In the hippocampus of 3xTg-AD mice, a model of combined amyloidosis and tauopathy, elevated SERT immunoreactivity has been observed by 3 months of age, i.e., prior to the manifestation of amyloid-β (Aβ)-induced memory impairment or the deposition of plaques [11, 12]. The gene discussed is SLC6A4; the disease is Alzheimer disease.