Factor VNew Brunswick: Ala221-to-Val substitution results in reduced cofactor activity

We have characterized the factor V protein and cDNA of a patient displaying factor V deficiency (parahemophilia) and correlated the reduced activity with a missense mutation of Ala221-to-Val. Plasma from the subject individual (C1) presented reduced factor V antigen (39% of normal) that displayed reduced activity (approximately 26% of normal). Factor V purified from this individual by standard techniques shows normal migration on sodium dodecyl sulfate gels and a normal pattern of activation by thrombin. Purified antigen from sibling C2 gives a much reduced specific activity of 263 U/mg (17% of normal). Sibling C3, the mother, and the father have antigen within the normal range (57% to 200%) that has approximately normal specific activity. The cDNA encoding the factor Va heavy and light chains of the subject individual was polymerase chain reaction-amplified and sequenced and revealed an A-to-G substitution at position 3 of codon 51 (silent mutation), a C-to-T substitution in position 2 of codon 221 (Ala221-Val), a T-to-C substitution at position 3 of codon 708 (silent mutation), and a G-to-A substitution at position 1 of codon 2185 (Thr2185-Ala). The latter mutation was also observed in control individuals and is proposed to be a possible polymorphism. Restriction analyses demonstrated the presence of one mutant and one normal allele in the father. The subject individual (C1) and sibling C2 carry only the mutant allele. The mother and sibling C3 carry only the normal allele. The inheritance pattern suggests the presence of a missing or nonexpressed allele in the mother that is passed on to all the siblings. Expression of only the mutant allele by the subject individual (C1) and sibling C2 is consistent with reduced factor V antigen and activity in these patients. We have designated this mutant as Factor VNew Brunswick.