Abstract: Objective To evaluate the efficacy of oral protein tolerance test in the diagnosis and treatment of a case of hyperinsulinism/hyperammonaemia syndrome. Methods Clinical features of a boy with hyperinsulinism/hyperammonaemia syndrome were reported.Result The boy developed hypoglycemia induced by hyperinsulinism after eating proteinaceous test meal in combination with hyperammoniemia. Direct DNA sequence analysis revealed the heterozygous mutation c.978G>A(R269H) in exon 7 of the GDH gene compared to the nomal gene. The oral protein tolerance test was positive and a test was designed to choose a proper ratio between carbohydrate and protein. It revealed that the combination of protein and carbohydrate could be helpful to avoid hypoglycemia. Follow-up showed that dietary and diazoxide therapy could be a useful method to treat it. Conclusions Oral protein tolerance test is a helpful method in the diagnosis of hyperinsulinism/hyperammonaemia syndrome. And as a basic treatment, dietary therapy could effectively control the symptom.

Key words: Hyperinsulinism/hyperammonaemia syndrome, hypoglycemia, oral protein tolerance