Several animal and human studies have reported reduced PACAP levels, altered PACAP receptor expression, and the beneficial effect of PACAP on cognition and memory in conditions associated with cognitive deficits, such as aging, Alzheimer’s, Parkinson’s, and Huntington’s disease, schizophrenia, and fragile X syndrome [77,78]. The gene discussed is ADCYAP1; the disease is Parkinsonism.