Maccarrone et al. (2013) analyzed the cerebrospinal fluid protein expression patterns and reported NEGR1 as a highly reliable biomarker for MDD. Protein analysis of male patients with schizophrenia revealed elevated NEGR1 protein levels, suggesting that altered NEGR1 levels may serve as a biological risk marker for a wide spectrum of psychiatric conditions (Karis et al., 2018). This evidence concerns the gene NEGR1 and major depressive disorder.