Egyptian glycogen storage disease type III - identification of six novel AGL mutations, including a large 1.5 kb deletion and a missense mutation p.L620P with subtype IIId.

BACKGROUND: Glycogen storage disease type III (GSD III) is caused by mutations in AGL which encodes for a single protein with two enzyme activities: oligo-1, 4-1, 4-glucantransferase (transferase) and amylo-1, 6-glucosidase. Activity of both enzymes is lost in most patients with GSD III, but in the very rare subtype IIId, transferase activity is deficient. Since the spectrum of AGL mutations is dependent on the ethnic group, we investigated the clinical and molecular characteristics in Egyptian patients with GSD III. METHODS: Clinical features were examined in five Egyptian patients. AGL was sequenced and AGL haplotypes were determined. RESULTS: Six novel AGL mutations were identified: a large deletion (c.3481-3588+1417del1525 bp), two insertions (c.1389insG and c.2368insA), two small deletions (c.2223-2224delGT and c.4041delT), and a missense mutation (p.L620P). p.L620P was found in a patient with IIId. Each mutation was located on a different AGL haplotype. CONCLUSIONS: Our results suggest that there is allelic and phenotypic heterogeneity of GSD III in Egypt. This is the second description of a large deletion in AGL. p.L620P is the second mutation found in GSD IIId.

A 60-y-old chylomicronemia patient homozygous for missense mutation (G188E) in the lipoprotein lipase gene showed no accelerated atherosclerosis.

BACKGROUND: Familial lipoprotein lipase (LPL) deficiency is a rare autosomal recessive disorder caused by mutations in the LPL gene. Patients with LPL deficiency have chylomicronemia; however, whether they develop accelerated atherosclerosis remains unclear. METHODS: We investigated clinical and mutational characteristics of a 60-y-old Japanese patient with chylomicronemia. RESULTS: The patient's fasting plasma triglyceride levels were >9.0 mmol/l. In postheparin plasma, one fifth of the normal LPL protein mass was present; however, LPL activity was undetectable. Molecular analysis of the LPL gene showed the patient to be a homozygote of missense mutation replacing glycine with glutamine at codon 188 (G188E), which had been known to produce mutant LPL protein lacking lipolytic activity. Ultrasonographic examination of the patient's carotid and femoral arteries showed no accelerated atherosclerosis. Moreover, 64-slice mechanical multidetector-row computer tomography (MDCT) angiography did not detect any accelerated atherosclerotic lesions in the patient's coronary arteries. The patient had none of the risk factors such as smoking, hypertension, and diabetes. CONCLUSIONS: Our case suggests that accelerated atherosclerosis may not develop in patients with LPL deficiency, when they have no risk factors.

A novel complex deletion-insertion mutation mediated by Alu repetitive elements leads to lipoprotein lipase deficiency.

Lipoprotein lipase (LPL) deficiency is a rare autosomal recessive inherited disorder, characterized by marked hypertriglyceridemia, eruptive xanthoma, hepatosplenomegaly, recurrent attacks of pancreatitis, and markedly low or absent LPL activity in postheparin plasma. A majority of LPL deficient patients have been reported to have point mutations in the LPL gene; however, we find a complex deletion-insertion mutation by Alu elements, mobile retrotransposons, in a patient with LPL deficiency. This patient suffered from acute pancreatitis, showed chylomicronemia and lacked detectable LPL activity or mass in her postheparin plasma. Southern blot analysis and long-range PCR of the patient's DNA demonstrated a 2.2-kb deletion encompassing exon 2. Sequence analysis revealed (1) a 2.3-kb deletion between an AT-rich region adjacent to an Alu element in intron 1 and another Alu element in intron 2; (2) an insertion of approximately 150bp 5'-truncated Alu sequence with a poly (A) tail at the deletion point. The inserted sequence belongs to Alu Yb9, the youngest subfamily of Alu elements. The deletion occurred at the consensus cleavage site (3'-A|TTTT-5') without target site duplication. These findings indicated that Alu retrotransposition caused the complex deletion-insertion. The patient was homozygous for this complex mutation, which eliminates exon 2 and leads to LPL deficiency. To our knowledge, the patient is the first case with LPL deficiency due to a complex deletion-insertion mediated by Alu repetitive elements.

A Japanese patient with cardiomyopathy caused by a novel mutation R285X in the AGL gene.

Left ventricular hypertrophy (LVH) is primarily or secondarily caused by a cardiovascular or systemic disease. The pattern of LVH is distinctive in hypertrophic or metabolic cardiomyopathy and differs from that seen in LVH caused by hypertension or aortic stenosis. A 42-year-old Japanese man had LVH similar to that with hypertrophic cardiomyopathy. The patient was diagnosed with glycogen storage disease type IIIa (GSD-IIIa). Echocardiography showed that he had severe LVH, and concomitant hepatomegaly and hypoglycemia, which led to measurement of glycogen debranching enzyme (GDE) activity; it was undetectable. Sequence analysis of the AGL gene encoding GDE showed a novel nonsense mutation: a C-to-T transition at codon 285 in exon 8, resulting in substitution of the arginine codon by the stop codon (R285X). The patient was homozygous for the mutation. Cardiomyopathy in this patient was caused by a nonsense mutation in the AGL gene. Five other Japanese GSD-IIIa patients over 30 years of age have all presented with cardiomyopathy, as well as hepatomegaly and hypoglycemia. Patients with LVH associated with hepatomegaly and hypoglycemia should undergo biochemical and genetic analyses for GSD-IIIa.

Molecular analysis of the AGL gene: heterogeneity of mutations in patients with glycogen storage disease type III from Germany, Canada, Afghanistan, Iran, and Turkey.

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder characterized by excessive accumulation of abnormal glycogen in the liver and/or muscles and caused by deficiency in the glycogen debranching enzyme (AGL). Previous studies have revealed that the spectrum of AGL mutations in GSD III patients depends on ethnic grouping. We investigated nine GSD III patients from Germany, Canada, Afghanistan, Iran, and Turkey and identified six novel AGL mutations: one nonsense (W255X), three deletions (1019delA, 3202-3203delTA, and 1859-1869del11-bp), and two splicing mutations (IVS7 + 5G > A and IVS21 + 5insA), together with three previously reported ones (R864X, W1327X, and IVS21 + 1G > A). All mutations are predicted to lead to premature termination, which abolishes enzyme activity. Our molecular study on GSD III patients of different ethnic ancestry showed allelic heterogeneity of AGL mutations. This is the first AGL mutation report for German, Canadian, Afghan, Iranian and Turkish populations.

Molecular characterization of Egyptian patients with glycogen storage disease type IIIa.

Glycogen storage disease type IIIa (GSD IIIa) is an autosomal recessive disorder characterized by excessive accumulation of abnormal glycogen in the liver and muscles and caused by a deficiency in the glycogen debranching enzyme. The spectrum of AGL mutations in GSD IIIa patients depends on ethnic group-prevalent mutations have been reported in the North African Jewish population and in an isolate such as the Faroe islands, because of the founder effect, whereas heterogeneous mutations are responsible for the pathogenesis in Japanese patients. To shed light on molecular characteristics in Egypt, where high rate of consanguinity and large family size increase the frequency of recessive genetic diseases, we have examined three unrelated patients from the same area in Egypt. We identified three different individual AGL mutations; of these, two are novel deletions [4-bp deletion (750-753delAGAC) and 1-bp deletion (2673delT)] and one the nonsense mutation (W1327X) previously reported. All are predicted to lead to premature termination, which completely abolishes enzyme activity. Three consanguineous patients are homozygotes for their individual mutations. Haplotype analysis of mutant AGL alleles showed that each mutation was located on a different haplotype. Our results indicate the allelic heterogeneity of the AGL mutation in Egypt. This is the first report of AGL mutations in the Egyptian population.