Summary
We investigated a family with prekallikrein deficiency, using both standard coagulation
tests and molecular biology techniques. The propositus was found to be a compound
heterozygote for a Trp383 stop codon and a Cys529Tyr point mutation. The former mutation
was located in exon 11, the latter in exon 14. The propositus inherited the first
defect from his father and the second from his mother. Both parents had slightly low
prekallikrein levels, but the combination of the two genetic defects produced a phenotype
characterized by an extremely low prekallikrein activity and antigen. The propositus’
plasma showed a progressive reduction in APTT when incubated for a long time. Conversely,
plasma deficient in factor XII, factor XI or high molecular weight kininogen (HMWK)
failed to show shortening of the APTT. No circulating anticoagulant was found because
the patient’s APTT was fully corrected by pooled normal and factor XII-, factor XI-
or HMWK deficient plasma. No associated abnormality was apparent in the propositus
or his parents. As expected, no tendency for bleeding was noted even after tonsillectomy.
Keywords
Prekallikrein deficiency - Fletcher factor - contact phase - gene mutations