Pyridoxal in the Cerebrospinal Fluid May Be a Better Indicator of Vitamin B6–dependent Epilepsy Than Pyridoxal 5′-Phosphate

We aimed to demonstrate the biochemical characteristics of vitamin B6–dependent epilepsy, with a particular focus on pyridoxal 5′-phosphate and pyridoxal in the cerebrospinal fluid. Using our laboratory database, we identified patients with vitamin B6–dependent epilepsy and extracted their data on the concentrations of pyridoxal 5′-phosphate, pyridoxal, pipecolic acid, α-aminoadipic semialdehyde, and monoamine neurotransmitters. We compared the biochemical characteristics of these patients with those of other epilepsy patients with low pyridoxal 5′-phosphate concentrations. We identified seven patients with pyridoxine-dependent epilepsy caused by an ALDH7A1 gene abnormality, two patients with pyridoxal 5′-phosphate homeostasis protein deficiency, and 28 patients with other epilepsies with low cerebrospinal fluid pyridoxal 5′-phosphate concentrations. Cerebrospinal fluid pyridoxal and pyridoxal 5′-phosphate concentrations were low in patients with vitamin B6–dependent epilepsy but cerebrospinal fluid pyridoxal concentrations were not reduced in most patients with other epilepsies with low cerebrospinal fluid pyridoxal 5′-phosphate concentrations. Increase in 3-O-methyldopa and 5-hydroxytryptophan was demonstrated in some patients with vitamin B6–dependent epilepsy, suggestive of pyridoxal 5′-phosphate deficiency in the brain. Low cerebrospinal fluid pyridoxal concentrations may be a better indicator of pyridoxal 5′-phosphate deficiency in the brain in vitamin B6–dependent epilepsy than low cerebrospinal fluid pyridoxal 5′-phosphate concentrations. This finding is especially helpful in individuals with suspected pyridoxal 5′-phosphate homeostasis protein deficiency, which does not have known biomarkers.