Pyridox(am)ine 5′-phosphate oxidase (PNPO) deficiency in zebrafish results in fatal seizures and metabolic aberrations



• PNPO deficient zebrafish (Danio rerio) and HEK293 cell line were generated using CRISPR/Cas9 gene editing technology.
• PNPO deficiency resulted in strong shortening of the survival and in development of fatal spontaneous seizures.
• PLP treatment increased survival and normalized PLP, pyridoxal, 4-pyridoxic acid, GABA, glutamate and glycine levels.
• PLP treatment did not prevent accumulation of pyridoxamine, pyridoxamine 5’-phosphate and several essential amino acids.
• Accumulation of pyridoxamine 5’-phosphate may play a role in the residual clinical phenotype of PNPO deficiency.



Pyridox(am)ine 5′-phosphate oxidase (PNPO) catalyzes oxidation of pyridoxine 5′-phosphate (PNP) and pyridoxamine 5′-phosphate (PMP) to pyridoxal 5′-phosphate (PLP), the active form of vitamin B6. PNPO deficiency results in neonatal/infantile seizures and neurodevelopmental delay. To gain insight into this disorder we generated Pnpo deficient (pnpo−/−) zebrafish (CRISPR/Cas9 gene editing). Locomotion analysis showed that pnpo−/− zebrafish develop seizures resulting in only 38% of pnpo−/− zebrafish surviving beyond 20 days post fertilization (dpf). The age of seizure onset varied and survival after the onset was brief. Biochemical profiling at 20 dpf revealed a reduction of PLP and pyridoxal (PL) and accumulation of PMP and pyridoxamine (PM). Amino acids involved in neurotransmission including glutamate, γ-aminobutyric acid (GABA) and glycine were decreased. Concentrations of several, mostly essential, amino acids were increased in pnpo−/− zebrafish suggesting impaired activity of PLP-dependent transaminases involved in their degradation. PLP treatment increased survival at 20 dpf and led to complete normalization of PLP, PL, glutamate, GABA and glycine. However, amino acid profiles only partially normalized and accumulation of PMP and PM persisted. Taken together, our data indicate that not only decreased PLP but also accumulation of PMP may play a role in the clinical phenotype of PNPO deficiency.


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