- Perinatal hypophosphatasia: tissue levels of vitamin B6 are unremarkable despite markedly increased circulating concentrations of pyridoxal-5'-phosphate. Evidence for an ectoenzyme role for tissue-nonspecific alkaline phosphatase. Whyte, M.P., Mahuren, J.D., Fedde, K.N., Cole, F.S., McCabe, E.R., Coburn, S.P. J. Clin. Invest. (1988)