912. Long-Term Efficacy of AAV Vector-Mediated Gene Therapy in the Mouse Model for Glycogen Storage Disease Type la (GSD-Ia)

Abstract

The deficiency of glucose-6-phosphatase (G6Pase) underlies glycogen storage disease type Ia (GSD-Ia, also known as von Gierke disease; MIM 232200), an autosomal recessive disorder of metabolism associated with life-threatening hypoglycemia and growth retardation. Regulation of G6Pase at the level of transcription occurs in response to glucose and insulin levels. The main hypothesis asked whether regulated G6Pase expression with an AAV vector containing a glucose-response promoter would achieve efficacy in GSD-I mice. A secondary hypothesis predicted that efficacy in GSD-Ia would correct the unique gene expression and metabolomic abnormalities of this disorder. An AAV vector containing the glucose-responsive G6Pase promoter driving G6Pase expression (AAV-cG6PGH) was pseudotyped as AAV8 (AAV2/8), and administered intravenously (1 1012 DNAse-resistant vector particles) to 2 week-old affected G6Pase-KO mice (n=7). AAV2/8 vectors previously transduced murine liver >100-fold more efficiently than standard AAV2/2 vectors. Survival was prolonged following AAV vector administration, currently ranging from 3 to 6 months for all treated affected mice, in contrast to untreated affected mice that did not survive past 2-3 weeks of age. Growth was normalized following AAV vector administration, whereas untreated, affected mice initially weighed approximately 50% as much as unaffected littermates and remained growth-retarded. Mice that received the AAV2/8 vector encoding G6Pase had blood glucose in the normal range following 2 hours of fasting (81 +/- 30 mg/dL), in contrast to non-fasting, untreated G6Pase-KO mice, which were hypoglycemic (31 +/- 19 mg/dL) (p < 0.005). It was not necessary to give glucose injections to prolong survival following administration of the AAV2/8 vector, even though affected, untreated mice could only be sustained through twice daily glucose injections. GSD-Ia mice were further characterized to identify outcome measures for gene therapy: gene expression profiling revealed elevated transcripts in the glycolytic, signal transduction, and cell cycle pathways, and metabolomics revealed elevated lactate and ketones in urine of untreated, affected mice. Correction of gene expression profiling and metabolomics in 6 month-old affected mice following AAV vector administration will be analyzed. The efficacy of G6Pase expression with an AAV vector in GSD-Ia has been demonstrated by the correction of fasting hypoglycemia, growth retardation, and disease-specific outcome measures.