Defects in protein folding in congenital hypothyroidism

Clinical and molecular study of patients with thyroid dyshormogenesis and variants in the thyroglobulin gene

Introduction

Defects in any thyroid hormone synthesis steps cause thyroid dyshormonogenesis (THD). THD due to thyroglobulin (TG) gene variants is a cause of congenital hypothyroidism (CH) with a wide clinical spectrum, ranging from mild to severe permanent hypothyroidism. We present high-throughput sequencing results of patients with TG variants.

Methods

A CH high-throughput sequencing-panel of the main genes involved in the regulation of thyroid hormonogenesis was performed to identify those TG variants that may be related to patient THD phenotype.

Results

We identified 21 TG gene variants in 19 patients (11.8%) which could explain their phenotype. Ten of those (47.6%) were not previously described. CH was biochemically severe in these 19 patients. Eight of them were reevaluated after one month of discontinuing LT4 treatment and all had severe permanent hypothyroidism. We also identified another 16 patients who presented heterozygous TG variants, of whom, at reevaluation, five had mild permanent and only one had severe permanent hypothyroidisms.

Discussions

In this study, 10 novel and 11 previously reported variants in the TG gene have been identified that could explain the phenotype of 19 patients from non-consanguineous families from a large THD cohort. Although not all these TG gene variants can explain all the patients' THD phenotypes, some of them had severe or mild permanent hypothyroidism at reevaluation.

Disulfide Bonds of Thyroid Peroxidase Are Critical Elements for Subcellular Localization, Proteasome-Dependent Degradation, and Enzyme Activity

Background: Congenital hypothyroidism (CH) is caused by mutations in cysteine residues, including Cys655 and Cys825 that form disulfide bonds in thyroid peroxidase (TPO). It is highly likely that these disulfide bonds could play an important role in TPO activity. However, to date, no study has comprehensively analyzed cysteine mutations that form disulfide bonds in TPO. In this study, we induced mutations in cysteine residues involved in disulfide bonds formation and analyzed their effect on subcellular localization, degradation, and enzyme activities to evaluate the importance of disulfide bonds in TPO activity. Methods: Vector plasmid TPO mutants, C655F and C825R, known to occur in CH, were transfected into HEK293 cells. TPO activity and protein expression levels were measured by the Amplex red assay and Western blotting. The same procedure was performed in the presence of MG132 proteasome inhibitor. Subcellular localization was determined using immunocytochemistry and flow cytometry. The locations of all disulfide bonds within TPO were predicted using in silico analysis. All TPO mutations associated with disulfide bonds were induced. TPO activity and protein expression levels were also measured in all TPO mutants associated with disulfide bonds using the Amplex red assay and Western blotting. Results: C655F and C825R showed significantly decreased activity and protein expression compared with the wild type (WT) (p < 0.05). In the presence of the MG132 proteasome inhibitor, the protein expression level of TPO increased to a level comparable with that of the WT without increases in its activity. The degree of subcellular distribution of TPO to the cell surface in the mutants was lower compared with the WT TPO. Twenty-four cysteine residues were involved in the formation of 12 disulfide bonds in TPO. All TPO mutants harboring an amino acid substitution in each cysteine showed significantly reduced TPO activity and protein expression levels. Furthermore, the differences in TPO activity depended on the position of the disulfide bond. Conclusions: All 12 disulfide bonds play an important role in the activity of TPO. Furthermore, the mutations lead to misfolding, degradation, and membrane insertion.

GLIS3 expression in the thyroid gland in relation to TSH signaling and regulation of gene expression

Loss of GLI-Similar 3 (GLIS3) function in mice and humans causes congenital hypothyroidism (CH). In this study, we demonstrate that GLIS3 protein is first detectable at E15.5 of murine thyroid development, a time at which GLIS3 target genes, such as Slc5a5 (Nis), become expressed. This, together with observations showing that ubiquitous Glis3KO mice do not display major changes in prenatal thyroid gland morphology, indicated that CH in Glis3KO mice is due to dyshormonogenesis rather than thyroid dysgenesis. Analysis of GLIS3 in postnatal thyroid suggested a link between GLIS3 protein expression and blood TSH levels. This was supported by data showing that treatment with TSH, cAMP, or adenylyl cyclase activators or expression of constitutively active PKA enhanced GLIS3 protein stability and transcriptional activity, indicating that GLIS3 activity is regulated at least in part by TSH/TSHR-mediated activation of PKA. The TSH-dependent increase in GLIS3 transcriptional activity would be critical for the induction of GLIS3 target gene expression, including several thyroid hormone (TH) biosynthetic genes, in thyroid follicular cells of mice fed a low iodine diet (LID) when blood TSH levels are highly elevated. Like TH biosynthetic genes, the expression of cell cycle genes is suppressed in ubiquitous Glis3KO mice fed a LID; however, in thyroid-specific Glis3 knockout mice, the expression of cell cycle genes was not repressed, in contrast to TH biosynthetic genes. This indicated that the inhibition of cell cycle genes in ubiquitous Glis3KO mice is dependent on changes in gene expression in GLIS3 target tissues other than the thyroid.

HOXB3 promotes trophoblast cell proliferation, invasion, and migration to alleviate preeclampsia via mediating the Notch/Wnt/β-catenin pathway

Preeclampsia (PE) harms a significant number of pregnant women and fetuses. However, because of its complex pathological mechanisms, there is no cure except for delivery. This study identified the impact and mechanisms of action of HOXB3 in PE. The behaviors of HTR-8/SVneo cells were analyzed using a cell counting kit-8, EdU, and transwell assays. The interaction between HOXB3 and Notch1 was assessed using a luciferase reporter and chromatin immunoprecipitation assays. Expression was measured by quantitative real-time polymerase chain reaction, western blotting, and immunofluorescence assays. Additionally, the function of HOXB3 was evaluated in an established rat model of PE. We found that HOXB3 was upregulated in PE. HOXB3 overexpression facilitated trophoblast cell proliferation, migration, and invasion. HOXB3 transcriptionally regulated Notch1 by binding to its promoter. Notch1 knockdown abrogated the functions of HOXB3 and the-catenin pathway in trophoblasts. Suppression of the Wnt/β-catenin pathway abrogated the effects of HOXB3. Additionally, HOXB3 alleviated the symptoms in PE rats. In conclusion, HOXB3 transcriptionally activated Notch1 expression and the-catenin pathway, promoting trophoblast cell proliferation, invasion, and migration, thereby alleviating PE progression. This study provides a novel approach for PE therapy.

Genetic Screening and Functional Analysis of Thyroid Peroxidase Variants in Chinese Patients with Congenital Hypothyroidism

INTRODUCTION

Congenital hypothyroidism (CH), the most common neonatal endocrine disorder worldwide, can be caused by variants in the thyroid peroxidase (TPO) gene. This study aimed to identify TPO variants in Chinese patients with CH, analyze their impact on TPO function, and establish relationships between TPO genotypes and clinical characteristics.

METHODS

A total of 328 patients with CH were screened for TPO variants by performing whole-exome sequencing. The function of the detected TPO variants was investigated via transfection assays in vitro. The pathogenic effect of five novel variants was further assessed in silico.

RESULTS

Among 328 patients with CH, 19 TPO variants, including six novel ones, were identified in 43 patients. Eighteen patients (5.5%) carried biallelic TPO variants. In vitro experiments showed that TPO activity was impaired to varying degrees in 17 variants. Furthermore, we determined that a residual TPO enzyme activity threshold of 15% may serve as a criterion for differentiating CH severity.

CONCLUSIONS

According to our study, the prevalence of TPO variants among Chinese patients with CH was 13.1%. Five novel variants led to impaired TPO function by altering its structure or by affecting its expression or cellular localization, which should result in impaired thyroid hormone synthesis.

The Severity of Congenital Hypothyroidism With Gland-In-Situ Predicts Molecular Yield by Targeted Next-Generation Sequencing

INTRODUCTION

Congenital hypothyroidism with gland-in-situ (CH-GIS) is usually attributed to mutations in the genes involved in thyroid hormone production. The diagnostic yield of targeted next-generation sequencing (NGS) varied widely between studies. We hypothesized that the molecular yield of targeted NGS would depend on the severity of CH.

METHODS

Targeted NGS was performed in 103 CH-GIS patients from the French national screening program referred to the Reference Center for Rare Thyroid Diseases of Angers University Hospital. The custom targeted NGS panel contained 48 genes. Cases were classified as solved or probably solved depending on the known inheritance of the gene, the classification of the variants according to the American College of Medical Genetics and Genomics, the familial segregation, and published functional studies. Thyroid-stimulating hormone at CH screening and at diagnosis (TSHsc and TSHdg) and free T4 at diagnosis (FT4dg) were recorded.

RESULTS

NGS identified 95 variants in 10 genes in 73 of the 103 patients, resulting in 25 solved cases and 18 probably solved cases. They were mainly due to mutations in the TG (n = 20) and TPO (n = 15) genes. The molecular yield was, respectively, 73% and 25% if TSHsc was ≥ and < 80 mUI/L, 60% and 30% if TSHdg was ≥ and < 100 mUI/L, and 69% and 29% if FT4dg was ≤ and > 5 pmol/L.

CONCLUSION

NGS in patients with CH-GIS in France found a molecular explanation in 42% of the cases, increasing to 70% when TSHsc was ≥ 80 mUI/L or FT4dg was ≤ 5 pmol/L.

Role of GLIS3 in thyroid development and in the regulation of gene expression in thyroid specific Glis3KO mice

Loss of GLI-Similar 3 (GLIS3) function in mice and humans causes congenital hypothyroidism (CH). In this study, we demonstrate that GLIS3 protein is first detectable at E15.5 of murine thyroid development, a time when GLIS3 target genes, such as Slc5a5 (Nis), become also expressed. We further show that Glis3KO mice do not display any major changes in prenatal thyroid gland morphology indicating that CH in Glis3KO mice is due to dyshormonogenesis rather than thyroid dysgenesis. Analysis of thyroid-specific Glis3 knockout (Glis3-Pax8Cre) mice fed either a normal or low-iodine diet (ND or LID) revealed that, in contrast to ubiquitous Glis3KO mice, thyroid follicular cell proliferation and the expression of cell cycle genes were not repressed suggesting that the inhibition of thyroid follicular cell proliferation in ubiquitous Glis3KO mice is related to loss of GLIS3 function in other cell types. However, the expression of several thyroid hormone biosynthesis-, extracellular matrix (ECM)-, and inflammation-related genes was still suppressed in Glis3-Pax8Cre mice particularly under conditions of high blood levels of thyroid stimulating hormone (TSH). We further demonstrate that treatment with TSH, protein kinase A (PKA) or adenylyl cyclase activators or expression of constitutively active PKA enhances GLIS3 protein and activity, suggesting that GLIS3 transcriptional activity is regulated in part by TSH/TSHR-mediated activation of the PKA pathway. This mechanism of regulation provides an explanation for the dramatic increase in GLIS3 protein expression and the subsequent induction of GLIS3 target genes, including several thyroid hormone biosynthetic genes, in thyroid follicular cells of mice fed a LID.

The length of FOXE1 polyalanine tract in congenital hypothyroidism: Evidence for a pathogenic role from familial, molecular and cohort studies

INTRODUCTION

FOXE1 is required for thyroid function and its homozygous mutations cause a rare syndromic form of congenital hypothyroidism (CH). FOXE1 has a polymorphic polyalanine tract whose involvement in thyroid pathology is controversial. Starting from genetic studies in a CH family, we explored the functional role and involvement of FOXE1 variations in a large CH population.

METHODS

We applied NGS screening to a large CH family and a cohort of 1752 individuals and validated these results by in silico modeling and in vitro experiments.

RESULTS

A new heterozygous FOXE1 variant segregated with 14-Alanine tract homozygosity in 5 CH siblings with athyreosis. The p.L107V variant demonstrated to significantly reduce the FOXE1 transcriptional activity. The 14-Alanine-FOXE1 displayed altered subcellular localization and significantly impaired synergy with other transcription factors, when compared with the more common 16-Alanine-FOXE1. The CH group with thyroid dysgenesis was largely and significantly enriched with the 14-Alanine-FOXE1 homozygosity.

DISCUSSION

We provide new evidence that disentangle the pathophysiological role of FOXE1 polyalanine tract, thereby significantly broadening the perspective on the role of FOXE1 in the complex pathogenesis of CH. FOXE1 should be therefore added to the group of polyalanine disease-associated transcription factors.

The iodide transporter Slc26a7 impacts thyroid function more strongly than Slc26a4 in mice

SLC26A4 is a known iodide transporter, and is localized at the apical membrane of thyrocytes. Previously, we reported that SLC26A7 is also involved in iodide transport and that Slc26a7 is a novel causative gene for congenital hypothyroidism. However, its detailed role in vivo remains to be elucidated. We generated mice that were deficient in Slc26a7 and Slc26a4 to delineate differences and associations in their roles in iodide transport. Slc26a7^-/- mice showed goitrous congenital hypothyroidism and mild growth failure on a normal diet. Slc26a7^-/- mice with a low iodine environment showed marked growth failure. In contrast, Slc26a4^-/- mice showed no growth failure and hypothyroidism in the same low iodine environment. Double-deficient mice showed more severe growth failure than Slc26a7^-/- mice. RNA-seq analysis revealed that the number of differentially expressed genes (DEGs) in Slc26a7^-/- mice was significantly higher than that in Slc26a4^-/- mice. These indicate that SLC26A7 is more strongly involved in iodide transport and the maintenance of thyroid function than SLC26A4.

Clinical characteristics and genetics analysis for the ITD of congenital hypothyroidism

OBJECTIVES

Iodide transport defect (ITD) is one of the principal causes of congenital hypothyroidism (CH) and its primary molecular mechanism is a mutation of the sodium/iodide symporter (NIS) gene. This study aims to analyse the clinical characteristics and genetic mutations of ITD.

METHODS

The participants were a pair of siblings diagnosed with congenital hypothyroidism. Inductively coupled plasma mass spectrometry was used to determine the concentration of salivary iodine and serum iodine and to calculate their ratio. At the same time, next-generation sequencing (NGS) was applied to detect all exons of congenital hypothyroidism-related genes. All suspicious variants were further validated in the patients and their parents by PCR and Sanger sequencing.

RESULTS

Both patients were conclusively diagnosed with thyroid iodine transport defect (ITD). NGS identified two variants of the NIS gene in the siblings: c.1021G>A (p.Gly341Arg) with paternal origin and c.1330-2A>C with maternal origin. Both of these variants have not been reported to date. They are predicted to be pathogenic based on these clinical symptoms and comprehensive software analysis.

CONCLUSIONS

This is the first reported family study of congenital hypothyroidism with SLC5A5 mutation in China. Next-generation sequencing technology is an effective means of studying the genetics of congenital hypothyroidism. The therapeutic effect of potassium iodide needs to be further evaluated.

Thyroid hypogenesis is associated with a novel AKT3 germline variant that causes megalencephaly and cortical malformation

The molecular mechanisms involved in thyroid organogenesis have not been fully elucidated. We report a patient with a de novo germline AKT3 variant, NM_005465.7:c.233A > G, p.(Gln78Arg), who presented with congenital hypothyroidism in addition to typical AKT3-related brain disorders. The report of this patient contributes to delineating the associated yet uncertain endocrine complications of this AKT3 disease-causing variant.

Mutational screening of the TPO and DUOX2 genes in Argentinian children with congenital hypothyroidism due to thyroid dyshormonogenesis

PURPOSE

Primary congenital hypothyroidism (CH) is the most common endocrine disease in children and one of the preventable causes of both cognitive and motor deficits. We present a genetic and bioinformatics investigation of rational clinical design in 17 Argentine patients suspected of CH due to thyroid dyshormonogenesis (TDH).

METHODS

Next-Generation Sequencing approach was used to identify variants in Thyroid Peroxidase (TPO) and Dual Oxidase 2 (DUOX2) genes. A custom panel targeting 7 genes associated with TDH [(TPO), Iodothyrosine Deiodinase I (IYD), Solute Carrier Family 26 Member 4 (SLC26A4), Thyroglobulin (TG), DUOX2, Dual Oxidase Maturation Factor 2 (DUOXA2), Solute Carrier Family 5 Member 5 (SLC5A5)] and 4 associated with thyroid dysembryogenesis [PAX8, FOXE1, NKX2-1, Thyroid Stimulating Hormone Receptor (TSHR)] has been designed. Additionally, bioinformatic analysis and structural modeling were carried out to predict the disease-causing potential variants.

RESULTS

Four novel variants have been identified, two in TPO: c.2749-2 A > C and c.2752_2753delAG, [p.Ser918Cysfs*62] and two variants in DUOX2 gene: c.425 C > G [p.Pro142Arg] and c.2695delC [p.Gln899Serfs*21]. Eighteen identified TPO, DUOX2 and IYD variants were previously described. We identified potentially pahogenic biallelic variants in TPO and DUOX2 in 7 and 2 patients, respectively. We also detected a potentially pathogenic monoallelic variant in TPO and DUOX2 in 7 and 1 patients respectively.

CONCLUSIONS

22 variants have been identified associated with TDH. All described novel mutations occur in domains important for protein structure and function, predicting the TDH phenotype.

Association of recessive c.430G>A (p.(Gly144Arg)) thyroid peroxidase variant with primary congenital hypothyroidism in cats

BACKGROUND

Primary congenital hypothyroidism (CH) is a rare endocrine disorder in cats with a largely unknown genetic cause.

OBJECTIVES

Describe the clinical presentation of CH in 11 affected cats and identify the causal genetic variant.

ANIMALS

Eleven CH-cats from 10 unrelated families, 11 CH-free family members, 21 unrelated CH-free cats, and 155 unrelated nondiagnosed cats from different breeds.

METHODS

Case control study of CH-cats and their siblings (2019-2021). Diagnosis was based on low to low-normal serum thyroxine (T4) concentrations, high thyroid-stimulating hormone (TSH) concentrations and clinical signs compatible with CH. We identified the causal variant using Sanger sequencing, genotyping via PCR-RFLP and variant interpretation using ACMG/AMP guidelines.

RESULTS

All CH-cats (5 weeks-8 years) had disproportionate dwarfism. A goiter was not palpable in all. Thyroid scintigraphy with radiopertechnetate showed abnormally high uptake by thyroid glands, whereas scintigraphy with radioiodine showed abnormally low uptake, compatible with a defect in iodine organification by thyroid peroxidase (TPO). All cases were homozygous for TPO variant XM_006930524.4:c.430G>A(p.(Gly144Arg)), while none of the CH-free cats were. All sampled parents were heterozygous for this recessive variant. This variant was found in 15 cat breeds with an estimated allele frequency of 9%.

CONCLUSIONS AND CLINICAL IMPORTANCE

Disproportionate dwarfism, abnormally high TSH and abnormally low to low-normal T4 concentrations are diagnostic for CH in cats. All cases had dyshormonogenesis demonstrated by thyroid scintigraphy. This novel TPO missense variant (not described in humans) causes CH in cats and awareness of it can assist in diagnosis and breeding.

Intra-amniotic levothyroxine infusions in a case of fetal goiter due to novel Thyroglobulin gene variants

Indications and administration of intra-amniotic infusions of L-thyroxine in the context of non-immune fetal hypothyroidism with goiter lack of standardization. Systematic follow-up of clinical features related to thyroid hormonal homeostasis may be useful to evaluate their efficiency and develop standardized management guidelines.

Curating the gnomAD database: Report of novel variants in the thyrogobulin gene using in silico bioinformatics algorithms

Thyroglobulin (TG) is a large glycosylated protein of 2767 amino acids, secreted by the thyrocytes into the follicular lumen. It plays an essential role in the process of thyroid hormone synthesis. TG gene variants lead to permanent congenital hypothyroidism. In the present work, we report a detailed population and bioinformatic prediction analyses of the TG variants indexed in the Genome Aggregation Database (gnomAD). The results showed a clear predominance of nonsense variants in the European (Finnish), European (Non-Finnish) and Ashkenazi Jewish ethnic groups, whereas the splice site variants predominate in South Asian and African/African-American populations. In total, 282 novel TG variants were described (47 missense involving the wild-type cysteine residues, 177 missense located in the ChEL domain and 58 splice site variants) which were not reported in the literature and that would have deleterious effects in prediction programs. In the gnomAD population, the estimated prevalence of heterozygous carriers of the potentially damaging variants was 1:320. In conclusion, we provide an updated and curated reference source for the diagnosis of thyroid disease, mainly to congenital hypothyroidism due to TG deficiency. The identification and characterization of TG variants is undoubtedly a valuable approach to study the TG structure/function relations and an important tool for clinical diagnosis and genetic counseling.

Variant of TSHR is Not a Frequent Cause of Congenital Hypothyroidism in Chinese Han Patients

PURPOSE

To screen variants of the thyroid stimulating hormone receptor (TSHR) gene among congenital hypothyroidism (CH) patients.

PATIENTS AND METHODS

We conducted a genetic screening of the TSHR gene in a cohort of 125 Chinese CH patients. Variants were detected by customized targeted next-generation sequencing.

RESULTS

A total of 11 TSHR missense heterozygous variants were identified in 14 CH patients. Six variants were in the transmembrane domains, four variants were in the leucine-rich repeats and one variant was located in the hinge region of the TSHR protein. p.F525S was the most prevalent variant with an allele frequency of 0.016, followed by p.R450H with an allele frequency of 0.012. The allele frequency of most variants was higher in our cohort than those of other populations.

CONCLUSION

The prevalence of TSHR variants was 11.2%. Variant p.F525S was the most prevalent variant with an allele frequency of 0.016. The prevalence of TSHR variants was different from other populations.

Genome-wide data mining to construct a competing endogenous RNA network and reveal the pivotal therapeutic targets of Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative movement disorders, for which there has been no effective treatments. To clarify the pathogenesis of PD, we constructed a competing endogenous RNA (ceRNA) network based on the genome-wide RNA sequencing data. It was found that 92 RNAs were differentially expressed, including 50 mRNAs, 25 miRNAs and 17 lncRNAs, based on which a ceRNA network was constructed and evaluated from 4 aspects of number of nodes, topological coefficients, closeness centrality and betweenness centrality. The functional annotation and enrichment analysis suggested that 6 functional modules, particularly the peripheral nervous system development and toxin metabolic process, dominated the development of PD. To validate the assumption, the gene set enrichment analysis (GSEA) was conducted basing on the genome-wide RNAs regardless whether they were differentially expressed or not. Consistently, the results revealed that dysregulation of MAG, HOXB3, MYRF and PLP1 led to metabolic disorders of sphingolipid and glutathione, which contributed to the pathogenesis of PD. Also, in-depth mining of previous literature confirmed a pivotal role of these dysregulated RNAs, which had been indicated to be potential diagnostic and therapeutic biomarkers of PD. Overall, we constructed a ceRNA network based on the dysregulated mRNAs, lncRNAs and miRNAs in PD, and the aberrant expression of MAG, HOXB3, MYRF and PLP1 caused metabolism disorder of sphingolipid and glutathione, and these genes are of great significance for the diagnosis and treatment of PD.

Structure and genetic variants of thyroglobulin: Pathophysiological implications

Thyroglobulin (TG) plays a main role in the biosynthesis of thyroid hormones (TH), and, thus, it is involved in a wide range of vital functions throughout the life cycle of all vertebrates. Deficiency of TH production due to TG genetic variants causes congenital hypothyroidism (CH), with devastating consequences such as intellectual disability and impaired growth if untreated. To this day, 229 variations in the human TG gene have been identified while the 3D structure of TG has recently appeared. Although TG deficiency is thought to be of autosomal recessive inheritance, the introduction of massive sequencing platforms led to the identification of a variety of monoallelic TG variants (combined with mutations in other thyroid gene products) opening new questions regarding the possibility of oligogenic inheritance of the disease. In this review we discuss remarkable advances in the understanding of the TG architecture and the pathophysiology of CH associated with TG defects, providing new insights for the management of congenital disorders as well as counseling benefits for families with a history of TG abnormalities. Moreover, we summarize relevant aspects of TH synthesis within TG and offer an updated analysis of animal and cellular models of TG deficiency for pathophysiological studies of thyroid dyshormonogenesis while highlighting perspectives for new investigations. All in all, even though there has been sustained progress in understanding the role of TG in thyroid pathophysiology during the past 50 years, functional characterization of TG variants remains an important area of study for future advancement in the field.

Molecular and clinical characteristics of congenital hypothyroidism in a large cohort study based on comprehensive thyroid transcription factor mutation screening in Henan

BACKGROUND

Congenital hypothyroidism (CH), the most common neonatal endocrine disorder worldwide, can be caused by variants in thyroid transcription factor (TTF) genes including NKX2-1, FOXE1, PAX8, NKX2-5 and HHEX. This study aims to perform targeted next-generation sequencing (NGS) panel for comprehensive mutation screening on these genes in a cohort of 606 CH patients with various types from Henan Province, China, to investigate the mutation rate of TTF genes, and to analyze the clinical, biochemical and molecular characteristics of our CH cohort.

METHODS

High-throughput sequencing combined with statistical calculation were applied for mutation screening and analyses of the clinical data.

RESULTS

Twenty-two likely disease-causing monoallelic mutations in the TTF genes were identified in our cohort (3.63%, 22/606). Mutated PAX8 was the most predominant genetic alteration among these TTF mutations. Interestingly, PAX8 defects were only found in TD cases and variants in the five TTF genes were detected in gland in situ (GIS) patients. CH patients with the same genotype may have significant phenotypic variability and permanent CH (PCH) patients in the GIS group were significantly fewer than those in the TD group.

CONCLUSIONS

Our study showed the estimated TTF mutation rate among CH cases was 3.63% in Henan Province and genetic alternations in TTF genes played a role not only in TD but also in GIS, especially in goiter. Although we speculated that the five TTF genes may be involved in certain steps of thyroid hormone biosynthesis, more researches are needed to verify the conclusions of the present study.

A novel mutation in intron 11 donor splice site, responsible of a rare genotype in thyroglobulin gene by altering the pre-mRNA splincing process. Cell expression and bioinformatic analysis

Thyroglobulin (TG) is a homodimeric glycoprotein synthesized by the thyroid gland. To date, two hundred twenty-seven variations of the TG gene have been identified in humans. Thyroid dyshormonogenesis due to TG gene mutations have an estimated incidence of approximately 1 in 100,000 newborns. The clinical spectrum ranges from euthyroid to mild or severe hypothyroidism. The purpose of the present study was to identify and characterize new variants in the TG gene. We report an Argentine patient with congenital hypothyroidism, enlarged thyroid gland and low levels of serum TG. Sequencing of DNA, expression of chimeric minigenes as well as bioinformatics analysis were performed. DNA sequencing identified the presence of compound heterozygous mutations in the TG gene: the maternal mutation consists of a c.3001+5G > A, whereas the paternal mutation consists of p.Arg296*. Minigen analysis of the variant c.3001+5A performed in HeLa, CV1 and Hek293T cell lines, showed a total lack of transcript expression. So, in order to validate that the loss of expression was caused by such variation, site-directed mutagenesis was performed on the mutated clone, which previously had a pSPL3 vector change, to give rise to a wild-type clone c.3001+5G, endorsing that the mutation c.3001+5G > A is the cause of the total lack of expression. In conclusion, we demonstrate that the c.3001+5G > A mutation causes a rare genotype, altering the splicing of the pre-mRNA. This work contributes to elucidating the molecular bases of TG defects associated with congenital hypothyroidism and expands our knowledge in relation to the pathologic roles of the position 5 in the donor splice site.

Congenital Hypothyroidism Patients With Thyroid Hormone Receptor Variants Are Not Rare: A Systematic Review

Background

Primary congenital hypothyroidism (CH) is a common endocrine and metabolic disease. Various genetic factors, including the thyroid hormone receptor (TSHR), play an important role in CH.

Aim

To explore the occurrence of pathogenic TSHR variants in CH.

Methods

We searched published articles in PubMed, Web of Science, and Cochrane Library databases, from the establishment of the database to September 26, 2021. Studies with sequencing partial or full exons of TSHR in CH patients were included. Gene polymorphism was excluded.

Results

A total of 66 articles (44 case-control studies and 22 case reports) were selected from the database. Though case-control studies, we found the incidence of pathogenic TSHR variants were not rare (range from 0% to 30.6%) and varied greatly in different countries and race. The pathogenic genotypes varied in different regions. All the variants were “loss-of-function” mutations, in which the p.(Arg450His) variant was the most common variant. In addition, we analyzed the case reports and found that CH patients with a family genetic background expressed homozygous genotypes. Homozygotes had more obvious symptoms of hypothyroidism and higher risk of comorbidities than heterozygotes.

Conclusion

Pathogenic TSHR variants are not uncommon cause of the CH, especially in the Arabs. The role of TSHR gene detection in the treatment of children with CH needs to be further studied.

Derivation of Thyroid Follicular Cells From Pluripotent Stem Cells: Insights From Development and Implications for Regenerative Medicine

Stem cell-based therapies to reconstitute in vivo organ function hold great promise for future clinical applications to a variety of diseases. Hypothyroidism resulting from congenital lack of functional thyrocytes, surgical tissue removal, or gland ablation, represents a particularly attractive endocrine disease target that may be conceivably cured by transplantation of long-lived functional thyroid progenitors or mature follicular epithelial cells, provided a source of autologous cells can be generated and a variety of technical and biological challenges can be surmounted. Here we review the emerging literature indicating that thyroid follicular epithelial cells can now be engineered in vitro from the pluripotent stem cells (PSCs) of mice, normal humans, or patients with congenital hypothyroidism. We review the in vivo embryonic development of the thyroid gland and explain how emerging discoveries in developmental biology have been utilized as a roadmap for driving PSCs, which resemble cells of the early embryo, into mature functional thyroid follicles in vitro. Finally, we discuss the bioengineering, biological, and clinical hurdles that now need to be addressed if the goals of life-long cure of hypothyroidism through cell- and/or gene-based therapies are to be attained.

Anaplastic Thyroid Cancer Arising from Dyshormonogenetic Goiter: c.3070T>C and Novel c.7070T>C Mutation in the Thyroglobulin Gene

Concomitant thyroid cancer in patients with congenital thyroid dyshormonogenesis (TD) is extremely rare and few cases of differentiated thyroid cancer in patients with TD have been reported thus far. In this study, we describe anaplastic thyroid cancer in a 46-year-old woman with TD who had two germline thyroglobulin (TG) gene mutation, c.3790T>C (p, Cys1264Arg) in exon 17 and a novel c.7070T>C (p.Leu2357Pro) in exon 41 of the TG gene. Two affected younger sisters were also found to have the same TG mutation but not anaplastic thyroid cancer. Any thyroid nodular lesions that develop in patients with TD should be investigated carefully.

Functional analysis of thyroid peroxidase gene mutations resulting in congenital hypothyroidism

OBJECTIVE

Thyroid peroxidase (TPO) is essential for thyroid hormone biosynthesis. TPO mutations might lead to congenital hypothyroidism. In the present study, we analysed the function of a compound heterozygous TPO mutation in a Chinese family.

DESIGN

We studied a 23-year-old Chinese girl with a history of growth retardation and severe constipation from the age of 3 months, who was diagnosed as having congenital hypothyroidism.

METHODS

Genomic DNA was extracted from peripheral blood samples obtained from the patient's family members. The genomic DNA was sequenced to detect mutations in a panel of genes associated with congenital hypothyroidism. Bioinformatic analysis and structural modelling predicted the potential disease-causing potential mutant genes and the microstructure of the mutant protein, respectively. Western blotting and ELISA were used to measure protein expression, and guaiacol oxidation assay measured the TPO activity of the mutant protein.

RESULTS

We identified a compound heterozygous mutation (c.C1993T, c.T2473C) in the TPO gene. Bioinformatic analysis predicted that the TPO mutations were potentially disease causing. Structural modelling predicted damage to the microstructure of the mutant TPO protein. Western blotting and ELISA showed reduced protein levels of the mutant TPO protein compared with that of the wild-type protein. The mutant TPO protein showed weaker activity compared with that of the wild-type protein.

CONCLUSIONS

A novel compound heterozygous mutation of TPO gene was identified in a Chinese family. This mutation might alter the extracellular microstructure of TPO, and decrease its expression and the activity, resulting in congenital hypothyroidism.

Upper and Lower Limb Strength and Body Posture in Children with Congenital Hypothyroidism: An Observational Case-Control Study

BACKGROUND

Congenital hypothyroidism (CH) is an endocrine disease with a precocious significant impairment of growth and neuromotor development. Thyroid hormones are essential for central nervous system development, maturation, and myelination. Furthermore, thyroid hormone deficiency affects the function of several systems, including the musculoskeletal system. The disease has a significant incidence in the general population (1:3000-1:2000 newborns in Italy). The aim of the present study was to evaluate any differences in upper and lower limb strength, body sway, and plantar loading distribution in children with CH compared to healthy children.

METHODS

In this study, the case group was composed of children with CH (CHG), while the control group included healthy children (CG). Both groups comprised 19 children (CHG: female = 12; CG: female = 9). The maximum isometric handgrip strength and explosive-elastic lower limb strength were assessed with the handgrip test and the Sargent test, respectively. The stabilometric and baropodometric analyses were used to measure the Center of Pressure displacements and the plantar loading distribution between feet, respectively. The differences between groups were analyzed by a univariate analysis of covariance using as covariates weight and height with the significant level set at < 0.05.

RESULTS

We found that CHG children were shorter and thinner than CG ones (p < 0.05). No significant difference in the upper and lower limb strength was found between groups. CHG exhibited a significant greater Sway Path Length (p < 0.01) and Ellipse Surface (p < 0.05) than CG. Moreover, CHG displayed an asymmetric plantar loading distribution with a significant lower percentage in the right than in the left foot (p < 0.05). Moreover, a significant lower plantar loading percentage in the right foot of CHG than in the right foot of CG was observed (p < 0.05).

CONCLUSIONS

These findings seem to suggest that CH does not affect muscle strength in early treated children. However, these patients show poor postural control ability and asymmetric plantar loading distribution. Increasing the physical activity in these children could improve their body posture.

The TPO mutation screening and genotype-phenotype analysis in 230 Chinese patients with congenital hypothyroidism

Inborn defects in thyroid hormone biosynthesis contribute to nearly half of congenital hypothyroidism (CH) cases in China. The thyroid peroxidase (TPO) mutation is one of the most frequent mutations that results in thyroid dyshormonogenesis. In this study, 35 non-synonymous mutations in 15 TPO sites, including 6 novel mutations, were identified in 230 Chinese patients with CH. The enzyme activity of the mutations in TPO was investigated in vitro, and patients with less than 15% residual enzyme activity showed severe CH, such as markedly increased thyroid-stimulating hormone (TSH) at diagnosis (>100 μIU/mL) and pronounced goiter, and required a higher dose of L-thyroxine to maintain the euthyroid. However, CH patients with greater than 16% TPO activity showed mild CH, a typical childhood socially without L-thyroxine treatment before 3 years of age, and the appearance of a macroscopic goiter at childhood. The findings indicated that the residual enzymatic activity of TPO was correlated with clinical phenotypes of CH patients with TPO biallelic mutations.

p.L571P in the linker domain of rat thyroglobulin causes intracellular retention

Thyroglobulin (TG), a large glycosylated protein secreted by thyrocytes into the thyroid follicular lumen, plays an essential role in thyroid hormone biosynthesis. Rattus norvegicus TG (rTG) is encoded by a large single copy gene, 186-kb long, located on chromosome 7 composed of 48 exons encoding a 8461-kb mRNA. Although the TG gene displays sequence variability, many missense mutations do not impose any adverse effect on the TG protein, whereas other nucleotide substitutions may affect its TG stability and/or TG intracellular trafficking. In order to gain a further understanding of the protein domains regulating its intracellular fate, we cloned a full-length cDNA from rTG into the pcDNA6/V5-His B expression vector. However, transient expression of the cDNA in HEK293T cells showed that the encoded protein was not a wild-type molecule, as it was unable to be secreted in the culture supernatant. Sequencing analyses revealed three random mutations, which accidentally emerged during the course of cloning: c.1712T>C [p.L571P] in the linker domain (amino acid positions 360 to 604), c.2027A>G [p.Q676R] in TG type 1-6 repeat and c.2720A>G [p.Q907R] in the TG type 1-7 repeat. Expression of cDNAs encoding a combination of two mutations [p.Q676R-p.Q907R], [p.L571P-p.Q907R] or [p.L571P-p.Q676R] indicated that any TG bearing the p.L571P substitution was trapped intracellularly. Indeed, we expressed the single point mutant p.L571P and confirmed that this point mutation was sufficient to cause intracellular retention of mutant TG in HEK293T cells. Endo H analysis showed that the p.L571P mutant is completely sensitive to the enzyme, whereas the will-type TG acquires full N-glycan modifications in Golgi apparatus. This data suggest that the p.L571P mutant contains the mannose-type N-glycan, that was added at the first stage of glycosylation. Complex-type N-glycan formation in the Golgi apparatus does not occur, consistent with defective endoplasmic reticulum exit of the mutant TG. Moreover, predictive analysis of the 3D linker domain showed that the p.L571P mutation would result in a significant protein conformational change. In conclusion, our studies identified a novel amino acid residue within the linker domain of TG associated with its conformational maturation and intracellular trafficking.

Thyrocyte cell survival and adaptation to chronic endoplasmic reticulum stress due to misfolded thyroglobulin

The large secretory glycoprotein thyroglobulin is the primary translation product of thyroid follicular cells. This difficult-to-fold protein is susceptible to structural alterations that disable export of the misfolded thyroglobulin from the endoplasmic reticulum (ER), which is a known cause of congenital hypothyroidism characterized by severe chronic thyrocyte ER stress. Nevertheless, individuals with this disease commonly grow a goiter, indicating thyroid cell survival and adaptation. To model these processes, here we continuously exposed rat PCCL3 thyrocytes to tunicamycin, which causes a significant degree of ER stress that is specifically attributable to thyroglobulin misfolding. We found that, in response, PCCL3 cells down-regulate expression of the "tunicamycin transporter" (major facilitator superfamily domain containing-2A, Mfsd2a). Following CRISPR/Cas9-mediated Mfsd2a deletion, PCCL3 cells could no longer escape the chronic effects of high-dose tunicamycin, as demonstrated by persistent accumulation of unglycosylated thyroglobulin; nevertheless, these thyrocytes survived and grew. A proteomic analysis of these cells adapted to chronic ER protein misfolding revealed many hundreds of up-regulated proteins, indicating stimulation of ER chaperones, oxidoreductases, stress responses, and lipid biosynthesis pathways. Further, we noted increased phospho-AMP-kinase, suggesting up-regulated AMP-kinase activity, and decreased phospho-S6-kinase and protein translation, suggesting decreased mTOR activity. These changes are consistent with conserved cell survival/adaptation pathways. We also observed a less-differentiated thyrocyte phenotype with decreased PAX8, FOXE1, and TPO protein levels, along with decreased thyroglobulin mRNA levels. In summary, we have developed a model of thyrocyte survival and growth during chronic continuous ER stress that recapitulates features of congenital hypothyroid goiter caused by mutant thyroglobulin.