RESEARCH ARTICLE |
https://doi.org/10.5005/jp-journals-10016-1347 |
Vitamin D Receptor Gene Polymorphism (ApaI and TaqI) and Serum Vitamin D Association with the Susceptibility of Female Genital Tuberculosis Risk
1Department of Obstetrics and Gynecology, All India Institute of Medical Sciences (AIIMS), Raebareli, Uttar Pradesh, India
2,3Department of Obstetrics and Gynecology, King George’s Medical University, Lucknow, Uttar Pradesh, India
4Department of Microbiology, King George’s Medical University, Lucknow, Uttar Pradesh, India
Corresponding Author: Shyam P Jaiswar, Department of Obstetrics and Gynecology, King George’s Medical University, Lucknow, Uttar Pradesh, India, Phone: +91 9415023358, e-mail: spjaiswar59@gmail.com
Received on: 27 September 2023; Accepted: 29 June 2024; Published on: 28 October 2024
ABSTRACT
Background: Genital tuberculosis (GTB) is a significant contributor to female infertility. Vitamin D receptor (VDR) and vitamin D deficiency (VDD) have been linked to increased mycobacterial immunity and susceptibility to female genital tuberculosis (FGTB).
Objective: The study was conducted to evaluate the association between serum vitamin D levels and ApaI and TaqI (VDR) gene polymorphisms to determine susceptibility to FGTB.
Materials and Methods: In a case–control study, blood samples were collected from 150 confirmed FGTB cases. The serum vitamin D level was measured by enzyme-linked immunosorbent assay (ELISA). Total genomic deoxyribonucleic acid (DNA) was extracted and the genotyping of (ApaI and TaqI) polymorphisms was performed using amplification refractory mutation system polymerase chain reaction (ARMS-PCR).
Results: According to this study, the mean serum vitamin D levels were significantly higher among healthy controls (29.04 ± 0.14) than FGTB cases (9.94 ± 0.14). The TaqI gene (C) allele frequency was found to be 60.0% in FGTB cases and 48.3% in healthy controls; the C allele was significantly associated with increased susceptibility to FGTB risk [odds ratio (OR) = 0.62; 95% confidence interval (CI); p < 0.0004]. A positive correlation was found between VDD and increased susceptibility to FGTB risk (p < 0.0001). The association between mean serum vitamin D level and frequency of TaqI gene (CC) (p < 0.0001) and (TC) (p < 0.01) was significant among cases; however, ApaI did not show a significant association with the susceptibility to FGTB risk.
Conclusion: The study concluded that TaqI gene polymorphism might be associated with VDD due to VDR dysfunction, providing additional information that it might be one of the contributors to increased susceptibility to developing FGTB risk.
How to cite this article: Priyadarshini A, Siddiqui U, Jaiswar SP, et al. Vitamin D Receptor Gene Polymorphism (ApaI and TaqI) and Serum Vitamin D Association with the Susceptibility of Female Genital Tuberculosis Risk. Int J Infertil Fetal Med 2024;15(2):101-107.
Source of support: This work was supported by the Uttar Pradesh— Council of Science and Technology through grant number (CST/D-2675)
Conflict of interest: None
Keywords: ApaI, Genital tuberculosis, TaqI polymorphism, Vitamin D receptor genotyping, Vitamin D receptor.
INTRODUCTION
Mycobacterium tuberculosis is the causative agent of tuberculosis (TB), a chronic infectious disease that constitutes a serious threat to public health. According to the World Health Organization Fact Sheet 2022, about one-fourth of the world’s population has been infected with TB.1 India represents 29% of all tuberculosis-related fatalities.2 M. tuberculosis mostly targets the lungs (pulmonary tuberculosis), but it may potentially affect any area of the body, known as extrapulmonary tuberculosis (EPTB). Female genital tuberculosis (FGTB), an EPTB that affects the female genitalia, accounts for around 20–30% of all current TB cases.3 FGTB is alarmingly prevalent, with recorded rates ranging from 45.1 per 1,00,000 women in the Andaman territory to 48.5% among infertile women in North India.4 Genital TB spreads from the lungs to the reproductive organs through hematogenous or lymphatic channels. The most common clinical presentation of FGTB is infertility, resulting from obstructed or damaged fallopian tubes, extremely low endometrial receptivity, and low ovarian reserve. On the long arm of chromosome 12, the vitamin D receptor (VDR) is a transcriptional regulator of the nuclear receptor superfamily. It has eight exons that code for proteins, six alternatively spliced untranslated exons, and at least five promoter regions.5 There are two different types of vitamin D: D2 and D3. The vital immunomodulatory process is carried out by the active form of vitamin D (1,25(OH)2D3) by interacting with the VDR complex that migrates into the nucleus and activates macrophages, which may restrict the development of M. tuberculosis.6 Therefore, deficiencies in vitamins and anomalies in receptor shape and function may reduce the host’s ability to fight off the tubercle bacillus.7 It has been shown that vitamin D deficiency (VDD) (serum 25(OH)D level <10 ng/mL) and insufficiency (serum 25(OH)D level 10–25 ng/mL) are associated with a higher risk of active TB.8 Studies have proven that vitamin D insufficiency and deficiency are related to a higher risk of tuberculosis.9,10 There are numerous potential candidate single nucleotide polymorphisms (SNP) that have been linked to tuberculosis in various ethnic populations. These polymorphisms may alter the expression or structure of genes, affecting innate and adaptive immunity, which in turn can influence the course of the disease and susceptibility to M. tuberculosis infection.11 The most common 3’ untranslated region (3’UTR) polymorphisms are FokI (rs10735810) (T→C) in exon 2, BsmI (rs1544410) (A→G) change in intron 8, ApaI (rs7975232) (A→C) change in intron 8, and TaqI (rs731236) (T→C) change in exon 9. Both ApaI and TaqI are silent genetic variations that may not produce any functional consequence or alter VDR function. In contrast, other studies suggest that TaqI could potentially affect the balance of T helper cells (TH1 and TH2). Individuals with the gene “tt” homozygotes tend to produce an immune response of TH1 type, while those with the gene “TT” homozygotes produce a response of TH2 type. Studies have demonstrated that individuals with the gene “tt” are resistant to pulmonary tuberculosis, suggesting that the immune response of TH1 is protective for those with TB.12 Apart from the genetic predisposition of VDR, it is still unclear how the genetic variants of VDR-ApaI, TaqI, and serum vitamin D influence susceptibility to or resistance against the progression of EPTB, particularly FGTB. Understanding the mechanism behind FGTB is crucial for gaining insight into its pathogenesis and may lead to the development of innovative prevention and treatment strategies. Since genital TB and pulmonary TB have unique underlying pathophysiology, such a study could provide valuable new information. As far as we know, no study has established a correlation between the ApaI and TaqI genetic polymorphisms and serum vitamin D levels with FGTB. Therefore, the aim of this study is to determine the possible correlation between the ApaI and TaqI variations within the VDR gene and their association with serum vitamin D levels as risk factors for susceptibility. This could shed light on how these polymorphisms may impact the development of this disease, leading to a better understanding of its underlying mechanisms and potentially exploring new therapeutic approaches.
MATERIALS AND METHODS
The Queen Mary’s Hospital, King George’s Medical University, Lucknow, Uttar Pradesh, India, hosted this case–control research from 2020 to 2022. The institutional ethical clearance committee for human research authorized this study (No: ECR/262/Inst/UP/2013/RR-19) at KGMU, Lucknow. Participants, who were women, provided written consent to participate. A total of 150 women aged 20–35 years with primary or secondary infertility for a period greater than 1 year and positive for conventional tests [acid-fast bacilli (AFB) smear, Lowenstein-Jensen (LJ) culture, histopathology] and molecular test cartridge-based nucleic acid amplification test (CBNAAT) in endometrial aspiration (EA) were recruited as FGTB cases. FGTB leads to infertility, so we recruited infertile women in this study. Similarly, an equal number of 150 healthy women with no previous history of antitubercular therapy (ATT) and all tests negative for TB in menstrual blood were recruited as healthy controls. Women with endometriosis, polycystic ovaries, chlamydia, gonorrhea, those already on ATT, or diagnosed with active pulmonary tuberculosis or active EPTB in regions other than the female genital tract were excluded from the study. The sample size was calculated with 80% power.
Serum Vitamin D Level Estimation
About 1 mL of blood was used for the quantification of serum vitamin D levels in both FGTB cases and healthy controls. The level of vitamin D was estimated using the 25-OH vitamin D enzyme-linked immunosorbent assay (ELISA) kit (Eagle Bio-Sciences cat#VID31-K01) with an ELISA (Bio-Rad) iMark Microplate reader. Each test was performed in duplicate, and the absorbance was measured using a dual-wavelength reference filter with 570 and 650 nm wavelengths. Serum 25(OH)D levels are categorized as deficient if they are <10 ng/mL, insufficient if they are between 10 and 25 ng/mL, and sufficient if they are greater than 25 ng/mL.
Conventional and Molecular Test
Premenstrual EA was performed on day 21 from the recruited infertile women for the confirmation of M. tuberculosis by conventional methods [AFB, LJ, mycobacteria growth indicator tube (MGIT) culture, histopathology examination (HPE)] and molecular test (CBNAAT) for the detection of genital tuberculosis.
Analysis of Vitamin D Receptor (ApaI and TaqI) Polymorphism
Genomic deoxyribonucleic acid (DNA) extraction: At the time of enrollment, 5.0 mL of venous blood was drawn from each patient and transferred into tubes prepared with ethylenediaminetetraacetic acid (EDTA). The plasma was promptly separated using centrifugation for 15 minutes at 4°C and 2000–2500 rpm. The cell pack was stored at –80°C until DNA extraction. Purified DNA, isolated from the genome using the phenol-chloroform method, was kept at –20°C.
Genotyping of ApaI and TaqI Vitamin D Receptor Gene
Genotyping of VDR gene variants ApaI at site rs7975232 (A/C) and TaqI at site rs731236 (T/C) was carried out using amplification refractory mutation system polymerase chain reaction (ARMS-PCR) methods, with each reaction performed in a different replicate manner (Jafari et al.).13 The VDR gene polymorphism of ApaI and TaqI was analyzed through two complementary reactions using three primers: one specific for the mutant allele, one for the wild-type allele, and a common primer for both alleles. The following primers were used: ApaI: A5’-TGGGATTGAGCAGTGAGGT-3’, C5’-TGGGATTGAGCAGTGAGGG-3’, and C5’-CCTCATTGAGGCTGCGCAG-3’ with an amplicon size of 229 bp; TaqI: T5’-CAGGACGCCGCGCTGATT-3’, C5’-CAGGACGCCGCGCTGATC-3’, and C5’-CCTCATTGAGGCTGCGCAG-3’ with an amplicon size of 148 bp. The PCR reaction was performed with 5 µL of extracted DNA and included 1X buffer, 1 U Taq DNA polymerase, 200 µM dNTP, 1.5 mM MgCl2, and 10 pmol of each primer, in a total volume of 25 µL using GoTaqGreen Master Mix (Promega, United States). The PCR amplification was carried out using an ABI-Veriti thermal cycler (Applied Biosystems, Singapore) with the following conditions: initial denaturation at 94°C for 3 minutes, followed by 35 cycles of final denaturation at 94°C for 30 seconds, annealing at 58°C for TaqI and 62°C for ApaI for 40 seconds, extension at 72°C for 1 minute, and final extension at 72°C for 4 minutes. Gene DireX, Inc.’s 100 bp DNA ladder was used to electrophorese PCR-amplified products on a 2% agarose gel, stained with ethidium bromide. PCR results were visualized using a UV Gel Doc and imaging lab software from Bio-Rad.
Statistical Analysis
GraphPad Prism software version 5.0 (La Jolla, California, United States) was used for statistical analysis and data interpretation. The genotype and allele frequency of the VDR gene polymorphism in FGTB cases and controls were tested for Hardy–Weinberg equilibrium. Differences in genotype frequencies between cases and controls were evaluated using the Pearson’s Chi-squared test. The association of ApaI and TaqI polymorphisms with the risk of FGTB was determined by calculating the unadjusted odds ratio (OR) and 95% confidence interval (CI) through univariate binary logistic regression analysis. A p-value of <0.05 was considered statistically significant.
RESULTS
Anthropometric Parameter and Serum Vitamin D Level
Table 1 shows the anthropometric and mean serum vitamin D levels between cases and controls. There was no statistically significant difference found in the anthropometric parameters; however, mean serum vitamin D levels were 9.94 ± 0.14 ng/mL in the FGTB cases and 29.04 ± 0.14 ng/mL in the controls, showing a positive correlation (p < 0.0001).
| Variables | FGTB case (n = 150) | Healthy control (n = 150) | p-value |
|---|---|---|---|
| Age (mean ± SD) (years/old) | 28.05 ± 3.63 | 27.25 ± 3.53 | 0.054a |
| Weight (mean ± SD) kg | 53.08 ± 0.48 | 54.36 ± 0.50 | 0.067a |
| BMI (kg/m2) | 22.51 ± 0.23 | 23.15 ± 0.24 | 0.062a |
| Serum vitamin D (ng/mL) | 9.94 ± 0.14 | 29.04 ± 0.14 | 0.0001*a |
aunpaired t-test; *significantly different from control (p < 0.05); BMI, body mass index; SD, standard deviation
Correlation of Diagnostic Conventional and Molecular Tests
Table 2 shows the results of standard conventional tests: AFB-smear, LJ culture, MGIT culture, HPE, and molecular test CBNAAT. Among the 150 FGTB patients, 11 (7.3%) were positive by AFB-smear, 6 (4%) by LJ culture, 4 (2.6%) by MGIT culture, 3 (2%) by HPE, and 149 (99.3%) by CBNAAT. When comparing the correlations of all four conventional tests, 149 (99.3%) were found positive only with CBNAAT and negative with the other conventional tests (Fig. 1).
| FGTB cases (n = 150) | Molecular test CBNAAT | ||||
|---|---|---|---|---|---|
| Conventional test | Criteria | Positive (n = 149) | Negative (n = 1) | p-value | |
| AFB smear | Positive | 11 (7.3%) | 11 (99.3%) | 0 | 0.001* |
| Negative | 139 (92.6%) | 138 (92.6%) | 1 (100%) | ||
| LJ | Positive | 6 (4%) | 6 (4%) | 0 | 0.001* |
| Negative | 144 (96%) | 143 (95.9%) | 1 (100%) | ||
| MGIT | Positive | 4 (2.6%) | 4 (2.6%) | 0 | 0.001* |
| Negative | 146 (97.3%) | 145 (97.3%) | 1 (100%) | ||
| HPE | Positive | 3 (2%) | 3 (2%) | 0 | 0.001* |
| Negative | 147 (98%) | 146 (98%) | 1 (100%) | ||
*p < 0.05 level of significance
Fig. 1: Correlation of conventional and molecular test
Association of ApaI and TaqI Gene Polymorphism and Female Genital Tuberculosis
The genotypic and allelic distribution of ApaI and TaqI polymorphisms in controls and FGTB cases are shown in Table 3.
| Genotype | FGTB case (n = 150) | Healthy control (n = 150) | χ2 | OR (95% CI) | p-value | ||
|---|---|---|---|---|---|---|---|
| No. | (%) | No. | (%) | ||||
| ApaI | |||||||
| AA | 56 | (37.3) | 63 | (42.0) | 1.24 | 0.76 (0.47–1.22) | 0.27 |
| AC | 84 | (56.0) | 72 | (48.0) | 1.65 | 1.75 (0.74–4.13) | 0.28 |
| CC | 10 | (6.6) | 15 | (10.0) | 0.41 | 1.33 (0.55–3.20) | 0.65 |
| Allele | |||||||
| A | 196 | (65.3) | 198 | (66.0) | 0.75 | 1.17 (0.90–1.29) | 0.38 |
| C | 104 | (34.6) | 102 | (34.0) | 0.02 | 0.97 (0.83–1.16) | 0.86 |
| Model | |||||||
| Dominant AA vs AC + CC | 56/94 | 63/87 | 0.68 | 0.82 (0.71–1.14) | 0.40 | ||
| Recessive CC vs AC + AA | 10/140 | 15/135 | 1.09 | 0.64 (0.47–1.28) | 0.29 | ||
| TaqI | |||||||
| TT | 35 | (23.3) | 50 | (33.3) | 0.78 | 0.77 (0.43–1.37) | 0.37 |
| TC | 50 | (33.3) | 55 | (36.6) | 2.84 | 0.62 (0.36–1.08) | 0.10 |
| CC | 65 | (43.3) | 45 | (30.0) | 6.15 | 0.48 (0.27–0.86) | 0.01* |
| Allele | |||||||
| T | 120 | (40.0) | 155 | (51.6) | 0.48 | 1.17 (0.74–1.84) | 0.48 |
| C | 180 | (60.0) | 145 | (48.3) | 8.22 | 0.62 (0.45–0.86) | 0.004* |
| Dominant TT vs CT + CC | 35/115 | 50/100 | 3.69 | 1.64 (0.98–2.7) | 0.07 | ||
| Recessive CC vs CT + TT | 65/85 | 45/105 | 5.74 | 1.78 (1.10–2.87) | 0.01* | ||
CI, confidence interval; OR, odds ratio; calculated by Chi-squared test; *p < 0.05 level of significance
The Hardy–Weinberg equilibrium was followed by the genotype frequencies of ApaI and TaqI in both cases and controls.
ApaI Polymorphism
Table 3 and Figure 2 show the distribution of genotypes and alleles of ApaI polymorphism. In controls, the AA, AC, and CC genotypes were 42.0, 48.0, and 10.0%, respectively, and in FGTB cases, they were 37.3, 56.0, and 6.6%. The frequency of the A allele was 66.0% in controls and 65.3% in FGTB cases, while the C allele frequency was 34.0% in controls and 34.6% in FGTB cases. There was no difference in the ApaI genotype and allele frequencies between the two groups (p > 0.05). Both the dominant (AC + CC vs AA) and recessive (AC + AA vs CC) models did not show any evidence of a significant association with FGTB (odds: 0.82, CI: 0.71–1.14, p = 0.408 and 0.64, CI: 0.47–1.28, p = 0.296, respectively).
Fig. 2: Genotype and allele frequency distribution of ApaI among FGTB case and controls
TaqI polymorphism
The genotype distribution of the TaqI gene for TT, TC, CC, and alleles T and C were 33.3, 36.6, 30.0, and 51.6%, 48.3% in controls, while in patients, the distributions were 23.3, 33.3, 43.3, and 40.0%, 60.0%, respectively, as shown in Table 3 and Figure 3. Regarding the susceptibility to FGTB risk, the analysis showed that the C allele was significantly associated with an increased risk of FGTB, with significant odds of 0.62 (0.45–0.86; 95% CI, p < 0.0004), while the T allele did not show a significant risk for FGTB, with odds of 1.17 (0.74–1.84; 95% CI, p = 0.48). A significant association was found between the genotype CC, with odds of 0.48 (0.27–0.86; 95% CI, p = 0.001) and the increased risk of FGTB, but not between the TT genotype, with odds of 0.77 (0.43–1.37; 95% CI, p = 0.37), or the TC genotype, with odds of 0.62 (0.36–1.08; 95% CI, p = 0.09) and the risk of FGTB. The odds for the recessive model (CT + TT vs CC) were 1.78 (CI = 1.10–2.87, p = 0.01), but the dominant model (CT + CC vs TT) had odds of 0.60 (CI = 0.36–1.01, p = 0.054), which did not demonstrate any significant relationships.
Fig. 3: Genotype and allele frequency distribution of TaqI among FGTB case and controls
Association between Serum Vitamin D Levels and Susceptibility to Female Genital Tuberculosis Risk
Out of 150 cases, 13 were found to have vitamin D levels of <10 ng/mL, 128 had levels between 10 and 25 ng/mL, and 9 had levels greater than 25 ng/mL. Table 4 shows that FGTB cases who were vitamin D insufficient (10–25 ng/mL; p < 0.0001) and deficient in 25(OH)D (<10 ng/mL; p < 0.0001) had an increased risk of FGTB susceptibility compared to those with vitamin D sufficient levels (greater than 25 ng/mL; p = 0.135).
| Serum vitamin D status | FGTB case (n = 150) | Healthy control (n = 150) | RR (95% CI) | OR (95% CI) | p-value |
|---|---|---|---|---|---|
| Insufficient vs deficient | 13/128 | 52/26 | 0.24 (0.14–0.39) | 0.05 (0.02–0.10) | 0.0001* |
| Insufficient vs sufficient | 13/9 | 52/72 | 1.80 (0.82–3.94) | 2.00 (0.79–5.02) | 0.135 |
| Deficient vs sufficient | 128/9 | 26/72 | 7.48 (4.02–13.9) | 39.3 (17.5–88.6) | 0.0001* |
CI, confidence interval; FGTB, female genital tuberculosis; OR, odds ratio; RR, risk ratio; 25(OH)D, 25 hydroxy vitamin D3. Deficient: 25(OH)D < 10 ng/mL, insufficient: 25(OH)D between 10 and 25 ng/mL, sufficient: 25(OH)D > 25 ng/mL; *p < 0.05 level of significance
Association of Serum Vitamin D Level and the Vitamin D Receptor—ApaI and TaqI Gene
Table 5 shows that no significant association was observed in the mean serum vitamin D levels among genotype groups of ApaI: (AA) (28.21 ± 0.376; p = 0.082), (AC) (25.45 ± 0.755; p = 0.510), and (CC) (27.40 ± 2.27; p = 0.781), as shown in Figure 4. However, there was a statistically significant difference in the mean serum vitamin D levels among genotype groups of TaqI: (CC) (9.125 ± 0.06; p < 0.0001) and (TC) (23.38 ± 0.330; p < 0.01) compared to (TT) (27.89 ± 2.14; p = 0.447) among FGTB cases, as shown in Figure 5.
| Genotype | FGTB case (n = 150) mean ± SD (ng/mL) | Healthy control (n = 150) mean ± SD (ng/mL) | p-value |
|---|---|---|---|
| ApaI | |||
| AA | 28.21 ± 0.376 | 29.21 ± 0.417 | 0.082 |
| AC | 25.45 ± 0.755 | 26.21 ± 0.871 | 0.510 |
| CC | 27.40 ± 2.27 | 28.07 ± 1.21 | 0.781 |
| TaqI | |||
| TT | 27.89 ± 2.14 | 28.44 ± 2.04 | 0.447 |
| TC | 23.38 ± 0.330 | 25.37 ± 0.366 | 0.01* |
| CC | 9.125 ± 0.06 | 27.12 ± 0.412 | 0.0001* |
Fig. 4: Mean ± standard deviation (SD) vitamin D levels (ng/mL) as per genotypic distribution of ApaI SNP
Fig. 5: Mean ± SD vitamin D levels (ng/mL) as per genotypic distribution of TaqI SNP
DISCUSSION
The major finding of our investigation is the correlation between susceptibility to FGTB and the genotype and allele frequencies of the VDRTaqI polymorphism. It was revealed that there was a substantial correlation between the TC and CC genotypes and serum vitamin D levels when this information was evaluated. Patients with FGTB showed a decreased frequency of the TT, TC, and T allele and an increased frequency of the TaqI CC genotype and C allele. The TT and TC genotypes are associated with resistance to developing FGTB risk, whereas the CC genotype is associated with increased susceptibility to FGTB. These data are in accordance with the ones obtained by Li et al.14 reported that TaqI tt genotype and t allele polymorphism are associated with an increased risk of TB in the Indian population. Similarly, other case–control studies, carried out in northern Indian,15 Iranian,16 and Chinese17 populations also reported the “tt” genotype may lead to an increase in the chance of mycobacterial infection or to progress the TB disease; however, Alexandra et al.17 conducted study on Romanian population, the polymorphism in 3’UTR, TaqI of VDR gene, allele “tt” is associated with resistance to the development of active TB, while the heterozygote genotype “Tt” is correlated with susceptibility to pulmonary TB. There are a few studies investigating SNPs in connection with TB susceptibility in various populations concerning the ApaI polymorphisms of the VDR gene. The metanalysis by Areeshi et al.18 reported that ApaI polymorphism of the VDR gene is significantly associated with a decreased risk of TB which supports our study. A case–control study conducted by Alexandra et al.17 and Selvaraj et al.19 reported that the “aa” genotype was associated with resistance to the development of TB. No recent studies have documented the association between ApaI and TaqI gene polymorphisms and serum vitamin D levels in relation to FGTB susceptibility. Therefore, the present study was conducted. Meta-analyses and studies have reported that serum VDD is associated with increased TB susceptibility.19,22 Rashedi et al.23 reported a significant association of VDR gene polymorphism and plasma vitamin D concentration with FokI but not with ApaI and TaqI with tuberculosis. The correlation between VDR gene polymorphisms and genetic susceptibility to TB has been investigated in populations with high TB incidence using case–control studies and meta-analyses. However, the results have been conflicting, partly due to the ethnical, geographical, and genetic diversity of the populations studied.24,27 Our results demonstrated a significant association (p < 0.0001) between lower vitamin 25-OHD levels (≤10 ng/mL) and increased susceptibility to FGTB, with a notable trend toward an increased frequency of the TaqI-CC genotype. This suggests that the TaqI-CC genotype is associated with an increased risk of genital tuberculosis. Additionally, the TaqI-TC genotype was significantly linked to insufficient vitamin D levels. Higher levels of vitamin 25-OHD might restore the functionality of the VDR protein in individuals with the TaqI genotype. Another study on the Paraguayans population by Wilbur et al.28 stated that the TaqI-t allele protects the carrier from both the infectious and active forms of tuberculosis. Numerous populations have been researched to determine the relationship between vitamin D, the VDR gene polymorphism, and susceptibility to tuberculosis, but the north Indian population was the only one included in our study. The genetic function of pulmonary TB has been identified to be significantly influenced by ethnicity (Sinaga et al.).29 Several contradictory study results have not supported this investigation due to heterogeneity in the study population. Differences in genetic background among different races have also led to varying genotype frequencies, sample collection times, and methods for determining serum vitamin D levels. Despite its limitations, the current study is one of the first in North India to assess the vitamin D link between ApaI and TaqI gene polymorphisms in FGTB. It provides further evidence to expand our understanding of the TaqI gene’s potential influence on disease progression.
CONCLUSION
The existing research explores the reported connections between vitamin D, ApaI, and TaqIVDR gene polymorphisms and genital TB in the north Indian population. If a female host is susceptible or resistant to M. tuberculosis, the polymorphic variations of the VDR gene and vitamin D may influence the host’s cell-mediated immunity. Beyond the VDR gene, other genes implicated in TB susceptibility contribute to the disparate results observed in various case–control studies. Additionally, interactions between environmental factors and genes can impact VDR gene expression and vitamin D function through this receptor. Although these SNPs are often considered nonfunctional, evidence suggests that the ApaI and TaqI restriction sites in the 3’ untranslated region of the VDR gene are associated with one or more functional polymorphisms critical for controlling VDR production. These findings enhance our understanding of the immunological and genetic mechanisms underlying genital TB (FGTB) and shed light on the potential efficacy of vitamin D supplementation as a prophylactic measure against M. tuberculosis infection. The VDR-TaqI gene polymorphism activity, along with reduced serum vitamin D levels, may serve as a significant genetic risk factor for FGTB progression.
The smaller number of patients who participated in the study is one of its shortcomings. Thus, further study is required, particularly with larger sample sizes. To improve the care for women who are at risk for FGTB, it is also suggested to identify the effect of other gene polymorphisms or genotypes on vitamin D levels.
ETHICAL APPROVAL
Ethical clearance was obtained from the institutional ethical clearance committee for human research (No: ECR/262/Inst/UP/2013/RR-19) of King George’s Medical University, Lucknow, Uttar Pradesh, India.
ACKNOWLEDGMENTS
We appreciate the doctors and personnel at King George’s Medical University’s Department of Obstetrics and Gynecology in Lucknow, Uttar Pradesh, India, who generously helped us in collecting patient samples.
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