Comparisons of Infant and Adult Mice Reveal Age Effects for Liver Depot Gene Therapy in Pompe Disease.

As a clinical biochemical geneticist and a director of the Duke Biochemical Genetics laboratory, my research interests are focused on improving laboratory diagnostics for rare inherited disorders of metabolism. I am actively involved in the development of assays using mass spectrometry and other analytical techniques. My current research on biomarkers for lysosomal storage disorders, such as Fabry and Pompe disease and the mucopolysaccharidoses includes monitoring the response to novel therapies in patients. I also have an interest in neurometabolic disorders such as the creatine deficiency syndromes and sulfite oxidase and molybdenum cofactors. These disorders can be diagnosed using liquid chromatography-tandem mass spectrometric assays that measure biomarkers in urine. Guanidinoacetate methyltransferase deficiency is a disorder that can be detected in the newborn period and is amenable to dietary therapy, and is thus a good candidate for newborn screening.

Our laboratory focuses on the control of breathing and pulmonary mechanics in murine models of several genetic diseases. These genetic diseases include Duchenne Muscular Dystrophy, Pompe Disease, ALS, and Spino-cerebellar ataxia Type 7. We also investigate the ability of gene therapy and neuromodulation to treat respiratory insufficiency in neuromuscular diseases. As a clinician-scientist, my goal is to bring therapy from the bench to the bedside and enhance our research at the bench through observations at the bedside.


Our clinical research focus is on the impact of novel therapies on respiratory function in Duchenne Muscular Dystrophy and Pompe Disease. We study the impact of recent therapies on breathing in these disorders and the impact of social determinants of health on clinical outcome measures.

As a physician-scientist practicing clinical and biochemical genetics, I am highly motivated to seek improved therapy for my patients with inherited disorders of metabolism. The focus of our research has been the development of gene therapy with adeno-associated virus (AAV) vectors, most recently by genome editing with CRISPR/Cas9. We have developed gene therapy for inherited disorders of metabolism, especially glycogen storage disease (GSD) and phenylketonuria (PKU). 
1) GSD Ia: Glucose-6-phosphatase (G6Pase) deficient animals provide models for developing new therapy for GSD Ia, although early mortality complicates research with both the murine and canine models of GSD Ia. We have prolonged the survival and reversed the biochemical abnormalities in G6Pase-knockout mice and dogs with GSD type Ia, following the administration of AAV8-pseudotyped AAV vectors encoding human G6Pase. More recently, we have performed genome editing to integrate a therapeutic transgene in a safe harbor locus for mice with GSD Ia, permanently correcting G6Pase deficiency in the GSD Ia liver. Finally, we have identified reduced autophagy as an underlying hepatocellular defect that might be treated with pro-autophagic drugs in GSD Ia.
2) GSD II/Pompe disease: Pompe disease is caused by the deficiency of acid-alpha-glucosidase (GAA) in muscle, resulting in the massive accumulation of lysosomal glycogen in striated muscle with accompanying weakness. While enzyme replacement has shown promise in infantile-onset Pompe disease patients, no curative therapy is available. We demonstrated that AAV vector-mediated gene therapy will likely overcome limitations of enzyme replacement therapy, including formation of anti-GAA antibodies and the need for frequent infusions. We demonstrated that liver-restricted expression with an AAV vector prevented antibody responses in GAA-knockout mice by inducing immune tolerance to human GAA. Antibody responses have complicated enzyme replacement therapy for Pompe disease and emphasized a potential advantage of gene therapy for this disorder. The strategy of administering low-dose gene therapy prior to initiation of enzyme replacement therapy, termed immunomodulatory gene therapy, prevented antibody formation and increased efficacy in Pompe disease mice. We are currently conducting a Phase I clinical trial of immunomodulatory gene therapy in adult patients with Pompe disease. Furthermore, we have developed drug therapy to increase the receptor-mediated uptake of GAA in muscle cells, which provides adjunctive therapy to more definitively treat Pompe disease.
3) PKU: In collaboration with researchers at OHSU, we performed an early gene therapy experiment that demonstrated long-term biochemical correction of PKU in mice with an AAV8 vector. PKU is a very significant disorder detected by newborn screening and currently inadequately treated by dietary therapy. Phenylalanine levels in mice were corrected in the blood, and elevated phenylalanine causes mental retardation and birth defects in children born to affected women, and gene therapy for PKU would address an unmet need for therapy in this disorder.

Currently we are developing methods for genome editing that will stably correct the enzyme  deficiency in GSD Ia and in Pompe disease.  Our long-term goal is to develop efficacious genome editing for glycogen storage diseases, which will allow us to treat these conditions early in life with long-term benefits.