Meta-analysis demonstrates lack of association of the GSK3B −50C/T polymorphism with risk of bipolar disorder

Proof-of-concept study of a multi-gene risk score in adolescent bipolar disorder

BACKGROUND

Few studies have examined multiple genetic variants concurrently for the purpose of classifying bipolar disorder (BD); the literature among youth is particularly sparse. We selected 35 genetic variants, previously implicated in BD or associated characteristics, from which to identify the most robustly predictive group of genes.

METHODS

215 Caucasian adolescents (114 BD and 101 healthy controls (HC), ages 13-20 years) were included. Psychiatric diagnoses were determined based on semi-structured diagnostic interviews. Genomic DNA was extracted from saliva for genotyping. Two models were used to calculate a multi-gene risk score (MGRS). Model 1 used forward and backward regressions, and model 2 used a PLINK generated method.

RESULTS

In model 1, GPX3 rs3792797 was significant in the forward regression, DRD4 exonIII was significant in the backward regression; IL1β rs16944 and DISC1 rs821577 were significant in both the forward and backward regressions. These variants are involved in dopamine neurotransmission; inflammation and oxidative stress; and neuronal development. Model 1 MGRS did not significantly discriminate between BD and HC. In model 2, ZNF804A rs1344706 was significantly associated with BD; however, this association did not predict diagnosis when entered into the weighted model.

LIMITATIONS

This study was limited by the number of genetic variants examined and the modest sample size.

CONCLUSIONS

Whereas regression approaches identified four genetic variants that significantly discriminated between BD and HC, those same variants no longer discriminated between BD and HC when computed as a MGRS. Future larger studies are needed evaluating intermediate phenotypes such as neuroimaging and blood-based biomarkers.

Genetic Variants Involved in Bipolar Disorder, a Rough Road Ahead

BACKGROUND

Bipolar Disorder (BD), along with depression and schizophrenia, is one of the most serious mental illnesses, and one of the top 20 causes of severe impairment in everyday life. Recent molecular studies, using both traditional approaches and new procedures such as Whole-Genome Sequencing (WGS), have suggested that genetic factors could significantly contribute to the development of BD, with heritability estimates of up to 85%. However, it is assumed that BD is a multigenic and multifactorial illness with environmental factors that strongly contribute to disease development/progression, which means that progress in genetic knowledge of BD might be difficult to interpret in clinical practice.

OBJECTIVE

The aim of this study is to provide a synthetic description of the main SNPs variants identified/confirmed by recent extensive WGS analysis as well as by reconstruction in an in vitro mechanism or by amygdala activation protocol in vivo.

METHOD

Bibliographic data, genomic and protein Data Banks were consulted so as to carry out a cross genomic study for mutations, SNPs and chromosomal alterations described in these studies in BD patients.

RESULTS

Fifty-five different mutations have been described in 30 research papers by different genetic analyses including recent WGS analysis. Many of these studies have led to the discovery of the most probable susceptibility genes for BD, including ANK3, CACNA1C, NCAN, ODZ4, SYNE1, and TRANK1. Exploration has started the role of several of these mutations in BD pathophysiology using in vitro and animal models.

CONCLUSION

Although new genomic research technology in BD opens up new possibilities, the current results for common variants are still controversial because of four broad conditions: analytical validity, clinical validity, clinical utility and a reasonable cost for genetic analysis are not yet accessible.

The gender-specific association of rs334558 in GSK3β with major depressive disorder

Major depressive disorder (MDD) is one of the most prevalent psychiatric illnesses with a heritability ranging from 40% to 50%. The single nucleotide polymorphism (SNP) rs334558 on the glycogen synthase kinase-3β (GSK3β) gene has been identified as a genetic risk loci associated with schizophrenia and bipolar disorder. However, results from replication studies examining the association between rs334558 and MDD remain inconsistent.In the present study, first, we conducted a meta-analysis of the association between rs334558 and MDD by combining 5 available case-control samples totaling 2311 cases and 2535 controls. Second, genotyping data from patients with MDD at our institution, after further stratification by gender, were analyzed to determine the association between rs334558 and MDD.All studies retrieved and included in the meta-analysis were from Korea and China. The meta-analysis suggested that the functional polymorphism rs334558 within the GSK3β promoter region was associated with MDD risk (P < 0.05). The associations were observed both in the allelic and genetic models. Analysis of the genotyping data extracted from our hospital database revealed that rs334558 exhibited exclusive association with MDD in female patients (P=0.015).Our findings suggest that GSK3β rs334558 polymorphisms might be a potential risk for MDD, and females with GSK3β rs334558 polymorphisms might have higher penetrance of MDD. If validated in larger scale samples and in different ethnic populations, these findings might be of value as diagnostic references for MDD.

The genetics of early-onset bipolar disorder: A systematic review

BACKGROUND

Early-onset bipolar disorder has been associated with a significantly worse prognosis than late-onset BD and has been hypothesized to be a genetically homogenous subset of BD. A sizeable number of studies have investigated early-onset BD through linkage-analyses, candidate-gene association studies, genome-wide association studies (GWAS), and analyses of copy number variants (CNVs), but this literature has not yet been reviewed.

METHODS

A systematic review was conducted using the PubMed database on articles published online before January 15, 2015 and after 1990. Separate searches were made for linkage studies, candidate gene-association studies, GWAS, and studies on CNVs.

RESULTS

Seventy-three studies were included in our review. There is a lack of robust positive findings on the genetics of early-onset BD in any major molecular genetics method.

LIMITATIONS

Early-onset populations were quite small in some studies. Variance in study methods hindered efforts to interpret results or conduct meta-analysis.

CONCLUSIONS

The field is still at an early phase for research on early-onset BD. The largely null findings mirror the results of most genetics research on BD. Although most studies were underpowered, the null findings could mean that early-onset BD may not be as genetically homogenous as has been hypothesized or even that early-onset BD does not differ genetically from adult-onset BD. Nevertheless, clinically the probabilistic developmental risk trajectories associated with early-onset that may not be primarily genetically determined continued to warrant scrutiny. Future research should dramatically expand sample sizes, use atheoretical research methods like GWAS, and standardize methods.