Patients with GSD type I GSD are now doing well, and the prognosis for children and adults with these conditions is outstanding. In fact, at the University of Florida, 34 children have now been born to mothers with GSD. While there have been tremendous advances over the past 2 decades, acute metabolic decompensations can occur at any time, and a missed dose of cornstarch or interruption in a feed can result in severe hypoglycemia, seizures, or even death. As a result, the ultimate goal is to cure the disease, and the team at the University of Florida is working on bringing potentially curative gene therapy to people with the disease.
Gene Therapy in Dogs with GSD Ia: GSD type Ia occurs naturally in maltese dogs. Without treatment, all of the dogs die within hours of birth. Even with medical therapy, no dog with the disease had survived for more than 4 weeks when this work started. Gene therapy was performed on a dog with GSD type Ia (Dulce) in Florida for the first time on September 11, 2007. Within 2 weeks, the duration of fasting markedly increased, and visually the dog improved with decreased hepatomegaly, increased energy, and improved growth. The effect of gene therapy waned so a second gene therapy was performed in January 2008. Following this treatment on Dulce the lactate concentration normalized, and she was able to fast for 9 hours without development of hypoglycemia. All glucose support was stopped at 6 months of age, and Dulce had no problems clinically while weaning off therapy. A liver biopsy 6 months after the 2nd gene therapy dose demonstrated 7% activity. Dulce remained off of therapy for 19 months (21 months following the last gene therapy treatment), but elevated lactates subsequently developed when she went into heat. As a result, low dose therapy was restarted, and Dulce had a third gene therapy treatment in February 2010. As of 4 years of age, Dulce has had no adenomas or evidence of complications.
Tucker and Jasmine were born April 9, 2010. Gene therapy was performed at 36 hours of life using a modified vector, and the response was even more dramatic. By 2 weeks of age, puppies were able to fast for 6 hours (baseline 45-60 minutes), and glucose support discontinued at 3 weeks. A second gene therapy treatment was performed at 8 weeks, and the dogs are doing well at 20 months of age.
Gene Therapy in an Older Dog with GSD: Since most children and adults will be treated outside of the newborn period, it is critical to assess gene therapy in older dogs. This was first attempted in Ginger who was born in September 2010. Following birth, Ginger was medically treated for 2-1/2 months. Without the gene therapy, the dog struggled to maintain her blood sugars. She had poor growth and extreme metabolic instability. Due to her poor health, gene therapy was performed, and she clinically normalized after 1 week. Three more dogs with GSD (Colin, Casper, and Gemini) were born in June 2011, and they are receiving the same treatment as Ginger.
Future of Gene Therapy:
- Gene therapy appears to be a promising therapy for the future in GSD Ia
- Meetings with NIH and Duke have been occurring since January 2011 as we attempt to bring gene therapy to humans in a collaborative way.
- Gene therapy trial in humans with GSD II in Florida was commenced in March 2011