular-weight kininogen (HK) deficiencies are ultra-rare, autosomal-recessive defects of the contact system caused by biallelic mutations in the KLKB1 and KNG1 genes, respectively. Since affected subjects do not manifest a bleeding phenotype, a correct diagnosis is essential to prevent the administration of prohemostatic agents or plasma and to avoid delay of surgery.
We describe a new case of PK deficiency identified at UMC Mainz. In addition, we performed a systematic review of the literature in order to i) collect blood material for genetic studies of reported PK deficient cases lacking this information, and ii) perform a comprehensive individual patient analysis for studying the clinical course and diagnostic criteria (analysis ongoing).
Methods. MEDLINE and EMBASE were searched without time and language restrictions. Reference lists of retrieved articles, abstract books of hematology congresses, theses, and grey literature were manually reviewed. All the authors of recent articles on PK deficient cases not assessed for genetic defects, were contacted in order to retrieve blood samples. Clotting activities of PK and HK (PK:C and HK:C) were measured using PK and HK deficient plasmas, respectively. PK and HK antigens (PK:Ag and HK:Ag) were determined by ELISA. Routine aPTT and coagulation factor measurements were performed using an ACL TOP (IL). Genetic testing was performed by Sanger-, Pyrosequencing and/or NGS.
Results. Our patient was a 69-year-old woman of African descent referred for preoperative evaluation of an isolated aPTT prolongation. Diagnosis of PK deficiency was based on absent PK:C and PK:Ag (≤1% of normal, each). The homozygous KLKB1 mutation p.Ser151Phefs*34 was found, which was not yet described as a cause of PK deficiency, but had been detected in the African sub-collective (MAF 1.3%) of the 1000 Genomes cohort.
A total of 1,913 studies were identified by systematic literature review. Eleven studies with genetic data were found. Blood from 4 unrelated European families without previous genetic testing was analysed, including 3 index cases and 5 relatives. The KLKB1 mutation p.Cys548Tyr was found in 2 families with one index patient being homozygous. This data and the literature suggest that p.Cys548Tyr may be the most frequent KLKB1 mutation in Caucasians, associated with lacking PK:C but low amount of PK:Ag.
One patient erroneously diagnosed with PK deficiency based on (incomplete) normalization of aPTT with increased preincubation time and low PK:C (7%) was found to carry compound heterozygous mutations in KNG1 (c.1038+1G>A and c.1165C>T, p.Arg389*) but no mutations in KLKB1. His low PK:C was explained by severe HK deficiency.
Conclusions. PK deficiency may not be as rare as previously thought, especially in subjects of African origin. Incomplete normalization of severely prolonged aPTT upon prolonged preincubation and low PK levels are not sufficient for the diagnosis of PK deficiency. Our latter case and data from literature suggest that patients with HK deficiency usually present with moderately low PK levels: therefore, PK:C, PK:Ag, HK:C, and HK:Ag should be determined for proper diagnosis.

Disclosures
Kremer Hovinga: Shire: Other: Member of Advisory Board, Research Funding; Ablynx: Other: Member of Advisory Board. Lammle:Siemens: Honoraria, Other: congress travel and accomodation support ; Bayer: Honoraria, Other: congress travel and accomodation support; Alexion: Other: congress travel and accomodation support ; Baxter: Other: congress travel and accomodation support ; Ablynx: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: congress travel and accomodation support .