The results showed that the serum levels of neurofilaments heavy chain and light chain [NfH and NfL, structural elements located in the axon endings of neurons (19)], and neuron-specific enolase [NSE, a neurotropic factor which localize mainly in the cytosol of neuronal cells (20)] increased and the changed levels of these proteins were correlated with insomnia severity and cognition impairment (21). Here, ENO2 is linked to insomnia.