Background and aim
Ketotic hypoglycemia (KH) is the most common cause of hypoglycemia in childhood, among non-diabetic children. KH is defined by episodes of hypoglycemia with high ketone levels in plasma and urine, provoked by periods of fasting, often in combination with an intercurrent illness. KH usually begins at 2 or 3 of age and it typically spontaneously remits by the age of 8 or 9.
The pathophysiology of KH has not been fully understood. However, studies have suggested that the glycogenolytic and gluconeogenic pathways are intact. Some even postulate that KH is not a true disease but represents the lower tail of the Gaussian distribution of fasting tolerance in children.
The hypothesis of this masters project is that polymorphic variations of a gene involved in the glucose homeostasis could be the cause of KH. In this master project, we have a particular interest for the PDK4 (pyruvate dehydrogenase kinase isoenzym 4) gene, located on the chromosome 7.
The mitochondrial pyruvate dehydrogenase complex (PDC) catalyses the conversion of pyruvate to acetyl-CoA. Its activity is regulated by the pyruvate dehydrogenase kinases (PDKs), which phosphorylate and inactivate the PDC, and the pyruvate dehydrogenase phosphatases (PDPs), which dephosphorylate and activate the PDC. In the starved state, the PDC is inactivated to maintain glucose levels by conserving substrate for gluconeogenesis. Studies have identified four PDK isoforms: PDK1, PDK2, PDK3 and PDK4.
PDK4 is found in heart, skeletal muscle, liver, kidney and the pancreatic islet. All these tissues ar involved in glucose homeostasis: high rates of glucose utilization, glucose production or production of glucoregulatory hormones. The expression of PDK4 is increased in response to starvation. Moreover, studies have shown that blood glucose levels are lower in PDK4 ¯/¯ mice than in wild type, suggesting that PDK4 is important for glucose homeostasis. That is why PDK4 gene has been chosen to be sequenced to look for any polymorphic variations that could be the basis of KH.
Methods
To study the PDK4 gene, we have collected DNA samples from ten patients with previous episodes of KH. Written informed consent was obtained from all participating individuals. The study has been approved by the ethics committee of the CHUV.
We will perform PCR amplification of all 11 exons and sequence the whole open reading frame. Depending on the results, we will have to evaluate possible polymorphisms versus pathogenic changes.