Liver Transplantation in PNPO Deficiency: Management Challenges and Biological Lessons.

Area of Science:

• Biochemistry
• Neurology
• Transplantation

Background:

• Pyridox(am)ine 5' Phosphate Oxidase deficiency (PNPO) causes refractory epilepsy treatable with Vitamin B6 forms.
• A 15-year-old boy with PNPO deficiency and cirrhosis underwent liver transplantation for hepatocellular carcinoma.

Purpose of the Study:

• To monitor and manage Vitamin B6 vitamers, particularly pyridoxal 5' phosphate (PLP), in a PNPO patient post-liver transplantation.
• To investigate the impact of liver transplantation on PLP requirements and identify factors contributing to encephalopathy.

Main Methods:

• Continuous EEG monitoring pre- and post-transplant to detect encephalopathy.
• Assay of B6 vitamers (PN, PM, PL, PNP, PMP, PLP) during encephalopathic episodes and for pharmacokinetics.
• Titration of intravenous (IV) and oral PLP doses to balance efficacy and toxicity.

Main Results:

• Encephalopathy occurred with low plasma PL and high PLP levels, indicating neuronal salvage issues.
• PLP demonstrated dose-dependent hepatotoxicity, necessitating careful dose adjustments.
• Transitioning to oral PLP post-transplant was challenging, requiring gradual increases and frequent dosing over 9 months.
• Six years post-transplant, moderate portal fibrosis was observed, with continued supraphysiologic PLP requirements.

Conclusions:

• Liver transplantation did not eliminate the need for supraphysiologic PLP doses in PNPO deficiency.
• Impaired neuronal PLP salvage is the primary determinant of PLP requirements in PNPO patients.
• Careful PLP dose titration and frequent administration are crucial for managing encephalopathy and minimizing hepatotoxicity.