HOMER1 and early-onset autosomal dominant Alzheimer disease: As SYN (synaptophysin), Homer, and NMDAR (N-methyl-D-aspartic acid receptor) are all important presynaptic (SYN) or postsynaptic (Homer and NMDAR) proteins involved in synaptic plasticity and closely related to cognition, it has been reported that hippocampal SYN and NMDAR1 expressions were downregulated in diabetic rats or AD (Alzheimer's disease) mice [5–8].