Schizophrenia (SCZ) is a common and severe mental disorder, with a lifetime prevalence estimate of 4.0 (1.6–12.1) per 1,000 persons and a median incidence of 15.2 per 100,000 individuals [1, 2]. The disease is characterized by positive and negative symptoms, including abnormalities in cognitive function and personality, such as language, thought, perception, emotion, and self-awareness. Despite the wide prevalence of SCZ and many decades of major progress, the underlying etiology of this disease remains elusive.
In contemporary practice, clinicians still diagnose clinical symptoms and evaluate progress and treatment responses based on clinical symptoms. The development of objective tests for the diagnosis of SCZ or monitoring of drug reactions is essential to providing early intervention for patients, which is beneficial for improving prognosis. In addition, several studies have shown that gene expression causes changes in different tissues of patients with SCZ [3-8]. The cystine/glutamate antiporter system xc- is a potential target for the treatment of SCZ, which releases glutamate into synapses and thus increases glutaminergic neurotransmission [9, 10]. A human study also showed that the peripheral expression of mRNA of the two subunits of system xc-, solute carrier 3A2(SLC3A2) and solute carrier 7A11(SLC7A11), was lower in SCZ than healthy individuals [11]. Since the detection of mRNA in peripheral whole blood is accessible and non-invasive, the pattern of gene expression serves as a potential biomarker for SCZ diagnosis and therapeutic monitoring [12].
The RELN gene is located on chromosome 7q22, and it encodes the protein reelin, a large extracellular matrix glycoprotein that plays a key role in brain development from neuronal migration to dendritic spine formation and synaptic transmission [13-15]. Moreover, it may be involved in memory formation, neurotransmission, and synaptic plasticity [16, 17], as well as SCZ [18]. The earliest direct evidence was based on the postmortem studies of patients with SCZ, which revealed that RELN mRNA was reduced up to 50% in several regions of the brain [19, 20]. Additionally, RELN had been shown to be expressed in organ systems, inter alia in human blood, liver, pancreas, mamma and intestines [21-23]. A recent study determined that the patients with SCZ had higher level of RELN gene methylation compared to healthy controls, leading to a subsequent 25-fold decrease in RELN expression in the methylated group [24]. The role of RELN was associated with SCZ in an earlier large genome-wide association study (GWAS), which found that the polymorphism rs7341475 accounted for a 1.4-fold increase in the risk of the disease in women [25]. Moreover, this gene variant was associated with working memory, episodic memory, and executive functioning in the nuclear families of one member with SCZ [26]. Subsequently, a growing number of studies have reported that a number of single nucleotide polymorphisms (SNPs) in the RELN gene were associated with the pathogenesis and/or severity of clinical symptoms of SCZ [27-34]. Hence, based on the low level of RELN in SCZ patients and the relationship between its genetic variation and SCZ, RELN may play a pathogenic role in SCZ [35]. This view was further supported by heterozygous reelin mouse model. Although the mice had fewer neuroanatomical defects, they had cognitive abnormalities of some common psychotic disorders [36].
In studies on SCZ, the healthy controls were not treated with antipsychotic drugs, whereas patients with SCZ were often treated with these drugs. It is important to determine whether changes in RELN gene expression in these patients are the result of long-term antipsychotic treatment or due to etiological characteristics of SCZ. Suzuki et al. reported that the level of the RELN receptor VLDLR in the peripheral blood lymphocytes of patients with SCZ was decreased. After six months of antipsychotic treatment, the gene expression increased [37]. Another study showed that protracted treatment with olanzapine resulted in the upregulation of RELN expression in the frontal cortex of rats [38, 39]. However, a previous postmortem study showed no correlation between the levels of RELN mRNA and reelin protein and lifetime doses of antipsychotics drugs [20]. Overall, the regulation of RELN in patients with SCZ requires broader research including other typical or atypical antipsychotic treatments.
In this study, we investigated the expression of RELN mRNA in whole blood before and after antipsychotic medication in patients with SCZ to explore the therapeutic value of RELN as a biomarker for SCZ.