Cumulative effect of the plasma total homocysteine-related genetic variants on schizophrenia risk

Sulfur-containing amino acids and risk of schizophrenia

BACKGROUND

Schizophrenia is a chronic and complex severe psychiatric disorder. Male and female are different in their risks for schizophrenia for the biologic and sociocultural reasons. Homocysteine (Hcy), Cysteine (Cys), and methionine (Met) play important roles in metabolism, and the three amino acids may also be involved in pathogenesis of schizophrenia.

OBJECTIVE

This study aimed to test the associations between sulfur-containing amino acid blood levels and risk of schizophrenia, evaluating the different risk in male and female.

METHODS

We organized a case-control study on 876 individuals with schizophrenia and 913 age- and sex-matched healthy subjects as control group. The concentrations of Hcy, Cys and Met were measured by liquid chromatography-tandem mass spectrometry technology. Subsequently, restricted cubic spline was applied to explore full-range associations of these amino acids with schizophrenia. Interactions between levels of the three amino acids and sex on additive scale were also tested.

RESULTS

Hcy levels at ≤29 μmol/L were associated with sharply increased risk of schizophrenia, inversely, Met was associated with sharply decreased risk of schizophrenia at levels ≤22 μmol/L. Increased Cys levels were associated with decreased risk of schizophrenia. Almost inverse associations were observed between Cys/Hcy and Met/Hcy ratios and schizophrenia. Significant synergistic interactions between levels of all the three amino acids and sex were discovered on an additive scale.

CONCLUSIONS

Our study suggests a close association between sulfur-containing amino acids and schizophrenia with different risk in male and female. Future studies are demanded to clarify the pathogenic role of Hcy, Cys and Met in schizophrenia.

Increased serum homocysteine in first episode and drug-naïve individuals with schizophrenia: sex differences and correlations with clinical symptoms

BACKGROUND

Accumulating evidence shows that homocysteine (Hcy) is implicated in the pathophysiology of schizophrenia, and plays an important role in clinical characteristics. This study evaluated the relationships between Hcy levels and clinical features in first-episode, Chinese Han, drug-naïve (FEDN) patients with schizophrenia.

METHODS

FEDN individuals (119 with schizophrenia and 81 healthy controls matched for age, sex, education, and body mass index (BMI)) were enrolled. The serum Hcy levels were determined by enzyme cycle assay experiments. Severities of clinical symptoms were rated on the Positive and Negative Syndrome Scale (PANSS).

RESULTS

FEDN individuals with schizophrenia had higher Hcy levels compared with healthy controls (F = 46.865, P < 0.001). Correlation analysis and multiple stepwise regression analyses showed that serum Hcy levels in FEDN schizophrenia individuals were positively correlated with PANSS general psychopathology subscale (r = 0.294, P = 0.001) and PANSS total score (r = 0.273, P = 0.003). No significant association was found between Hcy and age, BMI, PANSS positive subscale, and the PANSS negative subscale (all, P > 0.05). Male individuals had significantly higher serum Hcy levels than female individuals (F = 7.717, P = 0.006) after controlling for confounding factors (F = 0.759, P = 0.011).

CONCLUSIONS

Serum Hcy levels were increased in FEDN individuals with schizophrenia, and Hcy levels may be involved in pathophysiological mechanisms. Sex differences in Hcy levels were observed, with higher levels in male FEDN individuals compared to females.

Consensus on potential biomarkers developed for use in clinical tests for schizophrenia

Background

Schizophrenia is a serious mental illness affecting approximately 20 million individuals globally. Both genetic and environmental factors contribute to the illness. If left undiagnosed and untreated, schizophrenia results in impaired social function, repeated hospital admissions, reduced quality of life and decreased life expectancy. Clinical diagnosis largely relies on subjective evidence, including self-reported experiences, and reported behavioural abnormalities followed by psychiatric evaluation. In addition, psychoses may occur along with other conditions, and the symptoms are often episodic and transient, posing a significant challenge to the precision of diagnosis. Therefore, objective, specific tests using biomarkers are urgently needed for differential diagnosis of schizophrenia in clinical practice.

Aims

We aimed to provide evidence-based and consensus-based recommendations, with a summary of laboratory measurements that could potentially be used as biomarkers for schizophrenia, and to discuss directions for future research.

Methods

We searched publications within the last 10 years with the following keywords: ‘schizophrenia’, ‘gene’, ‘inflammation’, ‘neurotransmitter’, ‘protein marker’, ‘gut microbiota’, ‘pharmacogenomics’ and ‘biomarker’. A draft of the consensus was discussed and agreed on by all authors at a round table session.

Results

We summarised the characteristics of candidate diagnostic markers for schizophrenia, including genetic, inflammatory, neurotransmitter, peripheral protein, pharmacogenomic and gut microbiota markers. We also proposed a novel laboratory process for diagnosing schizophrenia in clinical practice based on the evidence summarised in this paper.

Conclusions

Further efforts are needed to identify schizophrenia-specific genetic and epigenetic markers for precise diagnosis, differential diagnosis and ethnicity-specific markers for the Chinese population. The development of novel laboratory techniques is making it possible to use these biomarkers clinically to diagnose disease.

Screening for inborn errors of metabolism in psychotic patients using Next Generation Sequencing

Inborn errors of metabolism (IEMs) are a group of rare genetic disorders which, when emerging later in life, are often characterized by neuropsychiatric manifestations including psychosis. This study aimed to determine whether it would be useful to screen patients presenting with a psychotic disorder for IEMs by a single blood sample using Next Generation Sequencing (NGS), in order to detect rare, treatable causes of psychotic disorders. Blood was drawn from 60 patients with a psychotic disorder, with a duration of illness of less than 5 years. Blood samples were screened for 67 genes using NGS (Illumina® MiSeq sequencing technique). The results were compared to the human reference genome (GoNL, n = 498). The identified variants were classified according to the ACMG classification. For the psychotic patients, 6 variants of a likely pathogenic (class 4, n = 2) or pathogenic (class 5, n = 4) origin were found. As all variants were heterozygous, no patients were considered to be affected by an IEM. For the GoNL control group, 73 variants of a likely pathogenic (class 4, n = 31) or pathogenic (class 5, n = 42) origin were found. All of these found variants were heterozygous. Therefore, these individuals from the control group were considered to be a carrier only. Thus, no patients were identified to have an IEM as an underlying disease using this approach. However, NGS may be useful to detect variants of genes associated with IEMs in an enriched subgroup of psychotic patients.

Involvements of Hyperhomocysteinemia in Neurological Disorders

Homocysteine (HCY), a physiological amino acid formed when proteins break down, leads to a pathological condition called hyperhomocysteinemia (HHCY), when it is over a definite limit. It is well known that an increase in HCY levels in blood, can contribute to arterial damage and several cardiovascular disease, but the knowledge about the relationship between HCY and brain disorders is very poor. Recent studies demonstrated that an alteration in HCY metabolism or a deficiency in folate or vitamin B12 can cause altered methylation and/or redox potentials, that leads to a modification on calcium influx in cells, or into an accumulation in amyloid and/or tau protein involving a cascade of events that culminate in apoptosis, and, in the worst conditions, neuronal death. The present review will thus summarize how much is known about the possible role of HHCY in neurodegenerative disease.

Early-Onset Schizophrenia: A Special Phenotype of the Disease Characterized by Increased MTHFR Polymorphisms and Aggravating Symptoms

BACKGROUND

Patients with early-onset schizophrenia usually exhibit more severe symptoms, revealing a potentially distinctive disease phenotype. Methylenetetrahydrofolate reductase (MTHFR) is a critical enzyme in folate conversion and methylation modification associated with the disease. We aimed to investigate the potential effects of MTHFR polymorphisms and related methylation patterns in patients with early-onset schizophrenia, which implies special phenotypes of schizophrenia.

METHODS

In 177 patients with schizophrenia, MTHFR polymorphism at three sites (C677T, A1298C, and G1793A) and the Positive and Negative Syndrome Scale (PANSS) were tested. Differential methylation positions (DMPs) and enrichment of genes and related pathways were analyzed by testing the genomic methylation level. Catechol-O-methyltransferase (COMT), solute carrier family 6 member 4 (SLC6A4), neuregulin1 (NRG1), and brain-derived neurotrophic factor (BDNF) were selected to evaluate the methylation levels of specific CpG regions by pyrosequencing.

RESULTS

Higher levels of symptom severity and MTHFR polymorphisms and lower levels of global DNA methylation in patients with early-onset schizophrenia were observed in this study. SLC6A4 was hypermethylated, and BDNF was hypomethylated in specific regions of patients with early-onset schizophrenia.

CONCLUSION

Aggravating symptoms, increased MTHFR polymorphisms, and reduced genomic methylation levels may be characteristics and underlying mechanisms of early-onset schizophrenia, which implies a special disease phenotype. Beyond that, specific genes and biological pathways may imply the potential phenotype of schizophrenia.

Association between serum folate levels and schizophrenia based on sex

AIM

Sex differences in serum folate concentrations are well known, but no studies have investigated the association between serum folate levels and schizophrenia based on sex. With this study in a Japanese population, we examined the difference in serum folate levels between patients with schizophrenia and non-psychiatric controls stratified by sex. The relations among serum folate levels, plasma total homocysteine (tHcy), and serum vitamin B6 (pyridoxal) levels were also examined using data from our previous studies.

METHODS

The serum folate concentrations of 482 patients diagnosed with schizophrenia and 1350 non-psychiatric control subjects were measured. We conducted an analysis of covariance to examine the differences in serum folate levels between the two groups based on sex. Spearman's rank correlation was used to evaluate the relations among folate, tHcy, and vitamin B6 levels.

RESULTS

In the control group, serum folate concentrations were higher in women than in men. Lower levels of serum folate were observed in both male and female patients with schizophrenia. An inverse correlation between serum folate and plasma tHcy and a weak positive correlation between serum folate and vitamin B6 were observed in the combined cohort.

CONCLUSION

Our findings suggest that: (i) a low serum folate level may be associated with schizophrenia regardless of sex; and (ii) folate administration may be beneficial for the treatment of schizophrenia. In schizophrenic patients with low serum folate levels, folate administration might result in improvements in high tHcy and an increase in low vitamin B6 levels.

Influence of BDNF and MTHFR polymorphisms on hippocampal volume in first-episode psychosis

BACKGROUND

The BDNF and MTHFR genes are independently linked to the pathogenesis of schizophrenia and its neuroimaging correlates. The aim of this study was to explore, for the first time, the individual and interactional effects of the Val66Met and C677T polymorphisms on hippocampal atrophy in first-episode psychosis (FEP).

METHOD

Multi-site case-control study based on clinical, genetic (rs 6265, rs 1801133) and structural magnetic resonance imaging data from 98 non-affective FEP patients and 117 matched healthy controls (HC). Hippocampal volume was estimated using FreeSurfer software and this volume was compared between diagnostic (FEP vs HC) and genotype (Val66Met, C677T) groups. The BDNF Val66Met x MTHFR C677T effect on hippocampal volume was further evaluated through stratified analyses.

RESULTS

After applying Bonferroni correction, diagnosis showed a significant effect for adjusted left and right hippocampal volume (FEP < HC). Stratified analyses showed that the interactive effect contributed to adjusted hippocampal size in both the HC (left and right hippocampus) and FEP groups (right hippocampus); among BDNF Met carriers, those with the CT-TT genotype exhibited decreased hippocampal volume compared to individuals with the homozygous normal CC genotype.

CONCLUSIONS

Our results provide preliminary evidence indicating that the Val66Met x C677T interaction may be a potential genetic risk factor for reduced hippocampal size in both healthy controls and in patients with FEP. Further research in independent samples including different ethnic groups is warranted to confirm this new finding.

[The study of the association between the C677T polymorphism of the methylenetetrahydrofolate reductase gene and severity of symptoms in patients with schizophrenia]

OBJECTIVE

To study the association of the C677T polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene with the risk of schizophrenia in a large sample, including schizophrenic patients and mentally healthy people, and to investigate the relationship of this polymorphism with the severity of schizophrenia symptoms and genotype-environment interaction effects on these symptoms.

MATERIAL AND METHODS

The sample for genotyping consisted of 1357 patients with schizophrenia and schizophrenia spectrum disorders and 711 people of the control group. The severity of symptoms was assessed with the PANSS. Obstetrical complications and a traumatic brain injury in medical history were studied as environmental factors.

RESULTS AND CONCLUSION

No association was found between MTHFR C677T polymorphism and schizophrenia. There was no genotype effect on the severity of symptoms on the PANSS subscales. The effect of genotype-environment interactions on the severity of schizophrenia symptoms was not detected. The results do not confirm the data of a number of studies on the relationship of MTHFR C677T polymorphism with schizophrenia symptoms.

A label-free aptasensor for highly sensitive detection of homocysteine based on gold nanoparticles

In the present study, an original electrode fabrication approach was devised to create a label free sensitive electrochemical aptasensor for the detection of Homocysteine (Hcy) (Homocysteine signal was used for detection). To bind certain targets, synthetic oligonucleotides used as aptamers (APs) were specifically selected. Aptamers are substitutes for antibodies for analytical devices because of their sensitivity and high affinity. In this study, Hcy-Binding-Aptamer (HBA) was grafted onto the surface of Au nanoparticles/Glassy Carbon Electrode (Au/GCE) in order to create an aptasensor. The effects of buffer concentration, buffer type, interaction time, and aptamer concentration were investigated and optimized. In addition, Differential Pulse Voltammetry (DPV) was implemented to identify homocysteine. Favorable performance was achieved at a detection limit of 0.01 μM (S/N = 3) and linear range 0.05-20.0 μM. Furthermore, the fabricated aptasensor displayed desirable stability and reproducibility. The developed electrochemical aptasensor was found to have reasonable selectivity for the detection of homocysteine in the presence of cysteine and methionine. Analysis of real samples showed good ability of the proposed homocysteine biosensor to provide sensitive, quick, easy, and cost effective measurement of homocysteine in human blood serum and urine samples.

The psychosis risk timeline: can we improve our preventive strategies? Part 1: early life

Psychosis is a complex presentation with a wide range of factors contributing to its development, biological and environmental. Psychosis is a feature present in a variety of psychiatric disorders. It is important for clinicians to keep up to date with evidence regarding current understanding of the reasons psychosis may occur. Furthermore, it is necessary to find clinical utility from this knowledge so that effective primary, secondary and tertiary preventative strategies can be considered. This article is the first of a three-part series that examines contemporary knowledge of risk factors for psychosis and presents an overview of current explanations. The articles focus on the psychosis risk timeline, which gives a structure within which to consider key aspects of risk likely to affect people at different stages of life. In this first article, early life is discussed. It covers elements that contribute in the prenatal and early childhood period and includes genetic, nutritional and infective risk factors.

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DECLARATION OF INTEREST

None.

Decreased serum pyridoxal levels in schizophrenia: meta-analysis and Mendelian randomization analysis

BACKGROUND

Alterations in one-carbon metabolism have been associated with schizophrenia, and vitamin B6 is one of the key components in this pathway.

METHODS

We first conducted a case-control study of serum pyridoxal levels and schizophrenia in a large Japanese cohort (n = 1276). Subsequently, we conducted a meta-analysis of association studies (n = 2125). Second, we investigated whether rs4654748, which was identified in a genome-wide association study as a vitamin B6-related single nucleotide polymorphism, was genetically implicated in patients with schizophrenia in the Japanese population (n = 10 689). Finally, we assessed the effect of serum pyridoxal levels on schizophrenia risk using a Mendelian randomization (MR) approach.

RESULTS

Serum pyridoxal levels were significantly lower in patients with schizophrenia than in controls, not only in our cohort, but also in the pooled data set of the meta-analysis of association studies (standardized mean difference -0.48, 95% confidence interval [CI] -0.57 to -0.39, p = 9.8 × 10-24). We failed to find a significant association between rs4654748 and schizophrenia. Furthermore, an MR analysis failed to find a causal relationship between pyridoxal levels and schizophrenia risk (odds ratio 0.99, 95% CI 0.65-1.51, p = 0.96).

LIMITATIONS

Food consumption and medications may have affected serum pyridoxal levels in our cross-sectional study. Sample size, number of instrumental variables and substantial heterogeneity among patients with schizophrenia are limitations of an MR analysis.

CONCLUSION

We found decreased serum pyridoxal levels in patients with schizophrenia in this observational study. However, we failed to obtain data supporting a causal relationship between pyridoxal levels and schizophrenia risk using the MR approach.