Gautschi M 1 , Christ E 2 , Salvisberg C 1 , Zürcher T 1 , Schütz B 1 , Nuoffer JM 3 1 Interdiscipl Metab Unit, Univ Child Hosp, Bern, Switzerland 2 Div Endocrinology, University Hospital, Bern, Switzerland 3 Institute Clin Chem, University Hospital, Bern, Switzerland Dyslipidemia, with increased triglycerides (TG) and cholesterol (total [TC], VLDL-more than LDL-C, but decreased HDL-C), is a typical biochemical finding in glycogen storage disease type 1 (GSD1a). Intriguingly, this dyslipidemia is not associated with increased cardiovascular morbidity and mortality. We describe a 15-year-old female patient with a GSD1a chronically difficult to manage, whose blood lipids increased massively at puberty, with TG up to 29 mmol/L and TC up to 13 mmol/L. For the last 18 months, she has been repeatedly hospitalized for episodes of acute abdominal pain with nausea and vomiting; but no biological signs of pancreatitis, the much feared complication of massive hypertriglyceridemia, nor of any other underlying cause were found. Various therapeutic trials, including optimizing continuous glucose uptake, supplementation with medium chain triglycerides, or omega fatty acids, improved the clinical picture and the lipid profile only transitorily. PPARγ agonists have been suggested to act positively on lipid metabolism in this context. We have used pioglitazone (Actos.) and studied its impact on both glucose and lipid homeostasis in our patient: TG were reduced by 40%, TC by 25%, compared to baseline. Changes were also observed in adiponectin and insulin levels (and HOMA), whereas glycemia remained stable. Considering the essential role of vitamin D in bone homeostasis and the prevalence of hypovitaminosis D in our GSD I patients, we suggest to routinary evaluate this parameter in all patients.