Two unrelated Chinese patients with hyperinsulinism /hyperammonemia (HI/HA) syndrome due to mutations in glutamate dehydrogenase gene.

BACKGROUND

Hyperinsulinism/ hyperammonemia (HI/HA) syndrome is caused by excessive activity of glutamate dehydrogenase (GDH) encoded by GLUD1 gene, which oxidizes glutamate to alpha-ketoglutarate and which is a potential regulator of insulin secretion in pancreatic beta cells and of ureagenesis in the liver. So GDH is important in normal glucose homeostasis. Mutations of GDH result in HI/ HA syndrome.

METHODS

We have performed protein (leucine) and fat loading test on one patient. We detected the level of serum glucose, insulin and blood ammonia. Genomic DNA of the two patients and their parents is isolated from blood and the exons of GLUD1 gene are amplified by polymerase chain reaction (PCR) for direct sequencing.

RESULTS

The leucine diet can evocate hypoglycemia obviously. Two heterozygous mutations c.978G>A (R269H) and c.1506C>T (S445L) are identified, respectively. These are both de novo. For one patient, a better blood glucose level can be gained from leucine-restriction diet, and without diazoxide while, for the other patient, diazoxide is necessary.

CONCLUSIONS

The heterozygous mutations in GLUD1 gene can cause HI/HA syndrome, it is sensitive to the leucine. The diazoxide and leucine-restriction diet do well in controlling the blood glucose level.