Stable isotope dilution analysis of galactitol in amniotic fluid: An accurate approach to the prenatal diagnosis of galactosemia

A stable isotope dilution assay for galactitol, in amniotic fluid has been developed using selected ion monitoring chemical ionization gas chromatography-mass spectrometry of the hexaacetate derivative. [1,1-2H2]Galactitol was synthesized for use as the internal standard. Galactitol is a component of normal amniotic fluid with a mean concentration of 0.70 ± 0.18 μmol/liter (n = 5). The amniotic fluid of a fetus with galactosemia had a concentration of 7.96 μmol/liter. Mannitol, sorbitol, and inositol were also found to be normal constituents of amniotic fluid. This stable isotope dilution assay is a rapid accurate method for measurement of galactitol in amniotic fluid for prenatal diagnosis of galactosemia.