Detection of Novel Gene Variants Associated with Congenital Hypothyroidism in a Finnish Patient Cohort

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.

FinnGen provides genetic insights from a well-phenotyped isolated population

Population isolates such as those in Finland benefit genetic research because deleterious alleles are often concentrated on a small number of low-frequency variants (0.1% ≤ minor allele frequency < 5%). These variants survived the founding bottleneck rather than being distributed over a large number of ultrarare variants. Although this effect is well established in Mendelian genetics, its value in common disease genetics is less explored^1,2. FinnGen aims to study the genome and national health register data of 500,000 Finnish individuals. Given the relatively high median age of participants (63 years) and the substantial fraction of hospital-based recruitment, FinnGen is enriched for disease end points. Here we analyse data from 224,737 participants from FinnGen and study 15 diseases that have previously been investigated in large genome-wide association studies (GWASs). We also include meta-analyses of biobank data from Estonia and the United Kingdom. We identified 30 new associations, primarily low-frequency variants, enriched in the Finnish population. A GWAS of 1,932 diseases also identified 2,733 genome-wide significant associations (893 phenome-wide significant (PWS), P < 2.6 × 10^-11) at 2,496 (771 PWS) independent loci with 807 (247 PWS) end points. Among these, fine-mapping implicated 148 (73 PWS) coding variants associated with 83 (42 PWS) end points. Moreover, 91 (47 PWS) had an allele frequency of <5% in non-Finnish European individuals, of which 62 (32 PWS) were enriched by more than twofold in Finland. These findings demonstrate the power of bottlenecked populations to find entry points into the biology of common diseases through low-frequency, high impact variants.

A case of syndromic congenital hypothyroidism with a 15.2 Mb interstitial deletion on 2q12.3q14.2 involving PAX8

Paired box 8 (PAX8) mutations are an established genetic cause of congenital hypothyroidism (CH). The majority of these mutations are found in the protein-coding exons of the gene. The proband, a 3-yr-old girl, had tetralogy of Fallot and polydactyly soon after birth. She was diagnosed with CH in the newborn screening for CH. She had a high serum TSH level (239 mU/L) and low free T4 level (0.7 ng/dL). Ultrasonography revealed thyroid hypoplasia. We performed array comparative genomic hybridization because the patient exhibited a variety of symptoms across multiple organ systems. The analysis revealed a novel heterozygous deletion that spanned a 15.2 Mb region in 2q12.3q14.3 (GRCh37; chr2:109,568,260-124,779,449). There were 71 protein-coding genes in this region, including two genes (PAX8 and GLI2) associated with congenital endocrine disorders. The common clinical features of the two previously reported patients with a total PAX8 deletion and our case were CH, short stature and intellectual disability, but the severity of hypothyroidism and other clinical features were variable. In conclusion, we describe a syndromic CH patient with a novel 2q12.3q14.3 deletion involving PAX8. Patients with CH, whose unifying diagnosis is not obvious, could have a genomic deletion involving PAX8.

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.

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.

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.

Insights of Noncanonical Splice-site Variants on RNA Splicing in Patients With Congenital Hypothyroidism

CONTEXT

Congenital hypothyroidism (CH) is caused by mutations in the genes for thyroid hormone synthesis. In our previous investigation of CH patients, approximately 53% of patients had mutations in either coding exons or canonical splice sites of causative genes. Noncanonical splice-site variants in the intron were detected but their pathogenic significance was not known.

OBJECTIVE

This work aims to evaluate noncanonical splice-site variants on pre-messenger RNA (pre-mRNA) splicing of CH-causing genes.

METHODS

Next-generation sequencing data of 55 CH cases in 47 families were analyzed to identify rare intron variants. The effects of variants on pre-mRNA splicing were investigated by minigene RNA-splicing assay.

RESULTS

Four intron variants were found in 3 patients: solute carrier family 26 member 4 (SLC26A4) c.1544+9C>T and c.1707+94C>T in one patient, and solute carrier family 5 member 5 (SLC5A5) c.970-48G>C and c.1652-97A>C in 2 other patients. The c.1707+94C>T and c.970-48G>C caused exons 15 and 16 skipping, and exon 8 skipping, respectively. The remaining variants had no effect on RNA splicing. Furthermore, we analyzed 28 previously reported noncanonical splice-site variants (4 in TG and 24 in SLC26A4). Among them, 15 variants (~ 54%) resulted in aberrant splicing and 13 variants had no effect on RNA splicing. These data were compared with 3 variant-prediction programs (FATHMM-XF, FATHMM-MKL, and CADD). Among 32 variants, FATHMM-XF, FATHMM-MKL, and CADD correctly predicted 20 (63%), 17 (53%), and 26 (81%) variants, respectively.

CONCLUSION

Two novel deep intron mutations have been identified in SLC26A4 and SLC5A5, bringing the total number of solved families with disease-causing mutations to approximately 45% in our cohort. Approximately 46% (13/28) of reported noncanonical splice-site mutations do not disrupt pre-mRNA splicing. CADD provides highest prediction accuracy of noncanonical splice-site variants.

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.

Further Evidence That Defects in Main Thyroid Dysgenesis-Related Genes Are an Uncommon Etiology for Primary Congenital Hypothyroidism in Mexican Patients: Report of Rare Variants in FOXE1, NKX2-5 and TSHR

Mexico shows a high birth prevalence of congenital hypothyroidism (CH) due to thyroid dysgenesis (TD). PAX8 defects underlie only 1% of these cases and NKX2-1 does not seem to be involved. Here, we analyzed other TD-related genes in 128 non-related Mexican patients (females 77.3%; 6 months to 16.6 years) with non-syndromic CH-TD diagnosis established by clinical evaluation, thyroid hormone serum profiling, and scintigraphy (74%) or ultrasonography (26%). We performed Sanger sequencing of FOXE1, NKX2-5, and TSHR and evaluated copy number variations (CNVs) in TSHR, FOXE1, PAX8, and NKX2-1 by multiplex ligation-dependent probe amplification. Odds ratios for TD risk were explored for FOXE1 polyalanine stretches [polyAla-rs71369530] in cases and controls (N = 116). Five rare missense changes cataloged as benign (NKX2-5:p.(Ala119Ser)-rs137852684), of unknown significance (FOXE1:p.(Ala335Gly)-rs543372757; TSHR:p.(Asp118Asn)-rs1414102266), and likely pathogenic (FOXE1:p.(Gly124Arg)-rs774035532; TSHR:p.(Trp422Arg)-rs746029360) accounted for 1.5% (N = 2/128) of clinically relevant genotypes (supported in part by protein modeling) in CH-TD. No CNVs were identified, nor did polyAla > 14 alanines in FOXE1 significantly protect against TD. The present and previously published data collectively show that small clinically relevant germline variants in PAX8, FOXE1, and TSHR are found in only a very small proportion (2.5%) of isolated CH-TD Mexican patients.

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.

Genetic Variability of the Paired Box Transcription Factor; PAX8 Gene: Guidance Towards Treatment Strategies in a Cohort of Congenital Hypothyroidism

The contribution of PAX8 genetic variants to congenital hypothyroidism (CH) is not well understood. We aimed to study the genetic variability of exons 3 and 5 of PAX8 gene among a cohort of children with congenital hypothyroidism in correspondence to their clinical aspect. Blood samples were collected from 117 children (63 girls and 54 boys) with CH and enrolled as cases (Group I). All cases underwent biochemical confirmation with low FT4 and high TSH levels and thyroid gland imaging, along with equal number of matched apparently healthy individuals who served as controls (Group II). Genomic materials for exons 3 and 5 of PAX8 gene were extracted, amplified by PCR, detected by electrophoresis, purified, and sequenced by the Sanger technique through the application of ABI 3730x1 DNA Sequencer. Out of 117 cases, eight different effective PAX8 mutations were detected in exon 3 (G23D, V35I, I34T, Q40P, p.R31C, p.R31H, p.R31A, and p.I47T) in 14 patients with their sonographic findings ranged from normal, hypoplastic to thyroid agenesis. Besides the reported mutations, one novel mutation; R31A was detected in 1 euotopic case. Exon 5 analysis revealed no detected mutations elsewhere. In contrast, all healthy control children showed no mutation and normal sonographic findings. Mutations in exon 3 of PAX8 gene, implies its important role in thyroid development and function, as a first estimate of PA8 mutation rate in Egyptian patients with CH having normal and dysgenetic gland. Using ultrasound is mandatory for diagnosis and guiding the treatment of children with CH.

Identification and analyzes of DUOX2 mutations in two familial congenital hypothyroidism cases

BACKGROUND

Mutations in DUOX2 are the frequent cause of congenital hypothyroidism (CH), a common neonatal metabolic disorder characterized by great phenotypic variability. CH can be traditionally subclassified into two subtypes: thyroid dysgenesis (TD) and thyroid dyshormonogenesis. The objectives of this study were to analyze the genetic data of two familial CH cases, to elucidate the pathogenesis from the perspective of genetics and to review and summarize the previous findings.

METHODS

Targeted regions sequencing (TRS) technology covering all exons and intron-exon boundaries of 35 known and potential CH-related candidate target genes in combination with Sanger sequencing were performed to identify the likely pathogenic mutations of the six patients with familial CH.

RESULTS

In family 1, two DUOX2 missense mutations, namely, c.1060C>T/p.R354W in exon 10 and c.3200C>T/p.S1067L in exon 25, were found. Patient 1 (P1), P2 and P3 were transient CH (TCH) patients with eutopic thyroid glands of normal size and function. In family 2, only the mutation c.3200C>T/p.S1067L was identified. P4, P5, and P6 were diagnosed with permanent CH (PCH), which requires lifelong levothyroxine (L-T4) treatment. Furthermore, both P4 and P5 harbored properly located thyroid glands, whereas P6 had a mildly reduced gland. P1, P3, P6, and other family members carrying monoallelic or biallelic DUOX2 mutations showed no obvious abnormal clinical symptoms or signs, while P2, P4, and P5 showed umbilical hernias.

CONCLUSIONS

The present study suggests that the phenotypic features resulting from DUOX2 mutations vary greatly. The p.R354W and p.S1067L alterations or the combination of the two alterations in DUOX2 are probably only predisposing to CH and DUOX2 may be involved in the morphogenesis of the human thyroid gland. Simultaneously, the compensation of DUOX1 for the loss of DUOX2, undetectable pathogenic mutations, the effects of environmental factors, epigenetic mechanisms and the involvement of multiple genes cannot be excluded in the explanation of these genetic results.

Congenital Hypothyroidism: A 2020-2021 Consensus Guidelines Update-An ENDO-European Reference Network Initiative Endorsed by the European Society for Pediatric Endocrinology and the European Society for Endocrinology

Background: An ENDO-European Reference Network (ERN) initiative was launched that was endorsed by the European Society for Pediatric Endocrinology and the European Society for Endocrinology with 22 participants from the ENDO-ERN and the two societies. The aim was to update the practice guidelines for the diagnosis and management of congenital hypothyroidism (CH). A systematic literature search was conducted to identify key articles on neonatal screening, diagnosis, and management of primary and central CH. The evidence-based guidelines were graded with the Grading of Recommendations, Assessment, Development and Evaluation system, describing both the strength of recommendations and the quality of evidence. In the absence of sufficient evidence, conclusions were based on expert opinion. Summary: The recommendations include the various neonatal screening approaches for CH as well as the etiology (also genetics), diagnostics, treatment, and prognosis of both primary and central CH. When CH is diagnosed, the expert panel recommends the immediate start of correctly dosed levothyroxine treatment and frequent follow-up including laboratory testing to keep thyroid hormone levels in their target ranges, timely assessment of the need to continue treatment, attention for neurodevelopment and neurosensory functions, and, if necessary, consulting other health professionals, and education of the child and family about CH. Harmonization of diagnostics, treatment, and follow-up will optimize patient outcomes. Lastly, all individuals with CH are entitled to a well-planned transition of care from pediatrics to adult medicine. Conclusions: This consensus guidelines update should be used to further optimize detection, diagnosis, treatment, and follow-up of children with all forms of CH in the light of the most recent evidence. It should be helpful in convincing health authorities of the benefits of neonatal screening for CH. Further epidemiological and experimental studies are needed to understand the increased incidence of this condition.

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.

Screening and Functional Analysis of TPO Gene Mutations in a Cohort of Chinese Patients With Congenital Hypothyroidism

BACKGROUNDS

As a crucial enzyme in thyroid hormone synthesis, the genetic defective thyroid peroxidase (TPO) was one of the main genetic factors leading to congenital hypothyroidism (CH).

METHODS

Mutations in the TPO gene were screened and identified in 219 patients with CH from northwest China by using high-throughput sequencing and bioinformatics analysis. The biological function of detected variants was studied by in vitro experiments and homology modeling.

RESULTS

Nineteen rare variants, including seven novel ones, were detected in 17 of 219 patients (7.8%). Most cases were detected with one single heterozygous variant, and only two patients were detected with multiple variants, i.e., compounds for (1) IVS7-1G>A, p.Ala443Val, and p.Arg769Trp and (2) p.Asn592Ser and p.Asn798Lys. The biological function of the four missense mutations (i.e., p.Ala443Val, p.Arg769Trp, p.Asn592Ser, and p.Asn798Lys) they carried were further studied. Experimental data showed that these four mutations did not affect the protein expression level of the TPO gene but remarkably reduced the peroxidase activity toward guaiacol oxidation, retaining 8-32% of activity of the wild-type protein. The comparison of the predicted 3-D structures of wild-type and mutant TPO proteins showed that these four amino acid substitutions changed the non-covalent interactions of studied residues that might alter the structure and function of the TPO protein.

CONCLUSION

This study was the first to analyze the TPO mutation spectrum of patients with CH in northwest China. Our data indicated that the TPO mutation was not a common reason to cause CH in China. The functional data may help to clarify the structure-function relationship of the TPO protein and provide further evidence for the elucidation of the genetic etiology of CH.

Next-Generation Sequencing Analysis Reveals Frequent Familial Origin and Oligogenism in Congenital Hypothyroidism With Dyshormonogenesis

CONTEXT

Congenital hypothyroidism (CH) is related to dyshormonogenesis in 15% to 40% of the world population and associated with homozygous or heterozygous variants in the main genes of the hormone synthesis pathway. Emerging diagnostic tools, such as next-generation sequencing (NGS), have been used to efficiently explore panels of genes and identify complex mechanisms of pathogenesis.

OBJECTIVE

We explored 19 candidate genes known to be causative for permanent or transient CH to evaluate the role of complex gene variations in CH phenotype.

PATIENTS DESIGN AND SETTING

Using the NGS approach, we studied 65 newborns with thyroid dyshormonogenesis (TDH). New variants were assessed in silico for pathogenicity.

RESULTS

Among the 65 infants, 56.9% presented a variant in one or more genes of the thyroid hormone synthesis axis. We identified homozygous or compound heterozygous variants in the TG, DUOX2, TPO, or SLC5A5 genes in 10 infants and heterozygous variants in DUOX2, TG, TPO, and TSHR in 19 others. In seven cases, a heterozygous variant in the TG gene was the unique anomaly detected, but related to disturbed hormonal balance. Oligogenic variants were found in eight infants associated with severe CH and goiter in five of them.

CONCLUSION

The systematic exploration of genes involved in thyroid hormone synthesis by NGS in TDH showed high diagnostic relevance. Oligogenic inheritance could be related to phenotypic heterogeneity and a high frequency of goiter.

Phenotypic Variability of Patients With PAX8 Variants Presenting With Congenital Hypothyroidism and Eutopic Thyroid

PURPOSE

Thyroid dyshormonogenesis is a heterogeneous group of hereditary diseases produced by a total/partial blockage of the biochemical processes of thyroid-hormone synthesis and secretion. Paired box 8 (PAX8) is essential for thyroid morphogenesis and thyroid hormone synthesis. We aimed to identify PAX8 variants in patients with thyroid dyshormonogenesis and to analyze them with in vitro functional studies.

PATIENTS AND METHODS

Nine pediatric patients with a eutopic thyroid gland were analyzed by the Catalan screening program for congenital hypothyroidism. Scintigraphies showed absent, low, or normal uptake. Only one patient had a hypoplastic gland. On reevaluation, perchlorate discharge test was negative or compatible with partial iodine-organization deficit. After evaluation, 8 patients showed permanent mild or severe hypothyroidism. Massive-sequencing techniques were used to detect variants in congenital hypothyroidism-related genes. In vitro functional studies were based on transactivating activity of mutant PAX8 on a TG-gene promoter and analyzed by a dual-luciferase assays.

RESULTS

We identified 7 heterozygous PAX8 exonic variants and 1 homozygous PAX8 splicing variant in 9 patients with variable phenotypes of thyroid dyshormonogenesis. Five were novel and 5 variants showed a statistically significant impaired transcriptional activity of TG promoter: 51% to 78% vs the wild type.

CONCLUSIONS

Nine patients presented with PAX8 candidate variants. All presented with a eutopic thyroid gland and 7 had deleterious variants. The phenotype of affected patients varies considerably, even within the same family; but, all except the homozygous patient presented with a normal eutopic thyroid gland and thyroid dyshormonogenesis. PAX8 functional studies have shown that 6 PAX8 variants are deleterious. Our studies have proven effective in evaluating these variants.

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.

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.

Congenital Hypothyroidism Due to Truncating PAX8 Mutations: A Case Series and Molecular Function Studies

CONTEXT

PAX8 is a transcription factor required for thyroid development, and its mutation causes congenital hypothyroidism (CH). More than 20 experimentally verified loss-of-function PAX8 mutations have been described, and all but one were located in the DNA-binding paired domain.

OBJECTIVE

We report the identification and functional characterization of 3 novel truncating PAX8 mutations located outside the paired domain.

METHODS

Three CH probands, diagnosed in the frame of newborn screening, had thyroid hypoplasia and were treated with levothyroxine. Next-generation sequencing-based mutation screening was performed. Functionality of the identified mutations were verified with Western blotting, intracellular localization assays, and transactivation assays with use of HeLa cells. Luciferase complementation assays were used to evaluate the effect of mutations on the interaction between PAX8 and its partner, NKX2-1.

RESULTS

Each proband had novel truncating PAX8 mutations that were I160Sfs*52, Q213Efs*27, and F342Rfs*85. Western blotting showed destabilization of the I160fs-PAX8 protein. Q213fs-PAX8 and F342fs-PAX8 showed normal protein expression levels and normal nuclear localization, but showed loss of transactivation of the luciferase reporter. By luciferase complementation assays, we showed that PAX8-NKX2-1 interaction was defective in Q213fs-PAX8. We also characterized the recombinant PAX8 proteins, and found that the protein sequence corresponding to exon 10 (363-400 aa residues) was essential for the PAX8-NKX2-1 interaction.

CONCLUSIONS

Clinical and molecular findings of 3 novel truncating PAX8 mutations located outside the paired domain were reported. Experiments using cultured cells and recombinant proteins showed that the C-terminal portion (ie, 363-400 aa) of PAX8 is required for the PAX8-NKX2-1 interaction.

Identification and functional characterization of a novel PAX8 mutation (p.His39Pro) causing familial thyroid hypoplasia

Mutations in PAX8, the gene for a thyroid-specific transcription factor, causes congenital hypothyroidism (CH) with autosomal dominant inheritance. All previously detected PAX8 mutations except one are located in the DNA-binding paired domain. The proband, a 1-yr-old boy, was diagnosed with CH in the frame of newborn screening. He had high serum TSH level (180 mU/L) and low serum free T₄ level (0.4 ng/dL). Ultrasonography revealed that the proband had thyroid hypoplasia. Importantly, he had a family history of CH, i.e., his mother also had CH and hypoplasia. Next generation sequencing-based mutation screening revealed a novel heterozygous PAX8 mutation (c.116A>C, p.His39Pro) that was transmitted to the proband from the mother. Expression experiments with HeLa cells confirmed that His39Pro-PAX8 exhibited defective transactivation of the TG promoter–luciferase reporter. In conclusion, we identified and described a novel loss-of-function PAX8 mutation in a family with thyroid hypoplasia. Patients with dominantly inherited CH and no extrathyroidal abnormalities could have PAX8 mutations.

GWAS of thyroid stimulating hormone highlights pleiotropic effects and inverse association with thyroid cancer

Thyroid stimulating hormone (TSH) is critical for normal development and metabolism. To better understand the genetic contribution to TSH levels, we conduct a GWAS meta-analysis at 22.4 million genetic markers in up to 119,715 individuals and identify 74 genome-wide significant loci for TSH, of which 28 are previously unreported. Functional experiments show that the thyroglobulin protein-altering variants P118L and G67S impact thyroglobulin secretion. Phenome-wide association analysis in the UK Biobank demonstrates the pleiotropic effects of TSH-associated variants and a polygenic score for higher TSH levels is associated with a reduced risk of thyroid cancer in the UK Biobank and three other independent studies. Two-sample Mendelian randomization using TSH index variants as instrumental variables suggests a protective effect of higher TSH levels (indicating lower thyroid function) on risk of thyroid cancer and goiter. Our findings highlight the pleiotropic effects of TSH-associated variants on thyroid function and growth of malignant and benign thyroid tumors.

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

PURPOSE

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder; however, its molecular etiology remains poorly understood.

METHODS

We performed genetic analysis of 24 causative genes using next-generation sequencing in 167 CH cases, comprising 57 dyshormonogenesis (DH), 32 dysgenesis (TD) and 78 undiagnosed. The pathogenicity of variants was assessed by the American College of Medical Genetics guidelines, inheritance pattern, and published evidence. Furthermore, we compared the oligogenic groups and monogenic groups to examine the correlation between variant dosage and severity.

RESULTS

We identified variants in 66.5% cases (111/167) and 15 genes, DUOX2, TSHR, PAX8, TG, TPO, DUOXA2, JAG1, GLIS3, DUOX1, IYD, SLC26A4, SLC5A5, SECISBP2, DIO1, and DIO3. Biallelic variants were identified in 12.6% (21/167), oligogenic in 18.0% (30/167), and monogenic in 35.9% (60/167); however, 68.5% of variants were classified as variant of unknown significance (VUS). Further examinations showed that 3 out of 32 cases with TD (9.4%) had pathogenic variants (2 of TSHR and 1 of TPO), and 8 out of 57 cases with DH (14.0%) (7 of DUOX2, 1 of TG) had pathogenic variants. In addition, TSH levels at the first visit were significantly higher in the oligogenic group than in the monogenic group.

CONCLUSIONS

The detection rate of pathogenic variants in Japanese CH was similar to that previously reported. Moreover, oligogenic cases were likely to be more severe than monogenic cases, suggesting that CH may exhibit a gene dosage effect. Further analysis of VUS pathogenicity is required to clarify the molecular basis of CH.

Genetics of Gland-in-situ or Hypoplastic Congenital Hypothyroidism in Macedonia

Neonatal screening in Macedonia detects congenital hypothyroidism (CH) with an incidence of 1 in 1,585, and more than 50% of cases exhibit a normally located gland-in-situ (GIS). Monogenic mutations causing dyshormonogenesis may underlie GIS CH; additionally, a small proportion of thyroid hypoplasia has a monogenic cause, such as TSHR and PAX8 defects. The genetic architecture of Macedonian CH cases has not previously been studied. We recruited screening-detected, non-syndromic GIS CH or thyroid hypoplasia cases (n = 40) exhibiting a spectrum of biochemical thyroid dysfunction ranging from severe permanent to mild transient CH and including 11 familial cases. Cases were born at term, with birth weight >3,000 g, and thyroid morphologies included goiter (n = 11), thyroid hypoplasia (n = 6), and apparently normal-sized thyroid. A comprehensive, phenotype-driven, Sanger sequencing approach was used to identify genetic mutations underlying CH, by sequentially screening known dyshormonogenesis-associated genes and TSHR in GIS cases and TSHR and PAX8 in cases with thyroid hypoplasia. Potentially pathogenic variants were identified in 14 cases, of which four were definitively causative; we also detected digenic variants in three cases. Seventeen variants (nine novel) were identified in TPO (n = 4), TG (n = 3), TSHR (n = 4), DUOX2 (n = 4), and PAX8 (n = 2). No mutations were detected in DUOXA2, NIS, IYD, and SLC26A7. The relatively low mutation frequency suggests that factors other than recognized monogenic causes (oligogenic variants, environmental factors, or novel genes) may contribute to GIS CH in this region. Future non-hypothesis-driven, next-generation sequencing studies are required to confirm these findings.

Perinatal risk factors for congenital hypothyroidism: A retrospective cohort study performed at a tertiary hospital in China

Congenital hypothyroidism (CH) is one of the most common neonatal endocrine diseases. This retrospective cohort study aimed to identify the potential perinatal risk factors for CH and to differentiate between transient and permanent CH (TCH and PCH, respectively) as well as determine their prevalence in a southeastern Chinese population.This study was based on an 18-year surveillance of a neonatal CH screening program in a large tertiary hospital. A retrospective review of the maternal and neonatal perinatal exposures was conducted.Of the 205,834 newborns screened between 2000 and 2018, 189 were diagnosed with CH (1/1089). Among the 131 CH patients who again underwent thyroid function testing (TFT) after discontinuation of levothyroxine at the age of 3 years, 61 (46.6%) were diagnosed with PCH and 70 (53.4%) were diagnosed with TCH. In the maternal characteristics model, women aged 35 years or older and those who had thyroid disease and/or diabetes mellitus during pregnancy had increased risk of having an offspring with CH (P = .001, .000, and .001, respectively). Significant associations were found with regard to parity and the risk of CH in the offspring (P = .000). In the neonatal characteristics model, infants with female sex, preterm birth, post-term birth, low birth weight, other birth defects, and those born as part of multiple births (P = .011, .034, .001, .000, .000, and .003, respectively) had increased risk of CH. The rate of newborns with other birth defects was higher in the PCH group than that in the TCH group (P = .008), whereas the rate of maternal thyroid disease, newborns with low birth weight, and newborns with preterm birth was higher in the TCH group than that in the PCH group (P = .041, .020, and .013, respectively). The levothyroxine dose (μg/kg/day) at 1 year, 2 years, and 3 years old was significantly lower in the TCH group than that in the PCH group (P = .000, .000, and .000, respectively).Perinatal factors should be considered during the diagnosis and treatment of CH.

The Thyrotropin Receptor Mutation Database Update

The thyrotropin receptor (TSHR) mutation database, consisting of all known TSHR mutations and their clinical characterizations, was established in 1999. The database contents are updated here with the same website (tsh-receptor-mutation-database.org). The new database contains 638 cases of TSHR mutations: 448 cases of gain of function mutations (7 novel mutations and 41 new cases for previously described mutations since its last update in 2012) and 190 cases of loss of function mutations (28 novel mutations and 31 new cases for previously described mutations since its last update in 2012). This database is continuously updated and allows for rapid validation of patient TSHR mutations causing hyper- or hypothyroidism or insensitivity to TSH.

Increased Prevalence of TG and TPO Mutations in Sudanese Children With Congenital Hypothyroidism

CONTEXT

Congenital hypothyroidism (CH) is due to dyshormonogenesis in 10% to 15% of subjects worldwide but accounts for 60% of CH cases in the Sudan.

OBJECTIVE

To investigate the molecular basis of CH in Sudanese families.

DESIGN

Clinical phenotype reporting and serum thyroid hormone measurements. Deoxyribonucelic acid extraction for whole-exome sequencing and Sanger sequencing.

SETTING

University research center.

PATIENTS

Twenty-six Sudanese families with CH.

INTERVENTION

Clinical evaluation, thyroid function tests, genetic sequencing, and analysis. Our samples and information regarding samples from the literature were used to compare TG (thyroglobulin) and TPO (thyroid peroxidase) mutation rates in the Sudanese population with all populations.

RESULTS

Mutations were found in dual-oxidase 1 (DUOX1), dual-oxidase 2 (DUOX2), iodotyrosine deiodinase (IYD), solute-carrier (SLC) 26A4, SLC26A7, SLC5A5, TG, and TPO genes. The molecular basis of the CH in 7 families remains unknown. TG mutations were significantly higher on average in the Sudanese population compared with the average number of TG mutations in other populations (P < 0.05).

CONCLUSIONS

All described mutations occur in domains important for protein structure and function, predicting the CH phenotype. Genotype prediction based on phenotype includes low or undetectable thyroglobulin levels for TG gene mutations and markedly higher thyroglobulin levels for TPO mutations. The reasons for higher incidence of TG gene mutations include gene length and possible positive genetic selection due to endemic iodine deficiency.

Mutation spectrum analysis of 29 causative genes in 43 Chinese patients with congenital hypothyroidism

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder with a genetic origin. The purpose of the present study was to analyze the mutation spectrum of CH patients in China. A targeted next-generation sequencing panel covering all exons of 29 CH-related causative genes was used in 43 Han Chinese patients with CH [11 dysgenesis and 32 glands in situ (GIS)]. The functional impact and pathogenicity of detected variants were analyzed using a comprehensive bioinformatics approach and co-segregation studies. A total of 47 rare non-polymorphic variants in 9 target genes associated with thyroid hormone synthesis (DUOX2, DUOXA2, TPO, TG, SLC26A4 and SLC5A5), thyroid stimulating hormone resistance (TSHR) and central hypothyroidism (PROP1 and TRHR) were identified in 31 patients (31/43, 72%). Of these variants, 8 were novel, including 3 in DUOX2, 2 in TPO, 3 in TSHR and 1 in SLC5A5. Variants were mostly affected by DUOX2, TG, TPO and TSHR. Approximately 44% of the patients (19/43) carried DUOX2 variants. The mutation detection rates in patients with GIS were higher compared with patients with dysgenesis [25/32 (78%) vs. 6/11 (54%)]. Oligogenic mutations were detected in 25.6% of the total cases and 35% of the mutated cases. Genetic basis was ascertained in 13 patients, reaching a diagnosis detection rate of 30%. In conclusion, genetic defects in dyshormonogenesis, mainly in DUOX2, were the main genetic cause of CH in the Chinese population. Oligogenicity is highly involved in CH pathogenesis and may thus be an important factor in common phenotypic variability observed in patients with CH.

High Diagnostic Yield of Targeted Next-Generation Sequencing in a Cohort of Patients With Congenital Hypothyroidism Due to Dyshormonogenesis

OBJECTIVE

To elucidate the molecular cause in a well-characterized cohort of patients with Congenital Hypothyroidism (CH) and Dyshormonogenesis (DH) by using targeted next-generation sequencing (TNGS).

STUDY DESIGN

We studied 19 well-characterized patients diagnosed with CH and DH by targeted NGS including genes involved in thyroid hormone production. The pathogenicity of novel mutations was assessed based on in silico prediction tool results, functional studies when possible, variant location in important protein domains, and a review of the recent literature.

RESULTS

TNGS with variant prioritization and detailed assessment identified likely disease-causing mutations in 10 patients (53%). Monogenic defects most often involved TG, followed by DUOXA2, DUOX2, and NIS and were usually homozygous or compound heterozygous. Our review shows the importance of the detailed phenotypic description of patients and accurate analysis of variants to provide a molecular diagnosis.

CONCLUSIONS

In a clinically well-characterized cohort, TNGS had a diagnostic yield of 53%, in accordance with previous studies using a similar strategy. TG mutations were the most common genetic defect. TNGS identified gene mutations causing DH, thereby providing a rapid and cost-effective genetic diagnosis in patients with CH due to DH.

Genetic analyses in a cohort of Portuguese pediatric patients with congenital hypothyroidism

Background Permanent primary congenital hypothyroidism (CH) can be caused by thyroid dysgenesis or dyshormonogenesis. A molecular genetic study is recommended in dyshormonogenesis, in syndromic hypothyroidism and when there is a family history of CH. The aim of this study was to identify a monogenic etiology for CH in selected individuals from a cohort of primary permanent CH. Methods From an initial cohort of 79 patients with permanent CH (3-19 years), 11 patients were selected for molecular analyses. Nine patients with dyshormonogenesis (normal in-situ gland or goiter) were screened for causative variants, by next-generation sequencing (NGS), in 28 genes known to be responsible for CH. One patient with a family history of CH was screened for the paired-box gene 8 (PAX8) gene and another patient with a syndromic CH was screened for the NKX2-1 gene. Results We found a monogenic basis of disease in eight patients, involving the thyroid peroxidase (TPO) gene (four patients), the thyroglobulin (TG) gene (two patients), and the PAX8 and NKX2-1 genes (one patient each). Two patients were heterozygotes, one harboring a variant in the TG gene and the other in the SLC5A5 gene. In one patient, we found no potential causative variants in any of the 28 genes screened. We described five novel variants: three in the TG gene, one in the NKX2-1 and one in the SLC5A5 gene, all of them classified as pathogenic. Conclusions In eight of the 11 screened patients, a monogenic disease was found. These results highlight the advantage of using an NGS panel and provide further data regarding the molecular basis of CH.

Maternal exposure to PM2.5 may increase the risk of congenital hypothyroidism in the offspring: a national database based study in China

Background

Maternal exposure to air pollution is related to fetal dysplasia. However, the association between maternal exposure to air pollution and the risk of congenital hypothyroidism (CH) in the offspring is largely unknown.

Methods

We conducted a national database based study in China to explore the association between these two parameters. The incidence of CH was collected from October 1, 2014 to October 1, 2015 from the Chinese Maternal and Child Health Surveillance Network. Considering that total period of pregnancy and consequently the total period of particle exposure is approximately 10 months, average exposure levels of PM_2.5, PM₁₀ and Air Quality Index (AQI) were collected from January 1, 2014 to January 1, 2015. Generalized additive model was used to evaluate the association between air pollution and the incidence of CH, and constructing receiver operating characteristic (ROC) curve was used to calculate the cut-off value.

Results

The overall incidence of CH was 4.31 per 10,000 screened newborns in China from October 1, 2014 to October 1, 2015. For every increase of 1 μg/m³ in the PM_2.5 exposure during gestation could increase the risk of CH (adjusted OR = 1.016 per 1 μg/m³ change, 95% CI, 1.001–1.031). But no significant associations were found with regard to PM₁₀ (adjusted OR = 1.009, 95% CI, 0.996–1.018) or AQI (adjusted OR = 1.012, 95% CI,0.998–1.026) and the risk of CH in the offspring. The cut-off value of prenatal PM_2.5 exposure for predicting the risk of CH in the offspring was 61.165 μg/m³.

Conclusions

The present study suggested that maternal exposure to PM_2.5 may exhibit a positive association with increased risk of CH in the offspring. We also proposed a cut-off value of PM_2.5 exposure that might determine reduction in the risk of CH in the offspring in highly polluted areas.

Systematic alanine scanning of PAX8 paired domain reveals functional importance of the N-subdomain

Thyroid-specific transcription factor PAX8 has an indispensable role in the thyroid gland development, which is evidenced by the facts that PAX8/Pax8 mutations cause congenital hypothyroidism in humans and mice. More than 90% of known PAX8 mutations were located in the paired domain, suggesting the central role of the domain in exerting the molecular function. Structure-function relationships of PAX8, as well as other PAX family transcription factors, have never been investigated in a systematic manner. Here, we conducted the first alanine scanning mutagenesis study, in which 132 alanine variants located in the paired domain of PAX8 were created and systematically evaluated in vitro. We found that 76 alanine variants (55%) were loss of function (LOF) variants (defined by <30% activity as compared with wild type PAX8). Importantly, the distribution of LOF variants were skewed, with more frequently observed in the N-subdomain (65% of the alanine variants in the N-subdomain) than in the C-subdomain (45%). Twelve out of 13 alanine variants in residues that have been affected in patients with congenital hypothyroidism were actually LOF, suggesting that the alanine scanning data can be used to evaluate the functional importance of mutated residues. Using our in vitro data, we tested the accuracy of seven computational algorithms for pathogenicity prediction, showing that they are sensitive but not specific to evaluate on the paired domain alanine variants. Collectively, our experiment-based data would help better understand the structure-function relationships of the paired domain, and would provide a unique resource for pathogenicity prediction of future PAX8 variants.

Genetic basis and outcome in a nationwide study of Finnish patients with hypertrophic cardiomyopathy

AIMS

Nationwide large-scale genetic and outcome studies in cohorts with hypertrophic cardiomyopathy (HCM) have not been previously published.

METHODS AND RESULTS

We sequenced 59 cardiomyopathy-associated genes in 382 unrelated Finnish patients with HCM and found 24 pathogenic or likely pathogenic mutations in six genes in 38.2% of patients. Most mutations were located in sarcomere genes (MYBPC3, MYH7, TPM1, and MYL2). Previously reported mutations by our study group (MYBPC3-Gln1061Ter, MYH7-Arg1053Gln, and TPM1-Asp175Asn) and a fourth major mutation MYH7-Val606Met accounted for 28.0% of cases. Mutations in GLA and PRKAG2 were found in three patients. Furthermore, we found 49 variants of unknown significance in 31 genes in 20.4% of cases. During a 6.7 ± 4.2 year follow-up, annual all-cause mortality in 482 index patients and their relatives with HCM was higher than that in the matched Finnish population (1.70 vs. 0.87%; P < 0.001). Sudden cardiac deaths were rare (n = 8). Systolic heart failure (hazard ratio 17.256, 95% confidence interval 3.266-91.170, P = 0.001) and maximal left ventricular wall thickness (hazard ratio 1.223, 95% confidence interval 1.098-1.363, P < 0.001) were independent predictors of HCM-related mortality and life-threatening cardiac events. The patients with a pathogenic or likely pathogenic mutation underwent an implantable cardioverter defibrillator implantation more often than patients without a pathogenic or likely pathogenic mutation (12.9 vs. 3.5%, P < 0.001), but there was no difference in all-cause or HCM-related mortality between the two groups. Mortality due to HCM during 10 year follow-up among the 5.2 million population of Finland was studied from death certificates of the National Registry, showing 269 HCM-related deaths, of which 32% were sudden.

CONCLUSIONS

We identified pathogenic and likely pathogenic mutations in 38% of Finnish patients with HCM. Four major sarcomere mutations accounted for 28% of HCM cases, whereas HCM-related mutations in non-sarcomeric genes were rare. Mortality in patients with HCM exceeded that of the general population. Finally, among 5.2 million Finns, there were at least 27 HCM-related deaths annually.

[Diagnosis and follow-up of patients with congenital hypothyroidism detected by neonatal screening]

The screening program of congenital hypothyroidism (CH) is probably one of the best achievements in paediatrics. Thyroid hormones are essential for brain development and brain maturation that continue through the neonatal period. Hypothyroidism that begins in the first months of life causes irreversible damage to the central nervous system, and is one of the most frequent and preventable causes of mental retardation. As children with congenital hypothyroidism are born with a normal appearance, analytical studies are required to immediately start the appropriate therapy. This article analyses the aims, diagnostic procedures, tests required, aetiology, and differential diagnosis in this disorder. Especially relevant is to perform frequent monitoring to ensure dose adjustments of L-Thyroxine therapy, avoiding infra- or supra-dosing that negatively affects neurosensory functions. Re-evaluation of the aetiology permanent vs transient hypothyroidism is always recommended after 3years of chronological age. The relevance of this screening program should be widely discussed in paediatrics. The main objective is to avoid cerebral damage in these patients, and has been highly successful and economically beneficial. Other aspects are required to optimise patient outcomes, to perform all the controls according to the recommendations and to include, in the near future, the diagnosis of central hypothyroidism. Implementation of this program is necessary to progress in accordance with current scientific knowledge.

Effects of PM2.5 and PM10 on congenital hypothyroidism in Qingdao, China, 2014-2017: a quantitative analysis

BACKGROUND

We aimed to quantify the impact of PM_2.5 and PM₁₀ pollution on congenital hypothyroidism (CH) in Qingdao in the period 2014-2017.

METHODS

A generalized additive mixed model (GAMM) with time-series Poisson regression was conducted to quantify the association between PM_2.5 and PM₁₀ variables in the month when cases of CH were born or in the two preceding the months (lag0, lag1 and lag2) and monthly morbidity of people with CH across different populations.

RESULTS

A total of 480,633 newborns were screened for CH during 2014-2017 in Qingdao, and there were 268 cases of CH diagnosed. The count of days per month for which average concentrations of PM_2.5 and PM₁₀ exceed legal limits were positively associated with monthly CH morbidity at lag1 month among all the populations, and the adjusted relative risks (RRs) with exposure per 10 μg/m³ were close among different populations. However, the number of days per month of PM_2.5 and PM₁₀ concentrations exceeding limits were negatively associated with CH morbidity. Additionally, the RRs of CH increase with worsening air pollution.

CONCLUSIONS

Concentrations of PM_2.5 and PM₁₀ exceeding the legal limits are significantly associated with CH in Qingdao. Moreover, it suggests that sudden and short-term particulate matter pollution events with high levels of particulates exceeding the legal limits may be related to risk of CH.

High frequency of mutations in 'dyshormonogenesis genes' in severe congenital hypothyroidism

OBJECTIVE

Results of the screening of disease causative mutations in congenital hypothyroidism (CH) vary significantly, depending on the sequence strategy, patients' inclusion criteria and bioinformatics. The objective was to study the molecular basis of severe congenital hypothyroidism, using the next generation sequencing (NGS) and the recent guidelines for assessment of sequence variants.

DESIGN

243 patients with CH (TSH levels at neonatal screening or retesting greater than 90 mU/l) and 56 control subjects were included in the study.

METHODS

A custom NGS panel targeting 12 CH causative genes was used for sequencing. The sequence variants were rated according to American College of Medical Genetics and Genomics (ACMG) guidelines.

RESULTS

In total, 48 pathogenic, 7 likely pathogenic and 57 variants of uncertain significance were identified in 92/243 patients (37.9%), while 4 variants of uncertain significance were found in 4/56 control subjects (7.1%). 13.1% (12/92) of the cases showed variants in 'thyroid dysgenesis' (TD) genes: TSHR, n = 6; NKX2-1, n = 2; NKX2-5, n = 1; PAX8, n = 3. The variants in 'dyshormonogenesis' (DH) genes were found in 84.8% (78/92) of cases: TPO, n = 30; DUOX2, n = 24; TG, n = 8; SLC5A5, n = 3; SLC26A4, n = 6; IYD, n = 1. 8 patients showed oligonenic variants. The majority of variants identified in DH genes were monoallelic.

CONCLUSIONS

In contrast to earlier studies demonstrating the predominance of TD in severe CH, the majority of variants identified in our study were in DH genes. A large proportion of monoallelic variants detected among DH genes suggests that non-mendelian mechanisms may play a role in the development of CH.

Molecular analysis of thyroglobulin mutations found in patients with goiter and hypothyroidism

Thyroid dyshormonogenesis due to thyroglobulin (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. Up to now, one hundred seventeen deleterious mutations in the TG gene have been identified and characterized. The purpose of the present study was to identify and characterize new mutations in the TG gene. We report eight patients from seven unrelated families with goiter, hypothyroidism and low levels of serum TG. All patients underwent clinical, biochemical and image evaluation. Sequencing of DNA, genotyping, as well as bioinformatics analysis were performed. Molecular analyses revealed three novel inactivating TG mutations: c.5560G>T [p.E1835*], c.7084G>C [p.A2343P] and c.7093T>C [p.W2346R], and four previously reported mutations: c.378C>A [p.Y107*], c.886C>T [p.R277*], c.1351C>T [p.R432*] and c.7007G>A [p.R2317Q]. Two patients carried homozygous mutations (p.R277*/p.R277*, p.W2346R/p.W2346R), four were compound heterozygous mutations (p.Y107*/p.R277* (two unrelated patients), p.R432*/p.A2343P, p.Y107*/p.R2317Q) and two siblings from another family had a single p.E1835* mutated allele. Additionally, we include the analysis of 48 patients from 31 unrelated families with TG mutations identified in our present and previous studies. Our observation shows that mutations in both TG alleles were found in 27 families (9 as homozygote and 18 as heterozygote compound), whereas in the remaining four families only one mutated allele was detected. The majority of the detected mutations occur in exons 4, 7, 38 and 40. 28 different mutations were identified, 33 of the 96 TG alleles encoded the change p.R277*. In conclusion, our results confirm the genetic heterogeneity of TG defects and the pathophysiological importance of the predicted TG misfolding and therefore thyroid hormone formation as a consequence of truncated TG proteins and/or missense mutations located within its ACHE-like domain.

GENETICS IN ENDOCRINOLOGY: Genetic diagnosis of endocrine diseases by NGS: novel scenarios and unpredictable results and risks

The technological advancements in genetics produced a profound impact on the research and diagnostics of non-communicable diseases. The availability of next-generation sequencing (NGS) allowed the identification of novel candidate genes but also an in-depth modification of the understanding of the architecture of several endocrine diseases. Several different NGS approaches are available allowing the sequencing of several regions of interest or the whole exome or genome (WGS, WES or targeted NGS), with highly variable costs, potentials and limitations that should be clearly known before designing the experiment. Here, we illustrate the NGS scenario, describe the advantages and limitations of the different protocols and review some of the NGS results obtained in different endocrine conditions. We finally give insights on the terminology and requirements for the implementation of NGS in research and diagnostic labs.

Genetics and management of congenital hypothyroidism

Several evidences support a relevant genetic origin for Congenital Hypothyroidism (CH), however familial forms are uncommon. CH can be due to morphogenetic or functional defects and several genes have been originally associated either with thyroid dysgenesis or dyshormonogenesis, with a highly variable expressivity and a frequently incomplete penetrance of the genetic defects. The phenotype-driven genetic analyses rarely yielded positive results in more than 10% of cases, thus raising doubts on the genetic origin of CH. However, more recent unsupervised approaches with systematic Next Generation Sequencing (NGS) analysis revealed the existence of hypomorphic alleles of these candidate genes whose combination can explain a significant portion of CH cases. The co-segregation studies of the hypothyroid phenotype with multiple gene variants in pedigrees confirmed the potential oligogenic origin of CH, which finally represents a suitable explanation for the frequent sporadic occurrence of this disease.

Genetically modified mouse models to investigate thyroid development, function and growth

The thyroid gland produces thyroid hormones (TH), which are essential regulators for growth, development and metabolism. The thyroid is mainly controlled by the thyroid-stimulating hormone (TSH) that binds to its receptor (TSHR) on thyrocytes and mediates its action via different G protein-mediated signaling pathways. TSH primarily activates the G_s-pathway, and at higher concentrations also the G_q/11-pathway, leading to an increase of intracellular cAMP and Ca²⁺, respectively. To date, the physiological importance of other G protein-mediated signaling pathways in thyrocytes is unclear. Congenital hypothyroidism (CH) is defined as the lack of TH at birth. In familial cases, high-throughput sequencing methods have facilitated the identification of novel mutations. Nevertheless, the precise etiology of CH yet remains unraveled in a proportion of cases. Genetically modified mouse models can reveal new pathophysiological mechanisms of thyroid diseases. Here, we will present an overview of genetic mouse models for thyroid diseases, which have provided crucial insights into thyroid gland development, function, and growth with a special focus on TSHR and microRNA signaling.

High-resolution melting analysis (HRM) for mutational screening of Dnajc17 gene in patients affected by thyroid dysgenesis

BACKGROUND

Congenital hypothyroidism is a frequent disease occurring with an incidence of about 1/1500 newborns/year. In about 75% of the cases, CH is caused by alterations in thyroid morphogenesis, defined "thyroid dysgenesis" (TD). TD is generally a sporadic disease but in about 5% of the cases a genetic origin has been demonstrated. Previous studies indicate that Dnajc17 as a candidate modifier gene for hypothyroidism, since it is expressed in the thyroid bud, interacts with NKX2.1 and PAX8 and it has been associated to the hypothyroid phenotype in mice carrying a single Nkx2.1 and Pax8 genes (double heterozygous knock-out).

PURPOSE

The work evaluates the possible involvement of DNAJC17 in the pathogenesis of TD.

METHODS

High-resolution DNA melting analysis (HRM) and direct sequencing have been used to screen for mutations in the DNAJC17 coding sequence in 89 patients with TD.

RESULTS

Two mutations have been identified in the coding sequence of DNAJC17 gene, one in exon 5 (c.350A>C; rs79709714) and one in exon 9 (c.610G>C; rs117485355). The last one is a rare variant, while the rs79709714 is a polymorphism. Both are present in databases and the frequency of the alleles is not different between TD patients and controls.

CONCLUSIONS

DNAJC17 mutations are not frequently present in patients with TD.

Molecular Analysis of Congenital Hypothyroidism in Saudi Arabia: SLC26A7 Mutation Is a Novel Defect in Thyroid Dyshormonogenesis

CONTEXT

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder, affecting one in 3000 to 4000 newborns. Since the introduction of a newborn screening program in 1988, more than 300 cases have been identified. The underlying genetic defects have not been systematically studied.

OBJECTIVE

To identify the mutation spectrum of CH-causing genes.

METHODS

Fifty-five patients from 47 families were studied by next-generation exome sequencing.

RESULTS

Mutations were identified in 52.7% of patients (29 of 55) in the following 11 genes: TG, TPO, DUOX2, SLC26A4, SLC26A7, TSHB, TSHR, NKX2-1, PAX8, CDCA8, and HOXB3. Among 30 patients with thyroid dyshormonogenesis, biallelic TG mutations were found in 12 patients (40%), followed by biallelic mutations in TPO (6.7%), SLC26A7 (6.7%), and DUOX2 (3.3%). Monoallelic SLC26A4 mutations were found in two patients, one of them coexisting with two tandem biallelic deletions in SLC26A7. In 25 patients with thyroid dysgenesis, biallelic mutations in TSHR were found in six patients (24%). Biallelic mutations in TSHB, PAX 8, NKX2-1, or HOXB3 were found once in four different patients. A monoallelic CDCA8 mutation was found in one patient. Most mutations were novel, including three TG, two TSHR, and one each in DUOX2, TPO, SLC26A7, TSHB, NKX2-1, PAX8, CDCA8, and HOXB3. SLC26A7 and HOXB3 were novel genes associated with thyroid dyshormonogenesis and dysgenesis, respectively.

CONCLUSIONS

TG and TSHR mutations are the most common genetic defects in Saudi patients with CH. The prevalence of other disease-causing mutations is low, reflecting the consanguineous nature of the population. SLC26A7 mutations appear to be associated with thyroid dyshormonogenesis.

Risk factors associated with congenital hypothyroidism: a case-control study in southeast Iran

Background and aim

Congenital hypothyroidism (CH) is known as one of the most common preventable cause of mental retardation. This study aimed to determine factors associated with CH in Iran.

Methods

This case-control study was conducted on 160 children under one year old in Zahedan in southeast Iran in 2016. The neonates who were born from March 1, 2015 to March 19, 2016 and had undergone a screening program for CH were the study population. The neonates with serum TSH > 10mIu/L and T4 < 6.5 or TSH > 30 mIu/L were considered as a case group. Each case was individually matched for sex, age at birth and place of residence with three neonates with normal TSH and T4 titers as a control group. Data was gathered using a standard checklist and analyzed using SPSS 20 and statistical tests, such as Chi-square and Fisher’s exact tests. Multivariable logistic regression analysis was also used to identify independent predictors of CH.

Results

About 25 of the 40 patients with CH (62.5%) were male who, in the univariate analysis, the following explanatory factors had no significant association with CH: history of parental consanguinity, type of delivery, weight at birth, height at birth, age of mother, sampling time, nationality, and birth season (p>0.05). Although, multivariate analysis showed no significant association between the studied factors and risk of CH (p>0.05), the likelihood of CH was greater among neonates born to consanguineous parents (AOR: 1.78, 95% CI: 0.82–3.89), those who were born to lower height at birth (AOR: 1.82, 95% CI: 0.85–3.91), neonates born to mothers younger than 18 years (AOR: 2.43, 95% CI: 0.57–10.29) and those who were born in the summer (AOR: 1.76, 95% CI: 0.57–5.44).

Conclusion

None of the studied factors were predictors for CH. Since consanguineous marriages are frequent in the province, and it may be a major contributory factor, future studies should be conducted on the genetic causes.

Mutational Spectrum Analysis of Seven Genes Associated with Thyroid Dyshormonogenesis

OBJECTIVE

Thyroid dyshormonogenesis (DH) is a genetically heterogeneous inherited disorder caused by thyroid hormone synthesis abnormalities. This study aims at comprehensively characterizing the mutation spectrum in Chinese patients with DH.

SUBJECTS AND METHODS

We utilized next-generation sequencing to screen for mutations in seven DH-associated genes (TPO, DUOX2, TG, DUOXA2, SLC26A4, SLC5A5, and IYD) in 21 Chinese Han patients with DH from Xinjiang Province.

RESULTS

Twenty-eight rare nonpolymorphic variants were found in 19 patients (90.5%), including 19, 5, 3, and 1 variants in DUOX2, TG, DUOXA2, and SLC26A4, respectively. Thirteen (62%) patients carried monogenic mutations, and six (28.5%) carried oligogenic mutations. Fifteen (71%) patients carried 2 or more DUOX2 (14) or DUOXA2 (1) variants. The genetic basis of DH in nine (43%) patients harboring biallelic or triallelic pathogenic variants was resolved. Seventeen patients (81%) carried DUOX2 mutations, most commonly p.R1110Q or p.K530X. No correlations were found between DUOX2 mutation types or numbers and clinical phenotypes.

CONCLUSIONS

DUOX2 mutations were the most predominant genetic alterations of DH in the study cohort. Oligogenicity may explain the genetic basis of disease in many DH patients. Functional studies and further clinical studies with larger DH patient cohorts are needed to validate the roles of the mutations identified in this study.