Adeno-Associated Virus-Mediated Correction of a Canine Model of Glycogen Storage Disease Type Ia

Abstract

Glycogen storage disease type Ia (GSDIa; von Gierke disease; MIM 232200) is caused by a deficiency in glucose-6-phosphatase-a. Patients with GSDIa are unable to maintain glucose homeostasis and suffer from severe hypoglycemia, hepatomegaly, hyperlipidemia, hyperuricemia, and lactic acidosis. The canine model of GSDIa is naturally occurring and recapitulates almost all aspects of the human form of disease. We investigated the potential of recombinant adeno-associated virus (rAAV) vector-based therapy to treat the canine model of GSDIa. After delivery of a therapeutic rAAV2/8 vector to a 1-day-old GSDIa dog, improvement was noted as early as 2 weeks posttreatment. Correction was transient, however, and by 2 months posttreatment the rAAV2/ 8-treated dog could no longer sustain normal blood glucose levels after 1 hr of fasting. The same animal was then dosed with a therapeutic rAAV2/1 vector delivered via the portal vein. Two months after rAAV2/1 dosing, both blood glucose and lactate levels were normal at 4 hr postfasting. With more prolonged fasting, the dog still maintained near-normal glucose concentrations, but lactate levels were elevated by 9 hr, indicating that partial correction was achieved. Dietary glucose supplementation was discontinued starting 1 month after rAAV2/1 delivery and the dog continues to thrive with minimal laboratory abnormalities at 23 months of age (18 months after rAAV2/1 treatment). These results demonstrate that delivery of rAAV vectors can mediate significant correction of the GSDIa phenotype and that gene transfer may be a promising alternative therapy for this disease and other genetic diseases of the liver.

Rescue administration of a helper-dependent adenovirus vector with long-term efficacy in dogs with glycogen storage disease type Ia

“…Both human and canine carriers for GSD-Ia maintain normal blood glucose during fasting for several hours, and do not accumulate glycogen in the liver. 1,8,9 Following a single neonatal administration of HDAd-cG6Pase vector, HDAd-treated dogs E and H with GSD-Ia had B20% of hepatic G6Pase activity observed in normal dogs (1.9 ± 0.2 mmol g -1 ), when biopsied at 7 and 22 months of age, respectively. GSD-Ia dogs that were maintained solely with diet demonstrated hepatic G6Pase activity of 0.48±0.18 mmol g -1 tissue per minute, B7% of normal's hepatic G6Pase activity ( Figure 2a).…”

“…9 In contrast to the experience reported with a small genome AAV2/8 vector that could be packaged as double-stranded AAV2/8 and prolonged survival for 411 months in three consecutive dogs with GSD-Ia, Weinstein et al reported that a single-stranded AAV2/8 vector failed to prevent hypoglycemia for 42 months of age in one dog with GSD-Ia. With regard to neonatal administration of the current HDAd-cG6Pase serotype 5 vector, it performed favorably in that symptoms were prevented for 6-22 months in two consecutive dogs with GSD-Ia.…”

“…The survival of these dogs with GSD-Ia can be viewed as a success, because early mortality usually cannot be prevented by any other treatment than efficacious gene therapy in this disorder. 4,[7][8][9] The reversal of hypoglycemia following the initial administration of HDAd, in comparison with untreated dogs, and prevention of hypoglycemia is the end point most relevant to human GSD-Ia. The reversal of hypoglycemia following vector readministration confirmed the efficacy of the second, serotype 2 HDAd vector.…”

“…4,8,9 The original colony established for characterization of the natural history for canine GSD-Ia confirmed abnormalities consisting of recurrent hypoglycemia, persistent lactic academia and hypercholesterolemia, and glycogen accumulations in liver and kidney. 4,18 Renal involvement was further confirmed by the presence of focal glomerulosclerosis, 4 which is typical of GSD-Ia.…”

“…Despite this very encouraging initial data, more recently it has become evident that eventually GSD-Ia dogs treated with an AAV2/8 vector will eventually need to be treated again when transgene expression wanes. 9 Helper-dependent adenovirus (HDAd) vectors have emerged as promising candidates for gene therapy. This Ad-based vector has all viral coding sequences removed, leaving only sequences for packaging and vector propagation.…”