NRXN1 and Alzheimer disease: Although CSF levels of VGF, a neuronal and neurosecretory protein, might be anticipated to decrease coincident with neuronal loss as AD progresses, CSF levels of several related neurosecretory and synaptic proteins, including chromogranin A, secretogranin II, 7B2, proSAAS, clusterin, neurexins 1, 2, and 3, and neuropentraxin 1, were either increased or unchanged in patients with AD compared to controls, while VGF levels were consistently reduced18,20.