NTNG1 and Alzheimer disease: We hypothesize that the increased abundance of Ntng1 highly expressed C3.1 excitatory neurons is a rapid response of the hippocampus to protect neurons from neurodegenerative damages at the onset stage of AD or under other neurodegenerative initiation stages because the positive terms of AD progression are downregulated in C3.1 excitatory neurons at the very early stage in AD mice.