Cholinotrophic basal forebrain connectome dysfunction in Down syndrome with and without dementia.

Cholinotrophic basal forebrain (CTBF) neurons depend upon the complex interaction of both upstream and downstream nerve growth factor (NGF) signaling pathways for survival and function. Although dysfunction of the NGF system occurs in both Down syndrome (DS), not all individuals with DS develop dementia. Whether NGF system dysregulation differs between demented individuals with DS (DSD+) versus those without dementia (DSD-) is unknown. Here, we report a significant reduction in neurons positive for the p75(NTR) within the nucleus basalis of Meynert in DSD+, but not DSD-, compared to aged-matched controls (AMC). ChAT positive cells were significantly lower in DSD+ compared to DSD- and AMC cases. FC levels of p75(NTR) and proNGF were increased, while ChAT levels decreased in DSD+ compared to AMC. A greater number of AT8 tau positive neuropil threads and Thioflavin-S labeled neurofibrillary tangles were found in DSD+. These findings suggest a greater role for p75(NTR)/proNGF in demented in individuals with DS compared to those with dementia. The factors that underlie cognitive resilience in DSD- remains to be determined.