Prekallikrein deficiency in a family of Belgian horses

Abstract

Summary A 7-year-old Belgian stallion hemorrhaged excessively after castration; the hemostatic mechanism was investigated. The horse had normal one-stage prothrombin time and markedly prolonged activated partial thromboplastin time (aptt). Results of intrinsic coagulation factor assays were all normal with the exception of prekallikrein activity, which was markedly reduced (< 1% activity; value for control population, 63 to 150%). Two of this horse's full siblings, a brother and sister, had markedly prolonged aptt and low prekallikrein values (2.5% and < 1%, respectively). The addition of plasma from a normal equine plasma pool corrected the prolonged aptt in the 3 Belgian siblings with low prekallikrein activity. Prekallikrein activity in 10 other closely related Belgian horses ranged between 12.5 and 64% (mean, 29.3%), compared with 63 to 150% (mean, 91%) in 10 mixed-breed horses. In the 3 Belgian siblings with low prekallikrein activity, the aptt approached normal after prolonged incubation (15 minutes) with the contact activator and in response to addition of an ellagic acid activator. The 3 Belgian siblings with low prekallikrein activity may be homozygous for prekallikrein deficiency, whereas the other close relatives may be heterozygous for the genetic defect.