PEPCK1 deficiency is a rare inborn error of metabolism disorder, characterized by the deficiency of the enzyme PEPCK1, one of the enzymes needed for gluconeogenesis, the process by which organisms produce sugars (namely glucose) from non-carbohydrate precursors (such as amino acids). The symptoms described in the few cases reported in the medical literature suggest that there may be variation in the severity of the symptoms ranging from severe early-onset cases, to milder late-onset presentations. In severe cases symptoms may include persistent and very low levels of blood's sugar in newborns (neonatal hypoglycemia), failure to thrive, build-up of lactic acid in the blood (lactic acidosis), liver enlargement (hepatomegaly) and liver failure leading to neurological degeneration. Milder cases present during childhood with fewer and less serious liver problems. Infections and fasting may trigger the symptoms. PEPCK1 deficiency inheritance is autosomal recessive. It is caused by mutations in the PEPCK1 gene. Some researchers believe that the severity of the disease depend upon the mutations resulting in less or more PEPCK1 activity (the more active the enzyme is, the less severe the disease is, and vice versa). Treatment depend on the symptoms and may include giving extra carbohydrates during heavy exercise and illness or other times of fasting (formal sick day regimen) by the dietitian.PEPCK1 is the cytosolic form of the phosphoenolpyruvate carboxykinase (PEPCK) enzyme, the other being the mitochondrial (PEPCK2). The disease is phosphoenolpyruvate carboxykinase deficiency, cytosolic (MONDO_0009866).