The Relevance of Vitamin B6 Plasma Profiles in the Diagnostic Work-up of Early Infantile Epileptic Encephalopathies
Background: To date, we know of five inborn errors of metabolism, that manifest with vitamin B6 responsive seizures. These defects lead to cerebral or systemic deficiency of pyridoxal 5′-phosphate (PLP) via reduced synthesis or secondary inactivation of PLP and therapy-resistant seizures. Thereby, the vitamin B6 profile in plasma can provide important information and be helpful in the therapeutic monitoring.
Methods: In our laboratory, we have established a sensitive Liquid Chromatography-Mass Spectrometry-Mass Spectrometry (LC-MS-MS) method for the analysis of all vitamin B6 vitamers (PLP, pyridoxal (PL), pyridoxamine (PM), pyridoxine, and pyridoxic acid (PA) in different body fluids. We analyzed the plasma samples of 4 patients with molecularly proven antiquitin deficiency, 1 patient with phosphate oxidase (PNPO) deficiency, both under high dose pyridoxine therapy, and samples of 50 patients with epileptic encephalopathy of unclear etiology, 2 of whom were on high-dose pyridoxine therapy. In each case, 1.5 mL of ethylenediamine tetra-acetic acid blood was drawn at our clinic, immediately light protected, centrifuged within 30 minutes and stored at −80 degrees until analysis.
Results: Patients with antiquitin deficiency did not show a specific vitamer profile, aside from very high absolute concentrations of PLP, PL, and PA. In contrast, the single patient with PNPO deficiency had a clearly distinct vitamer profile with elevated PM. Of the 50 patients with epileptic encephalopathy of unclear etiology, none had decreased PLP levels, despite multidrug therapy in the majority of patients. The two patients on high-dose pyridoxine therapy had profiles that were indistinguishable from antiquitin deficiency.
Conclusions: Our findings confirm preliminary observations that the plasma B6 vitamer profile may be a diagnostic clue to PNPO deficiency, which otherwise lacks a specific biomarker. For antiquitin deficiency measurement of α-aminoadipic semialdehyde and pipecolic acid remain reliable biomarkers. In contrast to findings in adults, our cohort of pediatric epilepsy patients had normal plasma PLP concentrations.