Association study of TPH2 polymorphisms and bipolar disorder in the Han Chinese population

The effects of gastrointestinal disturbances on the onset of depression and anxiety

Background

Stomach pain is an ailment that occurs frequently in the general population. It is not unusual if such stomach issues produce some amount of stress in an individual, but it can be worrying if these pains lead to significant mental health problems. The relationship between some abdominal pain, such as bowel syndrome, and depression or anxiety has been gaining much interest. However, previous studies that have empirically investigated this relationship are scarce.

Methods

To analyze the impact of having gastrointestinal problems, among other socioeconomic conditions, on the onset of depression and anxiety in the Spanish population, we compare treating gastrointestinal diseases as exogenous in a single-equation probit model with a bivariate probit model in which this variable is treated as endogenous. A likelihood-ratio test of the correlation coefficient of the disturbances suggests that gastrointestinal problems are endogenous. Thus, the approach taken herein allows the direct testing of the hypothesis that having gastrointestinal problems and the onset of mental illnesses such as depression and anxiety are jointly determined by certain socioeconomic factors. A cross-sectional analytical study was analyzed using data from a 2017 survey of health indicators and life conditions that was developed by the Statistics Spanish Office.

Results

The probability of having depression or anxiety increases with age, stress, daily limitations and gastrointestinal disorders. On the other hand, the probability is lower for men, married people and those who engage in exercise several times per week. Our findings estimate that having gastrointestinal problems increases the probability of having depression in 7% and the probability of anxiety in 8.8% of the sample.

Conclusions

Our empirical results suggest that not considering the endogeneity of gastrointestinal problems could result in an overestimate of the impact of this factor on the development of depression or anxiety.

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.