Detection and Differential Diagnosis of Prekallikrein Deficiency: Genetic Study of New Families and Systematic Review of the Literature

Objectives: 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 to collect blood material for genetic studies of reported PK deficient cases lacking this information, and perform a comprehensive individual patient analysis of clinical and diagnostic data (analysis ongoing).

Methods: MEDLINE, EMBASE, and the gray literature were searched. All the authors of recent articles on PK deficient cases not assessed for genetic defects were contacted 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: eleven studies with genetic data were found. Blood from 4 unrelated European families without previous genetic testing was analyzed, 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.