Decreased γ-aminobutyric acid levels in the parietal region of patients with Alzheimer's disease

Purpose To determine whether there are in vivo differences of γ-aminobutyric acid (GABA) levels in frontal and parietal regions of Alzheimer's disease (AD) patients, compared with healthy controls using magnetic resonance spectroscopy (¹H-MRS). Materials and Methods Fifteen AD patients and fifteen age- and gender-matched healthy controls underwent ¹H-MRS of the frontal and parietal lobes using the "MEGA-Point Resolved Spectroscopy Sequence" (MEGA-PRESS) technique, and cognitive levels of subjects were evaluated using Mini-Mental State Examination (MMSE) tests. MRS data were processed using the Gannet program. Because the signal detected by MEGA-PRESS includes contributions from GABA, macromolecules and homocarnosine, it is labeled as "GABA+" rather than GABA. Differences of GABA+/Cr ratios between AD patients and controls were tested using covariance analysis, adjusting for gray matter fraction. The relationship between GABA+/Cr and MMSE scores was also analyzed. Results Significant lower GABA+/Cr ratios were found in the parietal region of AD patients compared with controls (P=0.041). In AD patients, no significant correlations between GABA+/Cr and MMSE scores were found in either the frontal (r=-0.164; P=0.558) or parietal regions (r=0.025; P=0.929). Conclusion Decreased GABA+/Cr levels were present in the parietal region of patients with AD in vivo, suggesting that abnormalities of the GABAergic system may be present in the pathogenesis of AD. J. Magn. Reson. Imaging 2015;41:1326-1331.