Association analysis of genes in serotonin pathway with attention and executive function in patients with bipolar affective disorder

TPH2 polymorphisms across the spectrum of psychiatric morbidity: A systematic review and meta-analysis

Tryptophan hydroxylase 2 (TPH2) is the rate-limiting enzyme in brain serotonin synthesis. The TPH2 gene has frequently been investigated in relation to psychiatric morbidity. The aim of the present review is to integrate results from association studies between TPH2 single nucleotide polymorphisms (SNPs) and various psychiatric disorders, which we furthermore quantified with meta-analysis. We reviewed 166 studies investigating 69 TPH2 SNPs in a broad range of psychiatric disorders, including over 30,000 patients. According to our meta-analysis, TPH2 polymorphisms show strongest associations with mood disorders, suicide (attempt) and schizophrenia. Despite small effect sizes, we conclude that TPH2 SNPs in the coding and non-coding areas (rs4570625, rs11178997, rs11178998, rs10748185, rs1843809, rs4290270, rs17110747) are each associated with one or more psychopathological conditions. Our findings highlight the possible common serotonergic mechanisms of the investigated psychiatric disorders. Yet, the functional relevance of most TPH2 polymorphisms is unclear. Characterizing how exactly the different TPH2 variants influence the serotonergic neurotransmission is a next necessary step in understanding the psychiatric disorders where serotonin is implicated.

Contribution of genes in the GABAergic pathway to bipolar disorder and its executive function deficit in the Chinese Han population

In this study, we investigated the association between bipolar I disorder (BDI) and between cognitive deficits therein and SNPs in GABAergic receptor genes. The sample comprised 477 patients with BDI and 438 healthy controls, with three neurocognitive tests being administered in 123 patients and 164 controls. For three SNPs, rs505474, rs1398175, and rs4868029 in the GABRA2, GABRA4, and GABRP genes, respectively, their allele frequencies were significantly different between patients and controls (Bonferroni-adjusted p = values 3.84 × 10^-4 , 9.92 × 10^-3 , and 1.22 × 10^-2 , respectively). Four haplotypes were significantly associated with BDI (TA and AG for rs3815762 and rs4868029 in GABRP, GG for rs11636988 and rs8024256 in GABRB3 and GAGG for rs2197414, rs4921195, rs13188991, and rs11956731 in GABRA6, with p values of 0.0038, 0.044, 0.0176, and 0.0267, respectively, on 10,000 permutations). Furthermore, the SNP (rs2912585) within 250 kb upstream of the GABRB3 gene displayed a strong association with the Tower of Hanoi (TOH) executive time in the patient group (p = 2.844 × 10^-6 ). One other SNP (rs754661), which is located at the intronic region of the same gene, was associated with the global trait of the executive function and post hoc analysis showed significant SNP by group effect (p = 0.0094). Our study supports previous findings that GABA_A receptor genes are associated with bipolar disorder; it also suggests that the GABA_A genes, especially the GABRB3 gene, might play a role in the executive function deficit in bipolar disorder, although future replication with a larger sample size is needed.

Executive functioning deficits among adults with Bipolar Disorder (types I and II): A systematic review and meta-analysis

BACKGROUND

Executive functioning (EF) deficits contribute to a significant proportion of the burden of disease associated with bipolar disorder (BD). Yet, there is still debate in the literature regarding the exact profile of executive functioning in BD. The purpose of the present project was to assess whether EF deficits exist among adults suffering BD, and whether these deficits (if apparent) differ by BD subtype.

METHODS

A systematic search identified relevant literature. Randomised controlled trials that used neuropsychological assessment to investigate EF among adults 16-65 years) with a remitted DSM diagnosis of BD (type I or II) were included. Studies were published between 1994 and 2015. A systematic review and meta-analysis were undertaken. For individual studies, standardised mean differences (Cohen's d) and 95% confidence intervals were calculated and represented in forest plots to illustrate differences in executive performance between groups. Summary effects were produced and tests of heterogeneity employed to assess the dispersion and generalisability of results.

RESULTS

Thirty-six studies met criteria for inclusion. Six domains of EF were identified: Set-shifting (SS), inhibition (INH), planning (PLA), verbal fluency (VF), working memory (WM), and attention (ATT). BD1s performed worse than HCs in all domains. BD2s demonstrated impairment in VF, WM, SS, and ATT. The results were mixed for comparisons between BD1s and BD2s, but revealed that BD2s can experience similar (or sometimes greater) EF impairment.

LIMITATIONS

Only a limited number of studies that included BD2 samples were available for inclusion in the current study. Subgroup analysis to elucidate potential moderators of within-study variance was not undertaken.

CONCLUSION

This is the first systematic review and meta-analysis to have compared the EF of remitted BD1s, BD2s, and HCs. The results provided useful insight into the EF profile of patients with BD, and offered commentary as to some of the contradictory results reported in the literature. A standardised methodological protocol for assessment of EF in BD was proposed. The information in this review could enhance our understanding of EF impairment inherent in BD, and the methods and efficacy with which clinicians assess and treat this population.