Association between iodine intake and thyroid autoantibodies: a cross-sectional study of 7073 early pregnant women in an iodine-adequate region

Research progress in the construction of animal models of autoimmune thyroiditis

Autoimmune thyroiditis (AIT), also known as Hashimoto's thyroiditis (HT), is an autoimmune disease that is characterised by elevated thyroid-specific antibody titres. The incidence of AIT is increasing year over year, making it urgent to establish a suitable animal model for this condition, in order to better explore its pathogenesis and potential pharmaceutical mechanisms for treatment. Owing to a lack of basic research on this disease, problems such as disparate modelling methods with unclear and varying success rates make it difficult for researchers to obtain effective information on AIT in the short term. This report summarises and analyzes the current literature on AIT and combines actual operability to explain the selection and specific implementation processes behind the uses of different modelling approaches, to provide a better overall understanding of autoimmune thyroid diseases.

Associations of Ambient Particulate Matter with Maternal Thyroid Autoimmunity and Thyroid Function in Early Pregnancy

This prospective birth cohort study evaluated the association of exposure to PM2.5 (diameter ≤2.5 μm), PM1-2.5 (1-2.5 μm), and PM1 (≤1 μm) with maternal thyroid autoimmunity and function during early pregnancy. A total of 15,664 pregnant women were included at 6 to 13+6 gestation weeks in China from 2018 to 2020. Single-pollutant models using generalized linear models (GLMs) showed that each 10 μg/m3 increase in PM2.5 and PM1-2.5 was related with 6% (odds ratio [OR] = 1.06, 95% confidence interval [CI]: 1.01, 1.12) and 15% (OR = 1.15, 95% CI: 1.08, 1.22) increases in the risk of thyroid autoimmunity, respectively. The odds of thyroid autoimmunity significantly increased with each interquartile range increase in PM2.5 and PM1-2.5 exposure (P for trend <0.001). PM1 exposure was not significantly associated with thyroid autoimmunity. GLM with natural cubic splines demonstrated that increases in PM2.5 and PM1-2.5 exposure were associated with lower maternal FT4 levels, while a negative association between PM1 and FT4 levels was found when exposure exceeded 32.13 μg/m3. Only PM2.5 exposure was positively associated with thyrotropin (TSH) levels. Our findings suggest that high PM exposure is associated with maternal thyroid disruption during the early pregnancy.

Sex-specific associations between maternal thyroid peroxidase antibodies and cognitive development in preschool children: A prospective cohort study

BACKGROUND

An association between maternal thyroid dysfunction throughout pregnancy and subsequent risk of neurodevelopmental abnormalities in offspring has been demonstrated. However, the potential effects of maternal thyroid autoimmunity on neurodevelopment in the absence of maternal hypothyroidism remain unclear. Therefore, in this study, we explored the association between maternal thyroid peroxidase antibody (TPOAb) positivity and cognitive development in preschool children.

METHODS

A total of 1849 mother-child pairs were recruited from the Ma'anshan Birth Cohort Study. During the follow-up period, an electrochemiluminescence immunoassay was used to retrospectively measure serum TPOAb levels in pregnant women. The cognitive development of preschool children was evaluated by using the Chinese version of the Wechsler Preschool and Primary Scale of Intelligence-Fourth Edition. A growth mixture model was used to fit the trajectory of TPOAb. Multiple linear regression and logistic regression models were used to explore the associations between the developmental trajectory of TPOAb-positivity at different gestational periods and the cognitive development of preschool children by sex.

RESULTS

A total of 1849 mother-child pairs (mean [SD] age: 26.7 [3.6] years) were enrolled in the final study. Maternal TPOAb positivity in the first trimester was associated with a risk of below-average processing speed index in girls (OR: 2.07; 95% CI 1.06-4.01) and below-average full-scale intelligence quotient (FSIQ) in boys (OR: 2.36; 95% CI: 1.10-5.05). Maternal TPOAb positivity in the third trimester was associated with below-average working memory (WMI) (OR: 2.51; 95% CI: 1.02-6.20) in girls. In girls, the WMI (β = -3.17, 95% CI: -5.82--0.52), fluid reasoning index (FRI) (β = -4.49, 95% CI: -7.18--1.80), and FSIQ score (β = -2.43, 95% CI: -4.77--0.08) decreased, whereas in mothers, the level of lgTPOAb increased during pregnancy.

CONCLUSIONS

Positive maternal thyroid peroxidase antibody levels during pregnancy may be associated with poorer cognitive development in preschool children. These findings require independent confirmation in other populations.

Association of maternal thyroid peroxidase antibody during pregnancy with placental morphology and inflammatory and oxidative stress responses

Background

Studies suggest that thyroid peroxidase antibody (TPOAb) positivity exposure during pregnancy may contribute to changes in placental morphology and pathophysiology. However, little is known about the association of maternal TPOAb during pregnancy with placental morphology and cytokines. This study focuses on the effect of repeated measurements of maternal TPOAb during pregnancy on the placental morphology and cytokines.

Methods

Based on Ma'anshan Birth Cohort (MABC) in China, maternal TPOAb levels were retrospectively detected in the first, second and third trimesters. Placental tissues were collected 30 minutes after childbirth, placental morphological indicators were obtained by immediate measurement and formula calculation, and cytokine mRNA expression was detected by real-time quantitative polymerase chain reaction (RT-qPCR) afterward. Generalized linear models and linear mixed models were analyzed for the relationships of maternal TPOAb in the first, second and third trimesters with placental indicators.

Results

Totally 2274 maternal-fetal pairs were included in the analysis of maternal TPOAb levels and placental morphology, and 2122 pairs were included in that of maternal TPOAb levels and placental cytokines. Maternal TPOAb levels in early pregnancy were negatively associated with placental length, thickness, volume, weight and disc eccentricity, while positively correlated with placental IL-6, TNF-α, CRP, CD68, MCP-1, IL-10, HO-1, HIF-1α and GRP78. In mid-pregnancy, maternal TPOAb levels were negatively correlated with placental length, width and area. In late pregnancy, maternal TPOAb levels were negatively correlated with placental length, area, volume and weight. Repeated measures analysis showed that maternal TPOAb positivity tended to increase placental TNF-α, CD68 and MCP-1 while decreasing placental length, width and area than TPOAb negativity. Repeated measures analysis showed that maternal TPOAb levels were positively correlated with placental IL-6, TNF-α, CD68, MCP-1, IL-10, HO-1, HIF-1α and GRP78, while negatively correlated with placental length, area, volume, weight, and disc eccentricity.

Conclusion

There may be trimester-specific associations between maternal TPOAb levels and placental morphology and inflammatory and oxidative stress responses. The effect of maternal TPOAb levels on placental morphology is present throughout pregnancy. Early pregnancy may be the critical period for the association between maternal TPOAb levels and placental inflammatory and oxidative stress responses.

Urinary iodine concentration and its associations with thyroid function in pregnant women of Shanghai

Objective

To assess the iodine status and its associations with thyroid function in pregnant women of Shanghai.

Methods

In this cross-sectional study, a total of 562 pregnant women were enrolled from January to December 2021. Both serum thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), thyroid peroxidase antibody (TPOAB), thyroglobulin antibody (TGAB), and urinary iodine concentration (UIC) were detected. Participants were divided into four groups based on their UIC values. Correlation analysis was used to investigate the association between UIC and thyroid function-associated parameters.

Results

The median UIC of the pregnant women studied was 158.25µg/L (interquartile range [IQR] 90.15, 245.65µg/L). Among all the subjects, 45.55% had iodine deficiency according to the World Health Organization (WHO) criteria, and 15.65% had thyroid autoimmunity. FT3, FT4, TSH, TPOAB and TGAB levels were not different among different UIC groups (P > 0.05). UIC and TSH were negatively correlated (r=-0.127, p=0.043) in UIC<150 µg/L group. In the group with UIC 250- 499 µg/L, UIC was positively correlated with total T4 (TT4), total T3 (TT3) and TPOAB (r= 0.228, p=0.022, r=0.208, p= 0.039, r=0.190, p=0.042, respectively). A negative correlation between UIC and TPOAB values was observed in TPOAB-positive (+) pregnant women (r=-0.384, p=0.012). The prevalence of isolated hypothyroxinemia in UIC<150 µg/L group was significantly higher than that of other groups(p=0.033). The relationship between the prevalence of thyroid diseases and UIC embodied a U-shaped curve.

Conclusion

Pregnant women on Chongming Island of Shanghai were iodine sufficient during the second trimester, but iodine deficiency was still prevalent. Both low and high gestational iodine status was related to thyroid function and autoimmunity. Optimal iodine nutrition status during gestation was important.

Iodine Intakes of <150 μg/day or >550 μg/day are Not Recommended during Pregnancy: A Balance Study

BACKGROUND

Adequate iodine intake during pregnancy is critical for maintaining maternal and fetal thyroid function and development. There are only limited data from iodine-balance studies to inform iodine requirements during pregnancy.

OBJECTIVES

This is an iodine-balance study conducted to explore the associations among iodine intake, excretion, and retention to provide information regarding iodine requirements during pregnancy.

METHODS

A 7-d iodine-balance experiment enrolled 93 healthy pregnant Chinese women from Hebei, Tanjin, and Shandong. Duplicates of all foods and beverages consumed were systematically collected and measured for iodine content. Iodine excretion was measured by collecting 24-h urine and feces samples. Simple linear regression models were used to assess relationships between total iodine intake and iodine retention, whereas mixed effect models were used to assess the relationship between daily iodine intake and iodine retention.

RESULTS

The mean ± SD age of participating pregnant women was 29 ± 2 y at a median 22 (IQR: 13-30) wk of gestation. The mean 7-d iodine retention was 43.0 ± 1060 μg/7 d. A negative iodine balance was present in 56% of women whereas 44% had a positive balance. Pregnant women with iodine intakes <150 μg/d were in negative balance whereas those with intakes >550 μg/d were in positive balance. The daily iodine intake at zero balance was 343 μg/d, which was higher in women from Shandong (492 μg/d) than in those from Hebei and Tianjin (202 μg/d).

CONCLUSIONS

Iodine intake at zero balance determined in pregnant women with adequate iodine nutrition is 202 μg/d, and the calculated recommended nutrient intake (RNI) is 280 μg/d. Iodine intakes of <150 μg/d and >550 μg/d are not recommended during pregnancy. This trial was registered at clinicaltrials.gov as NCT03710148.

A Bayesian model to estimate the cutoff value of TSH for management of preterm birth

BACKGROUND

Determining a thyroid hormone cutoff value in pregnancy is challenging issue and several approaches have been introduced to optimize a utility function. We aimed to estimate the cutoff value of TSH using Bayesian method for prediction of preterm-birth.

METHODS

This study was a secondary-analysis of the population-based data collected prospectively within the framework of the Tehran Thyroid and Pregnancy Study. A total of 1,538 pregnant women attending prenatal clinics.

RESULTS

Using Bayesian method resulted a TSH-cutoff of (3.97mIU/L,95%CI:3.95-4.00) for distinguishing pregnant women at risk of preterm-birth. The cutoff was associated with acceptable positive predictive and negative predictive values (0.84,95% CI:0.80-0.88) and 0.92 (95%CI: 0.91-0.94), respectively). In women who were negative for thyroid peroxides antibody (TPOAb) with sufficient urinary iodine concentration (UIC), the TSH cutoff of 3.92 mIU/L(95%CI:3.70-4) had the highest predictive value; whereas in TPOAb positive women with insufficient UIC, the cutoff of 4.0 mIU/L(95%:CI 3.94-4) could better predict preterm birth. Cutoffs estimated in this study are close to the revised TSH value of 4.0mIU/L which is currently recommended by the American Thyroid Association.

CONCLUSION

Regardless of TPOAb status or iodine insufficiency, risk of preterm labor is increased in pregnant women with TSH value of > 3.92 mIU/L; these women may benefit from Levothyroxine (LT4) therapy for preventing preterm birth.

Association Between Iodine Nutritional Status and Adverse Pregnancy Outcomes in Beijing, China: a Single-Center Cohort Study

Iodine is an essential trace element for humans and the main raw material for thyroid hormone synthesis. However, the association between iodine nutritional status and adverse pregnancy outcomes in different regions remains controversial. This single-center cohort study was focused on the association between iodine nutritional status and adverse pregnancy outcomes in Beijing, China. We enrolled 726 pregnant women who were registered at the Peking University International Hospital between February 2017 and December 2019. To analyze the association between iodine nutritional status variations and adverse pregnancy outcomes, this study cohort included 390 (53.72%) participants with iodine deficiency, 206 (28.37%) with an adequate iodine level, 103 (14.19%) with a more than adequate iodine level, and 27 (3.72%) with iodine excess, according to the urinary iodine (UI) status of pregnant women. After adjusting for age, body mass index, parity, and history of spontaneous abortion, we identified iodine deficiency as a risk factor for anti-thyroid peroxidase antibody (TPOAb) positivity [odds ratio (OR), 3.646; 95% confidence interval (95% CI), 1.658-8.017], anti-thyroglobulin antibody (TGAb) positivity (OR, 3.109; 95% CI, 1.465-6.599), and thyroid autoimmunity (OR, 2.885; 95% CI, 1.539-5.407). There was a non-linear relationship between UI and the concentrations of TPOAb and TGAb (P_non-linear < 0.05). Iodine deficiency during the first trimester is a risk factor for thyroid autoantibody positivity. The relationship between UI and the concentrations of TPOAb and TGAb follows a nearly U-shaped curve. Thus, physicians should critically consider the iodine nutritional status of pregnant women during the first trimester. Clinical Trials.gov Identifier: NCT02966405.

Prevalence of insufficient iodine intake in pregnancy worldwide: a systematic review and meta-analysis

BACKGROUND/OBJECTIVES

Iodine deficiency in pregnant women is related to impaired foetal growth and development. The objective of this study was to estimate the prevalence of insufficient iodine intake in pregnant women from different regions of the world.

SUBJECTS/METHODS

Using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, five electronic databases and Google Scholar grey literature were searched until 10 April 2021. Two reviewers independently conducted article selection, data extraction, and assessment of the risk of bias. Meta-analyses with random effects, subgroup analyses, and meta-regressions were performed.

RESULTS

In total, 4639 observational articles were found, with 61 eligible for inclusion. The population consisted of 163,021 pregnant women adults and adolescents, and the overall prevalence of insufficient iodine intake was 53% (95% confidence interval [CI]: 47-60; I² = 99.8%). Pregnant women who live in insufficient iodine status country had a higher prevalence (86%; 95% CI: 78-93; I² =97.0%) of inadequate iodine nutritional status than to those living in country considered sufficient (51%; 95% IC: 45-57; I² = 99.8%).

CONCLUSION

Despite the progress in iodine fortification policies and periodic monitoring of the iodine nutritional status of the population worldwide, salt iodination alone may not be sufficient to provide adequate iodine status to pregnant women. Thus, other actions may be necessary to improve the nutritional clinical care of pregnant group.

[Epidemiology of benign thyroid disorders in the adult population of the Republic of Belarus: analysis of nationwide statistics 2009 to 2019]

BACKGROUND

Nowadays, the Republic of Belarus belongs to the countries with sufficient iodine supply, which made it possible to reduce the incidence of non-toxic goiter and congenital hypothyroidism. However, even a slight change in iodine consumption influences the pattern of thyroid diseases. In addition to iodine deficiency, other environmental conditions, as well as genetic factors, play a significant role in the etiology of thyroid diseases.

AIM

To analyze the dynamics of the main epidemiological indicators of benign thyroid diseases from 2009 to 2019 in the adult population of the Republic of Belarus, using the data of official state statistics.

MATERIALS AND METHODS

The indicators of the incidence and prevalence of benign thyroid diseases were studied on the basis of state statistics for 2009-2019. To analyze the dynamics of the studied indicators, regression analysis was used with the construction of linear and polynomial models.

RESULTS

A decrease in the incidence and prevalence of diffuse euthyroid goiter and an increase in the incidence and prevalence of nodular euthyroid goiter, thyroiditis, acquired hypothyroidism, Graves' disease, as well as the incidence of nodular toxic goiter were revealed.

CONCLUSION

Obtained data indicate, that there is an increase in the prevalence of most of the studied thyroid diseases, despite the adequate iodine supply. The above justifies the need for further study of the causes of the identified trends, as well as the necessity of developing new methods of diagnosis and treatment of thyroid diseases.

Association of exposure to PM2.5-bound metals with maternal thyroid function in early pregnancy

Epidemiological evidence linking metals bound to ambient particulate matters with aerodynamic diameter less than 2.5 μm (PM_2.5) and maternal thyroid function is limited. In this study, we investigated the association of PM_2.5-bound metals with maternal thyroid hormones (TH) during the first trimester. We retrospectively reviewed data for 2528 pregnant women attending prenatal care in Jinhua Maternal and Child Health Care Hospital, Jinhua, China, from January to December 2018. Information including thyroid hormone levels and demographics was retrieved from existing medical records. We analyzed the concentration of 10 metals for collected particulate samples, and estimated their exposure levels during the first trimester for each woman. We employed multivariate linear regression models to estimate the association of exposure to individual PM_2.5-bound metals with serum levels of maternal TH, and weighted quantile sum (WQS) to estimate the overall association of exposure to PM_2.5-bound metals within a mixture. Higher exposures to most of the PM_2.5-bound metals were associated with lower levels of maternal free thyroxine (FT4) and free triiodothyronine (FT3). The thyroid peroxidase antibody (TPOAb) or thyroglobulin antibody (TgAb) status had no effect modification on the observed associations. WQS analyses further suggested that Be, Ni, Tl and Ba contributed the most to the associations. These findings highlight the associations of exposure to PM_2.5-bound metals with maternal thyroid function, and emphasize the public health significance of commitments to improve air quality.

Iodine nutrition status and thyroid autoimmunity during pregnancy: a cross-sectional study of 4635 pregnant women

Background

Pregnant women in Shanghai have long been at risk for mild iodine deficiency. Because thyroid autoimmunity in pregnant women can lead to premature birth and miscarriage as well as neurodevelopmental deficits in the fetus, the aim of this study was to explore the association of iodine nutrition status with thyroid antibodies during pregnancy.

Methods

A pregnancy-birth cohort was conducted including 4635 pregnant women in Shanghai, China. The eligible participants underwent a face-to-face interview and completed questionnaire surveys to collect baseline information and diet intake. Spot urine samples were collected to test urine iodine. Thyroid antibodies including thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb) and thyrotrophic antibodies (TRAb) were tested. Single-factor analysis and logistic regression were used to evaluate the association between iodine status and thyroid autoimmunity during pregnancy.

Results

The median urinary iodine excretion level in the sample was 138.14 μg/L (interquartile range [IQR] 80.90–219.00 μg/L). Among all the subjects, 25.9% consumed non-iodized salt, 54.5% had iodine deficiency, and 31.0% had thyroid autoimmunity. The proportion of patients with iodine deficiency was significantly higher among those who consumed non-iodized salt (36.9% vs. 33.1%; p = 0.04). After adjusting for age, educational status, former smoker status, former drinker status, first pregnancy, and previous thyroid disease, non-iodized salt (odds ratio [OR] = 1.394 [confidence interval, CI, 1.165–1.562]; p = 0.003), iodine-rich food (OR = 0.681 [CI 0.585–0.793]; p = 0.003), iodized nutritional supplements (OR = 0.427 [CI 0.347–0.526]; p = 0.003), were found to be individually associated with thyroid autoimmunity in all participants. The results of the multivariable restricted cubic spline regression analysis showed a non-linear relationship between the continuous change in iodine intake and thyroid autoimmunity (p = 0.019). Participants with iodine deficiency (urinary iodine concentration, UIC,< 100 μg/L) had an increased risk of testing positive for thyroid antibodies (TPOAb/TgAb/TRAb[+]; OR = 1.324 [CI 1.125–1.559]; p < 0.001). Moreover, this associated existed even after removing participants with previous thyroid disease.

Conclusion

Inadequate iodine nutrition in pregnant women is an independent risk factor for thyroid autoimmunity in Shanghai. It’s important to maintain the adequate iodine status in pregnant women.

Iodine nutrition optimization: are there risks for thyroid autoimmunity?

Iodine deficiency is still the main cause of preventable thyroid disorders, worldwide. To optimize iodine intake, programs of voluntary or mandatory iodization of salt have been implemented in several iodine-deficient countries and iodine sufficiency has been achieved in many. Despite the clear beneficial effects on thyroid health, some concerns have been raised on the presumed detriment of iodine prophylaxis on thyroid autoimmunity. Very recent studies aimed at evaluating the long-term consequences of iodine supplementation on thyroid autoimmunity and related dysfunction, have clearly demonstrated that the early post-iodization increase in thyroid antibody positivity is largely transient and not clinically relevant, since the prevalence of overt thyroid dysfunction has remained reassuring low over two decades. The recommended iodine intake is therefore safe with regard to thyroid autoimmunity, the benefits largely outweighing the risks in a population with a stable median iodine concentration not exceeding 300 μg/L. Thus, a possible increase in thyroid autoimmunity should not represent a limitation to promoting iodine supplementation in the general population, also taking into account the steady rise in prevalence of autoimmune disorders which has occurred in the last few decades because of environmental factors other than iodine.

High Iodine Nutrition May Be a Risk Factor for Cervical Lymph Node Metastasis in Papillary Thyroid Cancer Patients

PURPOSE

The aim of this study was to retrospectively identify the effect of iodine on the papillary thyroid cancer (PTC) process and investigate the risk clinicopathologic characteristics of cervical lymph node metastasis (CLNM) for achieving a better preventive strategy of PTC.

METHODS

Totally 187 patients with CLNM and 279 without CLNM (NCLNM) were enrolled, and their urinary iodine concentration (UIC) and serum iodine concentration (SIC) were measured. Logistic regressions were used to reveal the effects of iodine nutrition on the CLNM status of PTC.

RESULTS

The levels of thyroid-stimulating hormone (TSH) and thyroglobulin (TG) were higher in the CLNM group than in the NCLNM group. UIC and SIC were positively correlated, and both of them were correlated with TSH, free thyroxine, and TG. The proportions of UIC >300 μg/L and of SIC >90 μg/L were higher in the CLNM than in the NCLNM. Logistic analysis showed that SIC >90 μg/L was an independent predictor for CLNM in PTC. Additionally, age ≥45, female, TG, multifocality, and diameter of cancer invasion >1 cm also affected CLNM status in PTC, and their logistic regression model showed a certain diagnostic accuracy (area under the receiver-operating characteristic curve = 0.72).

CONCLUSIONS

Relatively high iodine nutrition seemed to be a significant risk factor for the occurrence of CLNM in PTC and may promote lymphatic metastasis in PTC.

Iodoprophylaxis and thyroid autoimmunity: an update

Adequate iodine intake is necessary for normal thyroid function. Iodine deficiency is associated with serious complications, but also iodine excess can lead to thyroid dysfunction, and iodine supplementation aimed to prevent iodine deficiency disorders has been associated with development of thyroid autoimmunity. The epidemiology of thyroid diseases has undergone profound changes since the implementation of iodoprophylaxis, notably by means of iodine-enriched salt, specifically resulting in decreased prevalence of goiter and neonatal hypothyroidism, improved cognitive function development in infancy, and reduced incidence of more aggressive forms of thyroid cancer. The main question we address with this review is the clinical relevance of the possible effect on autoimmunity exerted by the use of iodine-enriched salt to correct iodine deficiency. In animal models, exogenous iodine is able to trigger or exacerbate thyroid autoimmunity, but it is still not clear whether the observed immunological changes are due to a direct effect of iodine on immune response, or whether they represent a secondary response to a toxic effect of iodine on thyroid tissue. Previous iodine status of a population seems to influence the functional thyroid response to increased iodine intake and possibly the development of thyroid autoimmunity. Moreover, the prevalence of thyroid antibodies, regarded as hallmark of autoimmune thyroid disease, varies between populations under the influence of genetic and environmental factors, and the presence of thyroid antibodies does not always coincide with the presence of thyroid disease or its future development. In addition, the incidence of autoimmune diseases shows a general increasing trend in the last decades. For all these reasons, available data are quite heterogeneous and difficult to analyze and compare. In conclusion, available data from long-term population surveys show that a higher than adequate population iodine intake due to a poorly controlled program of iodine prophylaxis could induce thyroid dysfunction, including thyroid autoimmunity mostly represented by euthyroid or subclinical hypothyroid autoimmune thyroiditis. Close monitoring iodine prophylaxis is therefore advised to ensure that effects of both iodine deficiency and iodine excess are avoided.

Relationship between Gene Polymorphisms and Urine Iodine Levels on Susceptibility to Thyroid Peroxidase Antibody Positivity in the Chinese Population

BACKGROUND/AIMS

Hashimoto thyroiditis, characterized by positive thyroid peroxidase antibodies (TPOAbs), is caused by the interaction of genetic and environment factors. The aim of this study was to clarify the interaction of gene polymorphisms and iodine intake in the incidence of TPOAb positivity.

METHODS

1,733 subjects were included in this study. Genomic DNA was extracted from peripheral blood white cells. Four SNPs (rs11675434 [TPO], rs3094228 [HCP5], rs9277555 [HLA-DPB1], and rs301799 [RERE]) were selected for genotyping. Weighted TPOAb genetic risk score (GRS) was calculated based on these 4 SNPs. Thyroid hormones and autoimmune antibodies (TPOAb and thyroglobulin antibody) were determined using the electrochemiluminescence immunoassay method.

RESULTS

The mean serum thyrotropin level in TPOAb-positive subjects was higher than in TPOAb-negative subjects (p < 0.01). Genotype GG of rs9277555 was associated with an increased risk of TPOAb positivity (OR = 1.64, 5-95% CI 1.09, 2.47, p = 0.02). Genotype TT of rs11675434 showed marginal increased risk of TPOAb positivity (OR = 1.57, 5-95% CI 1.01, 2.43, p = 0.048). Logistic regression analysis showed TPOAb-GRS and rs9277555 were associated with TPOAb positivity (OR = 5.09, 5-95% CI 1.30, 19.91, p = 0.02 and OR = 1.30, 5-95% CI 1.05, 1.61, p = 0.02). Subjects with a high TPOAb-GRS had a 52% increased risk of TPOAb positivity compared to subjects with a low TPOAb-GRS (OR 1.52, 5-95% CI 1.05, 2.21, p = 0.03).

CONCLUSION

TPOAb-GRS was associated with an increased risk of TPOAb positivity in a Chinese Han population. This effect might be attribute to rs9277555.

Understanding the Pathogenesis of Gestational Hypothyroidism

Pregnancy is a complex state with many endocrinological challenges to a woman's physiology. Gestational Hypothyroidism (GHT) is an emerging condition where insufficiency of the thyroid gland has developed during pregnancy in a previously euthyroid woman. It is different to overt hypothyroidism, where marked elevation of thyroid-stimulating hormone with corresponding reduction in free thyroxine levels, is well known to cause detrimental effects to both the mother and the baby. During the past couple of decades, it has been shown that GHT is associated with multiple adverse maternal and fetal outcomes such as miscarriage, pre-eclampsia, placental abruption, fetal loss, premature delivery, neurocognitive and neurobehavioral development. However, three randomized controlled trials and a prospective cohort study performed within the last decade, show that there is no neurodevelopmental improvement in the offspring of mothers who received levothyroxine treatment for GHT. Thus, the benefit of initiating treatment for GHT is highly debated within the clinical community as there may also be risks associated with over-treatment. In addition, regulatory mechanisms that could possibly lead to GHT during pregnancy are not well elucidated. This review aims to unravel pregnancy induced physiological challenges that could provide basis for the development of GHT. During pregnancy, there is increased renal clearance of iodine leading to low iodine state. Also, an elevated estrogen level leading to an increase in circulating thyroglobulin level and a decrease in free thyroxine level. Moreover, placenta secretes compounds such as human chorionic gonadotropin (hCG), placental growth factor (PIGF) and soluble FMS-like tyrosine kinase-1 (s-Flt1) that could affect the thyroid function. In turn, the passage of thyroid hormones and iodine to the fetus is highly regulated within the placental barrier. Together, these mechanisms are hypothesized to contribute to the development of intolerance of thyroid function leading to GHT in a vulnerable individual.