FACTOR-X FRANKFURT-I - MOLECULAR AND FUNCTIONAL-CHARACTERIZATION OF AHEREDITARY FACTOR-X DEFICIENCY (GLA(+25) TO LYS)

A family with hereditary factor X deficiency is presented. One member, a 25-year-old man, showed a mild bleeding tendency. His factor X acti vity (extrinsic: 56%; intrinsic: 55%; Russell's viper venom: 57%) and his level of circulating factor X antigen (55% of normal) were markedl y reduced. Analysis of his factor X gene revealed a single point mutat ion within exon II resulting in the substitution of +25 Gla (GAA) by L ys (AAA). The mutation was determined by gene analysis to be heterozyg ous in this patient, his mother and one of his brothers. Clotting assa ys of factor X purified from the plasma of the index patient revealed an activity of 89% of normal upon activation with Russell's viper veno m, 77% of normal in the intrinsic and 81% of normal in the extrinsic c oagulation pathway. The mutation responsible for the substitution of L ys for Gla(+25) 25 was introduced into an expression plasmid containin g a wild type factor X cDNA and expressed in a mammalian cell line. Fa ctor X antigen levels in the cell lysates and in the supernatant were identical in the mutant and wild type constructs. The specific activit y of the factor X expressed from the mutant construct was 3% compared with the wild type construct. These data demonstrate that the substitu tion of Lys for Gla(+25) 25 results not only in a reduced level of fac tor X in the affected family members, but also in a substantial loss o f specific factor X activity. (C) 1998 Lippincott-Raven Publishers.