Disorders of pyridoxine metabolism

Disorders of pyridoxine metabolism include pyridoxine-dependent epilepsy (PDE) due to antiquitin (ATQ) deficiency, PDE due to abnormalities in pyridoxal 5'-phosphate (PLP) homeostasis protein (PLPHP deficiency, a PLP-responsive epileptic encephalopathy due to a deficiency of pyridox(am)ine 5'-phosphate oxidase (PNPO deficiency), and tissue nonspecific isoenzyme of alkaline phosphatase deficiency. This chapter focuses primarily on ATQ deficiency, which is the most studied cause of autosomal recessive PDE and is characterized by early onset epileptic encephalopathy resistant to antiepileptic medications but responsive to pharmacologic dosages of pyridoxine, which is a lifelong requirement. ATQ, an aldehyde dehydrogenase in the lysine degradation pathway, is encoded by the ALDH7A1 gene. ATQ deficiency results in accumulation of α-aminoadipic semialdehyde (αAASA), piperideine-6-carboxylate (P6C), and pipecolic acid, which serve as diagnostic markers in urine, plasma, and CSF. Elevated αAASA/P6C and at least one pathogenic variant in ALDH7A1 are required for diagnostic confirmation. Unless pyridoxine monotherapy provides complete symptom resolution with cessation of seizures and the establishment of normal behavior and development, lysine restriction and/or arginine supplementation should be considered as adjunct therapies for all patients with ATQ deficiency.

Duke Scholars

Author Sidney M. Gospe Jr. Pediatrics, Neurology