Simultaneous genotyping of multiple polymorphisms in human serotonin transporter gene and detection of novel allelic variants

Identification and functional characterization of the extremely long allele of the serotonin transporter-linked polymorphic region

SLC6A4, which encodes the serotonin transporter, has a functional polymorphism called the serotonin transporter-linked polymorphic region (5-HTTLPR). The 5-HTTLPR consists of short (S) and long (L) alleles, each of which has 14 or 16 tandem repeats. In addition, the extralong (XL) and other rare alleles have been reported in 5-HTTLPR. Although they are more frequent in Asian and African than in other populations, the extent of variations and allele frequencies (AFs) were not addressed in a large population. Here, we report the AFs of the rare alleles in a large number of Japanese subjects (N = 2894) consisting of two cohorts. The first cohort (case-control study set, CCSS) consisted of 1366 subjects, including 485 controls and 881 patients with psychosis (bipolar disorder or schizophrenia). The second cohort (the Arao cohort study set, ACSS) consisted of 1528 elderly subjects. During genotyping, we identified 11 novel 5-HTTLPR alleles, including 3 XL alleles. One novel allele had the longest subunit ever reported, consisting of 28 tandem repeats. We named this XL_28-A. An in vitro luciferase assay revealed that XL_28-A has no transcriptional activity. XL_28-A was found in two unrelated patients with bipolar disorder in the CCSS and one healthy subject in the ACSS who did not show depressive symptoms or a decline in cognitive function. Therefore, it is unlikely that XL_28-A is associated with psychiatric disorders, despite its apparent functional deficit. Our results suggest that unraveling the complex genetic variations of 5-HTTLPR will be important for further understanding its role in psychiatric disorders.

Racial differences in platelet serotonin polymorphisms in acute coronary syndrome

INTRODUCTION

Genetic differences between races have been hypothesized to contribute to differences in outcome from acute coronary syndromes (ACS). Our objective was to assess racial differences in genetic variations in the platelet serotonin transporter (5HTT) and receptor in patients with ACS.

MATERIALS AND METHODS

127 consecutive patients, African Americans (AA) = 27; Caucasian (C) =100, admitted with ACS were evaluated for platelet function by serotonin (5HT) induced platelet activation. All patients were genotyped for two polymorphisms in the serotonin-transporter-linked polymorphic region (5-HTTLPR) S/L and L_G/L_A and one polymorphism of the serotonin 2A receptor (5-HT2A, T102C) gene. All patients were followed for major and minor adverse cardiac events at 12 months.

RESULTS

AA when compared to C had a lower prevalence of the HTTLPR S allele (21% vs 45%, p = 0.0003) and a higher prevalence of the L_G allele (24% vs 4.5%, p = 0.0001). Allelic frequency of the 5-HT2A T102C allele was not significantly different between the races. Platelet activation was lower in AA compared to C, median EC50 5HT was 12.08 μg vs 2.14 μg (p = 0.001). The 5-HTTLPR and the 5-HT2A polymorphisms were not associated with platelet functional responses to serotonin. There were no significant differences in major or minor adverse cardiac events in patients with serotonin transporter or receptor polymorphisms.

CONCLUSION

We found a lower prevalence of the S allele and a higher prevalence of the G allele in AA with ACS. We also found decreased platelet activation in AA which did not correlate with serotonin-related platelet polymorphisms. It is unclear if other contributing factors may explain these platelet functional differences.

Association of serotonin system-related genes with homicidal behavior and criminal aggression in a prison population of Pakistani Origin

The serotonin transporter (SLC6A4), 5-HT_2A (HTR2A) and 5-HT_2B (HTR2B) recepter genes, express proteins that are important regulators of serotonin reuptake and signaling, and thereby may contribute to the pathogenesis of aggressive criminal behavior. 370 sentenced murderers in Pakistani prisons and 359 men without any history of violence or criminal delinquency were genotyped for six candidate polymorphisms in SLC6A4, HTR2A and HTR2B genes. An association of higher expressing L/L and L_A/L_A variants of the 5-HTTLPR polymorphism was observed with homicidal behavior (bi-allelic: OR = 1.29, p = 0.016, tri-allelic: OR = 1.32, p = 0.015) and in the murderer group only with response to verbal abuse (OR = 2.11, p = 0.015), but not with other measures of self-reported aggression. L/L and L_A/L_A genotypes of the 5-HTTLPR polymorphism were associated with higher aggression scores on STAX1 scale of aggression compared to lower expressing genotypes (S/S, S/L_G, L_G/L_G) in prison inmates. No associations were apparent for other serotonergic gene polymorphisms analyzed. Using the Braineac and GTEx databases, we demonstrated significant eQTL based functional effects for rs25531 in HTTLPR and other serotonergic polymorphisms analyzed in different brain regions and peripheral tissues. In conclusion, these findings implicate SLC6A4* HTTLPR as a major genetic determinant associated with criminal aggression. Future studies are needed to replicate this finding and establish the biologic intermediate phenotypes mediating this relationship.

Investigation of the Association between 5-Hydroxytryptamine Transporter Gene-Linked Polymorphic Region with Type 2 Diabetes Mellitus, Obesity and Biochemical Profiles of Serum in Iranian Population

BACKGROUND

Type 2 Diabetes Mellitus (T2DM) is a serious problem in the world. 5-Hydroxytryptamine (5-HT, serotonin) plays an important role in obesity, glucose control and insulin resistance. The polymorphism of the serotonin transporter gene linked promoter region (5-HTTLPR) might influence 5-HTT expression and serotonin uptake. The polymorphism results in two alleles of L (Long) and S (Short). The aim of the present study was to evaluate the association between 5-HTTLPR genotypes in type 2 diabetes mellitus (T2DM), obesity as well as serum biochemical profiles in Iranian population from 2012 until 2015.

METHODS

180 patients with T2DM and 180 controls were selected and the frequency of S and L alleles was determined by PCR. Then, the relationship between genotypes, body mass index (BMI) and serum biochemical variables was investigated.

RESULTS

The frequency of S and L alleles in experimental and control groups was the same [for the L allele p=0.754, OR (95%CI)=1.103 (0.597 to 2.041) and for the S allele p=0.906, OR (95%CI)=(0.490 to 1.676)]. However, the mean triglyceride, cholesterol, LDL-C, systolic and diastolic blood pressure levels in the diabetic subjects with LL genotype were significantly higher than LS and SS genotypes (p<0.001) in this population.

CONCLUSION

The L allele of 5-HTTLPR was related to the increased serum lipids and blood pressure in the diabetic patients. However, there was no relationship between the polymorphism of 5-HTTLPR L/S and T2DM in Iranian population.

Serotonin and interleukin-6: the role of genetic polymorphisms in IFN-induced neuropsychiatric symptoms

BACKGROUND

Cytokines and serotonin neurotransmission may play an important role on the development of psychopathological symptoms during interferon (IFN) treatment. The aim of the present study was to investigate the association between IFN-induced depression, anxiety and fatigue and functional genetic variants at the interleukin-6 gene (IL-6) and serotonin transporter gene (SERT).

METHODS

385 consecutive Caucasian outpatients with chronic hepatitis C initiating treatment with IFN-alpha and ribavirin were included. All patients were interviewed at baseline using the Structured Clinical Interview for DSM-IV (SCID-I) and those with a current major depressive disorder or anxiety disorder before starting treatment were excluded. Depression and anxiety were assessed at baseline during the treatment (at 4, 12, 24 and 48 weeks) using the Hospital Anxiety and Depression Scale and fatigue was evaluated using a visual analogue scale. The 5-HTTLPR region of SERT gene and the functional polymorphism located at the promoter region of IL-6 gene (rs1800795) were genotyped.

RESULTS

Genotypic distribution was in the Hardy-Weinberg equilibrium for SERT (p=0.41) and for IL-6 (p=0.72) polymorphisms. At baseline we found only a significant effect of IL-6 polymorphism on fatigue symptoms. During antiviral treatment we reported that subjects with CC genotype (IL-6) presented significantly lower changes from baseline in IFN-induced depression (p=0.005) and IFN-induced anxiety (p=0.004). We did not find statistically significant differences on depression (p=0.21) or anxiety (p=0.15) between SS/SL and LL genotypes of SERT.

CONCLUSIONS

Genetic variations in the IL-6 gene increase the risk of IFN-induced depression and anxiety. The IL-6 polymorphism was associated with fatigue rates in patients with chronic hepatitis C before treatment. Our study confirms the role of inflammatory mechanisms in IFN-induced psychopathological symptoms.

5HTTLPR: White Knight or Dark Blight?

In over 100 neuroscience genetics reports on SLC6A4 published in the first part of 2012, >40% reported data from genotyping only the serotonin transporter-linked promoter region [5HTTLPR] indel, omitting genotyping of two nearby SNPs that substantially alter 5HTTLPR allele frequencies and functionality. And 25% of these papers did not report ethnicity of the subjects genotyped, another factor that alters allele frequencies. This field thus seems stultified. Improved science for the present and future will be better served by attention to more complete methods for genotyping and subject sample reporting.