Multi-omics and pathway analyses of genome-wide associations implicate regulation and immunity in verbal declarative memory performance.

BACKGROUND: Uncovering the functional relevance underlying verbal declarative memory (VDM) genome-wide association study (GWAS) results may facilitate the development of interventions to reduce age-related memory decline and dementia. METHODS: We performed multi-omics and pathway enrichment analyses of paragraph (PAR-dr) and word list (WL-dr) delayed recall GWAS from 29,076 older non-demented individuals of European descent. We assessed the relationship between single-variant associations and expression quantitative trait loci (eQTLs) in 44 tissues and methylation quantitative trait loci (meQTLs) in the hippocampus. We determined the relationship between gene associations and transcript levels in 53 tissues, annotation as immune genes, and regulation by transcription factors (TFs) and microRNAs. To identify significant pathways, gene set enrichment was tested in each cohort and meta-analyzed across cohorts. Analyses of differential expression in brain tissues were conducted for pathway component genes. RESULTS: The single-variant associations of VDM showed significant linkage disequilibrium (LD) with eQTLs across all tissues and meQTLs within the hippocampus. Stronger WL-dr gene associations correlated with reduced expression in four brain tissues, including the hippocampus. More robust PAR-dr and/or WL-dr gene associations were intricately linked with immunity and were influenced by 31 TFs and 2 microRNAs. Six pathways, including type I diabetes, exhibited significant associations with both PAR-dr and WL-dr. These pathways included fifteen MHC genes intricately linked to VDM performance, showing diverse expression patterns based on cognitive status in brain tissues. CONCLUSIONS: VDM genetic associations influence expression regulation via eQTLs and meQTLs. The involvement of TFs, microRNAs, MHC genes, and immune-related pathways contributes to VDM performance in older individuals.

Role of ST6GAL1 in Thyroid Cancers: Insights from Tissue Analysis and Genomic Datasets.

Thyroid cancer is the predominant endocrine-related malignancy. ST6 ß-galactoside α2,6-sialyltransferase 1 (ST6GAL1) has been studied in various types of cancers; however, the expression and function of ST6GAL1 in thyroid cancer has not been investigated so far. Previously, we conducted two genome-wide association studies and have identified the association of the ST6GAL1 gene with plasma thyroglobulin (Tg) levels. Since Tg levels are altered in thyroid pathologies, in the current study, we wanted to evaluate the expression of ST6GAL1 in thyroid cancer tissues. We performed an immunohistochemical analysis using human thyroid tissue from 89 patients and analyzed ST6GAL1 protein expression in papillary thyroid cancer (including follicular variant and microcarcinoma) and follicular thyroid cancer in comparison to normal thyroid tissue. Additionally, ST6GAL1 mRNA levels from The Cancer Genome Atlas (TCGA, n = 572) and the Genotype-Tissue Expression (GTEx) project (n = 279) were examined. The immunohistochemical analysis revealed higher ST6GAL1 protein expression in all thyroid tumors compared to normal thyroid tissue. TCGA data revealed increased ST6GAL1 mRNA levels in both primary and metastatic tumors versus controls. Notably, the follicular variant of papillary thyroid cancer exhibited significantly higher ST6GAL1 mRNA levels than classic papillary thyroid cancer. High ST6GAL1 mRNA levels significantly correlated with lymph node metastasis status, clinical stage, and reduced survival rate. ST6GAL1 emerges as a potential cancer-associated glycosyltransferase in thyroid malignancies, offering valuable insights into its diagnostic and prognostic significance.

Thyroid Function and Metabolic Syndrome: A Two-Sample Bidirectional Mendelian Randomization Study.

CONTEXT: Thyroid function has been associated with metabolic syndrome (MetS) in a number of observational studies but the direction of effects and the exact causal mechanism of this relationship is still unknown. OBJECTIVE: To examine genetically predicted effects of thyroid function on MetS risk and its components, and vice versa, using large-scale summary genetic association data. METHODS: We performed a two-sample bidirectional Mendelian randomization (MR) study using summary statistics from the most comprehensive genome-wide association studies (GWAS) of thyroid-stimulating hormone (TSH, n = 119 715), free thyroxine (fT4, n = 49 269), MetS (n = 291 107), and components of MetS: waist circumference (n = 462 166), fasting blood glucose (n = 281 416), hypertension (n = 463 010), triglycerides (TG, n = 441 016) and high-density lipoprotein cholesterol (HDL-C, n = 403 943). We chose the multiplicative random effects inverse variance weighted (IVW) method as the main analysis. Sensitivity analysis included weighted median and mode analysis, as well as MR-Egger and Causal Analysis Using Summary Effect estimates (CAUSE). RESULTS: Our results suggest that higher fT4 levels lower the risk of developing MetS (OR = 0.96, P = .037). Genetically predicted fT4 was also positively associated with HDL-C (ß = 0.02, P = .008), while genetically predicted TSH was positively associated with TG (ß = 0.01, P = .044). These effects were consistent across different MR analyses and confirmed with the CAUSE analysis. In the reverse direction MR analysis, genetically predicted HDL-C was negatively associated with TSH (ß = -0.03, P = .046) in the main IVW analysis. CONCLUSION: Our study suggests that variations in normal-range thyroid function are causally associated with the diagnosis of MetS and with lipid profile, while in the reverse direction, HDL-C has a plausible causal effect on reference-range TSH levels.

Vitamin D and the Thyroid: A Critical Review of the Current Evidence.

Vitamin D is necessary for the normal functioning of many organs, including the thyroid gland. It is, therefore, not surprising that vitamin D deficiency is considered a risk factor for the development of many thyroid disorders, including autoimmune thyroid diseases and thyroid cancer. However, the interaction between vitamin D and thyroid function is still not fully understood. This review discusses studies involving human subjects that (1) compared vitamin D status (primarily determined by serum calcidiol (25-hydroxyvitamin D [25(OH)D]) levels) with thyroid function assessed by thyroid stimulating hormone (TSH), thyroid hormones, and anti-thyroid antibody levels; and (2) evaluated the effect of vitamin D supplementation on thyroid function. Due to the many inconsistencies in the results between the studies, it is still difficult to draw a definite conclusion on how vitamin D status affects thyroid function. Studies in healthy participants observed either a negative correlation or no association between TSH and 25(OH)D levels, while the results for thyroid hormones showed high variability. Many studies have observed a negative association between anti-thyroid antibodies and 25(OH)D levels, but equally many studies have failed to observe such an association. Regarding the studies that examined the effect of vitamin D supplementation on thyroid function, almost all observed a decrease in anti-thyroid antibody levels after vitamin D supplementation. Factors that could contribute to the high variability between the studies are the use of different assays for the measurement of serum 25(OH)D levels and the confounding effects of sex, age, body-mass index, dietary habits, smoking, and the time of year when the samples were collected. In conclusion, additional studies with larger numbers of participants are needed to fully understand the effect of vitamin D on thyroid function.

Serotonin Receptor Gene Polymorphisms Are Associated with Cerebrospinal Fluid, Genetic, and Neuropsychological Biomarkers of Alzheimer's Disease.

A decrease in serotonergic transmission throughout the brain is among the earliest pathological changes in Alzheimer's disease (AD). Serotonergic receptors are also affected in AD. Polymorphisms in genes of serotonin (5HT) receptors have been mostly associated with behavioral and psychological symptoms of dementia (BPSD). In this study, we examined if AD patients carrying different genotypes in 5HTR1B rs13212041, 5HTR2A rs6313 (T102C), 5HTR2C rs3813929 (-759C/T), and 5HTR6 rs1805054 (C267T) polymorphisms have a higher risk of faster disease progression (assessed by neuropsychological testing), are more prone to develop AD-related pathology (reflected by levels of cerebrospinal fluid [CSF] AD biomarkers), or have an association with an apolipoprotein E (APOE) haplotype. This study included 115 patients with AD, 53 patients with mild cognitive impairment (MCI), and 2701 healthy controls. AD biomarkers were determined in the CSF of AD and MCI patients using enzyme-linked immunosorbent assays (ELISA), while polymorphisms were determined using either TaqMan SNP Genotyping Assays or Illumina genotyping platforms. We detected a significant decrease in the CSF amyloid ß1-42 (Aß1-42) and an increase in p-tau181/Aß1-42 ratio in carriers of the T allele in the 5HTR2C rs3813929 (-759C/T) polymorphism. A significantly higher number of APOE ε4 allele carriers was observed among individuals carrying a TT genotype within the 5HTR2A T102C polymorphism, a C allele within the 5HTR1B rs13212041 polymorphism, and a T allele within the 5HTR6 rs1805054 (C267T) polymorphism. Additionally, individuals carrying the C allele within the 5HTR1B rs13212041 polymorphism were significantly more represented among AD patients and had poorer performances on the Rey-Osterrieth test. Carriers of the T allele within the 5HTR6 rs1805054 had poorer performances on the MMSE and ADAS-Cog. As all four analyzed polymorphisms of serotonin receptor genes showed an association with either genetic, CSF, or neuropsychological biomarkers of AD, they deserve further investigation as potential early genetic biomarkers of AD.

Association between Thyroid Function and Ocular Parameters.

During development, thyroid hormones play an important role in eye development, while in adults, some pathological thyroid conditions can affect the normal functioning of the eyes. Thyroid eye disease is the most well-known eye pathology caused by a pathological thyroid condition. Few studies have investigated the association between ocular parameters and thyroid function. Thus, in this study, we aimed to examine whether thyroid activity affects ocular parameters. This cross-sectional study included 4633 healthy adults recruited within the 10,001 Dalmatians project of the Croatian Biobank. The plasma levels of thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), thyroglobulin (Tg), thyroglobulin antibodies (TgAb), and thyroid peroxidase antibodies (TPOAb) were measured by an immunoassay. We determined 20 ocular parameters for each participant (10 for each eye, including corneal radius, corneal thickness, anterior chamber depth, anterior chamber angle, lens thickness, posterior chamber length, axial length, intraocular lens power (IOL), spherical power, and cylinder power). Patients with hyperthyroidism had thicker corneas compared to euthyroid individuals. Corneal thickness was also negatively associated with plasma TSH levels. Intra-ocular lens power was higher in patients with clinical hypothyroidism, while spherical power was higher in euthyroid individuals with positive antibodies compared to euthyroid individuals. Intra-ocular lens power negatively correlated with fT4 levels, while spherical power positively correlated with TgAb, TPOAb, and Tg levels and negatively correlated with TSH levels. The anterior chamber angle was positively associated with plasma TSH levels and TPOAb levels and negatively associated with plasma fT4 levels. These findings suggest an interesting interplay between ophthalmic measures and thyroid status, detectable even in the general adult population.

Thyroid Hormones Are Not Associated with Plasma Osteocalcin Levels in Adult Population with Normal Thyroid Function.

Thyroid hormones (THs) play an indispensable role in skeletal development and bone remodeling. Some studies have reported associations of THs with serum osteocalcin (OC) levels, but the results are quite inconsistent and the molecular mechanism of their simultaneous or interdependent activity on bone is almost unknown. Therefore, the aim of this study was to determine the possible associations of plasma THs with plasma OC levels and the possible mediating effect of OC on the relationship between THs and bone mineral density (BMD). For this purpose, out of the initial 1981 participants, we selected healthy euthyroid participants controlled for available confounding factors that can affect thyroid function and bone metabolism (N = 694). Given our results, we could not confirm any associations of THs with plasma OC levels nor the mediating effect of OC on the relationship between THs and BMD in euthyroid population. In the group of women controlled for menopause status (N = 396), we found a significant negative association of body mass index (BMI) with OC levels (ß = −0.14, p = 0.03). We also found a negative association of free triiodothyronine (fT3) (ß = −0.01, p = 0.02) and age (ß = −0.003, p < 0.001) with BMD, and a positive association of BMI (ß = 0.004, p < 0.001) and male gender (ß = 0.1, p < 0.001) with BMD. In addition, we found significantly higher plasma OC levels and lower values of BMD in postmenopausal euthyroid women compared with premenopausal euthyroid women. In our opinion, the results of previous studies suggesting an association between circulating THs and serum OC levels may be influenced by an inconsistent selection of participants and the influence of confounding factors.

Epidemiology of Hypothyroidism, Hyperthyroidism and Positive Thyroid Antibodies in the Croatian Population.

Thyroid dysfunction appears to be the leading endocrine disorder. We conducted a cross-sectional study on 4402 individuals from three Croatian cohorts. The aim of this study was to analyse the prevalence of diagnosed and undiagnosed hypothyroidism, hyperthyroidism (subclinical and clinical) and positive thyroid antibodies in the Croatian population. The results of the study indicated that 17.6% of participants were euthyroid with positive antibodies. The prevalence of clinical and subclinical hypothyroidism was 3% and 7.4%, respectively, while the prevalence of clinical and subclinical hyperthyroidism was 0.2% and 1.1%, respectively. Among them, 92.6% subclinical hypothyroid, 93.9% clinical hypothyroid, 83% subclinical hyperthyroid and 71.4% clinical hyperthyroid participants were undiagnosed. Finally, the prevalence of undiagnosed subclinical and clinical hypothyroidism in our population was 6.9% and 2.8%, respectively, while the prevalence of undiagnosed subclinical and clinical hyperthyroidism was 0.9% and 0.1%, respectively. Women showed a higher prevalence of thyroid disorders; 1.57 times higher odds of euthyroidism with positive antibodies, 2.1 times higher odds of subclinical hyperthyroidism, 2.37 times higher odds of clinical hypothyroidism and 1.58 times higher odds of subclinical hypothyroidism than men. These results indicate an extremely high proportion of undiagnosed cases, and therefore require investments in a prevention programme.

Genome-Wide Association Analysis and Genomic Prediction of Thyroglobulin Plasma Levels.

Thyroglobulin (Tg) is an iodoglycoprotein produced by thyroid follicular cells which acts as an essential substrate for thyroid hormone synthesis. To date, only one genome-wide association study (GWAS) of plasma Tg levels has been performed by our research group. Utilizing recent advancements in computation and modeling, we apply a Bayesian approach to the probabilistic inference of the genetic architecture of Tg. We fitted a Bayesian sparse linear mixed model (BSLMM) and a frequentist linear mixed model (LMM) of 7,289,083 variants in 1096 healthy European-ancestry participants of the Croatian Biobank. Meta-analysis with two independent cohorts (total n = 2109) identified 83 genome-wide significant single nucleotide polymorphisms (SNPs) within the ST6GAL1 gene (p<5×10-8). BSLMM revealed additional association signals on chromosomes 1, 8, 10, and 14. For ST6GAL1 and the newly uncovered genes, we provide physiological and pathophysiological explanations of how their expression could be associated with variations in plasma Tg levels. We found that the SNP-heritability of Tg is 17% and that 52% of this variation is due to a small number of 16 variants that have a major effect on Tg levels. Our results suggest that the genetic architecture of plasma Tg is not polygenic, but influenced by a few genes with major effects.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels.

Thyroid hormones are necessary for the normal functioning of physiological systems. Therefore, knowledge of any factor (whether genetic, environmental or intrinsic) that alters the levels of thyroid-stimulating hormone (TSH) and thyroid hormones is crucial. Genetic factors contribute up to 65% of interindividual variations in TSH and thyroid hormone levels, but many environmental factors can also affect thyroid function. This review discusses studies that have analyzed the impact of environmental factors on TSH and thyroid hormone levels in healthy adults. We included lifestyle factors (smoking, alcohol consumption, diet and exercise) and pollutants (chemicals and heavy metals). Many inconsistencies in the results have been observed between studies, making it difficult to draw a general conclusion about how a particular environmental factor influences TSH and thyroid hormone levels. However, lifestyle factors that showed the clearest association with TSH and thyroid hormones were smoking, body mass index (BMI) and iodine (micronutrient taken from the diet). Smoking mainly led to a decrease in TSH levels and an increase in triiodothyronine (T3) and thyroxine (T4) levels, while BMI levels were positively correlated with TSH and free T3 levels. Excess iodine led to an increase in TSH levels and a decrease in thyroid hormone levels. Among the pollutants analyzed, most studies observed a decrease in thyroid hormone levels after exposure to perchlorate. Future studies should continue to analyze the impact of environmental factors on thyroid function as they could contribute to understanding the complex background of gene-environment interactions underlying the pathology of thyroid diseases.

The effect of food groups and nutrients on thyroid hormone levels in healthy individuals.

OBJECTIVES: The aim of the study was to analyze the association of dietary groups (groups of food items) with thyroid hormone levels in healthy individuals. METHODS: This cross-sectional study enrolled 4585 healthy individuals from the Dalmatian region of south Croatia with measurements of plasma free triiodothyronine (fT3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) levels. Dietary intake was assessed according to data of the completed food frequency questionnaire, containing 58 food items. Principal component analysis was performed to reduce food items into dietary groups, followed by linear regression analyses to test the association between dietary groups and fT3, fT4, and TSH levels. RESULTS: Among the 4585 healthy individuals, we observed lower plasma fT3 and fT4 levels and higher TSH levels in women than in men. Smokers were found to have significantly lower TSH levels than non-smokers and ex-smokers, and participants with higher fasting glucose levels had higher fT4 levels. Different dietary groups (factors) showed association with fT3, fT4, and TSH levels. It was observed that dietary factors (with frequent consumption of fruit juices, Cedevita vitamin drink, and non-alcoholic drinks) that negatively affected TSH levels simultaneously had a positive effect on fT4, satisfying the expected pattern of effects. CONCLUSIONS: In our study, frequent consumption of foods with a high glycemic index showed a positive association with fT3 and fT4 levels and a negative association with TSH levels, whereas foods rich in saturated fatty acids and with a high protein concentration showed a negative association with fT3 and fT4 levels.

Environmental Factors That Affect Parathyroid Hormone and Calcitonin Levels.

Calciotropic hormones, parathyroid hormone (PTH) and calcitonin are involved in the regulation of bone mineral metabolism and maintenance of calcium and phosphate homeostasis in the body. Therefore, an understanding of environmental and genetic factors influencing PTH and calcitonin levels is crucial. Genetic factors are estimated to account for 60% of variations in PTH levels, while the genetic background of interindividual calcitonin variations has not yet been studied. In this review, we analyzed the literature discussing the influence of environmental factors (lifestyle factors and pollutants) on PTH and calcitonin levels. Among lifestyle factors, smoking, body mass index (BMI), diet, alcohol, and exercise were analyzed; among pollutants, heavy metals and chemicals were analyzed. Lifestyle factors that showed the clearest association with PTH levels were smoking, BMI, exercise, and micronutrients taken from the diet (vitamin D and calcium). Smoking, vitamin D, and calcium intake led to a decrease in PTH levels, while higher BMI and exercise led to an increase in PTH levels. In terms of pollutants, exposure to cadmium led to a decrease in PTH levels, while exposure to lead increased PTH levels. Several studies have investigated the effect of chemicals on PTH levels in humans. Compared to PTH studies, a smaller number of studies analyzed the influence of environmental factors on calcitonin levels, which gives great variability in results. Only a few studies have analyzed the influence of pollutants on calcitonin levels in humans. The lifestyle factor with the clearest relationship with calcitonin was smoking (smokers had increased calcitonin levels). Given the importance of PTH and calcitonin in maintaining calcium and phosphate homeostasis and bone mineral metabolism, additional studies on the influence of environmental factors that could affect PTH and calcitonin levels are crucial.

Differences in food consumption between patients with Hashimoto's thyroiditis and healthy individuals.

Food is considered as important environmental factor that plays a role in development of Hashimoto's thyroiditis (HT). The goal of our study was to identify food groups, assessed by food frequency questionnaire, that differ in consumption frequency between 491 patients with HT and 433 controls. We also analysed association of food groups with the wealth of HT-related clinical traits and symptoms. We found significantly increased consumption of animal fat (OR 1.55, p < 0.0001) and processed meat (OR 1.16, p = 0.0012) in HT cases, whereas controls consumed significantly more frequently red meat (OR 0.80, p < 0.0001), non-alcoholic beverages (OR 0.82, p < 0.0001), whole grains (OR 0.82, p < 0.0001) and plant oil (OR 0.87, p < 0.0001). We also observed association of plant oil consumption with increased triiodothyronine levels in HT patients (ß = 0.07, p < 0.0001), and, association of olive oil consumption with decreased systolic blood pressure (ß = - 0.16, p = 0.001) in HT patients on levothyroxine (LT4) therapy. Analysis of food consumption between HT patients with and without LT4 therapy suggest that patients do not tend to modify their diet upon HT diagnosis in our population. Our study may be of relevance to nutritionists, nutritional therapists and clinicians involved in developing dietary recommendations for HT patients.

Thyroid hormone levels are associated with metabolic components: a cross-sectional study.

AIM: To analyze the association of thyroid function and hormone levels with metabolic syndrome (MetS) and its components. METHODS: This cross-sectional population-based study involved 2183 Croatian individuals with no history of thyroid disease, hypertension, diabetes, and hyperlipidemia. MetS was diagnosed according to the National Cholesterol Education Program's Adult Treatment Panel III criteria. RESULTS: We found no association between thyroid function groups and the prevalence of MetS and its components. Clinically hypothyroid participants showed significantly higher triceps skinfold measurements than subclinically hypothyroid and euthyroid participants. Furthermore, clinically hypothyroid participants had higher abdominal skinfold thickness than subclinically hypothyroid participants. Otherwise, suprailiac and abdominal skinfold measurements were higher in the subclinically and clinically hyperthyroid group of participants compared with euthyroid and subclinically hypothyroid participants. A strong positive association of thyroid-stimulating hormone (TSH) and strong negative association of free triiodothyronine (fT3) and free thyroxine (fT4) levels with HOMA-IR and cholesterol levels were found. Furthermore, the fT4 level also showed a strong negative association with HDL and triceps skinfold thickness. CONCLUSIONS: This study supports the standing that TSH, fT3, and fT4 levels are important variables to determine the association of thyroid function with MetS.

AATF and SMARCA2 are associated with thyroid volume in Hashimoto's thyroiditis patients.

Thyroid volume of Hashimoto's thyroiditis (HT) patients varies in size over the course of disease and it may reflect changes in biological function of thyroid gland. Patients with subclinical hypothyroidism predominantly have increased thyroid volume whereas patients with more pronounced hypothyroidism have smaller thyroid volumes. Suggested mechanism for thyroid atrophy is thyrocyte death due to apoptosis. We performed the first genome-wide association study (GWAS) of thyroid volume in two groups of HT patients, depending on levothyroxine (LT4) therapy, and then meta-analysed across. Study included 345 HT patients in total and 6 007 322 common autosomal genetic variants. Underlying hypothesis was that genetic components that are involved in regulation of thyroid volume display their effect in specific pathophysiologic conditions of thyroid gland of HT patients. We additionally performed immunohistochemical analysis using thyroid tissues and analysed differences in expression levels of identified proteins and apoptotic marker between HT patients and controls. We found genome-wide significant association of two loci, both involved in apoptosis, with thyroid volume of HT patients: rs7212416 inside apoptosis-antagonizing transcription factor AATF (P = 8.95 × 10-9) and rs10738556 near chromatin-remodeling SMARCA2 (P = 2.83 × 10-8). In immunohistochemical analysis we observed that HT patients with homozygous AATF risk genotypes have decreased AATF expression (0.46-fold, P < 0.0001) and increased apoptosis (3.99-fold, P = 0.0001) in comparison to controls. HT patients with heterozygous SMARCA2 genotypes have decreased SMARCA2 expression, albeit without reaching statistical significance (1.07-fold, P = 0.5876), and significantly increased apoptosis (4.11-fold, P < 0.0001). By two lines of evidence we show that two highly plausible genetic loci, AATF and SMARCA2, may be involved in determining the thyroid volume of HT patients. The results of our study significantly add to the current knowledge of disturbed biological mechanisms in thyroid gland of HT patients.

Rare and common genetic variations in the Keap1/Nrf2 antioxidant response pathway impact thyroglobulin gene expression and circulating levels, respectively.

Nuclear factor, erythroid 2-like 2 (Nrf2) is a transcription factor that has been gaining attention in the field of pharmacology and especially in the chemoprevention of diseases such as cancer, metabolic and neurodegenerative diseases, etc. This is because natural compounds such as sulforaphane, which is found in broccoli sprout extracts, can activate Nrf2. The repertoire of the roles of Nrf2 is ever increasing; besides its traditional antioxidant and cytoprotective effects, Nrf2 can have other functions as a transcription factor. We have recently shown that Nrf2 directly regulates the expression of thyroglobulin (Tg), which is the most abundant thyroidal protein and the precursor of thyroid hormones. Two functional binding sites for Nrf2 (antioxidant response elements, AREs) were identified in the regulatory region of the TG gene. Interestingly, we then observed that one of these AREs harbors a rare single-nucleotide polymorphism (SNP). Also recently, we performed the first genome-wide association study (GWAS) for common SNPs that impact the circulating levels of Tg. Based on these investigations, we were triggered (i) to investigate whether common SNPs in the Nrf2 pathway correlate with circulating Tg levels; and (ii) to examine whether the rare SNP in one of the TG regulatory AREs may affect gene expression. To address the first question, we analyzed GWAS data from a general population and its two subpopulations, one with thyroid disease and/or abnormal thyroid function tests and the other without, in which circulating Tg levels had been measured. Statistically significant associations with Tg levels were observed in the genes encoding Nrf2 and Keap1, including, notably, a known functional SNP in the promoter of the gene encoding Nrf2. Regarding the rare SNP (rs778940395) in the proximal ARE of the TG enhancer, luciferase reporter gene expression studies in PCCL3 rat thyroid follicular cells showed that this SNP abrogated the basal and sulforaphane- or TSH-induced luciferase activity, behaving as a complete loss-of-function mutation. Thus, both rare and common genetic variation in the Keap1/Nrf2 pathway can impact TG expression and Tg circulating levels, respectively.

Genome-Wide Analysis Identifies Two Susceptibility Loci for Positive Thyroid Peroxidase and Thyroglobulin Antibodies.

INTRODUCTION: Thyroid peroxidase (TPO) and thyroglobulin (Tg) are main components of the thyroid gland and play an essential role in thyroid hormone synthesis. The development of antibodies to thyroid peroxidase (TPOAb) and thyroglobulin (TgAb) is the major diagnostic hallmark and early indicator of autoimmune thyroid disease. TPOAb and TgAb are under strong genetic influence; however, genetic factors that determine thyroid antibody positivity are largely unknown. MATERIALS AND METHODS: To identify novel loci associated with TPOAb and/or TgAb positivity, we performed a genome-wide meta-analysis in a total of 2613 individuals from Croatia. Participants with elevated plasma TPOAb and/or TgAb were defined as cases (N = 619) and those with TPOAb and TgAb within reference values were defined as controls (N = 1994). RESULTS: We identified 2 novel loci, of which 1 is located within the YES1 gene (rs77284350, P = 1.50 × 10-8), and the other resides within the IRF8 gene (rs16939945, P = 5.04 × 10-8). CONCLUSIONS: Although the observed variants were associated with TPOAb and TgAb positivity for the first time, both YES1 and IRF8 were previously linked to susceptibility to other autoimmune diseases, and represent plausible biological candidates. This study adds to the knowledge of genetics underlying thyroid antibodies and provides a good basis for further research.

Genetic Variants in the ST6GAL1 Gene Are Associated with Thyroglobulin Plasma Level in Healthy Individuals.

Background: Thyroglobulin (Tg) is a 660 kDa iodoglycoprotein that serves as a scaffold for thyroid hormone synthesis. Although a twin study showed that variability of serum Tg levels has a substantial genetic basis, no genome-wide association study (GWAS) of serum/plasma Tg levels has been performed to date. The aim of this study was to identify genetic variants associated with plasma Tg levels among healthy individuals. Methods: A GWAS was conducted on two Croatian cohorts, and a combined analysis was performed. The analyses included 1094 individuals. A total of 7,597,379 variants, imputed using the 1000 Genomes reference panel, were analyzed for association. GWAS was performed under an additive model, controlling for age, sex, and relatedness within each data set. Combined analysis was conducted using the inverse-variance fixed-effects method. Results: Sixteen variants located on chromosome 3, within the ST6GAL1 gene, reached genome-wide significance. The lead SNP was rs4012172 ( \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$p = 1.29 \times {10^{ - 10}}$$ \end{document} ), which explained 3.19% of the variance in Tg levels. ST6GAL1 belongs to the sialyltransferase protein family, which has a fundamental role in the synthesis of specific sialylated structures on various glycoproteins, including Tg. It is known that only immature Tg (poorly sialylated or desialylated) can be transferred to the bloodstream. Conclusions: A highly biologically plausible locus was identified that could have a role in the regulation of plasma Tg levels in healthy individuals.

Genome-wide association analysis suggests novel loci underlying thyroid antibodies in Hashimoto's thyroiditis.

Thyroid antibodies against thyroglobulin (TgAb) and thyroid peroxidase (TPOAb) are key markers of Hashimoto's thyroiditis (HT), the most common autoimmune thyroid disorder. Genetic determinants of thyroid antibodies are still poorly known, especially as they were not studied in patients with thyroid diseases. We performed the first genome-wide association analysis of thyroid antibodies in 430 HT patients that may be considered as population extremes for thyroid antibodies distribution. We detected two suggestively associated genetic variants with TgAb, rs6972286 close to ANKRD7 and LSM8 (P = 2.34 × 10-7) and rs756763 inside CA10 (P = 6.05 × 10-7), and one with TPOAb, rs12507813 positioned between TRIM61 and TRIM60 (P = 4.95 × 10-7). Bivariate analysis resulted with three suggestively associated genetic variants that predispose to both antibodies: rs13190616 inside RP11-138J23.1 (P = 2.01 × 10-6), rs561030786 close to DUBR (P = 7.33 × 10-6) and rs12713034 inside FSHR (P = 7.66 × 10-6). All identified genomic regions have a substantial literature record of involvement with female-related traits, immune-mediated diseases and personality traits that are all characterized by increased thyroid antibody levels. Our findings demonstrate the existence of genetic overlap between thyroid autoimmunity in HT and different non-thyroid diseases characterized by the presence of thyroid antibodies. We also suggest that genetic variants that regulate antibody levels may differ between HT patients and individuals with normal thyroid function.