Molecular genetics of glycogen-storage disease type 1a in Chinese patients of Taiwan

Recurrent pancreatitis and sepsis in glycogen storage disease type Ia caused by complex heterozygous mutations in 2 sisters: Case report

RATIONALE

Glycogen storage disease (GSD) is a glycogen metabolism disorder caused by congenital enzyme defects, with type I being the most common. Owing to the rarity of glycogen storage disease type Ia (GSD Ia) and the involvement of diverse systems, patients are prone to delayed diagnosis and inappropriate treatment. Additional studies are required to standardize the diagnosis and treatment of GSD Ia.

PATIENT CONCERNS

We report 2 cases of GSD Ia that occurred in 2 sisters. The elder sister also had recurrent pancreatitis, and the pancreatic pseudocyst rupture resulted in sepsis, portal hypertension, and splenic infarction. The younger sister had the same mutation site, but the clinical phenotypes were not identical.

DIAGNOSIS

Abdominal computed tomography and laboratory examinations revealed regional portal hypertension, splenic infarction, and sepsis in the elder sister; diagnosis was confirmed by whole exome sequencing. Sanger sequencing was used to confirm that the younger sister and their parents also had the mutation site.

INTERVENTIONS

The elder sister was treated with corn starch therapy, and medication for antiinfection and reducing hypertriglyceridemia, inhibiting trypsin activity, relieving hyperuricemia. The younger sister was treated with raw cornstarch-based nutritional therapy and sodium bicarbonate.

OUTCOMES

The elder sister's infection was controlled and she gradually returned to a normal diet. After discharge, hyperlipidemia was not controlled satisfactorily, but hypoglycemia, hyperuricemia, hyperlactatemia, and anemia improved.

LESSONS

GSD should be considered in childhood patients with hypoglycemia, hypertriglyceridemia, hyperuricemia, and hyperlactatemia. Gene sequencing can enable quick identification of GSD subtypes. This case report highlights the common clinical manifestations can be linked to rare diseases. Clinical work requires careful observation of the correlations between patient history, physical examinations, and laboratory examinations.

Mutations in the glucose-6-phosphatase-alpha (G6PC) gene that cause type Ia glycogen storage disease

Glucose-6-phosphatase-alpha (G6PC) is a key enzyme in glucose homeostasis that catalyzes the hydrolysis of glucose-6-phosphate to glucose and phosphate in the terminal step of gluconeogenesis and glycogenolysis. Mutations in the G6PC gene, located on chromosome 17q21, result in glycogen storage disease type Ia (GSD-Ia), an autosomal recessive metabolic disorder. GSD-Ia patients manifest a disturbed glucose homeostasis, characterized by fasting hypoglycemia, hepatomegaly, nephromegaly, hyperlipidemia, hyperuricemia, lactic acidemia, and growth retardation. G6PC is a highly hydrophobic glycoprotein, anchored in the membrane of the endoplasmic reticulum with the active center facing into the lumen. To date, 54 missense, 10 nonsense, 17 insertion/deletion, and three splicing mutations in the G6PC gene have been identified in more than 550 patients. Of these, 50 missense, two nonsense, and two insertion/deletion mutations have been functionally characterized for their effects on enzymatic activity and stability. While GSD-Ia is not more prevalent in any ethnic group, mutations unique to Caucasian, Oriental, and Jewish populations have been described. Despite this, GSD-Ia patients exhibit phenotypic heterogeneity and a stringent genotype-phenotype relationship does not exist.

Mutation spectrum of the glucose-6-phosphatase gene and its implication in molecular diagnosis of Korean patients with glycogen storage disease type Ia

Glycogen storage disease type Ia (GSD Ia; MIM 232200) is an autosomal recessive inherited metabolic disorder resulting from a deficiency of the microsomal glucose-6-phosphatase (G6Pase), the enzyme that catalyzes the terminal step in gluconeogenesis and glycogenolysis. Various mutations in the G6Pase gene (G6PC) have been found in patients with GSD Ia. To elucidate the spectrum of the G6PC gene mutations, 13 unrelated Korean patients with GSD Ia were analyzed. We were able to identify mutant alleles in all patients, including three known mutations (727G > T, G122D, and T255I) and two novel mutations (P178A and Y128X). The frequency of the 727G > T mutation in Korean patients with GSD Ia was 81% (21/26), which was slightly lower than that (86-92%) in Japanese but much higher than that (44.4%) in Taiwan Chinese. Except one, all patients were either homozygous (9/13) or compound heterozygous (3/13) for the 727G > T mutation; the only patient without the 727G > T mutation was a compound heterozygote for the G122D and Y128X mutations. Our findings suggest that a DNA-based test can be used as the initial diagnostic approach in Korean patients clinically suspected to have GSD Ia, thereby avoiding invasive liver biopsy.

Mutation analysis of the MMAA and MMAB genes in Japanese patients with vitamin B(12)-responsive methylmalonic acidemia: identification of a prevalent MMAA mutation

Methylmalonic acidemia (MMA) is caused by the deficient activity of l-methylmalonyl-CoA mutase, which is a vitamin B(12) (or cobalamin, Cbl)-dependent enzyme. MMA due to the effect of insufficient Cbl metabolism is classified into three forms (cblA, cblB, and cblH). Recently, the genes responsible for cblA and cblB were identified as MMAA and MMAB, respectively. The MMAA protein likely transports Cbl into the mitochondria for adenosylcobalamin synthesis, while the MMAB protein appears to be an adenosyltransferase. We performed a mutation analysis of 10 unrelated Japanese patients with vitamin B(12)-responsive MMA. Seven patients had mutations in MMAA, whereas the other three patients showed no disease-causing substitutions in either MMAA or MMAB. Five novel mutations were identified in MMAA (R22X, R145X, L217X, R359G, and 503delC). The 503delC mutation was observed in five of the seven MMAA patients, suggesting that the mutation is prevalent in Japanese patients. This finding may facilitate the DNA diagnosis of vitamin B(12)-responsive MMA within the Japanese population.

Molecular genetic analysis of glycogen storage disease type Ia in 26 Chinese patients

Sequence analysis of 26 patients from Mainland China with glycogen storage disease type Ia revealed a high frequency of two mutations in the glucose-6-phosphatase gene. These mutations, 727G>T and R83H, were also found to be in linkage disequilibrium with a polymorphism at position 1176. These findings have implications for carrier detection and prenatal diagnosis of this disease in the Chinese population.