GNB3 C825T polymorphism and response to interferon-alfa/ribavirin treatment in patients with hepatitis C virus genotype 1 (HCV-1) infection

Viral and host factors associated with outcomes of hepatitis C virus infection (Review)

Hepatitis C virus (HCV) infection is a major health issue globally. Owing to the progress made in host genetics and HCV molecular virology, emerging data have suggested that the natural course and treatment response in patients with HCV infection are largely determined by complex host‑viral interactions. HCV genotype is the most important viral factor predicting the response to pegylated interferon‑α plus ribavirin therapy. The subtype of HCV genotype 1 is the key viral factor that predicts the efficacy of direct‑acting antiviral therapy. HCV genome heterogeneity and baseline viral load are additionally associated with the treatment response. Multiple host genetic variants localized in genes associated with the immune response have been identified as predictors of spontaneous disease course and therapy outcome in chronic HCV. However, most findings from candidate gene association studies have not been proven universal for all investigated populations and independent studies. Previous findings in independent large genome wide association studies confirmed that interferon‑λ3 gene polymorphisms are associated with spontaneous clearance and treatment responsiveness. A polymorphism of the inosine triphosphatase gene has been identified as a protective factor against ribavirin‑induced anemia and dose reductions. Another genetic variant in the patatin‑like phospholipase domain containing 3 genes is associated with hepatic steatosis and fibrosis in patients with HCV. The present review focused on the identified viral and host factors associated with outcomes of patients with HCV, and assessed the involvement of viral and host genetics in the natural history and treatment outcomes of HCV infection. This will provide novel ideas concerning personalized prevention and individualized clinical management.

Genetic variation in NOS2A is associated with a sustained virological response to peginterferon plus ribavirin therapy for chronic hepatitis C in Taiwanese Chinese

This study aimed to evaluate whether genetic polymorphisms of the inducible nitric oxide synthase (iNOS) gene NOS2A could be associated with a sustained virological response (SVR) among patients infected with hepatitis C virus genotypes 1 and 2 (HCV-1 and HCV-2) who were treated with peginterferon plus ribavirin (PEG-IFNα-RBV). We analyzed the associations between SVR to PEG-IFNα-RBV therapy and two single nucleotide polymorphisms (SNPs) in NOS2A. This study included Taiwanese Chinese patients infected with either HCV-1 (n = 265) or HCV-2 (n = 195) with or without a SVR. Among the NOS2A SNPs examined, the combination of genotypes A/A and A/G of rs2248814 was inversely correlated with SVR in patients infected with HCV-1 (P = 0.0048), particularly in males (P = 0.0281). This effect was not observed in patients infected with HCV-2. The AC NOS2A haplotype comprising two SNPs (rs2248814 and rs2072324) was found to be associated with SVR, and its presence may decrease the chances for a successful outcome of treatment of patients infected with HCV-1 (P = 0.0053). HCV-1 infected patients who carried the A-C diplotype will have a lower success rate of achieving a SVR (P = 0.0117). In addition, a multivariate logistic regression model for predicting a SVR revealed that the presence of the A-C diplotype interactively affected the outcome of PEG-IFNα-RBV treatment. The presence of NOS2A SNPs and the association with SVR showed that NOS2A polymorphisms may influence the therapeutic outcomes of patients infected with HCV-1 under standard of care treatment.

The role of pharmacogenetics in the treatment of chronic hepatitis C infection

Hepatitis C virus (HCV) chronically infects 170 million people worldwide. Until recently, combination therapy with peginterferon-α (pegIFN) and ribavirin (RBV) has been the standard of care. However, for many patients, especially those infected with the most common HCV genotype 1 (HCV-1), this treatment has resulted in unsatisfactory treatment response rates. Many clinical factors, including pharmacogenetics, influence the treatment response rate. Genetic variation in the interleukin 28B (IL28B) gene is the major determinant of treatment response, a finding that has been replicated in multiple independent cohorts. This review focuses on the association between pharmacogenetics and conventional pegIFN/RBV therapy in patients infected with HCV non-genotype 1; patients reinfected with HCV after liver transplantation; and patients coinfected with HCV and human immunodeficiency virus. We also review the pharmacogenetic data for boceprevir and telaprevir triple therapy in patients with HCV-1 infection, as well as viral genomic polymorphisms and genetic variants that may protect against anemia. Pharmacogenetic information offers a personalized medicine approach to help clinicians and patients make better informed decisions to maximize response and minimize toxicity for the treatment of chronic HCV infection.

G protein-coupled receptor accessory proteins and signaling: pharmacogenomic insights

The identification and characterization of the genes encoding G protein-coupled receptors (GPCRs) and the proteins necessary for the processes of ligand binding, GPCR activation, inactivation, and receptor trafficking to the membrane are discussed in the context of human genetic disease. In addition to functional GPCR variants, the identification of genetic disruptions affecting proteins necessary to GPCR functions have provided insights into the function of these pathways. Gsα and Gβ subunit polymorphisms have been found to result in complex phenotypes. Disruptions in accessory proteins that normally modify or organize heterotrimeric G-protein coupling may also result in disease states. These include the contribution of variants of the regulator of G protein signaling (RGS) protein to hypertension; the role variants of the activator of G protein signaling (AGS) proteins to phenotypes (such as the type III AGS8 variant to hypoxia); the contribution of G protein-coupled receptor kinase (GRK) proteins, such as GRK4, in disorders such as hypertension. The role of accessory proteins in GPCR structure and function is discussed in the context of genetic disorders associated with disruption of the genes that encode them. An understanding of the pharmacogenomics of GPCR and accessory protein signaling provides the basis for examining both GPCR pharmacogenetics and the genetics of monogenic disorders that result from disruption of given receptor systems.

The evolutionary significance of depression in Pathogen Host Defense (PATHOS-D)

Given the manifold ways that depression impairs Darwinian fitness, the persistence in the human genome of risk alleles for the disorder remains a much debated mystery. Evolutionary theories that view depressive symptoms as adaptive fail to provide parsimonious explanations for why even mild depressive symptoms impair fitness-relevant social functioning, whereas theories that suggest that depression is maladaptive fail to account for the high prevalence of depression risk alleles in human populations. These limitations warrant novel explanations for the origin and persistence of depression risk alleles. Accordingly, studies on risk alleles for depression were identified using PubMed and Ovid MEDLINE to examine data supporting the hypothesis that risk alleles for depression originated and have been retained in the human genome because these alleles promote pathogen host defense, which includes an integrated suite of immunological and behavioral responses to infection. Depression risk alleles identified by both candidate gene and genome-wide association study (GWAS) methodologies were found to be regularly associated with immune responses to infection that were likely to enhance survival in the ancestral environment. Moreover, data support the role of specific depressive symptoms in pathogen host defense including hyperthermia, reduced bodily iron stores, conservation/withdrawal behavior, hypervigilance and anorexia. By shifting the adaptive context of depression risk alleles from relations with conspecifics to relations with the microbial world, the Pathogen Host Defense (PATHOS-D) hypothesis provides a novel explanation for how depression can be nonadaptive in the social realm, whereas its risk alleles are nonetheless represented at prevalence rates that bespeak an adaptive function.

Association of genetic variations in GNB1 with response to peginterferon plus ribavirin therapy for chronic hepatitis C in a Chinese population in Taiwan

Background

The aim of this study was to evaluate whether polymorphisms in the guanine nucleotide binding (G protein), beta polypeptide 1 (GNB1) gene are associated with a rapid virological response (RVR) among HCV genotype 1 (HCV-1) and 2 (HCV-2) infected patients receiving peginterferon plus ribavirin treatment (PEG-IFNα-RBV).

Methods

We analyzed the association between RVR to PEG-IFNα-RBV therapy and 4 tagging single nucleotide polymorphisms (SNPs) of the GNB1 gene. This study included 265 HCV-1 and 195 HCV-2 infected patients in a Chinese population in Taiwan.

Results

Among the GNB1 SNPs examined, the combination of genotypes G/G and G/T populations of rs12126768 was significant inversely correlated with RVR in HCV-1 infected patients (P = 0.0330), whereas HCV-2 infected patients, combination of A/A and A/C genotypes populations at rs4648727 responded better to the PEG-IFNα-RBV treatment (P = 0.0089). However, there were no significant differences in the allele frequencies of those SNPs between RVR responders and non-responders. Several RVR susceptibility GNB1 haplotypes were identified, and the ACAT haplotype of the 4 SNPs may increase the successful outcomes of HCV-1 and HCV-2 infected patients (P = 0.0261 and P = 0.0253, respectively).

Conclusion

The data for GNB1 SNPs and the association of RVR showed that GNB1 polymorphisms might be associated with the therapeutic outcomes of HCV-1 and HCV-2 infected patients under standard of care (SOC) treatment.

The role of G protein gene GNB3 C825T polymorphism in HIV-1 acquisition, progression and immune activation

Background

The GNB3 C825T polymorphism is associated with increased G protein-mediated signal transduction, SDF-1α-mediated lymphocyte chemotaxis, accelerated HIV-1 progression, and altered responses to antiretroviral therapy among Caucasian subjects. The GNB3 825T allele is highly prevalent in African populations, and as such any impact on HIV-1 acquisition or progression rates could have a dramatic impact. This study examines the association of the 825T polymorphism with HIV-1 acquisition, disease progression and immune activation in two African cohorts. GNB3 825 genotyping was performed for enrolees in both a commercial sex worker cohort and a perinatal HIV transmission (PHT) cohort in Nairobi, Kenya. Ex vivo immune activation was quantified by flow cytometry, and plasma chemokine levels were assessed by cytokine bead array.

Results

GNB3 genotype was not associated with sexual or vertical HIV-1 acquisition within these cohorts. Within the Pumwani cohort, GNB3 genotype did not affect HIV-1 disease progression among seroconverters or among HIV-1-positive individuals after adjustment for baseline CD4 count. Maternal CD4 decline and viral load increase in the PHT cohort did not differ between genotypes. Multi-parametric flow cytometry assessment of T cell activation (CD69, HLA-DR, CD38) and Treg frequency (CD25⁺FOXP3⁺) found no differences between genotype groups. Plasma SDF-1α, MIP-1β and TRAIL levels quantified by cytokine bead array were also similar between groups.

Conclusions

In contrast to previous reports, we were unable to provide evidence to suggest that the GNB3 C825T polymorphism affects HIV-1 acquisition or disease progression within African populations. Ex vivo immune activation and plasma chemokine levels were similarly unaffected by GNB3 genotype in both HIV-1-negative and HIV-1-positive individuals. The paucity of studies investigating the impact of GNB3 polymorphism among African populations and the lack of mechanistic studies make it difficult to assess the true biological significance of this polymorphism in HIV-1 infection.

SNPs in genes encoding G proteins in pharmacogenetics

Heterotrimeric guanine-binding proteins (G proteins) transmit signals from the cell surface to intracellular signal cascades and are involved in various physiological and pathophysiological processes. Polymorphisms in the genes GNB3 (encoding the Gβ3 subunit), GNAS (encoding the Gαs subunit) and GNAQ (encoding the Gαq subunit) have been the primary focus of investigation. Polymorphisms in these genes could be associated with different complex phenotypes underlining that alterations in G-protein signaling can cause multiple disorders. G proteins present a point of convergence or ‘bottleneck’ between various receptors and effectors, thus making them a sensible tool for pharmacogenetic studies. The pharmacogenetic studies performed to date mostly demonstrate an association between G-protein polymorphisms and response to therapy or occurrence of adverse drug effects. Therefore, polymorphisms in genes encoding G-protein subunits may help to individualize drug treatment in various diseases with regard to both efficacy and safety.

Prospects for personalizing antiviral therapy for hepatitis C virus with pharmacogenetics

Chronic hepatitis C virus (HCV) infection is a major cause of liver disease worldwide. HCV infection is currently treated with IFNα plus ribavirin for 24 to 48 weeks. This demanding therapy fails in up to 50% of patients, so the use of pharmacogenetic biomarkers to predict the outcome of treatment would reduce futile treatment of non-responders and help identify patients in whom therapy would be justified. Both IFNα and ribavirin primarily act by modulating the immune system of the patient, and HCV uses multiple mechanisms to counteract the antiviral effects stimulated by therapy. Therefore, response to therapy is influenced by variations in human genes governing the immune system and by differences in HCV genes that blunt antiviral immune responses. This article summarizes recent advances in understanding how host and viral genetic variation affect outcome of therapy. The most notable human associations are polymorphisms within the IL28B gene, but variations in human leukocyte antigen and cytokine genes have also been associated with treatment outcome. The most prominent viral genetic association with outcome of therapy is that HCV genotype 1 is much less sensitive to treatment than genotypes 2 and 3, but genetic differences below the genotype level also influence outcome of therapy, presumably by modulating the ability of viral genes to blunt antiviral immune responses. Pharmacogenetic prediction of the outcome of IFN-based therapy for HCV will require integrating the efficacies of the immunosuppressive mechanisms of a viral isolate, and then interpreting the viral resistance potential in context of the genetic profile of the patient at loci associated with outcome of therapy. Direct-acting inhibitors of HCV that will be used in combination with IFNα are nearing approval, so genetic prediction for anti-HCV therapy will soon need to incorporate viral genetic markers of viral resistance to the new drugs.

Viral hepatitis: human genes that limit infection

Treatment response and susceptibility to chronic viral hepatitis C and B may be modified by host genetic factors. The majority of genetic variants that confer a significant risk have been localized in genes involved in immune response. However, many findings could not be replicated and almost none of the identified risk factors had a noticeable impact on clinical decisions. In contrast, recent findings in independent large genome wide association studies confirmed genetic variants in the interferon gamma gene locus as strong predictors of outcome with outstanding clinical relevance. This review gives an overview on significant genetic susceptibility factors for susceptibility and treatment outcome in chronic viral hepatitis C and B that have been identified by the classical candidate gene approach and genome wide studies and also highlights some recent findings on genetic factors for common adverse drug reactions.

Prognostic assessment of three single-nucleotide polymorphisms (GNB3 825C>T, BCL2-938C>A, MCL1-386C>G) in extrahepatic cholangiocarcinoma

BACKGROUND/AIMS

Cholangiocellular carcinoma (CCA) has a devastating prognosis and markers enabling a precise prediction of the clinical outcome have long remained scarce. Recently, it has been demonstrated that genotype distribution of several single-nucleotide polymorphisms (SNPs) in genes that modulate G protein-signal transduction and apoptosis can serve as helpful predictive parameters in various carcinomas. We here aimed at extending the panel of SNPs suitable for predicting the outcome of CCA.

METHODOLOGY

Forty Caucasian patients with extrahepatic CCA and 40 age- and sex-matched healthy white Caucasians were genotyped to elucidate putative associations between clinical outcome and genotypes of the three following SNPs: G protein beta 3 (GNB3) 825C>T, B-cell-lymphoma-2 (Bcl-2) -938C>A, and myeloid cell leukemia-1 (Mcl-1) -386C>G.

RESULTS

Patients homozygous for the C allele of the GNB3 825C>T polymorphism exhibited a significant prolonged overall survival compared with patients displaying the CT or TT genotype (median survival [months]: 31 vs. 13 vs. 7; p < .05) and also showed lower bilirubin serum levels. Additionally, the CC genotype of the BCL2-938C>A polymorphism was associated with higher GLDH serum activities (U/l; 29.8 +/- 7.1 vs. 11.4 +/- 4.3 vs. 5.6 +/- 1.7 comparing CC vs. CA vs. AA; p < .05). Genotype distributions for all SNPs were not significantly different in patients vs. controls.

CONCLUSIONS

GNB3 825C>T SNP may be a novel independent prognostic marker for patients suffering from extrahepatic CCA with the CC genotype to be associated with a favorable clinical outcome. Further prospective studies are needed to confirm these results and reveal additional functional SNP effects.

Emerging concepts in biomarker discovery; the US-Japan Workshop on Immunological Molecular Markers in Oncology

Supported by the Office of International Affairs, National Cancer Institute (NCI), the "US-Japan Workshop on Immunological Biomarkers in Oncology" was held in March 2009. The workshop was related to a task force launched by the International Society for the Biological Therapy of Cancer (iSBTc) and the United States Food and Drug Administration (FDA) to identify strategies for biomarker discovery and validation in the field of biotherapy. The effort will culminate on October 28th 2009 in the "iSBTc-FDA-NCI Workshop on Prognostic and Predictive Immunologic Biomarkers in Cancer", which will be held in Washington DC in association with the Annual Meeting. The purposes of the US-Japan workshop were a) to discuss novel approaches to enhance the discovery of predictive and/or prognostic markers in cancer immunotherapy; b) to define the state of the science in biomarker discovery and validation. The participation of Japanese and US scientists provided the opportunity to identify shared or discordant themes across the distinct immune genetic background and the diverse prevalence of disease between the two Nations. Converging concepts were identified: enhanced knowledge of interferon-related pathways was found to be central to the understanding of immune-mediated tissue-specific destruction (TSD) of which tumor rejection is a representative facet. Although the expression of interferon-stimulated genes (ISGs) likely mediates the inflammatory process leading to tumor rejection, it is insufficient by itself and the associated mechanisms need to be identified. It is likely that adaptive immune responses play a broader role in tumor rejection than those strictly related to their antigen-specificity; likely, their primary role is to trigger an acute and tissue-specific inflammatory response at the tumor site that leads to rejection upon recruitment of additional innate and adaptive immune mechanisms. Other candidate systemic and/or tissue-specific biomarkers were recognized that might be added to the list of known entities applicable in immunotherapy trials. The need for a systematic approach to biomarker discovery that takes advantage of powerful high-throughput technologies was recognized; it was clear from the current state of the science that immunotherapy is still in a discovery phase and only a few of the current biomarkers warrant extensive validation. It was, finally, clear that, while current technologies have almost limitless potential, inadequate study design, limited standardization and cross-validation among laboratories and suboptimal comparability of data remain major road blocks. The institution of an interactive consortium for high throughput molecular monitoring of clinical trials with voluntary participation might provide cost-effective solutions.

G protein beta3 subunit C825T polymorphism modifies the presentation of temporal lobe epilepsy

PURPOSE

Experimental studies suggest a role of G protein-mediated signaling pathways in epileptogenesis. A genetic variation affecting the G protein subunit Gbeta3 denoted the C825T polymorphism has been reported to increase the signaling efficiency through G(i) proteins and to modify responses to certain drugs. The C825T polymorphism has also been associated with several diseases including hypertension, diabetes type II, obesity, and major depressive disorder. In this study, we have explored whether the G protein polymorphism C825T is associated with or influences temporal lobe epilepsy (TLE).

METHODS

The study included 227 TLE patients, 186 controls, and 106 family members of TLE patients. DNA was extracted from blood samples and typing of the polymorphism was performed. Case record forms were analyzed for all the homozygote TLE patients and homozygote controls, i.e., carrying the TT genotype as well as for 28 matched TLE patients (16 females, 12 males) without the polymorphism (CC genotype).

RESULTS

Typing of the C825T polymorphism showed that 6.0% of the TLE patients, 7.0% of the controls, and 7.5% of the family members were homozygote for the polymorphism; i.e., carrying the TT genotype. TLE patients carrying the TT genotype had higher severity score on eight out of nine predefined parameters compared with the TLE patients without polymorphism, i.e., carrying CC genotype. TT genotype TLE patients also had increased body mass index, body weight, and waist circumference compared with the TLE patients carrying the CC genotype. There was no increased frequency of hypertension or diabetes.

CONCLUSIONS

There was no increased frequency of TLE between the carriers of the TT genotype compared with the healthy controls and/or family members without epilepsy. However, the TLE patients with the TT genotype showed tendencies of a more severe disease phenotype.

Association of TLR7 single nucleotide polymorphisms with chronic HCV-infection and response to interferon-a-based therapy

An efficient immune response against hepatitis C virus (HCV) is necessary to clear infection. As HCV is a single-stranded RNA virus, a role for TLR7 in the immune response against HCV is possible, and early clinical studies have demonstrated an antiviral effect of TLR7 stimulation. We tested the hypothesis that genetic variations of TLR7 are associated with chronic HCV-infection and outcome of therapy. The prevalence of three TLR7 variations was analysed in 978 patients with chronic HCV-infection, 898 patients with chronic liver disease of other aetiologies, and in 203 healthy controls. The prevalence of TLR7 variations was correlated with the response to interferon-alpha-based treatment in 544 patients with chronic HCV-infection. We analysed TLR7 polymorphisms by melting curve analysis and reconstructed haplotypes. The c.32A>T variation was over-represented in female patients with chronic HCV-infection compared to patients with other chronic liver diseases and to healthy controls (P < 0.05). In contrast, c.2403 G>A was less prevalent in male patients with chronic HCV-infection (P < 0.05). No association was observed for the third variant, c.1-120T>G. Haplotype analysis confirmed the differential distribution of TLR7 variants between the groups. Within the group of female patients with chronic HCV-infection, c.32T was predictive of an unfavourable outcome of interferon-alpha therapy (P < 0.05). This study reports the association of TLR7 variants with chronic HCV-infection and with the response to interferon-alpha therapy in patients with chronic HCV-infection. Our results suggest that variations of TLR7 impair the immune response to HCV and imply a gender-specific effect of this X-chromosomal variation.

Pharmacogenomics of G protein-coupled receptor signaling: insights from health and disease

The identification and characterization of the processes of G protein-coupled receptor (GPCR) activation and inactivation have refined not only the study of the GPCRs but also the genomics of many accessory proteins necessary for these processes. This has accelerated progress in understanding the fundamental mechanisms involved in GPCR structure and function, including receptor transport to the membrane, ligand binding, activation and inactivation by GRK-mediated (and other) phosphorylation. The catalog of G(s)alpha and Gbeta subunit polymorphisms that result in complex phenotypes has complemented the effort to catalog the GPCRs and their variants. The study of the genomics of GPCR accessory proteins has also provided insight into pathways of disease, such as the contributions of regulator of G protein signaling (RGS) protein to hypertension and activator of G protein signaling (AGS) proteins to the response to hypoxia. In the case of the G protein-coupled receptor kinases (GRKs), identified originally in the retinal tissues that converge on rhodopsin, proteins such as GRK4 have been identified that have been subsequently associated with hypertension. Here, we review the structure and function of GPCR and associated proteins in the context of the gene families that encode them and the genetic disorders associated with their altered function. An understanding of the pharmacogenomics of GPCR signaling provides the basis for examining the GPCRs disrupted in monogenic disease and the pharmacogenetics of a given receptor system.

The GNB3 C825T polymorphism affects response to HCV therapy with pegylated interferon in HCV/HIV co-infected but not in HCV mono-infected patients

BACKGROUND/AIMS

Response to HCV treatment with pegylated interferon-alpha is variable but might at least in part depend on genetic host factors. The G protein beta3 unit (GNB3) C825T polymorphism has been shown to affect treatment response in HCV mono-infection. Here, we analyzed the impact of the GNB3 genotype in the context of HCV/HIV co-infection.

METHODS

HIV/HCV co-infected (n=112) and HCV mono-infected patients (n=150), receiving therapy with pegylated IFN-alpha/ribavirin, were enrolled into this study. Furthermore, we analyzed 220 healthy and 92 HIV mono-infected patients. GNB3 genotype was defined and correlated with respect to treatment response.

RESULTS

GNB3 genotype distribution differed significantly between HIV/HCV co-infected patients and HIV-positive/HCV-negative (p=0.0002) or healthy controls (p=0.03). Patients with a GNB3 CC genotype had significantly lower SVR rates as compared to carriers of a non-CC genotype (52% versus 77%; p=0.018). In a logistic regression analysis the GNB3 genotype and the HCV genotype were significantly associated with response to treatment (p=0.018). In contrast to HIV/HCV co-infected patients, GNB3 genotype did not affect response to treatment in HCV mono-infected patients.

CONCLUSIONS

The GNB3 825 CC genotype is associated with poor SVR rates in HIV/HCV co-infected patients. This underlines the impact of genetic host factors for treatment response.

The G protein beta3 subunit 825C allele is associated with sudden infant death due to infection

AIM

To investigate the Gbeta3 subunit C825T polymorphism with regard to sudden unexpected infant death. The reported association between the Gbeta3s protein and increased immune cell function in humans makes this polymorphism highly interesting both with regard to sudden infant death syndrome (SIDS) and deleterious infectious disease.

METHODS

The cases investigated in the present study consist of 250 SIDS cases, 38 cases of sudden unexpected infant death due to infection and 99 living infant controls. Typing of the C825T polymorphism was performed by real-time PCR with allele-specific probes and melting curve analyses.

RESULTS

The cases of infectious death have a higher percentage of both the C allele (p=0.037 compared to the SIDS cases, p=0.022 compared to the controls) and the CC genotype (p=0.05 compared to the SIDS cases, p=0.016 compared to the controls). There were no differences between SIDS cases and controls.

CONCLUSION

The observed association between the 825C allele and infectious death may indicate that the presence of the 825T allele exerts a protective effect towards serious infection, possibly through enhanced G protein signalling. The C allele, on the other hand, appears to represent a disadvantage in this regard.

Is there an association between GNbeta3-C825T genotype and lower functional gastrointestinal disorders?

BACKGROUND & AIMS

GNbeta3 influences G-protein translation of a majority of ligand-receptor activations. It has been reported that functional dyspepsia (FD) is associated with homozygous genotypes of the C825T polymorphism in the GNbeta3 gene. It is unknown whether the GNbeta3 genotype is associated with lower functional gastrointestinal disorders (FGID). We aimed to compare the prevalence of the different GNbeta3-C825T genotypes in patients with lower FGID and healthy controls and to test the associations of these genetic variations with subgroups of irritable bowel syndrome (IBS), functional abdominal pain (FAP), lower FGID-FD overlap, and high somatic symptom scores.

METHODS

GNbeta3-C825T polymorphism was analyzed in DNA from blood samples of 233 patients with lower FGID and 152 healthy controls. A validated bowel questionnaire characterized the FGID phenotype: 82 with IBS constipation, 94 with IBS diarrhea, 38 with IBS alternating bowel function, and 19 with FAP. There were 159 patients with lower FGID and overlap FD using Rome II criteria. Regression analyses assessed associations of the GNbeta3 genotypes with lower FGID as a group, and subgroups of FGID and somatic symptom scores.

RESULTS

GNbeta3-C825T genotype distributions were similar between healthy controls (50.7% CC, 40.8% TC) and patients with lower FGID (8.6% TT, 51.5% CC, 40.8% TC, and 7.7% TT). There were no significant associations of GNbeta3-C825T polymorphism with lower FGID overall or with the separate symptom subgroups including IBS, FAP, lower FGID-FD overlap, or high somatic symptom scores.

CONCLUSIONS

In contrast to the reported association with FD, GNbeta3-C825T polymorphism is not associated significantly with lower FGID, with different IBS or FAP phenotypes, or lower FGID-FD overlap.

Genetic diseases associated with heterotrimeric G proteins

Heterotrimeric G proteins couple receptors for diverse extracellular signals to effector enzymes or ion channels. Each G protein comprises a specific alpha-subunit and a tightly bound betagamma dimer. Several human disorders that result from genetic G-protein abnormalities involve the imprinted GNAS gene, which encodes Gs alpha, the ubiquitously expressed alpha-subunit that couples receptors to adenylyl cyclase and cAMP generation. Loss-of-function and gain-of-function mutations, in addition to imprinting defects, of this gene lead to diverse clinical phenotypes. Mutations of GNAT1 and GNAT2, which encode the retinal G proteins (transducins), are rare causes of specific congenital visual defects. Common polymorphisms of the GNAS and GNB3 (which encodes Gbeta3) genes have been associated with multigenic disorders (e.g. hypertension and metabolic syndrome). To date, no other G proteins have been implicated directly in human disease.