A reduction in pyridoxal-5-phosphate (PLP) dependent enzyme, glutamic acid decarboxylase (GAD),which synthesizes GABA, is reported in a 3 month-old infant with seizures responsive to pyridoxine treated at University of California, Davis. The infant had asynchronous jerking of arms and legs and lip smacking at birth which responded to phenobarbital and phenytoin. MRI showed enlarged ventricles, and the EEG demonstrated bitemporal and left frontal epileptiform activity. Seizures recurred at 7 weeks and were not responsive to phenobarbital and carbamazepine. When admitted at 3 months, 100 mg pyridoxine IV stopped a seizure within 5 minutes. Anticonvulsants were discontinued and electrographic and clinical seizure activity was controlled with oral pyridoxine 25 mg daily. PLP independent GAD activities measured in skin fibroblasts of the patient and 5 controls were similar, whereas the patient’s PLP dependent GAD activity was reduced. [1]
COMMENT. An alteration in the function of PLP dependent GAD appears to be responsible for the autosomal recessive syndrome of pyridoxine dependent epilepsy.