A Review of Studies on Ethnic Differences of Brain-Derived Neurotrophic Factor Genes in Patients with Post-Traumatic Stress Disorder

In the regulation of human nervous system, cognitive function and other genes, epigenetics changes the expression of genes after being influenced by the external environment. DNA methylation levels are also different in different ethnic groups, and a large number of studies have shown that post-traumatic stress disorder (PTSD) has a certain genetic predisposition. Through the national differences of PTSD brain-derived neurotrophic factor genes, it not only provides new research directions for the pathogenesis and treatment of 5-HT-related mental diseases, but also provides information and new genetic indicators for forensic personal identification, paternity testing and assessment of mental status. A review studies on the national differences of brain-derived neurotrophic factor genes in patients with post-traumatic stress disorder.


Introduction
The characteristics of the distribution of various ethnic groups in China are: large scattered, small settlements, and mixed living. There are ethnic minorities living in the Han area, and Han people living in ethnic minority areas [1]. This

Post-Traumatic Stress Disorder (PTSD)
In recent years, with the increase of natural disasters, wars, terrorist incidents, etc., research on post-traumatic stress disorder (PTSD) has been increasing. The magnitude 8.0 earthquake that occurred in Wenchuan, Sichuan Province, China on May 12, 2008 has further promoted the attention and research on PTSD.
Post-traumatic stress disorder is a delayed and long-lasting mental disorder caused by unusual, threatening or catastrophic trauma [8]. Its specific symptoms include re-experience, avoidance, and increased alertness following traumatic events. The diagnostic criteria must include a specific number of each of the three types of symptoms: re-experience, avoidance, and increased vigilance [9].
In addition, the definition of the source of PTSD stress has made the necessary major changes based on existing research results. It was confined to an unusual war incident at first, and gradually expanded to withstand major disasters (large earthquakes, shipwrecks, floods, big bangs, mine disasters, fires, terrorist incidents, traffic accidents, etc.), physical attacks, violent sexual assaults, etc. In recent years, clinical psychology has also regarded life-threatening diseases as one of the stressors that cause PTSD, such as cancer. Many medical events such as surgery, maternal production, abortion, etc. can also lead to PTSD. The concept of stressors now extends to special occupations, emotional crises, criminal offences, etc. [10]. Epidemiological survey results show that wars, terrorist attacks,

Brain-Derived Neurotrophic Factor (BDNF)
Animal experiments and neurobiochemistry, neuroendocrine and other studies have suggested that BDNF may be related to the occurrence of PTSD, and may also participate in the occurrence of PTSD. First, existing studies have shown that BDNF is involved in the pathogenesis of a variety of mental disorders, and PTSD has a certain degree of commonality with regard to pathogenesis, clinical manifestations and genetic susceptibility [12]. Second, BDNF is expected to become a new target for prognosis and gene therapy for a variety of mental illnesses and brain trauma [13]. DNF is the most abundant neurotrophic factor in the body. Its expression is mainly located in the cerebral cortex, hippocampus, striatum, etc. It plays an important role in brain development, can affect the axial growth and connection of neurons, and mediate the proliferation of neurons, differentiation and survival [14]. Overexpression in the central nervous system plays an important role in promoting anxiety [15]. In the central nervous system, BDNF is mainly synthesized in neurons, transported by antegrade axoplasmic to axon terminals, and released by high-affinity receptor tyrosine protein kinase B (TrkB) to target cells. In addition, BDNF can also be secreted by target were widely distributed in the rat brain, especially in the hippocampus, thalamus striatum and cortex. In the hippocampus, BDNF mRNA content is 20 -30 times higher than NGF mRNA. In the peripheral nervous system, more BDNF appeared in the distal part of the nerve ending after nerve injury. In the ovary, heart, lung, and skeletal muscles other than nerve tissue, BDNF is also expressed in a small amount. BDNF is highly abundant in human plasma, while BDNF in whole blood is localized in platelets, but the source of BDNF in platelets is unclear. Due to the high content of BDNF in the blood, studies on the repair and regeneration of peripheral nervous system by BDNF have been focused. Some areas with weak blood-brain barriers such as the hypothalamus may have BDNF through the blood-brain barrier, so the mutual sensibility of peripheral blood and nerve center BDNF is not excluded. It is necessary to explore whether the change of BDNF content in peripheral blood can be used as a direct indicator of anti-psychiatric diseases.
Mayfair measured the microRNA content of brain cells treated with BDNF and compared it with microRNA content in neurons that were not stimulated with BDNF [16]. The researchers found that the level of certain microRNAs decreased after administration of BDNF to brain cells. This result suggests that BDNF regulates the levels of these microRNAs, which in turn affects protein production. BDNF has a wide and important role in the growth, development, differentiation, regeneration and functional maintenance of various types of neurons, and is essential for regulating hippocampal synaptic plasticity and memory. Clinically, it is found that the fear memory of patients with PTSD is difficult to subside or the fear memory has gradually reappeared, suggesting that fear memory regression can be the key to the occurrence and treatment of PTSD.
The research on the mechanism of fear memory regression needs to be further studied. The hippocampus is an important brain region for learning and memo- found that three SNPs of BDNF gene (G-712A, C270T, Val66Met) were associated with susceptibility to PTSD in a small sample of PTSD patients [24]. In other studies of mental illness, animal experiments found that BDNF gene protein levels and mRNA levels were reduced in depressive model rats, while long-term electroconvulsive therapy increased BDNF gene protein expression in hippocampus and frontal cortex [25]. Autopsy studies found that the expression of BDNF in the hippocampus of patients with PTSD was significantly lower than that of the normal control group, while the expression of BDNF in the dentate gyrus of patients who had received antidepressant treatment was significantly higher than that of the untreated patients [26]. It has been reported that the se-  [31]. At present, it is preliminarily speculated that BDNF is a candidate gene for psychiatric diseases such as PTSD and schizophrenia, but there are reports of inconsistent correlation results. The frequency of distribution of BDNF gene (C270T) C/T, T/T genotype and T allele frequency in children with schizophrenia were significantly higher than those in the control group. One of the main reasons for the inconsistency of the above findings may be the heterogeneity of schizophrenia [32]. Studies by Yuichiro Watanabe and others have shown associations between the T allele and schizophrenia [33].
Therefore, the correlation between BDNF gene polymorphism and PTSD requires a more in-depth analysis of expression levels, and requires a larger sample size and other regional and ethnic basic data to be confirmed in different ethnic groups, regions and populations. The results indicate a link between 5-HTTLPR genotype and PTSD diagnosis in NHB veterans [34]. but this effect may be specific anxiety arousal and re-experience symptoms [36].

BDNF Gene Expression of PTSD
MJ Telch et al. measured 5-HTTLPR, a biomarker that is susceptible to stress in war zones, which is essential for developing more effective treatment and prevention strategies for soldiers and civilians exposed to trauma [37]. These data suggest that the 5-HTTLPR genotype can modulate individual sensitivity to war zone stressors and expression of mood disorders, including PTSD symptoms.
This association of replication, as well as the identification of other risk genetic regulators, can drive the development of biomarkers that can predict relative elasticity and vulnerability to stress. Haixia Long's findings suggest that there are differences between Caucasian and Han subjects in the association between different forms of 5-HTTLPR and DMN (brain default state network) functional connections [38]. Noskova et al. found that racial differences in the allele frequency of 5-HTTLPR exist between Caucasians and Asians [39]. The study in-

National Differences in Brain-Derived Neurotrophic Factor Genes in Patients with Post-Traumatic Stress Disorder
The have shown that BDNF is a molecular marker of serotonin neurons in the central nervous system, which promotes the regeneration of neurons, and the two molecules interact at the molecular level. Therefore, the relevance of BDNF and PTSD needs to be further studied.

Outlook and Conclusion
Genetic imprinting is a category of epigenetics (

Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this paper.