Hepatic and neuromuscular forms of glycogen storage disease type IV caused by mutations in the same glycogen-branching enzyme gene.
Glycogen storage disease type IV (GSD-IV) is an autosomal recessive disease resulting from deficient glycogen-branching enzyme (GBE) activity. The classic and most common form is progressive liver cirrhosis and failure leading to either liver transplantation or death by 5 yr of age. However, the liver disease is not always progressive. In addition, a neuromuscular type of the disease has been reported. The molecular basis of GSD-IV is not known, nor is there a known reason for the clinical variability. We studied the GBE gene in patients with various presentations of GSD-IV. Three point mutations in the GBE gene were found in two patients with the classical presentation: R515C, F257L, and R524X. Transient expression experiments showed that these mutations inactivated GBE activity. Two point mutations, L224P and Y329S, were detected in two separate alleles of a patient with the nonprogressive hepatic form. The L224P resulted in complete loss of GBE activity, whereas the Y329S resulted in loss of approximately 50% of GBE activity. The Y329S allele was also detected in another patient with the nonprogressive form of GSD-IV but not in 35 unrelated controls or in patients with the more severe forms of GSD-IV. A 210-bp deletion from nucleotide 873 to 1082 of the GBE cDNA was detected in a patient with the fatal neonatal neuromuscular presentation. This deletion, representing the loss of one full exon, was caused by a 3' acceptor splicing site mutation (ag to aa). The deletion abolished GBE activity. Our studies indicate that the three different forms of GSD-IV were caused by mutations in the same GBE gene. The data also suggest that the significant retention of GBE activity in the Y329S allele may be a reason for the mild disease. Further study of genotype/phenotype correlations may yield useful information in predicting the clinical outcomes.
Bao
Y
Y
Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710, USA.
Kishnani
P
P
Wu
J Y
JY
Chen
Y T
YT
D015061:1,4-alpha-Glucan Branching Enzyme / Q000235:genetics* / Q000378:metabolism; D000483:Alleles; D001483:Base Sequence; D002675:Child, Preschool; D017931:DNA Primers / Q000737:chemistry; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D006011:Glycogen Storage Disease Type IV / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D007223:Infant; D008107:Liver Diseases / Q000201:enzymology*; D008969:Molecular Sequence Data; D009468:Neuromuscular Diseases / Q000201:enzymology*; D017354:Point Mutation; D012333:RNA, Messenger / Q000235:genetics; D017384:Sequence Deletion
D017931:DNA Primers; D012333:RNA, Messenger; D015061:1,4-alpha-Glucan Branching Enzyme