Severe prekallikrein deficiency due to a compound heterozygosis in the KLKB1-gene

SummaryA 14 year old boy was referred to us for a detailed coagulation study because a previously performed aPTT has been found prolonged. The boy had no history of bleeding symptoms and also the family history was negative for bleeding or thrombotic events. The aPTT in the patient was 96 s (reference range: 24–36 s), prothrombin time and thrombin time were both normal.As the cause for the prolonged aPTT we identified a severe prekallikrein deficiency (prekallikrein activity < 1%). The prekallikrein deficiency results from two mutations in the KLKB 1-gene: first, an insertion of 1 bp in codon 149 in exon 5 and,…