Combined method for the determination of gamma-aminobutyric and beta-alanine in cerebrospinal fluid by stable isotope dilution mass spectrometry.

A previously described method for the determination of GABA in CSF has been expanded to include both GABA and beta-ALA, using a single GC-MS analysis. A stable isotope labelled internal standard for beta-ALA was synthesised to achieve accurate quantification. This new combined method expands the diagnostic power compared to an isolated GABA measurement. Control values for free and total GABA and free and total beta-ALA are described. Age <2 years: free GABA 0.017-0.067 microM, total GABA 4.2-13.4 microM; free beta-ALA 0.049-0.11 microM, total beta-ALA 2.1-4.6 microM. Age >2 years: free GABA 0.032-0.17 microM, total GABA 3.3-12.2 microM; free beta-ALA 0.021-0.058 microM, total beta-ALA 0.91-3.5 microM.