Familial coagulation factor V deficiency caused by a novel 4 base pair insertion in the factor V gene: Factor v Stanford

An index patient with pseudohomozygosity for factor V Leiden was identified , Each of his two children inherited a different paternal factor V allele; a daughter was heterozygous for factor V Leiden, with 100% factor V activit y, and a son was heterozygous for factor V deficiency, with 50% factor V ac tivity. Genomic DNA was obtained from family members, and the 25 factor V e xons and flanking intronic regions were sequenced in the proband and confir med in the children. Within exon 13 of factor V, a 4 base insertion was fou nd at NT 2856 in the proband and son, but not the daughter. This mutation, here designated factor V Stanford, results in a frameshift with loss of a t hrombin activation site (R1545V) and premature termination of translation a t amino acid 1560.