Prospective study of nesidioblastosis in newborns and infants: hypoglycemic seizures, epileptogenesis and the significance of the C-peptide suppression test in pancreatectomy

Central nervous system hyperexcitability associated with glutamate dehydrogenase gain of function mutations

OBJECTIVE

To describe seizure phenotypes associated with the hyperinsulinism/hyperammonemia syndrome (HI/HA), which is caused by gain of function mutations in the enzyme glutamate dehydrogenase (GDH).

STUDY DESIGN

A retrospective review of records of 14 patients with HI/HA.

RESULTS

Nine patients had seizures as the first symptom of HI/HA, and six had seizures in the absence of hypoglycemia. No electroencephalogram (EEG) background abnormalities were identified. In four patients, EEG recordings during seizures in the setting of normal blood glucose contained generalized epileptiform discharges. EEGs of three of these patients showed 0.5- to 2-second generalized irregular spike-and-wave discharge at 3 to 6 Hz corresponding to eye blinks, eye rolling, or staring. The EEG of the fourth patient consisted of 20 seconds of generalized regular spike-and-wave discharge at 3 Hz in the clinical context of staring and unresponsiveness. In two patients, seizure control worsened with carbamezapine or oxcarbezapine treatment.

CONCLUSIONS

In patients with HI/HA, generalized seizures are common and can occur in the absence of hypoglycemia. The drugs carbamazepine and oxcarbazepine should be used with caution for treatment. Pathogenesis of epilepsy in these patients may be related to effects of GDH mutations in the brain, perhaps in combination with effects of recurrent hypoglycemia and chronic hyperammonemia.

Persistent hyperinsulinemic hypoglycaemia followed as benign infantile convulsion

An 18-month-old boy developed seizures at 3 months of age. He developed normally and, his EEG and brain CT revealed no abnormal findings. The blood sugar level was normal at that time, thus he was diagnosed as having benign infantile convulsion. At 7 months of age seizures reappeared, and hypoglycaemia associated with hyperinsulinism was observed during the seizures. With conservative therapy his blood sugar level was well controlled and he had no further seizures. Hypoglycaemic seizures are sometimes misdiagnosed as epilepsy. We have to pay attention to hyperinsulinemic hypoglycaemia when we see seizures with normal EEG even in infants.