Pyridoxine-dependent epilepsy-PLPBP (PDE-PLPBP) or PLP binding protein deficiency is caused by a recessive mutation resulting in pathogenic variants of PLPBP. Inefficacy and deficiency of this enzyme are manifested by encephalopathy with early-onset intractable seizures responsive to pyridoxine and/or PLP. The gene discussed is PLPBP; the disease is protein S deficiency.