Targeted Next-Generation Sequencing for Congenital Hypothyroidism With Positive Neonatal TSH Screening

Genetic etiology in patients diagnosed with congenital hypothyroidism with new-generation sequencing: A single-center experience

AIM

Congenital hypothyroidism (CH) is the most common endocrine disorder of the newborn; it is seen in every 3000-4000 births. Genetic features can guide treatment for patients with in situ glands. The present study aimed to contribute to the literature on CH variants and to show the benefit that genetic analysis can provide to patients in follow-up.

METHOD

A total of 52 patients (47 families) diagnosed with CH were included in the study. Overall, 32 target genes involved in thyroid physiology were investigated by next-generation sequencing (NGS).

RESULTS

In total, 29 (55 %) of the patients were male, and the rate of dysgenesis was 19.2 %. In this study, 29 of 52 patients had at least one variant in one gene involved in CH (n = 29, 33 different variants) (Including likely benign variants and variants of unknown significance). There were 21 patients (40.3 %) with gland in situ. The most common variant was DUOX2 (20 %). The second most common variants were those in the TPO and TG genes (15 % and 15 %, respectively); 41.1 % of these were variants of uncertain significance (VUS), 26.4 % were pathogenic, 23.5 % were likely benign, and 11.7 % were likely pathogenic. On the basis of their zygosity, we identified 73.5 % heterozygous, 17.6 % homozygous, and 8.9 % combined heterozygous variants. There were mutant variants in two genes in six patients and three in one patient.

CONCLUSION

This study found a variant in 55 % of the patients and shed light on the etiology of some cases of CH. The frequency of VUS was high. Although variants were identified in this study, their implication in the etiology of CH is not certain and, for most of the patients, it is also not sufficient for explaining the pathology with the current state of knowledge.

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.

Molecular and Clinical Features of Congenital Hypothyroidism Due to Multiple DUOX2 Variants

Background: DUOX2 is one of the major causative genes of congenital hypothyroidism (CH). Still, the mutation spectrum and clinical outcomes of biallelic DUOX2 variants are not fully understood. This study aimed to elucidate the molecular features and long-term clinical manifestations of CH caused by multiple pathogenic DUOX2 variants. Methods: A total of 255 patients with CH were screened for rare variants of 11 known causative genes. DUOX2 variants were classified according to their protein structure and residual activity. In vitro assays were performed for several variants of unknown functions. Clinical analyses were conducted for patients with multiple pathogenic variants of DUOX2 but not of other genes. Results: We identified 24 pathogenic variants of DUOX2, together with two benign variants and seven variants of uncertain significance, in 63 patients. The pathogenic variants included three missense substitutions and one frameshift variant that have not yet been linked to CH. Twenty-one patients carried multiple pathogenic DUOX2 variants without any other pathogenic gene variants. Three of the 21 patients harbored homozygous variants. Family analysis, long-read amplicon sequencing, and haplotype phasing confirmed compound heterozygosity of the DUOX2 variants in 14 patients, whereas the allelic positions of the variants in the remaining four patients could not be determined. Of the 21 patients, 19 were treated with levothyroxine; their ages at drug withdrawal ranged from 9 months to 21.4 years. Three patients required retreatment after drug-free intervals of 6 months, 8 months, and 10 years. There were no differences in clinical severity among patients with DUOX2 amorphic/amorphic, amorphic/hypomorphic, and hypomorphic/hypomorphic variants. Conclusions: These results broaden the mutational spectrum of DUOX2. Furthermore, our data imply that patients with multiple pathogenic DUOX2 variants typically exhibit transient CH without significant genotype-phenotype correlations. Most importantly, this study demonstrated for the first time that these patients are at risk of developing recurrent hypothyroidism after a long drug-free interval.

Late-onset dyshormonogenic goitrous hypothyroidism due to a homozygous mutation of the SLC26A7 gene: a case report

BACKGROUND

In this study, we used targeted next-generation sequencing (NGS) to investigate the genetic basis of congenital hypothyroidism (CH) in a 19-year-old Tunisian man who presented with severe hypothyroidism and goiter.

CASE PRESENTATION

The propositus reported the appearance of goiter when he was 18. Importantly, he did not show signs of mental retardation, and his growth was proportionate. A partial organification defect was detected through the perchlorate-induced iodide discharge test. NGS identified a novel homozygous mutation in exon 18 of the SLC26A7 gene (P628Qfs*11), which encodes for a new iodide transporter. This variant is predicted to result in a truncated protein. Notably, the patient's euthyroid brother was heterozygous for the same mutation. No renal acid-base abnormalities were found and the administration of 1 mg of iodine failed to correct hypothyroidism.

CONCLUSIONS

We described the first case of goitrous CH due to a homozygous mutation of the SLC26A7 gene diagnosed during late adolescence.

Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020-2023)

Newborn bloodspot screening (NBS) began in the early 1960s based on the work of Dr. Robert "Bob" Guthrie in Buffalo, NY, USA. His development of a screening test for phenylketonuria on blood absorbed onto a special filter paper and transported to a remote testing laboratory began it all. Expansion of NBS to large numbers of asymptomatic congenital conditions flourishes in many settings while it has not yet been realized in others. The need for NBS as an efficient and effective public health prevention strategy that contributes to lowered morbidity and mortality wherever it is sustained is well known in the medical field but not necessarily by political policy makers. Acknowledging the value of national NBS reports published in 2007, the authors collaborated to create a worldwide NBS update in 2015. In a continuing attempt to review the progress of NBS globally, and to move towards a more harmonized and equitable screening system, we have updated our 2015 report with information available at the beginning of 2024. Reports on sub-Saharan Africa and the Caribbean, missing in 2015, have been included. Tables popular in the previous report have been updated with an eye towards harmonized comparisons. To emphasize areas needing attention globally, we have used regional tables containing similar listings of conditions screened, numbers of screening laboratories, and time at which specimen collection is recommended. Discussions are limited to bloodspot screening.

Congenital Hypothyroidism with Thyroid in situ: A Case Report with NKX2-1 and DUOX2 Hypomorphic Variants

INTRODUCTION

NK2 homeobox 1 (NKX2-1) encodes a transcription factor, NKX2-1, that is expressed in the thyroid gland, lung, and brain. Dual oxidase 2 (DUOX2) encodes an enzyme which generates hydrogen peroxide and is involved in the thyroid hormone synthesis. Cases of congenital hypothyroidism (CH) with dyshormonogenesis showing two or more genetic variants are increasingly reported. We describe the first case of transient dyshormonogenesis who had experimentally verified a loss-of-function NKX2-1 variant and DUOX2 variants.

CASE PRESENTATION

The proband was a 15-year-old female patient with CH who was diagnosed in the frame of newborn screening for CH. She had a mildly elevated serum TSH level (14.56 mU/L), a low free thyroxine level (0.87 ng/dL), and a high thyroglobulin (Tg) level (>800 ng/mL). Ultrasonography revealed goiter. She was followed clinically without levothyroxine treatment and showed normal growth and development. She had slightly high Tg levels throughout the clinical course. Next-generation sequencing-based genetic analysis revealed that the patient was heterozygous for an NKX2-1 variant (p.Ile228Ser), a nonsense DUOX2 variant (p.[Lys530*;His678Arg]), and a functional DUOX2 polymorphism (p.His678Arg). NKX2-1 p.Ile228Ser showed about 50% reduced residual activity on the Tg promoter.

CONCLUSION

A partial loss-of-function NKX2-1 variant with a monoallelic nonsense DUOX2 variant and a DUOX2 functional polymorphism can cause transient CH with high serum Tg levels.

JAG1 Variants Confer Genetic Susceptibility to Thyroid Dysgenesis and Thyroid Dyshormonogenesis in 813 Congenital Hypothyroidism in China

Background and Objective

Congenital hypothyroidism (CH) is indeed a prevalent neonatal endocrine disorder, affecting approximately 1 in 2000-3000 newborns worldwide, and 1 in 2400 newborns in China. Despite its high incidence, the genetic causes of CH, particularly those related to thyroid dysgenesis (TD), are still not well understood. However, previous studies have suggested that JAG1 may be a potential susceptibility gene for congenital thyroid defects. To explore the association between JAG1 and CH, we screened JAG1 variants in a large cohort of 813 CH patients.

Methods

We performed genetic analysis of JAG1 using next-generation sequencing in 813 CH cases. The pathogenicity of the variants was assessed by bioinformatics softwares, protein sequence conservation analysis, and hydrophobic analysis. Further genetic analysis was conducted targeting 20 CH-related genes in these 25 JAG1 variant carriers.

Results

We identified 10 pathogenic missense mutations (p.V45L, p.V272I, p.P552L, p.G610E, p.G852D, p.A891T, p.E1030K, p.R1060W, p.A1131T, p.P1174L) carried by 25 patients, the mutation rate of JAG1 in CH was 3.08%. Among these 25 patients, 16 with 1 variant, 6 with 2 variants, and the other 3 with 3 variants. Our findings indicated that JAG1 variants confer genetic susceptibility to both TD and DH, but with different inheritance models. JAG1 variants lead to TD mainly through monogenic model, while for DH cases, both monogenic mechanisms and oligogenic mechanisms play a pivotal role. Oligogenicity may contribute to the disease severity of DH.

Conclusion

JAG1 is a shared genetic factor in TD and DH, with a detection rate of 3.08% in Chinese individuals with CH. A comparison between the oligogenic and monogenic groups suggests a gene dosage effect in CH. Patients with the same JAG1 mutation exhibit diverse clinical phenotypes, indicating complex mechanisms underlying phenotypic heterogeneity.

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.

Novel JAG1 variants leading to Alagille syndrome in two Chinese cases

Alagille Syndrome (ALGS) is a complex genetic disorder characterized by cholestasis, congenital cardiac anomalies, and butterfly vertebrae. The variable phenotypic expression of ALGS can lead to challenges in accurately diagnosing affected infants, potentially resulting in misdiagnoses or underdiagnoses. This study highlights novel JAG1 gene mutations in two cases of ALGS. The first case with a novel p.Pro325Leufs*87 variant was diagnosed at 2 months of age and exhibited a favorable prognosis and an unexpected manifestation of congenital hypothyroidism. Before the age of 2, the second patient was incorrectly diagnosed with liver structural abnormalities, necessitating extensive treatment. In addition, he exhibited delays in language acquisition that may have been a result of SNAP25 haploinsufficiency. The identification of ALGS remains challenging, highlighting the importance of early detection and genetic testing for effective patient management. The variant p.Pro325Leufs*87 is distinct from reported variants linked to congenital hypothyroidism in ALGS patients, thereby further confirming the clinical and genetic complexity of ALGS. This emphasizes the critical need for individualized and innovative approaches to diagnosis and medical interventions, uniquely intended to address the complexity of this syndrome.

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.

Pathogenic variations in MAML2 and MAMLD1 contribute to congenital hypothyroidism due to dyshormonogenesis by regulating the Notch signalling pathway

BACKGROUND

In several countries, thyroid dyshormonogenesis is more common than thyroid dysgenesis in patients with congenital hypothyroidism (CH). However, known pathogenic genes are limited to those directly involved in hormone biosynthesis. The aetiology and pathogenesis of thyroid dyshormonogenesis remain unknown in many patients.

METHODS

To identify additional candidate pathogenetic genes, we performed next-generation sequencing in 538 patients with CH and then confirmed the functions of the identified genes in vitro using HEK293T and Nthy-ori 3.1 cells, and in vivo using zebrafish and mouse model organisms.

RESULTS

We identified one pathogenic MAML2 variant and two pathogenic MAMLD1 variants that downregulated canonical Notch signalling in three patients with CH. Zebrafish and mice treated with N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butylester, a γ-secretase inhibitor exhibited clinical manifestations of hypothyroidism and thyroid dyshormonogenesis. Through organoid culture of primary mouse thyroid cells and transcriptome sequencing, we demonstrated that Notch signalling within thyroid cells directly affects thyroid hormone biosynthesis rather than follicular formation. Additionally, these three variants blocked the expression of genes associated with thyroid hormone biosynthesis, which was restored by HES1 expression. The MAML2 variant exerted a dominant-negative effect on both the canonical pathway and thyroid hormone biosynthesis. MAMLD1 also regulated hormone biosynthesis through the expression of HES3, the target gene of the non-canonical pathway.

CONCLUSIONS

This study identified three mastermind-like family gene variants in CH and revealed that both canonical and non-canonical Notch signalling affected thyroid hormone biosynthesis.

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.

Clinical, biochemical characteristics and genotype-phenotype analysis of congenital hypothyroidism diagnosed by newborn screening in China

BACKGROUND

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder worldwide. However, the underlying etiology remains unclear in most patients.

METHODS

The newborn screening was performed for TSH in dried blood spots. Serum TSH, T3, T4, free T3(FT3) and free T4 (FT4) were detected for the recalled children. High-throughput sequencing were applied to detect 29 known CH genes. The statistical analyses were performed to analyze the differences between biochemical data, thyroid volume, clinical prognosis and genetic results for 97 patients who had one or more variants in CH related genes.

RESULTS

DUOX2 gene has the highest variant rate, followed by TG, TPO and TSHR gene. The "DUOX2 biallelic variants" group was associated with "Goiter", while "DUOX2 monoallelic variants" group was associated with "Agenesis". In addition, the TSH levels and initial L-T4 dose were significantly higher in "TPO biallelic variants" group than those in "DUOX2 and TSHR biallelic variants" groups.

CONCLUSIONS

Our study showed dyshormonogenesis (DH) might be the leading pathophysiology of CH in Chinese populations. DUOX2 gene mostly caused goiter, but also could be associated with hypoplasia. TPO might play a more irreplaceable role than DUOX2. The digenic variants combination indicated the complexity of genetic etiology in CH.

GLIS3 regulates transcription of thyroid hormone biosynthetic genes in coordination with other thyroid transcription factors

BACKGROUND

Loss of the transcription factor GLI-Similar 3 (GLIS3) function causes congenital hypothyroidism (CH) in both humans and mice due to decreased expression of several thyroid hormone (TH) biosynthetic genes in thyroid follicular cells. Whether and to what extent, GLIS3 regulates thyroid gene transcription in coordination with other thyroid transcriptional factors (TFs), such as PAX8, NKX2.1 and FOXE1, is poorly understood.

METHODS

PAX8, NKX2.1, and FOXE1 ChIP-Seq analysis with mouse thyroid glands and rat thyrocyte PCCl3 cells was performed and compared to that of GLIS3 to analyze the co-regulation of gene transcription in thyroid follicular cells by these TFs.

RESULTS

Analysis of the PAX8, NKX2.1, and FOXE1 cistromes identified extensive overlaps between these TF binding loci and those of GLIS3 indicating that GLIS3 shares many of the same regulatory regions with PAX8, NKX2.1, and FOXE1, particularly in genes associated with TH biosynthesis, induced by thyroid stimulating hormone (TSH), and suppressed in Glis3KO thyroid glands, including Slc5a5 (Nis), Slc26a4, Cdh16, and Adm2. ChIP-QPCR analysis showed that loss of GLIS3 did not significantly affect PAX8 or NKX2.1 binding and did not cause major alterations in H3K4me3 and H3K27me3 epigenetic signals.

CONCLUSIONS

Our study indicates that GLIS3 regulates transcription of TH biosynthetic and TSH-inducible genes in thyroid follicular cells in coordination with PAX8, NKX2.1, and FOXE1 by binding within the same regulatory hub. GLIS3 does not cause major changes in chromatin structure at these common regulatory regions. GLIS3 may induce transcriptional activation by enhancing the interaction of these regulatory regions with other enhancers and/or RNA Polymerase II (Pol II) complexes.

Clinical and genetic investigation in patients with permanent congenital hypothyroidism

BACKGROUND

Permanent congenital hypothyroidism (CH) is usually a more severe type of CH. However, the molecular etiology and clinical features of permanent CH remain unclear.

METHODS

We recruited 42 patients who were diagnosed with CH and followed-up after diagnosis. Demographic information and data at diagnosis and treatment were recorded. Genetic analyses were performed using whole exome sequencing. Based on the presence or absence of variants and differences in clinical features, we grouped the study participants and analyzed their characteristics.

RESULTS

A total of 29 patients (69.0 %) were identified as having variants potentially related to their disease. Among the 24 patients with normal-sized thyroid gland-in-situ (GIS) or goiter, 23 (95.8 %, P < 0.001) had variants. This is compared to 18 patients with thyroid dysgenesis (TD), of which six (33.3 %) had genetic variants. We detected 55 variants in six genes, the most frequently mutated gene being DUOX2 (70.9 %). Biallelic DUOX2 variants were detected in 14 of 24 (58.3 %) GIS or goiter patients. Compared to the cases with variants, the L-T4 dose at 2 and 3 years of age and current dose were higher in the unmutated cases. At 2 years of age, patients with TD required higher doses of L-T4 supplementation. Patients with DUOX2 variants showed lower doses of L-T4 being required at 2 and 3 years of age and current. Furthermore, patients with GIS or goiter with DUOX2 variants showed lower doses of L-T4.

CONCLUSIONS

Patients with CH, whether TD or GIS or goiter, are at risk of developing a permanent condition. Compared with patients with TD, the detection of variants was higher in patients with GIS or goiter. The most frequently mutated gene was DUOX2, with a biallelic type. Patients with TD required higher doses of L-T4 supplementation with age, whereas those patients with the DUOX2 variant required relatively lower doses.

Guidelines for Newborn Screening of Congenital Hypothyroidism (2021 Revision)

Purpose of developing the guidelines: Newborn screening (NBS) for congenital hypothyroidism (CH) was started in 1979 in Japan, and early diagnosis and treatment improved the intelligence prognosis of CH patients. The incidence of CH was once about one in 5,000-8,000 births, but has been increased with diagnosis of subclinical CH. The disease requires continuous treatment and specialized medical facilities should conduct differential diagnosis and treatment in patients who are positive by NBS to avoid unnecessary treatment. The Guidelines for Mass Screening of Congenital Hypothyroidism (1998 version) were developed by the Mass Screening Committee of the Japanese Society for Pediatric Endocrinology in 1998. Subsequently, the guidelines were revised in 2014. Here, we have added minor revisions to the 2014 version to include the most recent findings. Target disease/conditions: Primary congenital hypothyroidism. Users of the Guidelines: Physician specialists in pediatric endocrinology, pediatric specialists, physicians referring pediatric practitioners, general physicians, laboratory technicians in charge of mass screening, and patients.

Knowns and unknowns about congenital hypothyroidism: 2022 update

Several excellent guidelines and expert opinions on congenital hypothyroidism (CH) are currently available. Nonetheless, these guidelines do not address several issues related to CH in detail. In this review, the authors chose the following seven clinical issues that they felt were especially deserving of closer scrutiny in the hope that drawing attention to them through discussion would help pediatric endocrinologists and promote further interest in the treatment of CH. 1. How high should the levothyroxine (L-T4) dose be for initial treatment of severe and permanent CH? 2. What is the optimal method for monitoring treatment of severe CH? 3. At what level does maternal iodine intake during pregnancy affect fetal and neonatal thyroid function? 4. Does serum thyroglobulin differ between patients with a dual oxidase 2 (DUOX2) variants and those with excess iodine? 5. Who qualifies for a genetic diagnosis? 6. What is the best index for distinguishing transient and permanent CH? 7. Is there any cancer risk associated with CH? The authors discussed these topics and jointly edited the manuscript to improve the understanding of CH and related issues.

Mutation screening of eight genes and comparison of the clinical data in a Chinese cohort with congenital hypothyroidism

BACKGROUND

Congenital hypothyroidism (CH) is a common neonatal endocrine disorder, characterized by irreversible intellectual disability and short stature if left untreated. It can be divided into thyroid dysgenesis (TD), including athyreosis, ectopy and hypoplasia, and dyshormonogenesis (DH), also referring to gland in situ (GIS), in which patients have eutopic thyroids with normal size or goiter. This study aims to analyze the clinical and genetic data of 375 Chinese CH patients without DUOX2 and thyroid transcription factor (TTF) variants, and to explore the mutation frequencies of the eight genes and the inheritance pattern of CH.

METHODS

Targeted next generation sequencing (NGS) and statistical analysis were performed for mutation screening on eight CH-related genes and the comparison of clinical data in a cohort of 606 Chinese CH patients from Henan Province.

RESULTS

A total of 104 variants were detected in genes required for thyroid formation (TSHR, GLIS3, BOREALIN, NTN1, JAG1 and TUBB1) and thyroid hormone synthesis (TG and TPO) in 83 subjects. Monogenic variants were the most prevalent with a percentage of 75.00% (78/104) followed by oligogenic variants (25.00%, 26/104). No differences were found in various clinical data between patients with and without variants. However, it should be noted that only initial L-T4 dose was statistically different between patients with monogenic variants and oligogenic variants.

CONCLUSIONS

Our results suggested that apart from Mendelian monogenic inheritance, oligogenic inheritance of CH could not be excluded and also involves other factors, such as penetrance, epigenetic mechanisms and environmental factors.

Genetic Factors Causing Thyroid Dyshormonogenesis as the Major Etiologies for Primary Congenital Hypothyroidism: Clinical and Genetic Characterization of 33 Patients

BACKGROUND AND AIMS

Although the significance of primary congenital hypothyroidism (CH) is supported by an increasing amount of evidence, the clinical and genetic characteristics of this condition are still poorly understood. This study aimed to explore the underlying genetic etiologies in a cohort of primary CH patients.

SUBJECTS AND METHODS

The clinical data of 33 patients with primary CH were collected and analyzed via a cross-sectional study. Genetic analysis was performed by high-throughput sequencing and Sanger verification, and the pathogenicity of the novel missense variants was predicted using a variety of comprehensive bioinformatic tools.

RESULTS

Among the 33 patients, 22 (22/33, 66.7%) harbored pathogenic variants in the causative genes of thyroid dysgenesis or dyshormonogenesis, with DUOX2 (15/33, 45.5%) topping the list, followed by TG, TPO, DUOXA2 and PAX8. Four novel genetic variants were detected, including a pathogenic frameshift and three likely pathogenic missense variants. Positive neonatal screening for TSH, neonatal jaundice and abnormal thyroid morphology were the main positive findings among all cases. Although 31 of the total 33 CH patients exhibited normal anthropometric and social performance, the other 2 had poor prognosis in this study.

CONCLUSIONS

This study reported 33 new CH patients bearing four novel genetic variants, which enriched the variant spectrum of CH genes. In this cohort, genetic factors causing thyroid dyshormonogenesis were the main etiologies of CH development. Most patients exhibited a favorable prognosis; however, systematic management remains a challenge in achieving improved clinical outcomes for CH patients.

Curating the gnomAD database: Report of novel variants in the thyroid peroxidase gene using in silico bioinformatics algorithms and a literature review

Thyroid peroxidase (TPO) is a membrane-bound glycoprotein located at the apical side of the thyroid follicular cells that catalyzes both iodination and coupling of iodotyrosine residues within the thyroglobulin molecule, leading to the synthesis of thyroid hormone. Variants in TPO cause congenital hypothyroidism (CH) by iodide organification defect and are commonly inherited in an autosomal recessive fashion. In the present work, we report a detailed population analysis and bioinformatic prediction of the TPO variants indexed in the Genome Aggregation Database (gnomAD) v2.1.1. The proportion of missense cysteine variants and nonsense, frameshift, and splice acceptor/donor variants were analyzed in each ethnic group (European (Non-Finnish), European (Finnish), African/African Americans, Latino/Admixed American, East Asian, South Asian, Ashkenazi Jewish, Other). The results showed a clear predominance of frameshift variants in the East Asian (82%) and European (Finnish) (75%) population, whereas the splice site variants predominate in African/African Americans (99.46%), Other (96%), Latino/Admixed American (94%), South Asian (86%), European (Non-Finnish) (56%) and Ashkenazi Jewish (56%) populations. The analysis of the distribution of the variants indexed in gnomAD v2.1.1 database revealed that most missense variants identified in the An peroxidase domain map in exon 8, followed by exons 11, 7 and 9, and finally in descending order by exons 10, 6, 12 and 5. In total, 183 novel TPO variants were described (13 missense cysteine's variants, 158 missense variants involving the An peroxidase domain and 12 splicing acceptor or donor sites variants) which were not reported in the literature and that would have deleterious effects on prediction programs. In the gnomAD v2.1.1 population, the estimated prevalence of heterozygous carriers of the potentially damaging variants was 1:77. In conclusion, we provide an updated and curated reference source of new TPO variants for application in clinical diagnosis and genetic counseling. Also, this work contributes to elucidating the molecular basis of CH associated with TPO defects.

Newborn Genetic Screening Revealed Increased Levels of Biochemical Indicators in Carriers of Heterozygous Variants

Background: Conventional newborn screening (NBS) is usually based on biochemical methods to predict the risk of inborn errors of metabolism. Recent studies have applied next-generation sequencing in NBS and revealed much more information, including carrier status. Whether these carriers of variants differ from other individuals was not fully determined. Objective: This research investigated the effect of heterozygous carrier status of pathogenic variants on biochemical indicators during NBS. Methods: We enrolled newborns participating in both conventional NBS and our previous Newborn Screening with Targeted Sequencing (NESTS) program from January 2021 to December 2021 in the Shunyi Maternal and Children's Hospital of Beijing Children's Hospital. Newborn levels of phenylalanine (Phe), thyroid stimulating hormone (TSH), and 17-hydroxyprogesterone (17-OHP) were measured to be analyzed together with associated sequencing results. Results: A total of 2351 newborns in the NESTS program was examined in the study. None had biallelic variants in genes related to congenital hypothyroidism (CH), hyperphenylalaninemia (HPA) or congenital adrenal hyperplasia. Forty-nine heterozygous carriers with phenylalanine hydroxylase (PAH) variants had significantly higher levels of Phe (p < 0.0001), and 11 heterozygous carriers of thyroid-stimulating hormone receptor (TSHR) variants had significantly higher levels of TSH (p < 0.05). Although heterozygous carriers had higher biochemical levels, they were below the diagnostic threshold of HPA and CH. Conclusions: Carriers of heterozygous variants in PAH or TSHR had significantly increased biochemical levels of associated factors in NBS. For individuals with higher Phe or TSH levels within the normal reference intervals, attention should be paid to the possibility of heterozygous carrier status.

New insights in pediatrics in 2021: choices in allergy and immunology, critical care, endocrinology, gastroenterology, genetics, haematology, infectious diseases, neonatology, neurology, nutrition, palliative care, respiratory tract illnesses and telemedicine

In this review, we report the developments across pediatric subspecialties that have been published in the Italian Journal of Pediatrics in 2021. We highlight advances in allergy and immunology, critical care, endocrinology, gastroenterology, genetics, hematology, infectious diseases, neonatology, neurology, nutrition, palliative care, respiratory tract illnesses and telemedicine.

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.

Whole-Exome Sequencing in Congenital Hypothyroidism Due to Thyroid Dysgenesis

Context: Congenital hypothyroidism due to thyroid dysgenesis (CHTD) is a predominantly sporadic and nonsyndromic (NS) condition of unknown etiology. NS-CHTD shows a 40-fold increase in relative risk among first-degree relatives (1 in 100 compared with a birth prevalence of 1 in 4000 in the general population), but a discordance rate between monozygotic (MZ) twins of 92%. This suggests a two-hit mechanism, combining a genetic predisposition (incomplete penetrance of inherited variants) with postzygotic events (accounting for MZ twin discordance). Objective: To evaluate whether whole-exome sequencing (WES) allows to identify new predisposing genes in NS-CHTD. Methods: We performed a case-control study by comparing the whole exome of 36 nonconsanguineous cases of NS-CHTD (33 with lingual thyroid ectopy and 3 with athyreosis, based on technetium pertechnetate scintigraphy at diagnosis) with that of 301 unaffected controls to assess for enrichment in rare protein-altering variants. We performed an unbiased approach using a gene-based burden with a false discovery rate correction. Moreover, we identified all rare pathogenic and likely pathogenic variants, based on in silico prediction tools, in 27 genes previously associated with congenital hypothyroidism (CH) (thyroid dysgenesis [TD] and dyshormonogenesis). Results: After correction for multiple testing, no enrichment in rare protein-altering variants was observed in NS-CHTD. Pathogenic or likely pathogenic variants (21 variants in 12 CH genes) were identified in 42% of cases. Eight percent of cases had variants in more than one gene (oligogenic group); these were not more severely affected than monogenic cases. Moreover, cases with protein-altering variants in dyshormonogenesis-related genes were not more severely affected than those without. Conclusions: No new predisposing genes were identified following an unbiased analysis of WES data in a well-characterized NS-CHTD cohort. Nonetheless, the discovery rate of rare pathogenic or likely pathogenic variants was 42%. Eight percent of the cases harbored multiple variants in genes associated with TD or dyshormonogenesis, but these variants did not explain the variability of hypothyroidism observed in dysgenesis. WES did not identify a genetic cause in NS-CHTD cases, confirming the complex etiology of this disease. Additional studies in larger cohorts and/or novel discovery approaches are required.

Screening of 23 candidate genes by next-generation sequencing of patients with permanent congenital hypothyroidism: novel variants in TG, TSHR, DUOX2, FOXE1, and SLC26A7

PURPOSE

To date, many genes have been associated with congenital hypothyroidism (CH). Our aim was to identify the mutational spectrum of 23 causative genes in Turkish patients with permanent CH, including thyroid dysgenesis (TD) and dyshormonogenesis (TDH) cases.

METHODS

A total of 134 patients with permanent CH (130 primary, 4 central) were included. To identify the genetic etiology, we screened 23 candidate genes associated with CH by next-generation sequencing. For confirmation and to detect the status of the specific familial variant in relatives, Sanger sequencing was also performed.

RESULTS

Possible pathogenic variants were found in 5.2% of patients with TD and in 64.0% of the patients with normal-sized thyroid or goiter. In all patients, variants were most frequently found in TSHR, followed by TPO and TG. The same homozygous TSHB variant (c.162 + 5G > A) was identified in four patients with central CH. In addition, we detected novel variants in the TSHR, TG, SLC26A7, FOXE1, and DUOX2.

CONCLUSION

Genetic causes were determined in the majority of CH patients with TDH, however, despite advances in genetics, we were unable to identify the genetic etiology of most CH patients with TD, suggesting the effect of unknown genes or environmental factors. The previous studies and our findings suggest that TSHR and TPO mutations is the main genetic defect of CH in the Turkish population.

Screening of frequent variants associated with congenital hypothyroidism: a comparison with next generation sequencing

Congenital hypothyroidism (CH) is considered the most common congenital endocrine disorder of genetic origin. Next generation sequencing (NGS) is the standard method for identifying genetic mutations, but it is an expensive and complex technique. Therefore, we propose to use Sanger sequencing to identify selected variants of the four most common CH-causative genes: DUOX2, TG, TSHR, and PAX8. To analyze the performance of Sanger sequencing, we compared its variant detection ability with that of a CH NGS panel containing 53 genes. We performed Sanger sequencing of selected variants and panel NGS analysis of 25 Japanese patients with CH. Sanger sequencing identified nine variants in seven patients, while NGS identified 24 variants in 14 patients. Of these, eight, five, eight, two, and one were found to be potentially pathogenic in DUOX2, TSHR, TG, UBR1, and TPO genes, respectively. The percentage of detectable variants using Sanger sequencing compared with NGS was 37.5% (9/24 variants), whereas the percentage of detectable cases carrying variants using Sanger sequencing compared with NGS was 50% (7/14 patients). We proposed a system for screening commonly identified CH-related variants by Sanger sequencing. Sanger sequencing could therefore identify about a third of CH-causative variants, so is considered an effective and efficient form of pre-screening before NGS.

Impact of the Mutational Landscape of the Sodium/Iodide Symporter in Congenital Hypothyroidism

Background: Iodide transport defect is an uncommon cause of dyshormonogenic congenital hypothyroidism due to homozygous or compound heterozygous pathogenic variants in the SLC5A5 gene, which encodes the sodium/iodide symporter (NIS), causing deficient iodide accumulation in thyroid follicular cells, thus impairing thyroid hormonogenesis. Methods:SLC5A5 gene variants were compiled from public databases and research articles exploring the molecular bases of congenital hypothyroidism. Using a dataset of 198 missense NIS variants classified as either benign or pathogenic, we developed and validated a machine learning-based NIS-specific variant classifier to predict the impact of missense NIS variants. Results: We generated a manually curated dataset containing 7793 unique SLC5A5 variants. As most databases compiled exome sequencing data, variant mapping revealed an increased density of variants in SLC5A5 coding exons. Based on allele frequency (AF) analysis, we established an AF threshold of 1:10,000 above which a variant should be considered benign. Most pathogenic NIS variants were located in the protein-coding region, as most patients were genetically diagnosed by using a candidate gene strategy limited to this region. Significantly, we evidenced that 94.5% of missense NIS variants were classified as of uncertain significance. Therefore, we developed an NIS-specific variant classifier to improve the prediction of pathogenicity of missense variants. Our classifier predicted the clinical outcome of missense variants with high accuracy (90%), outperforming state-of-the-art pathogenicity predictors, such as REVEL, PolyPhen-2, and SIFT. Based on the excellent performance of our classifier, we predicted the mutational landscape of NIS. The analysis of the mutational landscape revealed that most missense variants located in transmembrane segments are frequently pathogenic. Moreover, we predicted that ∼28% of all single-nucleotide variants that could cause missense NIS variants are pathogenic, thus putatively leading to congenital hypothyroidism if present in homozygous or compound heterozygous state. Conclusions: We reported the first NIS-specific variant classifier aiming at improving the interpretation of missense NIS variants in clinical practice. Deciphering the mutational landscape for every protein involved in thyroid hormonogenesis is a relevant task for a deep understanding of the molecular mechanisms causing dyshormonogenic congenital hypothyroidism.

Urinary iodine and thyroglobulin are useful markers in infants suspected of congenital hypothyroidism based on newborn screening

OBJECTIVES

Iodine deficiency and excess both cause thyroid dysfunction. Few data describe the relationship between iodine status and outcomes of congenital hypothyroidism (CH) in iodine-sufficient areas. We investigated urinary iodine (UI) concentration and its relationship with the clinical course of CH.

METHODS

We reviewed and retrospectively analyzed patients with positive newborn screening (NBS) for CH from January 2012 to June 2019 in Japan, obtaining UI and UI-urine creatinine ratio (UI/Cr), serum TSH, free T₄, free T₃ and thyroglobulin (Tg) at the first visit, TSH at NBS, levothyroxine (LT4) dose, and subsequent doses. A UI value of 100-299 μg/L was considered adequate.

RESULTS

Forty-eight patients were included. Median UI and UI/Cr were 325 μg/L and 3,930 µg/gCr, respectively. UI was high (≥300 μg/L) in 26 (54%) and low (≤99 μg/L) in 11 (23%). LT4 was administered to 34 patients. Iodine status was not related to the need for treatment. We found a U-shaped relationship between Tg and UI/Cr. Patients with high Tg (≥400 ng/mL) and abnormal UI levels required significantly lower LT4 doses (≤20 µg/day) at three years of age. Even if they showed severe hypothyroidism initially, they did not need subsequent dose increments.

CONCLUSIONS

Abnormal UI levels with Tg elevation were associated with lower LT4 dose requirements. The evaluation of iodine status and Tg concentrations were considered useful in patients suspected of CH.

Novel DIO1 Gene Mutation Acting as Phenotype Modifier for Novel Compound Heterozygous TPO Gene Mutations Causing Congenital Hypothyroidism

A family with congenital hypothyroidism was identified with two novel deleterious compound heterozygous thyroid peroxidase (TPO) mutations (c.962C>A, and c.1577C>T). Serum thyroid tests showed higher-than-expected serum-free thyroxine (T4) relative to TT3, while reverse triiodothyronine (rT3) was also elevated. Two siblings manifested a more severe phenotype of developmental delay compared with another sibling and were found to harbor an additional novel heterozygous deleterious iodothyronine deiodinase 1 (DIO1) mutation (c.395G>A). In the context of L-T4 replacement, the decreased D1 activity results in abnormal thyroid hormone metabolism with decreased triiodothyronine (T3) generation from L-T4 and may result in decreased T3 bioavailability during critical stages of development.

Case Report: Expanding the Digenic Variants Involved in Thyroid Hormone Synthesis-10 New Cases of Congenital Hypothyroidism and a Literature Review

Congenital hypothyroidism (CH) is the most common neonatal metabolic disorder. Although it has been understood to be a monogenic disease, some CH patients are reported to carry two or more variants at different genes. Here, ten permanent congenital hypothyroidism (PCH) patients were retrospectively reviewed, with elevated levels of serum thyroid-stimulating hormone and levothyroxine dependence during follow-up between 2015 and 2019. Each affected individual carried digenic variants, which were heterozygous at two of pathogenic genes. In total, five pathogenic genes, TSHR, TG, TPO, DUOX2 and DUOXA2, were simultaneously identified in subjects that were involved in the same metabolic pathway: thyroid hormone biosynthesis. There were digenic variants at TSHR and DUOX2 combined in three patients, DUOX2 and TG combined in two patients, DUOX2 and DUOXA2 combined in two patients, TG and DUOXA2 combined in two patients, and TG and TPO combined in one patient. Additionally, seven novel variants, TSHR c.679G>A, DUOX2 c.127A>T, c.608-619del, c.959T>C, TG c.2307G>A, and c.6759_6765del, and DUOXA2 c.93T>G, were identified in these PCH patients. Along with a literature review on digenic variants in patients with CH, our findings illustrated the complexity of genetic etiology in CH.

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.

Newborn Screening for Congenital Hypothyroidism in Japan

Congenital hypothyroidism (CH) is the most common preventable cause of intellectual impairment or failure to thrive by early identification and treatment. In Japan, newborn screening programs for CH were introduced in 1979, and the clinical guidelines for newborn screening of CH were developed in 1998, revised in 2014, and are currently undergoing further revision. Newborn screening strategies are designed to detect the elevated levels of thyroid stimulating hormone (TSH) in most areas of Japan, although TSH and free thyroxine (FT4) are often measured simultaneously in some areas. Since 1987, in order not to observe the delayed rise in TSH, additional rescreening of premature neonates and low birth weight infants (<2000 g) at four weeks of life or when their body weight reaches 2500 g has been recommended, despite a normal initial newborn screening. Recently, the actual incidence of CH has doubled to approximately 1:2500 in Japan as in other countries. This increasing incidence is speculated to be mainly due to an increase in the number of mildly affected patients detected by the generalized lowering of TSH screening cutoffs and an increase in the number of preterm or low birth weight neonates at a higher risk of having CH than term infants.

A Novel SLC5A5 Variant Reveals the Crucial Role of Kinesin Light Chain 2 in Thyroid Hormonogenesis

CONTEXT

Iodide transport defect (ITD) (Online Mendelian Inheritance in Man No. 274400) is an uncommon cause of dyshormonogenic congenital hypothyroidism due to loss-of-function variants in the SLC5A5 gene, which encodes the sodium/iodide symporter (NIS), causing deficient iodide accumulation in thyroid follicular cells.

OBJECTIVE

This work aims to determine the molecular basis of a patient's ITD clinical phenotype.

METHODS

The propositus was diagnosed with dyshormonogenic congenital hypothyroidism with minimal 99mTc-pertechnetate accumulation in a eutopic thyroid gland. The propositus SLC5A5 gene was sequenced. Functional in vitro characterization of the novel NIS variant was performed.

RESULTS

Sanger sequencing revealed a novel homozygous missense p.G561E NIS variant. Mechanistically, the G561E substitution reduces iodide uptake, because targeting of G561E NIS to the plasma membrane is reduced. Biochemical analyses revealed that G561E impairs the recognition of an adjacent tryptophan-acidic motif by the kinesin-1 subunit kinesin light chain 2 (KLC2), interfering with NIS maturation beyond the endoplasmic reticulum, and reducing iodide accumulation. Structural bioinformatic analysis suggests that G561E shifts the equilibrium of the unstructured tryptophan-acidic motif toward a more structured conformation unrecognizable to KLC2. Consistently, knockdown of Klc2 causes defective NIS maturation and consequently decreases iodide accumulation in rat thyroid cells. Morpholino knockdown of klc2 reduces thyroid hormone synthesis in zebrafish larvae leading to a hypothyroid state as revealed by expression profiling of key genes related to the hypothalamic-pituitary-thyroid axis.

CONCLUSION

We report a novel NIS pathogenic variant associated with dyshormonogenic congenital hypothyroidism. Detailed molecular characterization of G561E NIS uncovered the significance of KLC2 in thyroid physiology.

[Main biological tools applied to newborn screening: Landscape and future perspectives]

Over the past fifty years, neonatal screening has become essential in the public health programs of a large number of countries. During all these years, the number of detectable diseases has continued to grow, following the possibilities offered by technical advances in clinical biology. The Guthrie test has enabled the miniaturization of blood sampling, opening up the possibilities of biological screening in the newborn population. Fluorimetry, immunoassay and more recently tandem mass spectrometry have subsequently allowed to detect many treatable disorders. The new developments of next generation sequencing and artificial intelligence may open a new era despite many ethical questions that will arise. This review provides an overview of the biological techniques currently used for neonatal screening and opens up perspectives on the place of new technological developments.

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.

Three-dimensional microscopy and image fusion reconstruction analysis of the thyroid gland during morphogenesis

Thyroid dysgenesis (TD) is a major cause of primary congenital hypothyroidism; however, the molecular mechanism underlying this process is unclear. Current knowledge regarding the morphogenesis of the thyroid gland and vascular anomalies affecting thyroid development is limited. To monitor the early stages of thyroid gland development, we generated double transgenic zebrafish embryos Tg(tg:mCherry/flk1:EGFP). We described the volume of the thyroid from 2 days postfertilization (dpf) to 5 dpf using 3D reconstruction images. We treated zebrafish embryos with the fibroblast growth factor (FGF) inhibitor PD166866 to better understand the impact of vascular defects on thyroid development and the effects of drug administration at specific time periods on different stages of thyroid development. The 3D reconstruction data revealed that the thyroid glands underwent significant transformation at critical time points. PD166866 treatment from 48 to 72 hours postfertilization (hpf) and from 72 to 96 hpf did not cause obvious reductions in thyroid volume but did result in observable abnormalities in thyroid morphology. The treatment also affected thyroid volume from 36 to 48 hpf, thus indicating that there are time-point-specific effects of drug administration during thyroid development. Three-dimensional image reconstruction provides a comprehensive picture of thyroid anatomy and can be used to complement anatomical fluorescence information. The effects of an FGF pathway inhibitor on thyroid development were determined to be time-point-dependent.

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.

Genetic and Phenotypic Characteristics of Congenital Hypothyroidism in a Chinese Cohort

BACKGROUND

The molecular etiology and the genotype-phenotype correlation of congenital hypothyroidism (CH) remain unclear.

METHODS

We performed genetic analysis in 42 newborns with CH using whole-exome sequencing. Patients were divided into a single-gene group and a multi-gene group according to the number of affected genes, or divided into a monoallelic group, a biallelic group, and an oligogenic group according to the pattern of the detected variants. The clinical characteristics were compared between groups.

RESULTS

Thyroid dysgenesis (TD) was observed in 10 patients and goiter in 5 patients, whereas 27 patients had normal-sized gland-in-situ (GIS). We identified 58 variants in five genes in 29 patients. The genes with the most frequent variants were DUOX2 (70.7%), followed by TSHR (12.1%), DUOXA2 (10.3%), and TPO (5.2%). Variants in the genes causing dyshormonogenesis (DH) were more common than those in the genes causing TD (87.9% versus 12.1%). Among the patients with detected variants, 26 (89.7%) were harboring a single gene variant (single-gene group), which include 22 patients harboring biallelic variants (biallelic group) and four patients harboring monoallelic variants (monoallelic group). Three (10.3%) patients harbored variants in two or three genes (multi-gene group or oligogenic group). Compared with the single-gene group, the levothyroxine (L-T4) dose at 1 year of age was higher in the multi-gene group (p = 0.018). A controllable reduction in the L-T4 dose was observed in 25% of patients in the monoallelic group and 59.1% of patients in the biallelic group; however, no patients with such reduction in the L-T4 dose were observed in the oligogenic group.

CONCLUSIONS

Patients with normal-sized GIS accounted for the majority of our cohort. Genetic defects in the genes causing DH were more common than those in the genes causing TD, with biallelic variants in DUOX2 being dominant. DH might be the leading pathophysiology of CH in Chinese individuals.

DUOX2 variants are a frequent cause of congenital primary hypothyroidism in Thai patients

OBJECTIVE

To identify the genetic etiologies of congenital primary hypothyroidism (CH) in Thai patients.

DESIGN AND METHODS

CH patients were enrolled. Clinical characteristics including age, signs and symptoms of CH, pedigree, family history, screened thyroid-stimulating hormone results, thyroid function tests, thyroid imaging, clinical course and treatment of CH were collected. Clinical exome sequencing by next-generation sequencing was performed. In-house gene list which covered 62 potential candidate genes related to CH and thyroid disorders was developed for targeted sequencing. Sanger sequencing was performed to validate the candidate variants. Thyroid function tests were determined in the heterozygous parents who carried the same DUOX2 or DUOXA2 variants as their offsprings.

RESULTS

There were 118 patients (63 males) included. Mean (SD) age at enrollment was 12.4 (7.9) years. Forty-five of 118 patients (38%) had disease-causing variants. Of 45 variants, 7 genes were involved (DUOX2, DUOXA2, TG, TPO, SLC5A5, PAX8 and TSHR). DUOX2, a gene causing thyroid dyshormonogenesis, was the most common defective gene (25/45, 56%). The most common DUOX2 variant found in this study was c.1588A>T. TG and TPO variants were less common. Fourteen novel variants were found. Thyroid function tests of most parents with heterozygous state of DUOX2 and DUOXA2 variants were normal.

CONCLUSIONS

DUOX2 variants were most common among Thai CH patients, while TG and TPO variants were less common. The c.1588A>T in DUOX2 gene was highly frequent in this population.

Transcription factor GLIS3: Critical roles in thyroid hormone biosynthesis, hypothyroidism, pancreatic beta cells and diabetes

GLI-Similar 3 (GLIS3) is a member of the GLIS subfamily of Krüppel-like zinc finger transcription factors that functions as an activator or repressor of gene expression. Study of GLIS3-deficiency in mice and humans revealed that GLIS3 plays a critical role in the regulation of several biological processes and is implicated in the development of various diseases, including hypothyroidism and diabetes. This was supported by genome-wide association studies that identified significant associations of common variants in GLIS3 with increased risk of these pathologies. To obtain insights into the causal mechanisms underlying these diseases, it is imperative to understand the mechanisms by which this protein regulates the development of these pathologies. Recent studies of genes regulated by GLIS3 led to the identification of a number of target genes and have provided important molecular insights by which GLIS3 controls cellular processes. These studies revealed that GLIS3 is essential for thyroid hormone biosynthesis and identified a critical function for GLIS3 in the generation of pancreatic β cells and insulin gene transcription. These observations raised the possibility that the GLIS3 signaling pathway might provide a potential therapeutic target in the management of diabetes, hypothyroidism, and other diseases. To develop such strategies, it will be critical to understand the upstream signaling pathways that regulate the activity, expression and function of GLIS3. Here, we review the recent progress on the molecular mechanisms by which GLIS3 controls key functions in thyroid follicular and pancreatic β cells and how this causally relates to the development of hypothyroidism and diabetes.