The levels of the enzyme that catalyze the synthesis of acetylcholine (ACh) and choline acetyltransferase (ChAT) and of the enzymes that degrade ACh (i.e., acetylcholinesterase (AChE)), the vesicular acetylcholine transporter (VAChT) that transports ACh into the vesicles of mAChR and nAChR, are lower in AD and DS than in the normal population. This evidence concerns the gene ACHE and Alzheimer disease.