Summary A 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, second, a base exchange Cys 548 (TGC) > Tyr (TAC) in exon 14. The boy inherited the first mutation from his father and the second from his mother. The mutation in the paternal allele was not described before the completion of our study. There are two brothers of the propositus, one with normal prekallikrein activity and no mutations in the KLKB1-gene, the other showed the same constellation as the propositus.
Haemophilia A is a recessive X linked bleeding disorder caused by deficiency or functional abnormality of coagulation factor VIII. This disease usually has no visible phenotype in female carriers; hence, great efforts are made to offer all haemophilia A families accurate carrier diagnosis. Significant progress in this direction was made with the identification of the intron 13 variable number tandem repeat (VNTR), which is hitherto the most informative single marker within the factor VIII gene. The authors have established intron 13 VNTR detection in their laboratory by adapting its analysis to an automated sequencer using different primers of which one is fluorescent dye labelled. With this method, which is more rapid and convenient than that originally described, 67 haemophilia A families of German origin were screened and two new alleles (alleles 17 and 25) were identified. The informativeness of the VNTR in these families based on the patients maternal X chromosomes (134) is about 67%.
