Increased de novo lipogenesis and delayed conversion of large VLDL into intermediate density lipoprotein particles contribute to Hyperlipidemia in glycogen storage disease type 1a

Glycogen storage disease type 1a (GSD-1a) is a metabolic disorder characterized by fasting-induced hypoglycemia, hepatic steatosis, and hyperlipidemia. The mechanisms underlying the lipid abnormalities are largely unknown. To investigate these mechanisms seven GSD-1a patients and four healthy control subjects received an infusion of [1-C-13]acetate to quantify cholesterogenesis and lipogenesis. In a subset of patients, [1-C-13] valine was given to assess lipoprotein metabolism and [2-C-13] glycerol to determine whole body lipolysis. Cholesterogenesis was 274 +/- 112 mg/d in controls and 641 +/- 201 mg/d in GSD-1a patients (p <0.01). Plasma triglyceride-palmitate derived from de novo lipogenesis was 7.1 +/- 9.4 and 86.3 +/- 42.5 mu mol/h in controls and patients, respectively.(p <0.01). Production of VLDL did not show a consistent difference between the groups, but conversion of VLDL into intermediate density lipoproteins was relatively retarded in all patients (0.6 +/- 0.5 pools/d) compared with controls (4.3 +/- 1.8 pools/d). Fractional catabolic rate of intermediate density lipoproteins was lower in patients (0.8 +/- 0.6 pools/d) compared with controls (3.1 +/- 1.5 pools/d). Whole body lipolysis was similar, i.e., 4.5 +/- 1.9 mu mol/kg/min in patients and 3.8 +/- 1.9 mu mol/kg/min in controls. Hyperlipidemia in GSD-1a is associated with strongly increased lipid production and a slower relative conversion of VLDL to LDL.