Clinical Information

Vitamin B6 is a generic term that refers to the pyridine-based compounds pyridoxine, 4-pyridoxic acid (PA), pyridoxamine, pyridoxal, and their phosphorylated derivatives. Pyridoxal-5'-phosphate (PLP) is the biologically active form and serves as a cofactor for more than 140 different enzymatic reactions, representing 4% of all known catalytic activity. Deficiencies can occur in individuals with genetic variants of pyridoxal kinase (PLXK) or PLP oxidase (PNPO), as well as in individuals who are pregnant, have kidney disease, are severely malnourished, or have malabsorption syndromes. Additionally, deficiencies have been observed with the usage of certain drugs such as isoniazid, penicillamine, benserazide, and carbidopa. Vitamin B6 deficiency is a potential cause of burning mouth syndrome and a possible potentiating factor for carpal tunnel and tarsal tunnel syndromes. Persons who present chronic, progressive nerve compression disorders may be deficient in vitamin B6 and should be evaluated. Vitamin B6 deficiency is associated with symptoms of scaling of the skin, severe gingivitis, irritability, weakness, depression, dizziness, peripheral neuropathy, and seizures. In the pediatric population, deficiencies have been characterized by diarrhea, anemia, and seizures. Conversely, exceptionally high levels of vitamin B6 can also have toxic effects resulting in sensory and motor neuropathies. Markedly elevated PLP in conjunction with low or normal levels of pyridoxic acid are observed in cases of hypophosphatasia, a disorder caused by loss-of-function variants in ALPL, which encodes the tissue-nonspecific isoenzyme of alkaline phosphatase.