Balkan Journal of Medical Genetics

A CASE OF GLYCOGEN STORAGE DISEASE TYPE 1a MIMICKING FAMILIAL CHYLOMICRONEMIA SYNDROME
Olgac A1,*, Okur İ2, Biberoğlu G2, Ezgü FS2, Tümer L2
*Corresponding Author: Dr. Asburce Olgac, Department of Pediatric Metabolism, University of Health Sciences, Dr. Sami Ulus Maternity and Child Health, Training and Research Hospital, Ankara, Turkey. Tel.: +90-312-305-600. Fax: +90-312-317-03-53. E-mail: mabolgac@yahoo.com
page: 103

DISCUSSION

HTG in childhood may be due to genetic factors or secondary to several conditions (e.g., metabolic syndrome, drugs, inborn errors of metabolism). Severe HTG, in which fasting plasma TG levels are above 885.0 mg/dL (10.0 mmol/L), is usually due to high levels of intestinally derived chylomicron particles (TG-rich lipoproteins). In pediatric patients, this condition is mainly due to endothelial- bound lipoprotein lipase (LPL) deficiency, which is an autosomal recessive disorder affecting the catabolism of chylomicrons, or its coactivators. It is also called FCS, and occurs due to biallelic mutations of several genes [2]. Triglyceride levels are variable in FCS, but may rise up to 100-fold, and the diagnosis should be made early to prevent acute pancreatitis due to HTG. Although hypoglycemia is not a direct symptom of FCS, pancreatic involvement due to HTG may cause distruption of glucose homeostasis [3]. Treatment includes dietary fat restriction (<15.0% of daily caloric intake), avoidance of high glycemic index foods, supplementation with omega-3 and medium-chain TGs. Fibrates and niacin may be used that are somewhat effective [1]. Several patients with FCS diagnosed in the neonatal period have been reported in the literature [2,4,5]. Shah et al. [2] have reported a 23-day-old baby with confirmed LPL deficiency and acute pancreatitis, who was admitted due to fever, vomiting, lethargy and lipemia (elevated TG levels up to 10,300 mg/dL), similar to the initial presentation of our patient. Hypertriglyceridemia may also occur due to glycogen storage diseases, of which GSD1a is the most frequent, and the incidence is estimated to be 1/100,000 births [1]. The disease occurs due to the defects on the G6PC gene, which is located on chromosome 17q21.31. The G6PC gene encodes the catalytic subunit of the enzyme G6Pase-α that is responsible for the last step of glycogenolysis [6]. As a result of the deficient activity of this enzyme, the patients are unable to tolerate short-term fasting (2-4 hours) and hypoglycemia occurs. Disturbed glucose homeostasis, leads to secondary metabolic derangement causing hyperlipidemia and hepatosteatosis due to TG accumulation in the liver. Patients display lactic acidosis, a protruded abdomen due to hepatomegaly, anemia and bleeding tendency due to platelet dysfunction, a round doll-like face, muscle weakness, osteopenia and short stature [1]. Hyperlipidemia is a frequently encountered symptom that usually involves TGs and cholesterol. Talente et al. [7] reported HTG to be 100.0% in adults with GSD1a. Hypertriglyceridemia and hypercholesterolemia (HC) mainly occur due to poor metabolic control and sustained hypoglycemia that causes lipid synthesis in the liver. Although the exact mechanism is unknown, increased lipidogenesis and decreased clearance and uptake of lipids due to the deficient activity of lipoprotein lipase and hepatic lipase, are the suggested factors that increase blood TG and TC levels. Excessive intake of carbohydrates can also increase lipid synthesis in the liver, and the activation of lipidogenic genes due to the accumulation of glucose 6-phosphatase (G6P), could be another probability. Since insulin levels are low in GSD1a patients, increased very low-density lipoprotein (VLDL) levels that are rich in TGs, may be another contributing factor. Blood TG and TC levels are variable among cases, and during the followup period, even in the same patient. Patients with poorly managed GSD1a sometimes develop variable levels of HTG that is a significant risk factor for acute pancreatitis, especially if above 1000.0 mg/dL [8]. Treatment is mainly diet therapy with frequent feedings to prevent hypoglycemia and elimination of lactose and fructose from diet. Patients may require continuous nocturnal gastric drip feeding. Uncooked cornstarch and maltodextrin can be used after the age of 1 to prevent hypoglycemia. Unfortunately, hyperlipidemia does not completely resolve with dietary therapy [9]. Medium-chain TGs are known to have beneficial effects on TG levels, as they are directly absorbed from the portal vein. Longterm complications, including liver failure, are also not prevented by dietary treatment. Liver transplantation is only indicated in patients with hepatic malignancies that are unresectable or do not benefit from dietary therapy [10].

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