AGL gene mutation and clinical features in Korean patients with glycogen storage disease type III

ABSTRACT

PURPOSE: Glycogen storage disease type III (GSD-III) is a rare autosomal recessive disorder of glycogen metabolism. The affected enzyme, amylo-1,6-glucosidase, 4-alpha-glucanotransferase (AGL, glycogen debranching enzyme), is responsible for the debranching of the glycogen molecule during catabolism. The disease shows clinical and biochemical heterogeneity, reflecting genotype-phenotype heterogeneity among different patients. In this study, we aim at analyzing mutations of the AGL gene in three unrelated Korean GSD-III patients, and characterizing their clinical and laboratory findings. METHODS: We characterized the clinical features of three unrelated Korean GSD-III patients by biochemical, histological and imaging studies. The 35 exons and part of exon-intron boundaries of AGL were analyzed by direct sequencing using genomic DNA extracted from the peripheral leukocytes of patients. RESULTS: Diverse clinical features were observed in these patients including hepatomegaly (all patients), seizures (patient 2), growth failure (patients 1 and 2), hyperlipidemia (patients 1 and 3), raised transaminase and creatine kinase concentrations (all patients), and mild cardiomyopathy (patient 2). Liver transplantation was performed in patient 2 due to progressive hepatic fibrosis. Administration of uncooked corn starch maintained normoglycemia and improved biochemical and growth profiles. DNA sequence analysis revealed mutations in 5 out of 6 alleles. Patient 1 was a compound heterozygote of c.1282 G>A (p.R428K) and c.1306delA (p.S603PfsX6), patient 2 had c.1510_1511insT (p.Y504LfsX10), and patient 3 had c.3416 T>C (p.L1139P) and c.1735+1 G>T (p.Y538_R578delfsX4) mutations. Apart from the p.R428K mutation, the 4 other substitutions identified were novel. CONCLUSION: GSD-III patients display variable phenotypic characteristics resembling those of GSD-Ia. Molecular defects in the AGL gene of Korean GSD-III patients are genetically heterogeneous.