GAD1 and Alzheimer disease: Reduced expression of vesicular glutamate transporter (VGLUT) 1 and VGLUT2 has been observed in prefrontal regions of AD patients, correlating with cognitive decline36 and reduced Gad1 (encoding for the glutamate decarboxylase 1 protein) expression has previously been observed in the prefrontal cortex of AD patients35, which inevitably disrupts the glutamate-glycine-GABA cycle.