Molecular Defects of Vitamin B6 Metabolism Associated with Neonatal Epileptic Encephalopathy

Neonatal epileptic encephalopathy (NEE) is a seizure disorder that occurs within hours from birth and arises from central nervous system (CNS) dysfunctions of various origins, including metabolic or inflammatory conditions, abnormalities of brain structure and cerebrovascular diseases. In some rare circumstances, NEE is refractory to conventional antiepileptic drugs (AEDs) but responds very well to treatment with vitamin B6 in the form of either pyridoxine (PN) or pyridoxal 5’-phosphate (PLP). Vitamin B6-dependent NEE derives either from a deficiency of PLP, from inborn errors in enzymes, such as pyridoxine 5’-phosphate oxidase (PNPOx) and pyridoxal kinase (PL kinase) involved in the PLP salvage pathway or from inherited mutations of enzymes, such as -aminoadipic semialdehyde dehydrogenase (also known as antiquitin) involved in other metabolic pathways, which lead to the accumulation of intermediates that react with PLP, reducing its availability. Clinical phenotypes observed in vitamin B6-dependent NEE patients may include fetal distress, hypoglycemia, acidosis, anemia, and asphyxia. The health state of untreated patients may undergo progressive deterioration, which can lead to death within weeks. Surviving children are usually mentally retarded and are dependent on vitamin B6 to control the disease. Several known cases of B-dependent NEE, however do not or only mildly manifest some of the above clinical features, and are characterized by mild to moderate developmental delay. This chapter will review the molecular mechanism of how in-born errors in PNPOx or antiquitin affect PLP levels in the cell and lead to NEE. We will also review important clinical and general features associated with PLP dependent NEE, and provide some directions for clinicians to diagnose and treat or manage the disease