Quantification of the neurotoxin 2-amino-3-(methylamino)-propanoic acid (BMAA) in cycadales

Cycads have been recognized as toxic for many years and are known to cause hind limb ataxia in grazing animals. The l-isomer of 2-amino-3-(methylamino)propanoic acid (BMAA; β-methyldiaminopropanonic acid), a constituent of cycads, has recently been implicated in the onset of human neurologic disorders. We have used combined gas chromatography-mass spectrometry (GC-MS) to determine the BMAA content of the leaves (n = 30) and female gametophyte (n = 11) of a variety of cycads. A stable isotopomer of BMAA (i.e. [²H₃] BMAA) was used as an internal standard to optimize specificity and precision. BMAA content is greater in members of the genus Cycas (i.e. up to 1800 μg g^-1 fr. wt) whereas smaller amounts (i.e. < 40 μg g^-1) are present in members of the six other genera tested. Where BMAA content of both leaves and seeds was determined in the same species (n = 4), values were comparable. Based on our results we estimate that grazing animals are exposed to exceedingly low doses of BMAA. These data would tend to exclude BMAA as the etiologic agent in hind limb ataxia in grazing animals.