Prothrombin "Carmel": Identification of a Novel Homozygous Mutation in the Prothrombin Gene Causing Coagulation Factor II Deficiency and Inherited Bleeding Disorder in an Israeli Arab Family

Congenital prothrombin deficiency, also known as hypoprothrombinemia is a rare autosomal recessive disorder characterized by severe bleeding manifestations and decreased prothrombin antigen levels below 10% activity of normal. Dysprothrombinemia, which is characterized by normal antigen levels but a dysfunctional prothrombin molecule, shows a more variable level in bleeding tendency, and there is often a good correlation between the levels of prothrombin activity and clinical severity. We have studied a large consanguineous family of thirteen members contains two patients with a prolonged protrombine time (PT) and activated partial thromboplastin time (aPTT) with prothrombin activity of 11%. DNA was isolated from leukocytes and the thrombin exons were amplified by polymerase chain reaction and sequenced. Exon 14 revealed a point mutation in the codon of Tyrosine 560 which is substituted by Histidine (Tyr560His). Mutation at this residue most probably distorts the structure of the peptidase catalytic domain. The variation segregated as expected in the family, it did not appear in dbSNP, EVS or the 1000 genome project. Further investigation is needed to determine the antigen level and to elucidate the potential effect of the mutation on the structure and the activity of the enzyme. This prothrombin is designated as Prothrombin "Carmel".