Prekallikrein deficiency in a family of miniature horses.

Abstract

Two sibling miniature horses, a male and a female, had a normal 1-stage prothrombin time and a prolonged activated-partial thromboplastin time (APTT). The addition of as little as 5% of a normal equine plasma pool to the plasma samples of both horses shortened their prolonged APTT to within normal limits. Coagulation factor analysis revealed deficiencies in factor XII (12 and 13 U/dl, control population 77 to 128 U/dl), when determined with a feline factor XII-deficient plasma substrate, but normal concentrations (119 and 96 U/dl) when a human factor XII-deficient plasma substrate was used. Deficiencies of another factor, prekallikrein, were detected with a human prekallikrein-deficient plasma substrate (16 and 6 U/dl, control population 70 to 173 U/dl). Other intrinsic coagulation factors were present in normal concentrations. The APTT was measured with plasma from the 2 horses after various incubation periods (1 to 15 minutes) with a contact activator before the addition of Ca ions. With incubation times of greater than or equal to 10 minutes, the APTT of both horses were essentially the same as that of the normal equine plasma pool. Several family members of the 2 prekallikrein-deficient miniature horses appeared to be heterozygous carriers of the prekallikrein deficiency.