Abstract
The basic biochemical defect in B6 dependency seizures has not been elucidated, though it has been postulated that brain GAD or perhaps another system may be B6 dependent in such patients. We have examined free amino acids (umoles/gm fresh tissue) and GAD activity in brain from one of the original patients, who died in status epilepticus after not having been given B6 for 3 days. Glutamic acid was increased in frontal (71.8 vs. 47.8 ± 11.9) and occipital lobes (68.0 vs. 48.8 ± 10.1) whereas GABA was decreased (frontal 1.3 vs. 7.4 ± 2.8; occipital 1.1 vs. 10.1 ± 4.0). Cystathionine (cysta) was increased in both frontal (4.4 vs. 2.0 ± 1.6) and occipital (11.3 vs. 3.3 ± 1.4) lobes but cystine was virtually undetectable in both patient and control brains. Frontal lobe GAD activity, as measured by 14CO2 formation from DL-glu (1-14C), was undetectable in the patient without added pyridoxal -5'-PO4, (PLP) as was true in 3 of 4 controls. However, activity was detectable by the addition of as little as .1 uM PLP (30 cpm/mg protein vs. 0-160 in controls) and was enhanced comparable to controls upon further PLP additions (.2-100 uM). Thus GLU and GABA concentrations suggested reduced GAD activity in vivo but no specific B6 dependency could be shown. Cysta increase suggested the possibility of B6 dependent brain cystathionase deficiency.
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Levy, H., Coulombe, J. & Lott, I. BRAIN FREE AMINO ACID CONCENTRATIONS AND L-GLUTAMIC ACID DECARBOXYLASE (GAD) ACTIVITY IN A PATIENT WITH VITAMIN B6 DEPENDENCY SEIZURES. Pediatr Res 8, 434 (1974). https://doi.org/10.1203/00006450-197404000-00567
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DOI: https://doi.org/10.1203/00006450-197404000-00567