Canine model and genomic structural organization of glycogen storage disease type Ia (GSD Ia)

A canine model of glycogen storage disease Ia (GSD Ia), similar clinically, biochemically, and pathologically to the human disease, was established by crossbreeding Maltese and Beagle dogs carrying a mutated, defective glucos e-6-phosphatase (G-6-Pase) gene. Ten puppies were born in three litters fro m these crossbreedings. Six were homozygous for the previously described M1 211 GSD Ia mutation. Of these six affecteds, two were stillborn, and one di ed at 2, 32, and 60 days of life, respectively (puppies A, B, C, D, E), whi le one is alive at age 15 months (puppy F). Affected puppies exhibited trem ors, weakness, and neurologic signs when hypoglycemic. They had postnatal g rowth retardation and progressive hepatomegaly. Biochemical abnormalities i ncluded fasting hypoglycemia, hyperlactacidemia, hypercholesterolemia. hype rtriglyceridemia, and hyperuricemia. Microscopic examination of tissues fro m affected puppies showed diffuse, marked hepatocellular vacuolation, with distended clear hepatocytes and central to marginally located rounded nucle i. In the kidneys of puppies D and E, there was segmental glomerular sclero sis and vacuolation of proximal convoluted tubular epithelium. Biochemical analysis revealed increased liver glycogen content and isolated markedly re duced G-6-Pase enzyme activity in liver and kidney. The canine G-6-Pase gen e was characterized by screening a canine genomic library. It spans similar to 11.8 kb and consists of five exons with >90% amino acid sequence homolo gy to the derived human sequence. The first 1.5 kb of the 5' region was seq uenced and contains several putative response element motifs homologous to the human 5' region. Establishment of this canine colony of GSD Ia that clo sely resembles human disease and isolation of the canine genomic gene provi des an excellent model for studying pathophysiology and long-term complicat ions and an opportunity to develop novel therapeutic approaches such as dru g and gene therapy.