The association of a variant of
antithrombin III (
AT III Bligny) and
protein C deficiency is described in a 36-year-old patient having suffered from severe thrombotic episodes. His mother has
protein C deficiency and showed a single episode of
thrombophlebitis following surgery. His father, sister and daughter have the variant AT III and are asymptomatic. The abnormal AT III was characterized in plasma by the discrepancy between a normal progressive activity and a reduced
heparin cofactor activity. This variant AT III was purified, separated from the normal
protein by
heparin-Sepharose chromatography and was eluted with increased NaCl concentrations. At pH 7.4, the variant AT III eluted at lower (0.3 to 0.5 M) NaCl concentrations than normal (1 to 1.5 M) AT III, thus demonstrating a decreased affinity for
heparin. At pH 6.0, however, the abnormal molecule bound more avidly to
heparin-Sepharose and was eluted like normal AT III at pH 7.4. Similarly, the
heparin enhancement of intrinsic fluorescence of the variant AT III, markedly reduced at pH 7.4, was normalized at pH 6.0. The abnormal AT III showed a normal
antiprotease activity, a normal molecular weight by SDS-PAGE, but displayed only a partial immunological identity with the normal
protein. Analysis of amplified genomic
DNA from this patient by dot-blot demonstrates a heterozygous substitution of
arginine by
histidine at position 47.