Molecular and clinical delineation of 12 patients with glycogen storage disease type III in Western Turkey

Background: Glycogen storage disease type III (GSD III; MIM #232400) is an autosomal recessive inherited disorder characterized by fasting hypoglycemia, growth retardation, hepatomegaly, progressive myopathy, and cardiomyopathy. GSD III is caused by deficiency in the glycogen debranching enzyme (gene symbol: AGL). Molecular analyses of AGL have indicated heterogeneity depending on ethnic groups. In Turkey we reported 13 different AGL mutations from GSD III patients in the Eastern region; however, the full spectrum of AGL mutations in Turkish population remains unclear. Here we investigated 12 GSD III patients mostly from Western Turkey.

Methods: The full coding exons, their relevant exon-intron boundaries, and the 5'- and 3'-flanking regions of the patients' AGL were sequenced. AGL haplotypes were determined. Splicing mutations were characterized by RNA transcript analysis.

Results: Twelve different mutations were identified: 7 novel AGL mutations [69-base pair deletion (c.1056_1082+42del69), 21-base par deletion (c.3940_3949+11del21), two small duplications (c.364_365dupCT and c.1497_1500dupAGAG), and 3 splicing mutations (c.1736-11A>G, c.3259+1G>A and c.3588+2T>G)], along with 5 known mutations (c.1019delA, c.958+1G>A, c.4161+5G>A, p.R864X and p.R1218X). Transcripts of splicing mutations (c.1736-11A>G, c.3588+2T>G and c.4161+5G>A) were shown to cause aberrant splicing. AGL haplotype analyses suggested that c.1019delA and c.958+1G>A are founder mutations in Turkish patients, while p.R864X is a recurrent mutation.

Conclusions: Our study broadens the spectrum of AGL mutations and demonstrates that mutations in Western Turkey are different from those in the Eastern region.