The impact of COMT, BDNF and 5-HTT brain-genes on the development of anorexia nervosa: a systematic review

Association of serotonin receptor gene polymorphisms with anorexia nervosa: a systematic review and meta-analysis

PURPOSE

Several studies have investigated the association between anorexia nervosa and polymorphisms of genes regulating serotonin neurotransmission, with a focus on the rs6311 polymorphism of 5-HTR2A. However, inconsistent results of these studies and conflicting conclusions of existing meta-analyses complicate the understanding of a possible association. We have updated these results and evaluated the involvement of other serotonin receptor gene polymorphisms in anorexia nervosa.

METHODS

Adhering to PRISMA guidelines, we have searched studies on anorexia nervosa and serotonin-regulating genes published from 1997 to 2022, selected those concerning receptor genes and meta-analyzed the results from twenty candidate gene studies on the 5-HTR2A rs6311 polymorphism and the 5-HTR2C rs6318 polymorphism.

RESULTS

Present analyses reveal an association for the 5-HTR2A rs6311 polymorphism, with G and A alleles, across eighteen studies (2049 patients, 2877 controls; A vs. G allele, Odds Ratio = 1.24; 95% Confidence Interval = 1.06-1.47; p = 0.009). However, after geographic subgrouping, an association emerged only in a Southern European area, involving five studies (722 patients, 773 controls; A vs. G allele, Odds Ratio = 1.82; 95% Confidence Interval = 1.41-2.37; p < 0.00001). No association was observed for the 5-HTR2C rs6318 polymorphism across three studies.

CONCLUSIONS

To date, the involvement in the pathophysiology of anorexia nervosa of the 5-HTR2A rs6311 polymorphism appears limited to a specific genetic and/or environmental context, while that of the 5-HTR2C rs6318 polymorphism seems excluded. Genome-wide association studies and epigenetic studies will likely offer deeper insights of genetic and environmental factors possibly contributing to the disorder.

LEVEL OF EVIDENCE

III Evidence obtained from well-designed cohort or case-control analytic studies. Clinical trial registration PROSPERO registration number: CRD42021246122.

The role of the brain-derived neurotrophic factor (BDNF) in anorexia nervosa

The brain-derived neurotrophic factor (BDNF) is a growth factor belonging to the neurotrophin family which plays a pivotal role in the differentiation, survival, and plasticity of neurons in the central nervous system. Evidence suggests that BDNF is an important signal molecule in the regulation of energy balance and thus implicated in body weight control. The discovery of BDNF-expressing neurons in the paraventricular hypothalamus which is important in the regulation of energy intake, physical activity, and thermogenesis gives more evidence to the suggested participation of BDNF in eating behavior. Until now it remains questionable whether BDNF can be used as a reliable biomarker for eating disorders such as anorexia nervosa (AN) as available findings on BDNF levels in patients with AN are ambiguous. AN is an eating disorder characterized by a pathological low body weight in combination with a body image disturbance typically developing during adolescence. A severe drive for thinness leads to restrictive eating behavior often accompanied by physical hyperactivity. During therapeutic weight restoration an increase of BDNF expression levels seems desirable as it might improve neuronal plasticity and survival which is essential for learning processes and thereby essential for the success of the psychotherapeutic treatment of patients. On the contrary, the well-known anorexigenic effect of BDNF might favor relapse in patients as soon as the BDNF levels significantly increase during weight rehabilitation. The present review summarizes the association between BDNF and general eating behavior and especially focuses on the eating disorder AN. In this regard findings from preclinical AN studies (activity-based anorexia model) are outlined as well.

Hypermethylation of the serotonin transporter gene and paternal parenting styles in untreated anorexia nervosa patients: A pilot study

Purpose

It has been reported that serotonergic systems and parenting styles are involved in the pathogenesis of anorexia nervosa (AN). The present study made attempts to examine the DNA methylation profiles in the promoter region of serotonin transporter (5-HTT) encoding gene SLC6A4, and explore the association between the methylation level and severity of symptoms, 5-HTT linked polymorphic region (5-HTTLPR) genotypes and parenting styles in untreated Chinese Han AN patients.

Methods

Ninety-one untreated female AN patients (ANs) and eighty-seven matched healthy controls (HCs) were analyzed for DNA methylation status at CpG islands in the promoter region of SLC6A4 using MassARRY EpiTYPER, and genotypes of 5-HTTLPR using PCR-RFLP. The severity of eating disorder (ED) symptoms was evaluated by body mass index (BMI) and Questionnaire Version of the Eating Disorders Examination (EDE-Q 6.0), and part of participants were assessed parenting styles using the short Chinese Egna Minnen av Barndoms Uppfostra (s-EMBU-C).

Results

ANs had greater methylation levels at CpG26.27.28, CpG 31.32, and CpG 37 than HCs (P = 0.039, 0.042, 0.018 respectively). A positive association of methylation level at CpG26.27.28 with ED symptoms detected by EDEQ-6.0 was discovered in AN group (r = 0.216, P = 0.047). Methylation level at CpG26.27.28 was showed to be or tend to be positively correlated with the parenting styles of paternal rejection (r = 0.425, P = 0.038) and paternal overprotection (r = 0.362, P = 0.062) in ANs. No significant differences were found in SLC6A4 promoter region methylation levels among 5-HTTLPR genotypes in our samples (P > 0.05) and no interaction effect between 5-HTTLPR genotypes and parenting styles on SLC6A4 promoter region methylation was observed (P > 0.05).

Conclusions

This study suggested that hypermethylation of SLC6A4 promoter region may be implicated in the pathological mechanisms of untreated Chinese Han female ANs, which is possibly associated with poor parenting styles. This finding may provide a direction for the epigenetic and family treatments for ANs and further investigation with larger samples is warranted.

Identification of Alternative Splicing and LncRNA Genes in Brain Tissues of Fetal Mice at Different Developmental Stages

BACKGROUND

Brain development is an extremely complex and precisely regulated process, with about one-third of genes expressed and precisely regulated during brain development.

OBJECTIVE

This study aims to explore the molecular mechanisms involved in brain development.

METHODS

We first established the expression profile of long non-coding RNAs (lncRNAs) and mRNAs in brain tissues of fetal mice at 12.5d, 14.5d and 16.5d through high-throughput sequencing. Second, the associated functions, pathways, and networks of the co-differentially expressed lncRNAs and mRNAs were identified via Gene Ontology (GO), pathway analysis, and PPI network. After bioinformatic analysis and screening, 8 differentially expressed lncRNAs and mRNAs with the same genetic origin were verified by RT-qPCR analysis in brain tissues of fetal mice at different developmental stages.

RESULTS

The data revealed that there were 972 co-differentially expressed lncRNAs and 992 codifferentially expressed mRNAs in brain tissues of fetal mice at 12.5d, 14.5d and 16.5d. And we discovered 125 differentially expressed lncRNAs and mRNAs, which have the same genetic origin, in brain tissues of fetal mice at 12.5d, 14.5d and 16.5d through sequencing results and bioinformatics analysis. Besides, we proved that 8 lncRNAs, which have had the same genetic origin as differentially expressed mRNAs, were prominently downregulated, while their maternal genes were upregulated during brain development in fetal mice.

CONCLUSION

Our results preliminarily illustrated the differentially expressed lncRNAs and mRNAs, both of which were derived from the same parent genes, during brain development in fetal mice, which suggests that alternative splicing of lncRNA exists during brain development. Besides, our study provides a perspective on critical genes for brain development, which might be the underlying therapeutic targets for developmental brain diseases in children.

Escitalopram should be investigated in anorexia nervosa: Rationale and review of mechanisms

One of the biggest ambitions in the field of anorexia nervosa (AN) research is to find a reliable and effective pharmacological treatment. The fact that currently no pharmacological treatment is safe and effective in this disease is worrying and also challenging. On the basis of the progress in our understanding of AN neurobiology, we propose that escitalopram, a widely available drug, might be a safe and effective option that needs to be investigated. Escitalopram is the only selective serotonin reuptake inhibitor, without any catecholaminergic effect. As studies have shown decreased serotonergic and increased dopaminergic transmission in AN, we hypothesized that an ideal drug for AN management should boost serotonin levels to increase serotonergic and decrease dopaminergic transmission, the two main features of escitalopram action. Here, we present a short overview of pharmacological research in AN and discuss the theoretical rationale for escitalopram use in AN. We also call for double-blind, randomized, placebo-controlled trials to test whether this theoretical framework translates into clinical efficacy.

Serum and plasma levels of brain-derived neurotrophic factor in individuals with eating disorders (EDs): a systematic review and meta-analysis

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is essential for neuronal survival, differentiation, development, and plasticity. Evidence suggests that fluctuations in peripheral levels (i.e., plasma or serum) of BDNF are associated with eating behaviors. Nevertheless, the findings are inconsistent. The purpose of this study is to determine if serum or plasma levels of BDNF are altered in individuals with eating disorders (EDs) compared to controls.

METHODS

We conducted a systematic search of the core electronic medical databases from inception to March 2022 and identified observational studies that compared individuals with EDs to controls without EDs on serum or plasma levels of BDNF. R version 4.0.4 was used for all visualizations and calculations.

RESULTS

The current meta-analysis comprised 15 studies that fulfilled the inclusion criteria. Subjects with EDs (n = 795) showed lower BDNF levels compared to non-EDs controls (n = 552) (SMD: - 0.49, 95% CI [- 0.89; - 0.08], p-value = 0.01). Moreover, subgroup analysis was conducted based on the specimen (plasma and serum), which revealed no statistically significant difference in the levels of BDNF between the two subgroups (p-value = 0.92). Additionally, meta-regression results revealed that publication year, mean age of the individuals with EDs, NOS scores, and the number of individuals with EDs collectively accounted for 25.99% percent of the existing heterogeneity.

CONCLUSION

Lower BDNF levels are associated with EDs.

Correlation between 5-HTTLPR gene polymorphism and cognitive function of traumatic stress in Chinese Han children

BACKGROUND

Post-traumatic stress disorder (PTSD) is a trauma-related psychological disorder with serious social and familial impacts. The involvement of 5-hydroxytryptamine transporter gene-linked polymorphic region (5-HTTLPR) in numerous mental disorders has been documented. This study explored the correlation between 5-HTTLPR gene polymorphism and cognitive function in Chinese Han children with PTSD.

METHODS

A total of 60 PTSD children treated from December 2019 to December 2021 were selected as study participants, with another 60 healthy children selected as controls. We assessed the cognitive function of participants using the Mini-Mental State Examination (MMSE). Additionally, the PTSD level was estimated by the Children's Revised Impact of Event Scale (CRIES). The 5-HTTLPR gene polymorphism was detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR). The genotype and allele frequency were evaluated via case-control association analysis.

RESULTS

Children in the PTSD group showed low MMSE scores and high CRIES scores. In terms of genotype, cases of LL, LS, and SS in PTSD children were 4 (6.67%), 20 (33.3%), and 36 (60.00%), and 18 (30.00%), 28 (46.67%), and 14 (23.33%) cases in healthy controls. In terms of allele gene frequency, incidences of L and S were 23.33% and 76.67% in PTSD children, respectively, and were 53.33% and 46.67% in healthy controls, respectively. Moreover, the CRIES and MMSE scores of LS and SS genotypes were evidently different from those of LL genotype in PTSD children.

CONCLUSIONS

Polymorphism of the 5-HTTLPR gene is correlated with cognitive dysfunction in Chinese Han children with PTSD.