Genetic associations with neonatal thyroid-stimulating hormone levels

A genome-wide association study of thyroid stimulating hormone and free thyroxine in Danish children and adolescents

Background

Hypothyroidism is associated with obesity, and thyroid hormones are involved in the regulation of body composition, including fat mass. Genome-wide association studies (GWAS) in adults have identified 19 and 6 loci associated with plasma concentrations of thyroid stimulating hormone (TSH) and free thyroxine (fT4), respectively.

Objective

This study aimed to identify and characterize genetic variants associated with circulating TSH and fT4 in Danish children and adolescents and to examine whether these variants associate with obesity.

Methods

Genome-wide association analyses of imputed genotype data with fasting plasma concentrations of TSH and fT4 from a population-based sample of Danish children, adolescents, and young adults, and a group of children, adolescents, and young adults with overweight and obesity were performed (N = 1,764, mean age = 12.0 years [range 2.5−24.7]). Replication was performed in additional comparable samples (N = 2,097, mean age = 11.8 years [1.2−22.8]). Meta-analyses, using linear additive fixed-effect models, were performed on the results of the discovery and replication analyses.

Results

No novel loci associated with TSH or fT4 were identified. Four loci previously associated with TSH in adults were confirmed in this study population (PDE10A (rs2983511: β = 0.112SD, p = 4.8 ∙ 10⁻¹⁶), FOXE1 (rs7847663: β = 0.223SD, p = 1.5 ∙ 10⁻²⁰), NR3C2 (rs9968300: β = 0.194SD), p = 2.4 ∙ 10⁻¹¹), VEGFA (rs2396083: β = 0.088SD, p = 2.2 ∙ 10⁻¹⁰)). Effect sizes of variants known to associate with TSH or fT4 in adults showed a similar direction of effect in our cohort of children and adolescents, 11 of which were associated with TSH or fT4 in our study (p<0.0002). None of the TSH or fT4 associated SNPs were associated with obesity in our cohort, indicating no pleiotropic effects of these variants on obesity.

Conclusion

In a group of Danish children and adolescents, four loci previously associated with plasma TSH concentrations in adults, were associated with plasma TSH concentrations in children, suggesting comparable genetic determinants of thyroid function in adults and children.

Primary Cell Culture Systems for Human Thyroid Studies

BACKGROUND

Cell models are key instruments for in vitro studies of the thyroid. Permanent thyroid cell lines that are widely used in laboratory research typically originate from tumors. For many purposes, it is desirable to compare tumor cells with cells originating from normal tissue. However, such cultures grow slowly, have a highly limited life-span, and are known to lose their thyroid characteristics. The aim of the present study was to type coding and noncoding thyroid markers in different culture systems in an attempt to determine the optimal conditions for in vitro experimentation.

METHODS

Human primary thyroid cells were isolated from histologically non-tumorous tissues. Two alternative media (6H and h7H) were used. The morphology and behavior of the ensuing monolayer (two-dimensional) cultures was monitored by microscopy. The expression of key thyroid-related genes (n = 9) was monitored by reverse transcription polymerase chain reaction on days 8, 21, and 43 after initiation. As a pilot study, the same markers were studied in a three-dimensional hanging-drop culture system.

RESULTS

In the cultures with 6H or h7H medium, the primary thyroid cells displayed growth in numbers and size. Most cells retained the main morphological characteristics of thyroid cells throughout the first two weeks of culture, and fibroblast-like cells appeared around day 19. By day 21, most thyroid gene markers were retained, but by day 43, several markers were no longer present. The lncRNA transcripts PTCSC2 (spliced) and PTCSC3 were the first to disappear. There were no fundamental differences between the two media in the early period of culture. In the three-dimensional system, most thyroid markers were retained by day 21.

CONCLUSION

Cultures of thyroid cells retain many thyroid characteristics up to day 21. Thereafter, fibroblast-like dedifferentiated cells begin to dominate.

A single nucleotide polymorphism associated with isolated cleft lip and palate, thyroid cancer and hypothyroidism alters the activity of an oral epithelium and thyroid enhancer near FOXE1

Three common diseases, isolated cleft lip and cleft palate (CLP), hypothyroidism and thyroid cancer all map to the FOXE1 locus, but causative variants have yet to be identified. In patients with CLP, the frequency of coding mutations in FOXE1 fails to account for the risk attributable to this locus, suggesting that the common risk alleles reside in nearby regulatory elements. Using a combination of zebrafish and mouse transgenesis, we screened 15 conserved non-coding sequences for enhancer activity, identifying three that regulate expression in a tissue specific pattern consistent with endogenous foxe1 expression. These three, located -82.4, -67.7 and +22.6 kb from the FOXE1 start codon, are all active in the oral epithelium or branchial arches. The -67.7 and +22.6 kb elements are also active in the developing heart, and the -67.7 kb element uniquely directs expression in the developing thyroid. Within the -67.7 kb element is the SNP rs7850258 that is associated with all three diseases. Quantitative reporter assays in oral epithelial and thyroid cell lines show that the rs7850258 allele (G) associated with CLP and hypothyroidism has significantly greater enhancer activity than the allele associated with thyroid cancer (A). Moreover, consistent with predicted transcription factor binding differences, the -67.7 kb element containing rs7850258 allele G is significantly more responsive to both MYC and ARNT than allele A. By demonstrating that this common non-coding variant alters FOXE1 expression, we have identified at least in part the functional basis for the genetic risk of these seemingly disparate disorders.

Genetic predisposition to papillary thyroid carcinoma: involvement of FOXE1, TSHR, and a novel lincRNA gene, PTCSC2

CONTEXT

By genome-wide association studies, the risk allele [A] of SNP rs965513 predisposes strongly to papillary thyroid carcinoma (PTC). It is located in a gene-poor region of 9q22, some 60 kb from the FOXE1 gene. The underlying mechanisms remain to be discovered.

OBJECTIVE

Our objective was to identify novel transcripts in the 9q22 locus and correlate gene expression levels with the genotypes of rs965513.

DESIGN

We performed 3' and 5' rapid amplification of cDNA ends and RT-PCR to detect novel transcripts. One novel transcript was forcibly expressed in a cell line followed by gene expression array analysis. We genotyped rs965513 from PTC patients and measured gene expression levels by real-time RT-PCR in unaffected thyroid tissue and matched tumor.

SETTING

This was a laboratory-based study using cells from clinical tissue samples and a cancer cell line.

MAIN OUTCOME MEASURES

We detected previously uncharacterized transcripts and evaluated the gene expression levels and the correlation with the risk allele of rs965513, age, gender, chronic lymphocyte thyroiditis (CLT), and TSH levels.

RESULTS

We found a novel long intergenic noncoding RNA gene and named it papillary thyroid cancer susceptibility candidate 2 (PTCSC2). Transcripts of PTCSC2 are down-regulated in PTC tumors. The risk allele [A] of rs965513 was significantly associated with low expression of unspliced PTCSC2, FOXE1, and TSHR in unaffected thyroid tissue. We also observed a significant association of age and CLT with PTCSC2 unspliced transcript levels. The correlation between the rs965513 genotype and the PTCSC2 unspliced transcript levels remained significant after adjusting for age, gender, and CLT. Forced expression of PTCSC2 in the BCPAP cell line affected the expression of a subset of noncoding and coding transcripts with enrichment of genes functionally involved in cell cycle and cancer.

CONCLUSIONS

Our data suggest a role for PTCSC2, FOXE1, and TSHR in the predisposition to PTC.

Genetic variants associated with serum thyroid stimulating hormone (TSH) levels in European Americans and African Americans from the eMERGE Network

Thyroid stimulating hormone (TSH) hormone levels are normally tightly regulated within an individual; thus, relatively small variations may indicate thyroid disease. Genome-wide association studies (GWAS) have identified variants in PDE8B and FOXE1 that are associated with TSH levels. However, prior studies lacked racial/ethnic diversity, limiting the generalization of these findings to individuals of non-European ethnicities. The Electronic Medical Records and Genomics (eMERGE) Network is a collaboration across institutions with biobanks linked to electronic medical records (EMRs). The eMERGE Network uses EMR-derived phenotypes to perform GWAS in diverse populations for a variety of phenotypes. In this report, we identified serum TSH levels from 4,501 European American and 351 African American euthyroid individuals in the eMERGE Network with existing GWAS data. Tests of association were performed using linear regression and adjusted for age, sex, body mass index (BMI), and principal components, assuming an additive genetic model. Our results replicate the known association of PDE8B with serum TSH levels in European Americans (rs2046045 p = 1.85×10⁻¹⁷, β = 0.09). FOXE1 variants, associated with hypothyroidism, were not genome-wide significant (rs10759944: p = 1.08×10⁻⁶, β = −0.05). No SNPs reached genome-wide significance in African Americans. However, multiple known associations with TSH levels in European ancestry were nominally significant in African Americans, including PDE8B (rs2046045 p = 0.03, β = −0.09), VEGFA (rs11755845 p = 0.01, β = −0.13), and NFIA (rs334699 p = 1.50×10⁻³, β = −0.17). We found little evidence that SNPs previously associated with other thyroid-related disorders were associated with serum TSH levels in this study. These results support the previously reported association between PDE8B and serum TSH levels in European Americans and emphasize the need for additional genetic studies in more diverse populations.