[Molecular genetic analysis of 10 Chinese patients with glycogen storage disease type III].
OBJECTIVE
Glycogen debranching enzyme (AGL) plays an important role in complete degradation of the glycogen, and has two independent catalytic activities, i.e., those of alpha-1, 4-glucanotransferase (EC 2.4. 1.25) and amylo-1,6-glucosidase (EC 3.2. 1.33). A deficiency in activities of AGL causes excessive accumulation of glycogen with short branched outer chains and results in glycogen storage disease type III (GSD III; MIM #232 400), an autosomal recessive inborn disorder of glycogen metabolism. The present study aimed to investigate the mutation of AGL in 10 Chinese patients with GSD III.


METHODS
Clinical and laboratory data of 10 patients with typical clinical manifestations of GSD III suggesting hypoglycemia, hyperlipidemia, increased creatine-phosphokinase and its isozyme were collected. The coding regions and their flanking introns of AGL gene of the 10 patients were amplified by PCR and analyzed by direct DNA sequencing. All the mutated alleles were confirmed by bidirectional DNA sequencing. The 3 novel splicing mutations were analyzed by restriction fragment length polymorphism (RFLP) in 50 healthy children (control). The 2 small deletions (c.408-411delTTTG, c.2717-2721delAGATC) were analyzed by fluorescent polymerase chain reaction and gene scan analysis to confirm the number of deleted bases.


RESULTS
Thirteen different mutations were identified, including 4 splicing mutations (IVS6 + 1G > A, IVS6-1G > A, IVS14 + 1G > T, IVS26-2A > C), 5 nonsense mutations (R469X, R864X, S929X, R977X, Y1428X), 3 small deletions (c.408-411delTTTG, c.2717-2721delAGATC, c.2823delT) and 1 insert mutation (c.4234insT). Except for IVS14 + 1G > T, R864X, and R977X, the other 10 mutations are novel; 18 mutated alleles were identified in the 20 alleles (90%). IVS14 + 1G > T was the most frequently seen mutation, accounting for 5 of 20 (25%) alleles examined. None of homozygote and heterozygote of the 3 novel splicing mutations was found in the 50 healthy controls by RFLP analysis. With the fluorescent polymerase chain reaction and gene scan analysis, c.408411deTTTG mutation and c.2717-2721delAGATC mutation were confirmed to have 4 and 5 bases deletion respectively.


CONCLUSIONS
Thirteen mutations were identified in the 10 cases with GSD III, with 10 novel mutations. IVS14 + 1G > T was a relatively common mutation. This study revealed the heterozygosity of AGL gene in Chinese patients with GSD III.
Wang
Xia
X
Department of Paediatric Endocrinologic, Genetic and Metabolic Diseases, Shanghai Institute of Pediatric Research, Xinhua Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200092, China.
Qiu
Wen-juan
WJ
Ye
Jun
J
Han
Lian-shu
LS
Zhang
Hui-wen
HW
Jiang
Li-rong
LR
Zhang
Ya-fen
YF
Gu
Xue-fan
XF
D000293:Adolescent; D044466:Asian People / Q000235:genetics; D001483:Base Sequence; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D006004:Glycogen Debranching Enzyme System / Q000235:genetics*; D006010:Glycogen Storage Disease Type III / Q000235:genetics*; D006801:Humans
D006004:Glycogen Debranching Enzyme System; C030563:amylo-1,6-glucosidase