FACTOR V-NEW (BRUNSWICK) - ALA(221)-TO-VAL SUBSTITUTION RESULTS IN REDUCED COFACTOR ACTIVITY

We have characterized the factor V protein and cDNA of a patient displ aying factor V deficiency (parahemophilia) and correlated the reduced activity with a missense mutation of Ala(221)-to-Val, Plasma from the subject individual (C1) presented reduced factor V antigen (39% of nor mal) that displayed reduced activity (approximately 26% of normal). Fa ctor V purified from this individual by standard techniques shows norm al migration on sodium dodecyl sulfate gels and a normal pattern of ac tivation by thrombin. Purified antigen from sibling C2 gives a much re duced specific activity of 263 U/mg (17% of normal). Sibling C3, the m other, 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 pol ymerase chain reaction-amplified and sequenced and revealed an A-to-G substitution at position 3 of codon 51 (silent mutation), a C-to-T sub stitution in position 2 of codon 221 (Ala(221)-Val), a T-to-C substitu tion at position 3 of codon 708 (silent mutation), and a G-to-A substi tution at position 1 of codon 2185 (Thr(2185)-Ala). The latter mutatio n was also observed in control individuals and is proposed to be a pos sible 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 sibl ing 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 b y the subject individual (C1) and sibling C2 is consistent with reduce d factor V antigen and activity in these patients. We have designated this mutant as Factor V-New (Brunswick). (C) 1995 by The American Soci ety of Hematology.