NLGN4X and Alzheimer disease: A PRM method for the simultaneous quantification of four neurexins (NRXN-1α, NRXN-1β, NRXN-2α, and NRXN-3α) and four neuroligins (Nlgn1, Nlgn2, Nlgn3, and Nlgn4) in CSF was developed and used to measure the proteins in a clinical cohort including CSF from controls, MCI, MCI-AD, AD, and a group of non-AD dementia (123).