Hemophilia B is an X-linked coagulopathy caused by absence of functional coagulation factor IX (FIX). Using adeno-associated virus (AAV)-mediated, liver-directed gene therapy, we achieved long-term (> 17 months) substantial correction of canine hemophilia B in 3 of 4 animals, including 2 dogs with an FIX null mutation. This was accomplished with a comparatively low dose of 1 ؋ 10 12 vector genomes/kg. Canine FIX (cFIX) levels rose to 5% to 12% of normal, high enough to result in nearly complete phenotypic correction of the disease. Activated clotting times and whole blood clotting times were normalized, activated partial thromboplastin times were substantially reduced, and anti-cFIX was not detected. The fourth animal, also a null mutation dog, showed transient expression (4 weeks), but subsequently developed neutralizing anti-cFIX (inhibitor IntroductionHemophilia B is a sex-linked bleeding disorder caused by a deficiency of functional coagulation factor IX (FIX). Current replacement therapy consists of intravenous infusion of protein concentrate. However, this treatment is costly and inconvenient and carries with it the risk of blood-borne disease transmission. Furthermore, bleeds are often treated only after they have occurred, rather than prophylactically, so that chronic joint damage occurs and the risk of a fatal bleed is always present. Hemophilia is an ideal model for gene therapy because precise regulation and tissue-specific transgene expression are not required. 1,2 A number of animal models are available including knockout mice and well-described hemophilic dog colonies with phenotypes corresponding to the human disease. [3][4][5] Clinical end points for treatment are well defined. An increase of factor levels to more than 1% will improve the phenotype of the disease from severe to moderate, with reduced frequency of spontaneous bleeds, and a further increase to more than 5% will result in a mild phenotype; that is, patients would likely require factor infusion only after severe injury or during surgery. Currently the most serious complication of treatment is the formation of inhibitory antibodies to the deficient protein, which occurs with a frequency of 3% to 4% in patients with hemophilia B. 6,7 Inhibitor formation is observed mostly in those patients with extensive loss of FIX coding information. 6,8 Sustained expression of canine FIX (cFIX) in dogs with a missense mutation has been observed following administration of an adeno-associated virus (AAV) vector into the portal vein for hepatic gene transfer or into skeletal muscle. 9-11 The latter approach is currently being tested in a phase 1 clinical trial. 12 AAV vectors can be produced in a helper virus-free system, are devoid of any viral gene products, and often fail to activate antigen-specific cytotoxic T lymphocytes. 13 However, inhibitor formation is still a frequent complication following intramuscular administration of AAV vector in hemophilia B mice (with a large F9 gene deletion) and dogs with a FIX null mutation. 14,15 In these anima...

Cases diagnosed with portosystemic shunting between the years 1993 and 2001 were reviewed. Sensitivities of screening tests and abdominal ultrasonographic evaluation for the detection of portosystemic shunting were evaluated. Prognosis for surgically treated shunts was also evaluated. Results indicated that both paired serum bile acids and blood ammonia levels were useful screening tests for portosystemic shunting. However, paired bile acid tests were significantly more sensitive than blood ammonia levels. Overall postoperative mortality rates for extrahepatic shunts and intrahepatic shunts were 8.7% and 20%, respectively. Postoperative mortality rates were slightly higher for animals treated with partial ligation when compared to those treated with ameroid ring placement, although this did not reach statistical significance. Long-term complication rates for animals with single extrahepatic portosystemic shunts treated with complete ligation, ameroid ring placement, and partial ligation alone were 9%, 15.4%, and 42%, respectively. Animals >2 years of age with extrahepatic shunts had almost identical postoperative mortality and long-term complication rates as animals < or = 2 years of age. No animal in this study had paired bile acid samples within the reference range postoperatively, indicating continued abnormal liver function after surgery.