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ORIGINAL ARTICLE
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Vitamin D receptor gene variations and their haplotypic association: Possible impact on gastric cancer risk


1 Department of Biochemistry, Associated SMHS and Super Speciality Hospital and Research Centre, Government Medical College, University of Kashmir, Srinagar, Jammu and Kashmir, India
2 Department of Surgery, Associated SMHS and Super Speciality Hospital, Government Medical College, Srinagar, Jammu and Kashmir, India
3 Department of Biotechnology, Government College for Women, Cluster University, Srinagar, Jammu and Kashmir, India

Date of Submission28-Aug-2021
Date of Acceptance05-Oct-2021
Date of Web Publication03-May-2022

Correspondence Address:
Sabhiya Majid,
Department of Biochemistry, Government Medical College and Associated Hospitals and Research Centre, University of Kashmir, Srinagar - 190 010, Jammu and Kashmir
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcrt.jcrt_1479_21

 > Abstract 


Background: Vitamin D receptor (VDR) gene alterations have been associated with the occurrence and prognosis of various types of cancers, but only few studies have focussed on gastric cancer (GC) risk.
Objectives: This case–control study was conceived to evaluate possible association of VDR polymorphisms (Fok1, Taq1, and Cdx2) with GC risk.
Materials and Methods: A total of 293 subjects, including 143 GC patients and 150 controls were included in this study. The genotypes were elucidated by polymerase chain reaction-restriction fragment length polymorphism followed by DNA sequencing.
Results: The frequency of Fok1 genotypes (TC and TT) was found higher in GC cases compared to controls (P ≤ 0.05). In the stratified analysis, we observed a significant association of the (CT + TT) variant with GC risk in males, rural dwellers, smokers, and preobese cases, and those having no family history of Gastrointestinal cancer (P ≤ 0.05). In silico analysis predicted that the Fok1 variant impacts the stability and functional efficiency of the protein. Some exact haplotypes (CCG and CCA) of the VDR gene may act as low penetrance alleles in inclination to GC.
Conclusion: VDR Fok1 polymorphism is significantly associated with GC risk in the Kashmiri population. Specific haplotypes in the VDR gene could act synergistically in the development of GC

Keywords: Cdx2, Fok1, gastric cancer, Kashmiri population, Taq1, Vitamin D receptor polymorphism



How to cite this URL:
Qadir J, Majid S, Khan MS, Wani MD, Naikoo NA. Vitamin D receptor gene variations and their haplotypic association: Possible impact on gastric cancer risk. J Can Res Ther [Epub ahead of print] [cited 2022 Nov 29]. Available from: https://www.cancerjournal.net/preprintarticle.asp?id=344713




 > Introduction Top


Gastric cancer (GC) is responsible for over one million new cases in 2020 and an estimated 769,000 deaths, ranking fifth for incidence and fourth for mortality globally.[1] In men, it is the most commonly diagnosed cancer and the leading cause of cancer death in several South Central Asian countries.[1],[2] The Kashmir Valley is located at a high altitude in the Northern region of India with ethnic population and peculiar dietary habits. In the Kashmir valley, GC is the most common type of cancer that accounts about 18.8% of all cancers.[3] The development of GC is associated with several risk factors, including high salt diet, age, family history, smoking, and infection with Helicobacter pylori.[4]

Vitamin D receptor (VDR) gene is present on chromosome 12q12-q14.[5],[6] Recent studies have reported that the VDR gene is associated with the number of diseases, including cancer, autoimmune diseases, diabetes, cardiovascular diseases, and tuberculosis.[5],[6] VDR, a Type II nuclear receptor, having molecular mass of approximately 48 kDa, belongs to the superfamily of the steroid/thyroid hormone receptor that act through 1,25 dihydroxy Vitamin D3 or calcitriol.[7] The binding of 1,25 dihydroxy Vitamin D3 initiates a sequence of conformational changes, and various corepressors are released that lead to the formation of VDR-retinoid X receptor (RXR) heterodimer and the recruitment of coactivators to initiate the transcription.[6] VDR-RXR complex binds at specific sites in the promoter region of target genes and directly regulates gene transcription via recruitment of several components of the transcription initiation complex that leads to chromatin remodeling.[8]

Several in vivo and in vitro studies have indicated that VDR has a significant effect on cancer etiology.[9],[10] VDR gene is reported to have a potential influence to suppress tumor formation by modulating different signaling pathways and modifying the gene expression of several important proteins involved in the regulation of the cell cycle.[10] A number of investigations have shown that VDR genetic variations are significantly associated with the increased risk of several cancers, including colon, breast, ovarian, cervical, lung, skin, kidney.[6],[10] Although the impact of VDR gene alterations on the susceptibility of GC remains unknown due to lack of data, VDR gene polymorphisms may have a definite effect in the etiology of GC as it is involved in a number of complex biological processes such as the cell cycle regulation, cell proliferation, differentiation and apoptosis via multiple pathways.[11]

The VDR Fok1 (rs2228570), Taq1 (rs731236), and Cdx2 (rs11568820) single-nucleotide polymorphisms (SNPs) effect the functional efficiency of VDR protein; hence, their association with cancer risk is most frequently studied. Therefore, we conducted a case–control study to evaluate any possible association of VDR variants and GC risk. To our knowledge, it is the first study that examines the association of VDR gene polymorphism and the risk of GC among the Kashmiri population.


 > Materials and Methods Top


Ethics

The study was approved by the Institutional Ethical Clearance Committee of Government Medical College Srinagar (CDSCO U/P No: 666/ETH/GMC). All the samples were collected after taking written informed consent from the patients, and proper ethical procedures were followed.

Study design

It was a case–control study conducted by the Department of Biochemistry in collaboration with the Department of General Surgery, Government Medical College Srinagar and Associated Shri-Maharaja Hari Singh and Super Speciality Hospital in Kashmir valley (North India). Written informed consent was obtained from study subjects. The study was approved by the Institutional Ethical Committee of Government Medical College Srinagar in accordance with the ethical standards of the World Medical Association Declaration of Helsinki involving human subjects and/or animals.

Sample size and study subjects

Sample size for this study was calculated by statistical software G POWER 3.1.9.7. Keeping the power of the study (1− β) as 80% (0.8) the sample size for cases and controls came out to be 136 and 148, respectively.

This study included a total of 293 subjects that were recruited between October 2017 and January 2020. Among the 293 subjects, 143 were newly diagnosed GC patients. All subjects were of Kashmiri ethnicity. The cases were histopathologically confirmed GC cases. Another pool of 150 normal healthy controls (free from any tumor and genetic disorder) were recruited for the study. The cases and controls were frequency-matched by age and gender.

Inclusion and exclusion criteria

Patients freshly diagnosed with GC; having no prior history of cancer and not received any Chemo-radio adjuvant therapy were included in the study. Patients with any other type of cancer and/or genetic disorder were excluded from the study.

Sample and DNA extraction

Around 03 ml of blood sample was taken from subjects in EDTA coated vials from and then stored at − 80°C until further processing. Genomic DNA was extracted from these samples by using GenElute™ Blood Genomic DNA kit (Sigma-Aldrich, USA) according to the given protocol. The quality of DNA was assessed by agarose gel electrophoresis and purity by measuring the optical density at A260/A280.

Genotyping

Gene polymorphisms were analyzed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) by using specific primers [Supplementary Table 1] in a reaction mixture of 50 μl.



Vitamin D receptor Fok1 polymorphism

The VDR Fok1 specific fragments of 265 bp were amplified in a PCR reaction mixture of 50 μL containing 200 μM dNTPs (Biotools, Spain); 2 pmol/μL of forward and reverse primers (Eurofins Genomics India). 50–150 ng genomic DNA; 1X PCR buffer (2 mM MgCl2) (Biotools, Spain); 1.5 Units of Taq polymerase (Biotools, Spain). The cycling condition included the initial denaturation at 94°C for 9 min, followed by 34 cycles: Denaturation 45 s at 94°C, annealing 45 s at 60°C, extension 72°C for 45 s and final extension for 5 min. The amplicons were then digested at 37°C for 15–20 min with Fast Digest Fok1 (Thermo Scientific, EU, Lithuania) restriction enzyme. The digested products were then loaded into 3.5% agarose gel and analyzed under the UV illuminator. The homozygous wild-type CC genotype lacked the Fok1 restriction and exhibited only one band of 265 bp. The homozygous mutant TT genotypes yielded two bands of 196 and 69 bp, whereas the heterozygous CT genotypes has three bands of 265, 196, and 96 bp.

Vitamin D receptor Taq1 Polymorphism

The PCR conditions are as under: Initial denaturation 94°C for 5 min, followed by 35 cycles denaturation 1 min at 94°C, annealing 1 min at 61°C, extension 72°C for 2 min and then final extension for 4 min. The reaction mixture contains genomic DNA of 50–150 ng; 1X PCR buffer (2 mM MgCl2) (Biotools, Spain); 200 μM dNTPs (Biotools, Spain); 1.5 Units of Taq polymerase (Biotools, Spain); 2 pmol/μl of forward and reverse primers (Eurofins Genomics India) in 50 μl of the reaction mixture. The PCR products of 740 bp were verified on 1.5% agarose gel and digested with Taq1 (Thermo Scientific, (EU) Lithuania) restriction enzyme at 65°C for 16 h. The digested products of 8 μl were loaded into 3.0% agarose gel and then analyzed under the UV illuminator. The TaqI digestion had an obligatory restriction site, the wild TT genotype exhibited two bands of 245 and 495 bp, whereas the CC genotype shows three bands of 205, 245, and 290 bp. The TC genotype yielded four bands of 495, 205, 245, and 290 bp.

Vitamin D receptor Cdx2 polymorphism

The PCR amplification was accomplished with a 50 μl reaction mixture containing 200 μM dNTPs (Biotools, Spain); 1.5 Units of Taq polymerase (Biotools, Spain); 50–150 ng genomic DNA; 1X PCR buffer (2 mM MgCl2) (Biotools, Spain); 2 pmol/μl of forward and reverse primers (Eurofins Genomics India Pvt. Ltd.,). The PCR conditions are as under: Initial denaturation at 94°C for 5 min, followed by 35 cycles of denaturation 1 min at 94°C, annealing 1 min at 61°C, extension for 72°C for 1 min and final extension for 5 min. The PCR products of 135 bp fragments were verified on 2% agarose gel and then digested with Bpu10I (Thermo scientific, USA) restriction enzyme for 16 h at 37°C. The digested product of the reaction mixture of 9 μl was loaded into 4% agarose gel containing ethidium bromide and analyzed under the UV illuminator. Site in wild genotype GG produced only one band of 135 bp, whereas, the presence of restriction site at AA genotype exhibits two bands of 72 and 63 bp. The GA genotype exhibits three bands of 135, 72, and 63 bp.

DNA sequencing

To re-confirm the PCR-RFLP results for Fok1 SNP, the amplicons with wild sequence and amplicons showing variations were subjected to DNA sequencing, using the automated DNA sequencer ABI prism 310 (Applied Biosystems, USA).

Computational prediction tool

To predict the possible effect of amino acid substitution on protein, the missense variants were analysed by MUpro and Hope project tool.

Statistical analysis

Statistical analysis was performed using SPSS 16.0 statistical package (SPSS Inc., Chicago IL, USA). The body mass index was analyzed by an independent t-test between the groups. To compare the categorical variables such as age, sex, smoking status, etc., between the cases and controls Chi-square test was used. The allelic and genotypic frequencies of cases and controls were compared by Chi-square test and Hardy-Weinberg equilibrium. The association of VDR genotypes with GC risk was estimated by odds ratios (ORs) and 95% confidence intervals (95% CIs), P < 0.05 was considered as significant.


 > Results Top


Patient characteristics

In this study, blood samples from 143 GC patients and 150 healthy controls were analyzed for VDR genotyping. All cases and controls were well matched as per their age, gender, dwelling, smoking status, and body mass index (BMI). 40.6% of GC cases were <50 years of age as compared to 46.7% of controls who were <50 years of age (P = 0.3). The calculated mean age (in years) of cases and controls was 55.3 ± 11.7 and 53.8 ± 11.8, respectively. About 71.4% of GC cases consumed ≥5 cups of salt tea/day compared to only 31.3% of controls who consumed ≥5 cups of salt tea/day (P < 0.0001). The high rate of cancer incidence was found among the GC patients who had any previous family history of Gastrointestinal cancer when compared to controls (P = 0.004). However, when compared, no significant difference between BMI of cases and controls (22.68 ± 4.27 vs. 23.81 ± 3.71, P > 0.001). Sociodemographic and clinicopathological parameters of cases and controls are summarized in [Table 1].
Table 1: Demographic and clinicopathological parameters of the study subjects

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Genotypes and allele distribution

The partial electrophoretograms pertaining to all genotypes of FokI, TaqI, and Cdx2 SNPs are depicted in [Figure 1], [Figure 2], [Figure 3], respectively. Genotypic and allelic frequency distributions of VDR polymorphisms of cases and controls is summarized in [Table 2]. In the present study, distributions of genotype frequencies of all SNPs were in agreement with Hardy-Weinberg equilibrium (P > 0.05). Logistic regression analysis revealed that the patients with CT and TT genotypes of Fok1 SNP (rs2228570) showed significantly increased risk of GC than those with CC genotype with respect to their control counterparts (CC vs. CT, OR = 1.8, P = 0.018; CC vs. TT, OR = 2.3, P = 0.016). Variant (T) allele was also significantly associated with GC risk among the cases compared to controls (OR = 1.6, P = 0.004). However, no significant association of VDR Taq1 (rs731236) and Cdx2 (rs11568820) SNPs was observed with GC risk (P > 0.05).
Figure 1: Partial electrophoretograms of FokI (rs2228570; C to T) single nucleotide polymorphism showing (a) homozygous wild (C/C) genotype (b) heterozygous (C/T) genotype and (c) homozygous mutant (T/T) genotype

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Figure 2: Partial electrophoretograms of TaqI (rs731236; T to C) single nucleotide polymorphism showing (a) Homozygous wild (T/T) genotype (b) heterozygous (T/C) genotype and (c) homozygous mutant (C/C) genotype

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Figure 3: Partial electrophoretograms of Cd× 2 (rs11568820; G to A) single nucleotide polymorphism showing (a) Homozygous wild (G/G) genotype (b) Heterozygous (G/A) genotype and (c) homozygous mutant (A/A) genotype

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Table 2: Association between genotypic and allelic frequencies of the Vitamin D receptor polymorphisms in gastric cancer cases and controls

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Stratification analysis of Vitamin D receptor polymorphisms and risk of gastric cancer

We further analyzed the effect of VDR Fok1, Taq1, and Cdx2 on GC risk in relation to different variables of GC cases and controls. Due to the low frequency and increased risk of association with GC, the homozygous variant and heterozygous genotypes were combined and compared against the wild genotype. Stratification analysis of VDR SNPs is shown in [Table 3], [Table 4], [Table 5].
Table 3: Association between FokI Vitamin D receptor genotypes and various sociodemographic and clinicopathological characteristics of gastric cancer cases and controls

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Table 4: Association between TaqI Vitamin D receptor genotypes and various sociodemographic and clinicopathological characteristics of gastric cancer cases and controls

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Table 5: Association between Cdx2 Vitamin D receptor genotypes and various sociodemographic and clinicopathological characteristics of gastric cancer cases and controls

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In case of Fok1 VDR polymorphism, there was a significantly higher frequency of variant genotypes (CT + TT) in male cases compared to male controls (70.5% vs. 55.6%; OR = 1.9; P = 0.04). Among rural dwellers, the GC cases with CT + TT genotype were significantly higher than controls (71.2% vs. 55.4%; OR = 1.9, P = 0.028). Furthermore, our study found the significantly higher number of rare alleles (CT + TT) in smoker cases (76.6%) than in smoker controls (60.4%) (OR = 2.1; P = 0.017). Interestingly, among GC patients consuming <5 cups of salt tea/day, almost 90.0% had CT + TT genotype compared to 51.4% of controls consuming <5 cups of salt tea/day but having CT + TT genotype (OR = 8.7; P = 0.00). We found higher percentage of the variant allele (CT + TT) in cases who were preobese (58.5%) as compared to control who were preobese (19.0%) and the association was found significant (OR = 6.0, P = 0.00). Interestingly, cases with normal BMI were having significantly higher frequency of CT + TT genotype compared to controls (OR = 3.2; P = 0.008). Surprisingly, CT + TT genotype was significantly higher in GC cases with no history of Gastrointestinal cancer (69.5%) compared to controls (53.0%) (OR = 2.03; P = 0.007). Surprisingly, GC patients with wild genotype (CC) and having neural invasion were at higher risk of getting GC compared to those with CC genotype but negative for neural invasion (P = 0.03) [Table 3].

Although, we did not find a significant overall association of Taq1 VDR polymorphism with GC risk (P = 0.08) but when stratified, we found that variant genotypes (TC + CC) were significantly higher in GC cases with ≥50 years of age (OR = 2.2; P = 0.016); GC cases consuming <5 cups of salt tea/day (OR = 2.6; P = 0.01); GC cases with normal BMI (OR = 2.3; P = 0.01); GC cases with no history of gastrointestinal cancer (OR = 1.8; P = 0.02) as compared to control counterparts as shown in [Table 4]. In addition, GC patients with TC + CC genotype and having H. pylori infection were at 2.1 times higher risk of getting GC compared to those with TC + CC genotype but negative for H. pylori (P = 0.03). However, no further association was found with any other clinicopathological parameter in GC patients (P > 0.05) [Table 4].

In addition, in case of Cdx2 VDR polymorphism, we do not observe any overall significant difference of genotypes (wild vs. variant) between cases and controls (P = 0.43). Furthermore, no noted association of genotypes was found with any of the clinicopathological characteristics of GC patients (P > 0.05) except a significant negative correlation of variant genotype (GA + AA) with neural invasion [Table 5].

Computational prediction analysis

To predict whether the amino acid substitution affects protein, the FokI nonsynonymous SNP was analyzed by MUpro and Hope project tools. The MUpro tool predicts that variants of Fok1 VDR reduces the stability of protein as compared to its wild type with ΔΔG = −1.02, and Hope project tool revealed that the variant residue (methionine) has large size and has greater hydrophobic nature compared to wild residue (threonine)

Genetic association study of FokI Vitamin D receptor polymorphism

For significant SNP, various inheritance models were applied. The dominant inheritance model was found to be correct for the investigation of Fok1 VDR polymorphism [Supplementary Table 2].



Haplotype frequencies estimation and haplotype association with disease

To assess the combined effect of the three polymorphisms on GC risk, the Haplotype analyses were conducted. Both the cases and controls had haplotypes frequencies >5%. CTG was the most common haplotype, having frequencies of 50.5% and 52.5% in cases and controls, respectively. There was a clear difference between the overall distribution of two haplotypes (CCG and CCA) in cases versus controls (P < 0.0001). Haplotype frequencies were stratified by smoking status, age, and gender. [Table 6] reveals the haplotype pattern for three SNPs among patients and controls.
Table 6: Haplotype frequencies estimation and haplotype association with disease (adjusted by gender + age + smoking status + dwelling + family history + body mass index)

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 > Discussion Top


VDR gene is involved in 1,25 dihydroxy Vitamin D3 mediated transcriptional activation or repression of target genes, and controls the process of the cell cycle by upregulating the cyclin dependant kinase inhibitors (p21 and p27), resulting in the cell cycle arrest at G1/G0 phase.[9],[10] VDR acts as an anticancer agent by inhibiting the proliferation and inducing the process of differentiation and apoptosis in cancer cells.[10] VDR binds to calcitriol and acts as an important mediator in various downstream signaling pathways of Vitamin D that are involved in cancer development.[10],[12] Furthermore, it has been reported that Vitamin D plays a positive prognostic role in GC.[13],[14] The VDR polymorphism and its association with cancer have been explored in numerous studies and it has been observed that it has a significant effect in the development of various cancers such as Endometrial, Ovarian, Cervical, Skin, Breast cancers especially GC.[11],[14],[15],[16],[17],[18] Several SNPs of the VDR gene, including FokI, TaqI, Cdx2 are positively correlated with the increased cancer risk and depending upon their location, these polymorphisms have different effect on the functioning of the VDR protein.[14]

In our study, Fok1 polymorphism was significantly associated with GC risk, in line with recent studies.[14],[15],[16] In the present study, CT and TT genotypes were shown to have a 1.8 and 2.3 fold increased risk of GC than CC genotype (P < 0.01). This pattern of genotype distribution was found consistent with two studies conducted by Cong et al. and Yin et al. wherein they have found T allele showing higher risk of GC and may be involved in Gastric tumorigenesis.[12],[19] In coherence with our study, some recent studies have also reported the possible association of Fok1 polymorphisms with susceptibility to GC.[14],[15],[16] A number of studies have reported the significant association of Fok1 polymorphism with a broad spectrum of cancer, including Breast, Prostrate, Colorectal, Gastric, Skin, and Ovary.[9],[11],[14],[15],[16],[20],[21],[22]

In stratification analysis, we observed a strong association of Fok1 polymorphism with male GC cases when compared to controls. The association of Fok1 polymorphism in male cases with colorectal cancer has been reported previously by few studies.[23],[24] The male folk of Kashmir valley are under chronic stress for more than three decades due to turmoil and uprising in the region and since adrenergic signaling plays a fundamental role in chronic stress-induced tumor progression and metastasis, there is every possibility that males might be incurring GC more often which in turn might have an effect on VDR gene alterations.[25] In addition, estrogen in females interferes with the recruitment or activity of neutrophils and macrophages responsible for the development of GC.[26] We reported strong association of Fok1 polymorphism in cases with rural dwelling. In consistence with our study, Rasool et al. have reported increased incidence of cancer among the rural backward class of Kashmir due to the deficiency of some micronutrients and high consumption of beef and sun-dried vegetables.[24] The cases who smoke had a higher frequency of variant allele (CT + TT; 76.6%) as compared to controls (60.4%) (P = 0.00), which is in line with majority of studies.[27],[28] but in contradiction with few studies done in thyroid cancer.[29] Our study yielded a positive statistical interaction between Fok1 polymorphism and GC among the Preobese cases whose BMI ranges from 25 to 29.99 kg/m2 which is consistent with the finding of Cauci et al. who reported preobese carriers of CT + TT genotype have 6.5 times increased risk of melanoma.[30] Interestingly, we also observed a significant association of Fok1 polymorphism with GC risk in individuals with no family history of Gastrointestinal cancer (P = 0.007), which is in coherence with a study done by Sinotte et al. in breast cancer.[31] In VDR Fok1 SNP, wild (CC) genotype was significantly associated with neural invasion with a positive correlation. Although most of the studies have associated Fok1 CC genotype with aggressive cancers[15],[21] as per few previous studies, CC genotype was associated with an increased risk for more aggressive cancer in terms of node metastasis and neural invasion.[32] However, as per a study by Tang et al. no association was found between neural invasion and thyroid cancer risk.[33]

Fok1 polymorphism involving C to T substitution on exon 2 of VDR gene changes ACG to ATG codon that leads change of threonine to methionine.[16] This substitution generates of an additional start codon and results in the formation of a longer VDR protein of 427 amino acids.[34] The variant protein exerts less efficiency and has a decreased transcriptional activity in mediating 1,25 dihydroxy Vitamin D3 action than wild protein.[6],[15] In consistence with the above studies, the MUpro tool predicted that substitution of threonine by methionine decreases the protein stability compared to the wild type.[35] The hope project tool predicted that the large size of methionine might lead to bumps in resultant protein; moreover, methionine is more hydrophobic than threonine that may lead to loss of hydrogen bonds and/or disturb the correct folding of the protein.[36]

In VDR Fok1 polymorphism, followed a “Dominant mode of inheritance” which assumes that carriers of wild genotypes are associated with the lowest cancer risk compared to heterozygous and rare genotypes.[37]

Moreover, The VDR Taq1 polymorphism involving T to C substitution at exon 9 does not change the amino acid sequence of the resultant protein, but may affect the mRNA expression and protein functioning of the VDR gene.[6],[16] VDR Taq1 polymorphism might alter the mRNA levels by regulating its stability.[6],[38] In the case of VDR Cdx 2 polymorphism, G to A substitution at the promoter region of exon 1e in the VDR gene decreases the transcriptional activity of the VDR promoter.[6],[39] However, we did not find any association of VDR Taq1 and Cdx 2 SNPs with GC in our study subjects.

To ascertain the synergistic effect of VDR polymorphic variants in the growth and expansion of GC, we examined, if the combination of gene variants, might increase GC risk. For this purpose, we considered for an association of haplotype(s) of VDR variants (Fok1/Taq1/Cdx 2) in GC cases and healthy controls. We found the most over-represented haplotype is CCG trailed by CCA depending on their Akaike information criteria (P value). Yin et al. who observed T C C G haplotype in Fok1/Cdx 2/rs2107301/rs1989969 to be over-represented in GC patients.[19] Furthermore, in another study, haplotype C C C A of Fok1/Taq1/Cdx 2/VDR-5132 variants were found significantly associated with greater risk of breast cancer.[40]

Limitation of the study

The population of North India (Kashmir) is ethnic so genetic susceptibility could be present in these individuals which could skew the results. Kashmiri population has high incidence of Gastric and Esophageal cancer, so we might be dealing with individual's high prevalence and these results might not be generalizable. However, further studies with a large sample size are needed to consolidate our findings and investigate the role of VDR polymorphisms in relation to GC outcome in the context of tumor and host characteristics.


 > Conclusions Top


Fok1 variant genotype significantly increases the risk of GC, particularly among males, rural dwellers, smokers, and pre-obese individuals, as it might affect Vitamin D metabolism and the cellular response to Vitamin D. Moreover, In silico analysis predicted that the resultant protein from Fok1 SNP has less stability and functional efficiency compared to wild protein and may contribute significantly towards initiation and development of GC. Further, some specific haplotypes (CCG and CCA) of VDR are over-represented and may act as low penetrance alleles in the predisposition toward GC. VDR FokI may represent an important target for GC therapeutics. In addition, genetic variation in the Vitamin D pathway should be considered when designing potential intervention strategies with Vitamin D supplementation.

Acknowledgment

We are very much thankful to the study participants attending the tertiary care hospital for their cancer care.

Financial support and sponsorship

The Study was funded by the Department of Biochemistry, Government Medical College Srinagar and Associated Hospitals -190010, J and K, India.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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