“…Increased plasma levels of p75 receptor protein are reported in first-episode psychosis patients compared to clinical high-risk individuals and controls ( He et al, 2019 ), with higher ratios of p75/TrkB protein found in serum of first-episode psychosis patients compared to unaffected siblings and controls ( Yesilkaya et al, 2022 ), reflecting a trophic imbalance preceding diagnosis and treatment that may favour apoptotic functions of the receptor. Whilst plasma p75 protein levels were found to positively correlate with positive and negative symptom scores in schizophrenia ( Zakowicz et al, 2023 ), other studies report no changes in p75 protein in the plasma of schizophrenia patients compared to controls ( Haack et al, 1999 ; Yesilkaya et al, 2022 ), with some reporting lower serum levels of p75 receptor protein ( Zakharyan et al, 2014 ; Chen et al, 2017 ; Turhan et al, 2016 ). A potential contributor to the heterogeneous results of studies assessing peripheral p75 receptor expression in schizophrenia is the prevalence of single nucleotide polymorphisms (SNPs) of the p75 receptor evident in patients.…”