Correction of glycogen storage disease type III with rapamycin in a canine model.

UNLABELLED: Recently, we reported that progression of liver fibrosis and skeletal myopathy caused by extensive accumulation of cytoplasmic glycogen at advanced age is the major feature of a canine model of glycogen storage disease (GSD) IIIa. Here, we aim to investigate whether rapamycin, a specific inhibitor of mTOR, is an effective therapy for GSD III. Our data show that rapamycin significantly reduced glycogen content in primary muscle cells from human patients with GSD IIIa by suppressing the expression of glycogen synthase and glucose transporter 1. To test the treatment efficacy in vivo, rapamycin was daily administered to GSD IIIa dogs starting from age 2 (early-treatment group) or 8 months (late-treatment group), and liver and skeletal muscle biopsies were performed at age 12 and 16 months. In both treatment groups, muscle glycogen accumulation was not affected at age 12 months but significantly inhibited at 16 months. Liver glycogen content was reduced in the early-treatment group but not in the late-treatment group at age 12 months. Both treatments effectively reduced liver fibrosis at age 16 months, consistent with markedly inhibited transition of hepatic stellate cells into myofibroblasts, the central event in the process of liver fibrosis. Our results suggest a potential useful therapy for GSD III. KEY MESSAGES: Rapamycin inhibited glycogen accumulation in GSD IIIa patient muscle cells. Rapamycin reduced muscle glycogen content in GSD IIIa dogs at advanced age. Rapamycin effectively prevented progression of liver fibrosis in GSD IIIa dogs. Our results suggest rapamycin as potential useful therapy for patients with GSD III.

Alglucosidase alfa enzyme replacement therapy as a therapeutic approach for glycogen storage disease type III.

We investigated the feasibility of using recombinant human acid-α glucosidase (rhGAA, Alglucosidase alfa), an FDA approved therapy for Pompe disease, as a treatment approach for glycogen storage disease type III (GSD III). An in vitro disease model was established by isolating primary myoblasts from skeletal muscle biopsies of patients with GSD IIIa. We demonstrated that rhGAA significantly reduced glycogen levels in the two GSD IIIa patients' muscle cells (by 17% and 48%, respectively) suggesting that rhGAA could be a novel therapy for GSD III. This conclusion needs to be confirmed in other in vivo models.

Efficacy of cornstarch therapy in type III glycogen-storage disease.

Type III glycogen-storage disease (GSD-III), due to decreased activity of the glycogen debranching enzyme amylo-1,6 glucosidase, may cause hepatic dysfunction, growth failure, and myopathy. The prevention of hypoglycemia by nocturnal intragastric formula infusion has been shown to enhance growth and improve the metabolic abnormalities associated with GSD-III. Cornstarch therapy was effective in preventing hypoglycemia in a few patients with GSD-III who were previously treated with nocturnal enteral formula infusion, but oral cornstarch had not been evaluated as an initial treatment. We studied three patients with GSD-III who exhibited growth failure, elevated serum aminotransferase concentrations, and asymptomatic hypoglycemia. Cornstarch therapy was associated with maintenance of normoglycemia, increased growth velocity, and decreased serum aminotransferase concentrations in all patients. Our experience suggests that cornstarch therapy can be effective as an initial treatment for patients with GSD-III.

Glycogen storage disease: effects of glucose infusions on [15N]glycine kinetics and nitrogen metabolism.

The effects of intragastric glucose infusions on [15N]glycine kinetics and whole body protein turnover were investigated in four children with type I and two children with type III glycogen storage disease. Either fasting or the administration of insufficient glucose was associated with a diminution in the glycine pool size relative to values observed when patients received adequate glucose. The cause of the smaller pool size was an increased fractional glycine turnover. Simultaneous determination of whole body protein turnover, using a stochastic model based on [15N]urea excretion, showed higher rates of protein synthesis, nitrogen flux, net tissue protein retention, and reutilization of amino acid nitrogen derived from protein catabolism, in patients receiving sufficient exogenous glucose. Depletion of amino acid pools, presumably because of intensive utilization of these gluconeogenic precursors when inadequate glucose is administered, was associated with a lower rate of whole body protein synthesis.

Renal tubular acidosis associated with type III glycogenosis.

Two children who presented with severe failure to thrive were found to have Type III glycogen storage disease. They both also had defects of tubular acidification, an association not previously described. The nature of the tubular lesion is characterized and the explanation and therapeutic implications are discussed.

[Serum lipoproteins in the generalized form of type III glycogenosis]. / Lipoproteidy syvorotki krovi pri generalizovannoi forme glikogenoza III tipa.

Distinct accumulation of glycogen, anomalous in structure, and absence of amylo-1,6-glucosidase activity were observed in studies of material obtained by biopsy from liver and muscle tissues of a patient with generalized form of glycogenosis type III. Anamalous glycogen (limitdextrin) was also found in erythrocytes. Concentration of lipoproteins, especially of low density lipoproteins 12.20 S and 0-12 S, was increased in blood serum. Spectrum of lipoproteins acquired a tendency to normalization simultaneously with clinical improvement after intravenous administration of glucose and treatment with cholesterolamine per os.