Vitamin B deficiency with normal plasma levels of pyridoxal 5'-phosphate in perinatal hypophosphatasia.

Pyridoxal 5'-phosphate (PLP), the principal circulating form of vitamin B (B), is elevated in the plasma of individuals with hypophosphatasia (HPP). HPP is the inborn-error-of-metabolism caused by loss-of-function mutation(s) of ALPL, the gene that encodes the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP). PLP accumulates extracellularly in HPP because it is a natural substrate of this cell-surface phosphomonoester phosphohydrolase.