Thyrotropin-stimulating hormone receptor gene analysis in pediatric patients with non-autoimmune subclinical hypothyroidism

Evaluation of the etiology of subclinical hypothyroidism in children

OBJECTIVES

Subclinical hypothyroidism (SH) is defined by normal free triiodothyronine (fT3) and free thyroxine (fT4) levels, elevated thyroid-stimulating hormone levels, and the absence of overt clinical signs of hypothyroidism. The natural course of SH is influenced by the underlying etiology. The purpose of this study was to evaluate the etiologic causes of SH.

METHODS

A total of 135 patients aged 1-18 years, diagnosed with SH by at least two analytical measurements, were included in the study. The anthropometric measurements, demographic characteristics, and laboratory findings of the patients were determined. A comparison was conducted between patients with Hashimoto's thyroiditis and patients with non-autoimmune etiology.

RESULTS

The median age was 9.7 (6.5) years, and 82 of the 135 patients were female. The most prevalent etiology was idiopathic, affecting 39 (28.9 %) patients. This was followed by obesity, which was identified in 21 (15.6 %) patients. Hashimoto's thyroiditis was the third most common cause, accounting for 18 (13.3 %) patients. In patients with Hashimoto's disease, fT4 levels were significantly lower, and the rate of initiation of LT4 treatment was higher than in patients with other etiologies. A heterozygous variation in the TSH receptor (TSHR) gene was detected in six patients.

CONCLUSIONS

In our study, idiopathic cases were the most frequently identified in the etiology of SH. It is important to determine whether there is autoimmune thyroiditis. In cases of idiopathic SH, it is recommended to perform TSHR gene analysis, particularly in the presence of positive family history and newborn screening results. This approach will help elucidate the underlying etiology.

Genetic Analyses in a Cohort of Pediatric Patients with Congenital Hypothyroidism Based on Congenital Hypothyroidism Consensus Guideline

INTRODUCTION

Pathogenic variants in the genes involved in the formation of thyroid tissue and thyroid hormone secretion have been reported to cause congenital hypothyroidism (CH) in some cases. This study aimed to evaluate the clinical and genetic findings of CH cases thought to be due to genetic variants.

METHODS

The study included cases whose genetic analysis was performed in accordance with the Congenital Hypothyroidism: A 2020-2021 Consensus Guidelines Update Guidelines recommendations criteria and analyzed them using the next-generation sequencing panel.

RESULTS

Sixty one Turkish patients from 45 families were included in the study. The overall frequency of variant detection was 37.7% (out of 45 families, 17 had a positive mutation). Segregation was carried out for all families with positive variants. Variants in the TPO gene are the most frequently encountered, and this situation was identified in 10 families. Variants followed this in the TSHR gene in 7 families, variants in the DUOX2 gene in 5 families, and two variants in the TG and NKX2-1 genes in 2 families each, which are six novel variants. Furthermore, among the NKX2-1 cases, one had thyroid involvement only, while the other had chorea only. We did not find differences between cases with detected mutations and mutation-negative cases regarding gender, neonatal/perinatal parameters, initial thyroid function values, and thyroid morphology.

CONCLUSION

In the current investigation, rare new variations in genes known to be related to CH were discovered, adding to the molecular genetic spectrum. When we compare the overall variant detection frequency, the selection criterion for genetic analysis based on the current guidelines is quite rational, considering the benefits and costs, on the other hand, present in new genes awaiting discovery. Also, TSHR mutations are likely to be common and may account for more than 5% of thyroid dysgenesis cases if we include nonfamilial thyroid dysgenesis.

Genetic and Functional Studies of Patients with Thyroid Dyshormonogenesis and Defects in the TSH Receptor (TSHR)

Genetic defects in the TSH receptor (TSHR) can cause poor thyroid differentiation (thyroid dysgenesis) and/or thyroid malfunction (thyroid dyshormonogenesis). The phenotype spectrum is wide: from severe congenital hypothyroidism to mild hyperthyrotropinemia. Over 250 TSHR variants have been published, many uncharacterized in vitro. We aimed to genetically characterize patients with thyroid dyshormonogenesis with TSHR defects and to study in vitro the effect of the genetic variants to establish the genotype-phenotype relationship. Pediatric patients with thyroid dyshormonogenesis (160 patients, Catalan CH neonatal screening program, confirmation TSH range: 18.4-100 mIU/L), were analyzed by a high-throughput gene panel. In vitro studies measuring the TSH-dependent cAMP-response-element activation were performed. Five patients with mild or severe thyroid dyshormonogenesis presented six TSHR variants, two unpublished. Each variant showed a different in vitro functional profile that was totally or partially deleterious. Depending on the genotype, some of the variants showed partial deficiency in both genotypes, whereas others presented a different effect. In conclusion, the percentage of patients with thyroid dyshormonogenesis and candidate variants in TSHR is 3.13%. Our in vitro studies contributed to the confirmation of the pathogenicity of the variants and highlighted the importance of studying the effect of the patient's genotype for a correct diagnostic confirmation.

TSHR Variant Screening and Phenotype Analysis in 367 Chinese Patients With Congenital Hypothyroidism

Background

Genetic defects in the human thyroid-stimulating hormone (TSH) receptor (TSHR) gene can cause congenital hypothyroidism (CH). However, the biological functions and comprehensive genotype-phenotype relationships for most TSHR variants associated with CH remain unexplored. We aimed to identify TSHR variants in Chinese patients with CH, analyze the functions of the variants, and explore the relationships between TSHR genotypes and clinical phenotypes.

Methods

In total, 367 patients with CH were recruited for TSHR variant screening using whole-exome sequencing. The effects of the variants were evaluated by in-silico programs such as SIFT and polyphen2. Furthermore, these variants were transfected into 293T cells to detect their Gs/cyclic AMP and Gq/11 signaling activity.

Results

Among the 367 patients with CH, 17 TSHR variants, including three novel variants, were identified in 45 patients, and 18 patients carried biallelic TSHR variants. In vitro experiments showed that 10 variants were associated with Gs/cyclic AMP and Gq/11 signaling pathway impairment to varying degrees. Patients with TSHR biallelic variants had lower serum TSH levels and higher free triiodothyronine and thyroxine levels at diagnosis than those with DUOX2 biallelic variants.

Conclusions

We found a high frequency of TSHR variants in Chinese patients with CH (12.3%), and 4.9% of cases were caused by TSHR biallelic variants. Ten variants were identified as loss-of-function variants. The data suggest that the clinical phenotype of CH patients caused by TSHR biallelic variants is relatively mild. Our study expands the TSHR variant spectrum and provides further evidence for the elucidation of the genetic etiology of CH.

[Pathogenic TSHR variants in children with thyroid dysgenesis]

BACKGROUND

Loss-of-function mutations in the TSH receptor gene (TSHR) (NP_000360.2) are the potential causes of thyroid dysgenesis in patients with congenital hypothyroidism. Heterozygous variants of the TSHR gene lead to partial resistance to TSH, homozygous and compound heterozygous variants have been shown to cause CH due to thyroid hypoplasia or TSH resistance. Recently more and more articles in this field have appeared in the international literature sources, while local publications are limited. The studies are necessary to understand the etiology, pathogenesis of the disease, to improve the management of these patients.

AIM

To assess the frequency of incidence of pathogenic variants of the TSHR gene in children with CH due to thyroid dysgenesis. To study inheritance and phenotypic patterns of CH in families.

MATERIALS AND METHODS

In this single-center interventional one-stage non-comparative study a group of CH patients was examined. The patients underwent neck ultrasound and radionuclide imaging. The examination was performed 14 days after hormone replacement therapy suspension or prior to its initiation. The structure of thyroid dysgenesis was estimated, genetic testing for mutations in the TSHR gene was performed using the NGS method.

RESULTS

The study included 95 children with primary CH (75 girls; 20 boys). The patients' median age at the time of examination was 6.2 years [4.5; 8.9], the median level of neonatal TSH was 157.5 mU/l [60.9; 257.2]. Ectopic thyroid was found in 52% of children, aplasia in 36%, hypoplasia and hemiagenesis in 10% and 2%, respectively. In 5.4% of cases (in 5 out of 95 patients), different variants of the TSH gene were detected. Two children had heterozygous p.R450H and p.D487N variants in TSHR gene, two patients was homozygous for the p.S49Afs * 9 variant, one child had compound heterozygous variants (p.A485D and p.R450H). According to ultrasound imaging, all patients had thyroid hypoplasia of varying severity. Three children underwent thyroid scintigraphy, which revealed decreased 99mТc pertechnetate uptake (0.3-0.9%).

CONCLUSION

In our study, the incidence of different variants in the TSHR gene in children with CH was 5.3%. Our analysis uncovered two previously undescribed variants. Genetic testing may be able to help with making the diagnosis, patient's management, 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.

Subclinical hypothyroidism in children: updates for pediatricians

Subclinical hypothyroidism (SH) is defined as serum thyroid-stimulating hormone (TSH) above the upper limit of the reference range in the presence of normal free T4 concentrations. Depending on the degree of TSH elevation, SH could be defined as mild (TSH, 4.5-10 mIU/L) or severe (TSH>10 mIU/L). While there is a general consensus to treat children with serum TSH levels above 10 mU/L, the management of the mild form is uncertain and should be individualized. In this mini-review, we present a brief review of SH in children based on extensive literature review and long-standing clinical experience. This review provides the prevalence, causes, clinical presentation, consequences, investigation, and up-to-date therapeutic approach of SH in children. Generally, the purpose of the review is to provide pediatricians with an update of this common and continuously evolving condition.

Genetics of primary congenital hypothyroidism-a review

PURPOSE

Congenital primary hypothyroidism (CH) is a state of inadequate thyroid hormone production detected at birth, caused either by absent, underdeveloped or ectopic thyroid gland (dysgenesis), or by defected thyroid hormone biosynthesis (dyshormonogenesis). A genetic component has been identified in many cases of CH. This review summarizes the clinical and biochemical features of the genetic causes of primary CH.

METHODS

A literature review was conducted of gene defects causing congenital hypothyroidism.

RESULTS

Mutations in five genes have predominantly been implicated in thyroid dysgenesis (TSHR, FOXE1, NKX2-1, PAX8, and NKX2-5), the primary cause of CH (85%), and mutations in seven genes in thyroid dyshormonogenesis (SLC5A5, TPO, DUOX2, DUOXA2, SLC6A4, Tg, and DEHAL1). These genes encode for proteins that regulate genes expressed during the differentiation of the thyroid, such as TPO and Tg genes, or genes that regulate iodide organification, thyroglobulin synthesis, iodide transport, and iodotyrosine deiodination. Besides thyroid dysgenesis and dyshormonogenesis, additional causes of congenital hypothyroidism, such as iodothyronine transporter defects and resistance to thyroid hormones, have also been associated with genetic mutations.

CONCLUSION

The identification of the underlying genetic defects of CH is important for genetic counseling of families with an affected member, for identifying additional clinical characteristics or the risk for thyroid neoplasia and for diagnostic and management purposes.

Sensitive Sequencing Analysis Suggests Thyrotropin Receptor and Guanine Nucleotide-Binding Protein G Subunit Alpha as Sole Driver Mutations in Hot Thyroid Nodules

Background: Constitutively activating mutations in the thyrotropin receptor (TSHR) and the guanine nucleotide-binding protein G subunit alpha (GNAS) are the primary cause of hot thyroid nodules (HTNs). The reported prevalence of TSHR and GNAS mutations in HTNs varies. Previous studies show TSHR mutations in 8-82% of HTNs and GNAS mutations in 8-75% of HTNs. With sensitive and comprehensive targeted next-generation sequencing (tNGS), we re-evaluated the prevalence of TSHR and GNAS mutations in HTNs. Methods: Samples from three previous studies found to be TSHR and GNAS mutation negative were selected and re-evaluated using high-resolution melting (HRM) PCR. Remaining mutation negative samples were further reanalyzed by tNGS with a sequencing depth between 3000 × and 10,000 × . Our tNGS panel covered the entire TSHR coding sequence along with mutation hot spots in GNAS. Sequencing reads were aligned to reference and variants were called using Torrent Suite software v5.8. Results: In total, 154 of 182 previously mutation negative HTNs were positive for TSHR or GNAS mutations, resulting in an 85% prevalence of TSHR and GNAS mutations in HTNs, 79% and 6%, respectively. In a subset of 25 HTNs with multiple samples per nodule, and analyzed by tNGS at high sequencing depth, TSHR mutations were detected in 23 (92%) HTNs and 1 GNAS mutation was detected in 1 (4%) HTN, 96% mutation positive HTNs in this subset. Conclusions: Owing to the higher sensitivity of tNGS as compared with denaturing gradient gel electrophoresis and HRM-PCR, TSHR or GNAS mutations could be detected in 85% of HTNs. The detection of TSHR and GNAS mutations occurred in 96% of HTNs in a sample set with multiple samples per nodule analyzed by tNGS. Taken together with the fact that no other driver mutations could be identified by whole exome sequencing, our study strongly supports the hypothesis that TSHR and GNAS mutations are the main somatic mutations leading to HTNs.

Levothyroxine and subclinical hypothyroidism in patients with recurrent pregnancy loss

PROBLEM

The association between subclinical hypothyroidism (SCH) and recurrent pregnancy loss (RPL) remains unclear. We evaluated whether SCH affects subsequent live births and whether levothyroxine is effective in improving the live birth rate in patients with RPL.

METHOD OF STUDY

This observational cohort study included 1418 pregnancies of 1014 patients with a history of 2 or more pregnancy losses, who were euthyroid or had hypothyroidism, and had at least one subsequent pregnancy outcome. Some patients with SCH, as defined as a TSH >2.5 mIU/L, were treated with levothyroxine, and these comprised the levothyroxine group. The prevalence of SCH, subsequent live birth rates per patient and per pregnancy were compared among patients with SCH treated with and without levothyroxine and patients with euthyroid.

RESULTS

The prevalence of SCH was 14.4%. Subsequent live birth rates were 75.0% for the levothyroxine group, 68.6% for the untreated SCH group, and 70.1% for the euthyroid group. After excluding miscarriages with abnormal karyotypes, live birth rates were 89.2%, 90.0%, and 91.1%. The adjusted odds ratio (95%CI) was 0.95 (0.23-3.83) after controlling covariables when comparing SCH patients with and without treatment. The live birth rates per pregnancy were 93.1%, 85.7%, and 90.9%, respectively. The adjusted OR was 0.95 (0.23-3.83).

CONCLUSION

Levothyroxine has no effect on improving the live birth rate in patients with RPL associated with SCH. Treatment in patients with RPL and SCH raised TSH levels (2.5-10mIU/L) might not be beneficial in improving the live birth rate.

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.

Mild Hypothyroidism in Childhood: Who, When, and How Should Be Treated?

Mild hypothyroidism, also known as subclinical hypothyroidism (SH), is biochemically defined as serum TSH levels above the upper limit of the reference range, in the presence of normal serum concentrations of total T4 and free T4 (FT4). In the neonatal period, mild hypothyroidism can be defined by the presence of a TSH value between 6 and 20 mIU/L and normal FT4 levels. After the neonatal period, SH can be defined mild if TSH ranges between 4.5 and 10 mIU/L. The management of mild hypothyroidism in childhood is challenging. The major concern is to establish whether this condition should always be considered an expression of mild thyroid dysfunction. Indeed, the effects of untreated mild hypothyroidism are still not completely defined. In the neonatal period, concern exists about neurocognitive outcome; in children, although there is no clear evidence of alterations in growth or neurocognitive development, subtle cardiovascular abnormalities have been documented. Therefore, there is still uncertainty about the need of treatment across all ages, and the management should be based on the age of the child, the etiology, and the degree of TSH elevation, as well as on other patient factors. This review updates current evidences on diagnosis and management of mild hypothyroidism in childhood.

Thyrotropin receptor, still much to be learned from the patients

In the absence of crystal available for the full-length thyrotropin receptor, knowledge of its structure and functioning has benefitted from the identification and characterization of mutations in patients with various thyroid dysfunctions. The characterization of activating mutations has contributed to the elaboration of a model involving the extracellular domain of the receptor as an inverse tethered agonist which, upon binding of the ligand, relieves the transmembrane domain from an inhibiting interaction and activates it. The models derived from comparisons with other receptors, enriched with the information provided by the study of mutations, have proven useful for the design of small-molecule agonists and antagonists that may be used in the future to treat thyroid dysfunctions. In this review, extrathyroidal expression of the thyrotropin receptor is described, the role of which is still poorly defined.

Generation and characterization of a hypothyroidism rat model with truncated thyroid stimulating hormone receptor

Thyroid stimulating hormone receptor (TSHR), a G-protein-coupled receptor, is important for thyroid development and growth. In several cases, frameshift and/or nonsense mutations in TSHR were found in the patients with congenital hypothyroidism (CH), however they have not been functionally studied in an animal model. In the present work, we generated a unique Tshr Df/Df rat model that recapitulates the phenotypes in TSHR Y444X patient by CRISPR/Cas genome editing technology. In this rat model, TSHR is truncated at the second transmembrane domain, leading to CH phenotypes as what was observed in the patients, including dwarf, thyroid aplasia, infertility, TSH resistant as well as low serum thyroid hormone levels. The phenotypes can be reversed, at least partially, by levothyroxine (L-T4) treatment after weaning. The thyroid development is severely impaired in the Tshr Df/Df rats due to the suppression of the thyroid specific genes, i.e., thyroperoxidase (Tpo), thyroglobulin (Tg) and sodium iodide symporter (Nis), at both mRNA and protein levels. In conclusion, the Tshr Df/Df rat serves as a brand new genetic model to study CH in human, and will greatly help to shed light into the development of terminal organs that are sensitive to thyroid hormones.

Association between monoallelic TSHR mutations and congenital hypothyroidism: a statistical approach

OBJECTIVE

Biallelic TSHR mutations cause congenital hypothyroidism (CH). Serum TSH levels of monoallelic mutation carriers range from normal to mildly elevated, and thus the size of its effect remains unclear. The objectives were to examine the association between monoallelic TSHR mutations and positivity at newborn screening (NBS) for CH, and to test whether the association was modified by another genetic factor.

SUBJECTS AND METHODS

We enrolled 395 patients that had a positive result in NBS and sequenced TSHR. Monoallelic TSHR mutation carriers were further sequenced for DUOX2. Molecular functions of the mutations were verified in vitro. The frequency of the mutations in the study subjects was compared with a theoretical value in the Japanese general population. Odds ratio (OR) for NBS positivity associated with the mutation was calculated. Using Bayes' theorem, we estimated a posterior probability of NBS positivity given the mutation.

RESULTS

Twenty-six monoallelic TSHR mutation carriers were found. Four out of the 26 also had a monoallelic DUOX2 mutation (double heterozygotes). The frequencies of monoallelic TSHR mutation carriers (6.6%) and double heterozygotes (1.0%) were significantly higher than those in the general population (0.58% and 0.0087%, respectively). OR for NBS positivity of having a monoallelic TSHR mutation or being a double heterozygote was 12.0 or 117.9, respectively. Posterior probability of NBS positivity was 0.38% in monoallelic TSHR mutation carriers and 3.8% in double heterozygotes.

CONCLUSIONS

Monoallelic TSHR mutations are significantly associated with NBS positivity, and the association is further strengthened by the coexistence of monoallelic DUOX2 mutations.

Mild TSH resistance: Clinical and hormonal features in childhood and adulthood

OBJECTIVE

Mutations in TSH receptor (TSHR) are associated with TSH resistance, a genetic defect characterized by a heterogeneous phenotype ranging from severe hypothyroidism to subclinical hypothyroidism (SCH). We assessed the clinical and hormonal pattern of TSHR variants in a series of pediatric patients, and the long-term outcome of growth, biochemical measurements of metabolism, and neuropsychological functions in TSHR mutations carriers.

DESIGN

Observational, retrospective study.

PATIENTS

Thirty four children (age 7 days to 11 years) and 18 adult carriers of TSHR variants.

MEASUREMENTS

The TSHR gene was sequenced by PCR-amplified direct sequencing in 111 pediatric patients with slight to moderate elevation of TSH and normal FT4 levels. The study focused on the: auxological and biochemical parameters, thyroid ultrasound, bone age, bone mineral density (BMD), and intellectual outcome (IQ) were collected during the long follow-up (1-15 years).

RESULTS

Seventeen different TSHR variants (eight novel) were identified in 34 of the 111 pediatric patients, with a high prevalence of familial cases (27/34). Neonatal screening for congenital hypothyroidism was positive in half of the TSHR carriers. Growth, IQ, BMD, and biochemical parameters were normal in all subjects. Twenty patients received L-T4 replacement therapy, in all cases before genetic analysis. After re-evaluation, six patients resumed L-T4 therapy: they were compound heterozygous, or single heterozygous and with associated conditions at risk of thyroid impairment (SGA). No adults presented clinical features consistent with impaired thyroid function.

CONCLUSIONS

Children carriers of TSHR variants, regardless of L-T4 treatment, show regular growth and neuropsychological development, with no evident biochemical and US alterations.

Subclinical hypothyroidism in paediatric population treated with levothyroxine: a real-world study on 2001-2014 Italian administrative data

OBJECTIVE

To estimate the prevalence of subclinical hypothyroidism (SH) among children, by using levothyroxine low dosage as disease proxy, and to describe prescription pattern.

DESIGN

An historical cohort study was performed through administrative databases of 12 Italian Local Health Units covering 3,079,141 inhabitants. A cohort of children (aged 0-13 years) was selected in the period 2001-2014. A subgroup of new users (aged 0-9 years) was identified and followed up for 5 years.

METHODS

The prevalence was provided as mean value of the whole period, as annual trend, by patient gender and age. Demographic details, information on levothyroxine dosage, comorbidities and co-medications were provided. Therapy duration and medication persistence were evaluated among new users.

RESULTS

644 children treated with levothyroxine low dosage was selected, with a mean annual prevalence of 0.20 per 1000 children. The temporal trend of prevalence was stable, with a slight reduction in the 2005-2008. Prevalence by age showed an increase after 10 years. Patients were treated with an average annual dose of 4290 µg/year and 66.9% of children were affected by comorbidities. Among 197 new users, 62.9% received therapy only for one year, whereas out of those treated two or more years, 89.0% resulted persistent to the therapy.

CONCLUSIONS

This study provides real-world epidemiology of SH among children, and it depicts the clinical and therapeutic characteristics of these subjects. Its findings showed that the SH treatment of this disorder was widely variable, also due to lack of evidence concerning paediatric population.

Disorders of thyroid morphogenesis

Developmental anomalies of the thyroid gland, defined as thyroid dysgenesis, underlie the majority of cases of congenital hypothyroidism. Thyroid dysgenesis is predominantly a sporadic disorder although a reported familial enrichment, variation of incidence by ethnicity and the monogenic defects associated mainly with athyreosis or orthotopic thyroid hypoplasia, suggest a genetic contribution. Of note, the most common developmental anomaly, thyroid ectopy, remains unexplained. Ectopy may result from multiple genetic or epigenetic variants in the germline and/or at the somatic level. This review provides a brief overview of the monogenic defects in candidate genes that have been identified so far and of the syndromes which are known to be associated with thyroid dysgenesis.

Resistance to thyrotropin

Resistance to thyrotropin (RTSH) is broadly defined as reduced sensitivity of thyroid follicle cells to stimulation by biologically active TSH due to genetic defects. Affected individuals have elevated serum TSH in the absence of goiter, with the severity ranging from nongoitrous isolated hyperthyrotropinemia to severe congenital hypothyroidism with thyroid hypoplasia. Conceptually, defects leading to RTSH impair both aspects of TSH-mediated action, namely thyroid hormone synthesis and gland growth. These include inactivating mutations in the genes encoding the TSH receptor and the PAX8 transcription factor. A common third cause has been genetically mapped to a locus on chromosome 15, but the underlying pathophysiology has not yet been elucidated. This review provides a succinct overview of currently defined causes of nonsyndromic RTSH, their differential diagnoses (autoimmune; partial iodine organification defects; syndromic forms of RTSH) and implications for the clinical approach to patients with RTSH.

Subclinical hypothyroidism in childhood - current knowledge and open issues

Subclinical hypothyroidism is defined as serum levels of TSH above the upper limit of the reference range, in the presence of normal concentrations of total T₄ or free T₄. This biochemical profile might be an indication of mild hypothyroidism, with a potential increased risk of metabolic abnormalities and cardiovascular disease recorded among adults. Whether subclinical hypothyroidism results in adverse health outcomes among children is a matter of debate and so management of this condition remains challenging. Mild forms of untreated subclinical hypothyroidism do not seem to be associated with impairments in growth, bone health or neurocognitive outcome. However, ongoing scientific investigations have highlighted the presence of subtle proatherogenic abnormalities among children with modest elevations in their TSH levels. Although current findings are insufficient to recommend levothyroxine treatment for all children with mild asymptomatic forms of subclinical hypothyroidism, they highlight the potential need for assessment of cardiovascular risk among children with this condition. Increased understanding of the early metabolic risk factors associated with subclinical hypothyroidism in childhood will help to improve the management of affected individuals.

Next-generation sequencing analysis of TSHR in 384 Chinese subclinical congenital hypothyroidism (CH) and CH patients

BACKGROUND

Defects in the human TSHR gene are reported to be one of the causes of CH due to thyroid dysgenesis, the purpose of this study was to examine the TSHR mutation spectrum and prevalence in congenital hypothyroidism (CH) and subclinical congenital hypothyroidism (SCH) patients in the Guangxi Zhuang Autonomous Region of China and to evaluate the genotype-phenotype correlations.

METHODS

Blood samples were collected from 384 patients including 240 CH and 144 SCH patients in Guangxi, China. Genomic DNA was extracted from peripheral blood leukocytes. All exons of the 11 known CH associated genes including TSHR together with their exon-intron boundaries were screened by next-generation sequencing (NGS).

RESULTS

NGS analysis of TSHR revealed nine different variants in ten individuals. Six (4.2%) of 144 patients with SCH were found to harbor monoallelic TSHR variants. Four (1.6%) of 240 patients with CH harbored TSHR variants combined with another monoallelic mutation in either DUOX2 or TG gene. The present study identified five novel variants c.1838A>G (p.Y613C), c.1576G>A (p.A526T), c.2087T>G (p.F696C), c.1631G>A (p.G544E) and c.2051C>A (p.A684D) in TSHR, seven known pathogenic variants c.1349G>A (p.R450H), c.326G>A (p.R109Q), c.2066T>G (p.V689G) and c.2272G>A (p.E758K) in TSHR, IVS3+2T>G in TG, and c.1588A>T (p.K530X) and c.2635G>A (p.E879K) in DUOX2. The previously reported hotspot mutation p.R450H was found in only one SCH patient.

CONCLUSION

The prevalence of TSHR mutations was 1.6% in CH patients and 4.2% in SCH patients in Guangxi Zhuang Autonomous Region of China. Monoallelic TSHR pathogenic variants were associated with SCH, while TSHR pathogenic variants combined with monoallelic mutations in DUOX2 or TG gene might contribute to CH. Our study expands the TSHR mutation spectrum and provides the best estimation of mutation rate for SCH and CH patients in this Chinese population.

Biochemical, radiological, and genetic characterization of congenital hypothyroidism in Abu Dhabi, United Arab Emirates

BACKGROUND

Congenital hypothyroidism (CH) is caused by thyroid gland (TG) dysgenesis or inadequate thyroid hormone biosynthesis in a structurally normal gland. Different etiologies are known to be associated with various clinical, biochemical and imaging markers and a subset of cases have an underlying genetic basis. Despite the presence of neonatal screening programs in the UAE, there is a lack of data on the disease etiology in the area. We aim to study the etiology of CH in our center and examine its relationship with the clinical, biochemical, genetic and radiological features.

METHODS

Patients with CH who were followed in our center between 2011 and 2014 are enrolled in the study. Data collected included gender, gestational age, history of CH in a first-degree relative, initial thyroid stimulating hormone (TSH) and thyroxine (T4) levels, imaging findings, associated disease/malformation and treatment details. Selected patients with associated systemic disease or familial CH underwent genetic testing.

RESULTS

Sixty-five patients were enrolled. Ten patients underwent genetic study: seven patients with associated congenital disease/malformation, one with a sibling and two with cousins with CH. Forty-nine subjects had technetium99 and/or ultrasound scans. Dyshormonogenesis was diagnosed in two-thirds of the patients. Three patients of 10 tested had likely causative genetic mutations; two homozygous thyroid peroxidase (TPO) and one heterozygous thyroid stimulating hormone receptor (TSHR) missense mutations.

CONCLUSIONS

Dyshormonogenesis is the commonest etiology in CH in the studied group. It is expected that genetic mutations are more prevalent in our region due to the nature of the CH etiology and the rate of high consanguinity rate.

Subclinical hypothyroidism in children

NEED AND PURPOSE OF REVIEW

Subclinical hypothyroidism is a biochemical diagnosis characterized by raised thyroid stimulating hormone and normal free T4, without clinical features of hypothyroidism. This review analyzes the current evidence to arrive at a consensus and algorithm to manage this condition.

METHODS

We searched Pubmed, Cochrane and Embase for articles published between 1990 to 2014, and identified 13 relevant articles dealing with pediatric subclinical hypothyroidism which were suitable to include in our review.

CONCLUSIONS

Subclinical hypothyroidism is often a benign problem which requires expectant management with periodic monitoring of thyroid function tests and natural progression to overt hypothyroidism occur lot less frequently than expected. There is a paucity of robust randomized intervention studies, especially studies focusing on clinical outcomes. Thyroid replacement therapy is not justified in children with subclinical hypothyroidism when Thyroid stimulating hormone is <10 mIU/L. The main risk factors for progression to overt hypothyroidism are female sex, goiter, family history of thyroid disorder, strongly positive thyroid peroxidase antibodies and symptoms suggesting hypothyroidism. An algorithm for managing this condition is suggested.

Heterogeneous phenotype in children affected by non-autoimmune hypothyroidism: an update

BACKGROUND

In the last decades, a higher incidence of congenital hypothyroidism (CH) has been recorded in Italy (1:1940) and worldwide, mainly due to the shift to lower screening TSH cutoffs. Although CH can also be caused by dysgenetic defects, most CH cases have recently been found to be more frequently associated with functional defects of an in situ thyroid gland. Although the clinical phenotype is milder with high prevalence of transient forms, some cases eventually prove to be permanent.

RESULTS

Possible explanations of the raised incidence of CH are ethnic modifications of the screened population and the increasing incidence of preterm birth and multiple pregnancies. These findings are important in terms of public health and standardization of screening programmes for special at-risk categories such as preterms, acutely ill term neonates, low birth weight and very low birth weight infants, and newborns with specific drug exposure. Other environmental factors have contributed to the increased incidence of hypothyroidism, including thyroid disrupting chemicals, iodine supply (excess/deficiency), and drugs interfering with thyroid function. Finally, an increased prevalence of hypothyroidism has been documented in obese children and patients with syndromic forms (Williams, Down, Turner, pseudohypoparathyroidism). The clinical and molecular phenotype of patients with CH will be better defined thanks to novel genetic approach based on the systematic analysis of a panel of genes (TSHR, DUOX2, DUOXA, TPO, PDS, TG, NKX2.1, JAG1, GLIS3, FOXE1, PAX-8).

CONCLUSIONS

This review summarizes significant advances in the epidemiology and aetiology of non-autoimmune hypothyroidism, with a focus on thyroid dysfunction in preterm infants.

Functional characterization of the novel sequence variant p.S304R in the hinge region of TSHR in a congenital hypothyroidism patients and analogy with other formerly known mutations of this gene portion

CONTEXT

Thyroid dysgenesis may be associated with loss-of-function mutations in the thyrotropin receptor (TSHR) gene.

OBJECTIVES

The aim of this study was to characterize a novel TSHR gene variant found in one patient harboring congenital hypothyroidism (CH) from a cohort of patients with various types of thyroid defects.

MATERIALS AND METHODS

This cross-sectional cohort study involved 118 patients with CH and their family members, including 45 with familial and 73 with sporadic diseases. The thyroid gland was normal in 23 patients, 25 patients had hypoplasia, 25 hemithyroid agenesis, 21 had athyreosis, and 21 had ectopy. Genomic DNA was extracted, and 10 exons of the TSHR gene were amplified and sequenced. Mutations in other candidate genes were investigated. Ortholog alignment was performed, and TSHR functional assays were evaluated.

RESULTS

We identified one previously unknown missense variation in the hinge region (HinR) of the TSHR gene (p.S304R) in one patient with thyroid hypoplasia. This variant is conserved in our ortholog alignment. However, the p.S304R TSHR variant presented a normal glycosylation pattern and signal transduction activity in functional analysis.

CONCLUSION

We report the ocurrence of a novel nonsynonymous substitution in the HinR of the large N-terminal extracellular domain of the TSHR gene in a patient with thyroid hypoplasia. In contrast with four others in whom TSHR mutations of the hinge portion were previously identified, the p.S304R TSHR variation neither affected TSH binding nor cAMP pathway activation. This TSHR gene variant was documented in a CH patient, but the current data do not support its role in the clinical phenotype.

Long-term outcome of loss-of-function mutations in thyrotropin receptor gene

BACKGROUND

Loss-of-function mutations in the thyrotropin receptor (TSHR) gene lead to resistance to TSH (RTSH) presenting with either congenital hypothyroidism (CH) or subclinical hypothyroidism (SCH). Despite several reports of patients with TSHR mutations, data on the long-term outcome of this condition are limited, and no consensus exists on the need for hormone replacement therapy. The aim of the present study was to assess the long-term outcome in children and adolescents with RTSH due to TSHR mutations.

METHODS

The TSHR gene was sequenced in 94 subjects (aged 3 days-21 years) with either nonautoimmune SCH or CH with RTSH.

RESULTS

Twenty-seven subjects (29%) carried mutations in TSHR. Fifteen infants were identified by neonatal screening, and the other 79 patients were detected in the process of testing for various other conditions or because of family occurrence of thyroid test abnormalities. Six different mutations were identified: c.484C>G (p.P162A), c.202C>T (p.P68S), c.790C>T (p.P264S), c.269A>C (p.Q90P), c.1957C>G (p.L653V), and c.1347C>T (p.R450C). Twelve subjects were homozygous, three were compound heterozygous, and 12 were heterozygous. Mean serum TSH levels at diagnosis and at last visit were significantly higher in patients with TSHR mutations than in those without mutations (29.04 vs. 14.15, p=0.002; 31.73 vs. 6.19, p<0.0001, respectively). Homozygous patients had a more severe phenotype (TSH 53.6 vs. 9.24, p<0.0001). Mean serum free thyroxine (fT4) levels at the last visit were significantly lower than at the first visit in the homozygous individuals (p=0.05) for a follow-up period of as long as 11 years. Heterozygous subjects had only mild hyperthyrotropinemia with stable TSH levels. However, homozygous subjects showed a trend toward increased TSH and decreased fT4 with time.

CONCLUSION

SCH in heterozygotes with TSHR mutations is a stable compensated condition with an appropriately adjusted set point for pituitary-thyroid feedback that does not require replacement therapy. However, homozygous subjects, with incompletely compensated SCH, show reduced fT4 levels over time and may require levothyroxine treatment. Replacement therapy should be considered on an individual basis, and long-term follow up is recommended.

Treatment with thyroid hormone

Thyroid hormone deficiency can have important repercussions. Treatment with thyroid hormone in replacement doses is essential in patients with hypothyroidism. In this review, we critically discuss the thyroid hormone formulations that are available and approaches to correct replacement therapy with thyroid hormone in primary and central hypothyroidism in different periods of life such as pregnancy, birth, infancy, childhood, and adolescence as well as in adult patients, the elderly, and in patients with comorbidities. Despite the frequent and long term use of l-T4, several studies have documented frequent under- and overtreatment during replacement therapy in hypothyroid patients. We assess the factors determining l-T4 requirements (sex, age, gender, menstrual status, body weight, and lean body mass), the major causes of failure to achieve optimal serum TSH levels in undertreated patients (poor patient compliance, timing of l-T4 administration, interferences with absorption, gastrointestinal diseases, and drugs), and the adverse consequences of unintentional TSH suppression in overtreated patients. Opinions differ regarding the treatment of mild thyroid hormone deficiency, and we examine the recent evidence favoring treatment of this condition. New data suggesting that combined therapy with T3 and T4 could be indicated in some patients with hypothyroidism are assessed, and the indications for TSH suppression with l-T4 in patients with euthyroid multinodular goiter and in those with differentiated thyroid cancer are reviewed. Lastly, we address the potential use of thyroid hormones or their analogs in obese patients and in severe cardiac diseases, dyslipidemia, and nonthyroidal illnesses.

2014 European thyroid association guidelines for the management of subclinical hypothyroidism in pregnancy and in children

This guideline has been produced as the official statement of the European Thyroid Association guideline committee. Subclinical hypothyroidism (SCH) in pregnancy is defined as a thyroid-stimulating hormone (TSH) level above the pregnancy-related reference range with a normal serum thyroxine concentration. Isolated hypothyroxinaemia (defined as a thyroxine level below the 2.5th centile of the pregnancy-related reference range with a normal TSH level) is also recognized in pregnancy. In the majority of SCH the cause is autoimmune thyroiditis but may also be due to iodine deficiency. The cause of isolated hypothyroxinaemia is usually not apparent, but iodine deficiency may be a factor. SCH and isolated hypothyroxinaemia are both associated with adverse obstetric outcomes. Levothyroxine therapy may ameliorate some of these with SCH but not in isolated hypothyroxinaemia. SCH and isolated hypothyroxinaemia are both associated with neuro-intellectual impairment of the child, but there is no evidence that maternal levothyroxine therapy improves this outcome. Targeted antenatal screening for thyroid function will miss a substantial percentage of women with thyroid dysfunction. In children SCH (serum TSH concentration >5.5-10 mU/l) normalizes in >70% and persists in the majority of the remaining patients over the subsequent 5 years, but rarely worsens. There is a lack of studies examining the impact of SCH on the neuropsychological development of children under the age of 3 years. In older children, the evidence for an association between SCH and impaired neuropsychological development is inconsistent. Good quality studies examining the effect of treatment of SCH in children are lacking.

Genetics of normal and abnormal thyroid development in humans

The most frequent cause of congenital hypothyroidism is thyroid dysgenesis. Thyroid dysgenesis summarizes a spectrum of developmental abnormalities of the embryonic thyroid ranging from complete absence of the thyroid gland (athyreosis), to a normally located but too small thyroid (hypoplasia), or an abnormally located thyroid gland (ectopy). Although considered a sporadic disease, distinct genetic forms of isolated or syndromic thyroid dysgenesis have been described in recent years. However, genetics of thyroid dysgenesis (TD) are mostly not following simple Mendelian patterns, and beside monogenic, multigenic and epigenetic mechanisms need to be considered. The review will highlight the molecular mechanisms of thyroid organogenesis, clinical and genetic features of the different monogenetic forms of thyroid dysgenesis, the aspects relevant for diagnosis and counseling of affected families and current research strategies to get more insight into the non-Medelian mechanisms of normal and abnormal thyroid development.

The W520X mutation in the TSHR gene brings on subclinical hypothyroidism through an haploinsufficiency mechanism

BACKGROUND

TSHR is a G-protein-coupled seven transmembrane domain receptor that activates the two major signal transduction pathways: the Gαs/adenylate cyclase and the Gαq/11/phospholipase C pathways. Inactivating mutations in the TSHR gene have been demonstrated to be responsible for subclinical hypothyroidism, a disorder characterized by elevated serum TSH concentrations despite normal thyroid hormones levels.

AIM

We identified in a child a nonsense mutation (W520X) in the third transmembrane domain of the TSHR that causes the lack of the C-terminus portion of the receptor. The functional significance of this variation was assessed in vitro.

MATERIAL/SUBJECT AND METHODS

The W520X mutation was introduced into the pSVL vector containing the wild-type sequence of TSHR gene. Wild-type and mutated vectors were expressed in Chinese Hamster Ovary (CHO) cells, and cAMP, inositol phosphate (IP), immunofluorescence and FACS analyses were performed.

RESULTS

Transfection with pSVL-TSHR vector induced basal cAMP and IP production in the absence of TSH stimulation, indicating a constitutive activity for the TSHR. An impairment of receptor function was demonstrated by the observation that cells expressing the mutant TSHR exhibited a lower second messenger production with respect to the wild-type, despite a normal expression of the receptor at the cell surface.

CONCLUSIONS

The mechanism through which the W520X mutation exerts its effect is more likely haploinsufficiency rather than a dominant-negative effect. This could explain the phenotype of our patient, who has a hormonal pattern in the range of a mild subclinical hypothyroidism, without an overt disease phenotype.

The molecular causes of thyroid dysgenesis: a systematic review

BACKGROUND

Congenital hypothyroidism (CH) is a frequent disease occurring with an incidence of about 1/2500 newborns/year. In 80-85% of the cases CH is caused by alterations in thyroid morphogenesis, generally indicated by the term "thyroid dysgenesis" (TD). TD is generally a sporadic disease, but in about 5% of the cases a genetic origin has been demonstrated. In these cases, mutations in genes playing a role during thyroid morphogenesis (NKX2-1, PAX8, FOXE1, NKX2-5, TSHR) have been reported.

AIM

This work reviews the main steps of thyroid morphogenesis and all the genetic alterations associated with TD and published in the literature.

Current loss-of-function mutations in the thyrotropin receptor gene: when to investigate, clinical effects, and treatment

Thyroid-stimulating hormone receptor (TSHR) loss-of-function (LOF) mutations lead to a wide spectrum of phenotypes, ranging from severe congenital hypothyroidism (CH) to mild euthyroid hyperthyrotropinemia. The degree of TSH resistance depends on the severity of the impairment of the receptor function caused by the mutation and on the number of mutated alleles In this review data about genotype-phenotype correlation and criteria for clinical work-up will be presented and discussed. Complete TSH resistance due to biallelic LOF TSHR mutations must be suspected in all patients with severe not syndromic CH and severe thyroid hypoplasia diagnosed at birth by neonatal screening. Partial forms of TSH resistance show a more heterogeneous hormonal and clinical pattern . In these cases TSH serum levels are above the upper limit of normal range for the age but with a very variable pattern, free thyroxine (T4) concentrations are within the normal range and thyroid size can be normal or hypoplastic at ultrasound scan. An early substitutive treatment with L-T4 must be mandatory in all patients with severe CH due to complete uncompensated TSH resistance diagnosed at birth by neonatal screening. The usefulness of substitutive treatment appears much more controversial inpatients with subclinical hypothyroidism due to partial TSH resistance in whom the increased TSH concentration should be able to compensate the mild functional impairment of the mutant receptor. Together with standard criteria we recommend also an accurate clinical work-up to select patients who are candidates for a LOF TSHR mutation.

Non-autoimmune subclinical hypothyroidism due to a mutation in TSH receptor: report on two brothers

Subclinical hypothyroidism (SH) is a condition characterized by a mild persistent thyroid failure. The main cause is represented by autoimmune thyroiditis, but mutations in genes encoding proteins involved in TSH pathway are thought to be responsible for SH, particularly in cases arising in familial settings. Patients with the syndrome of TSH unresponsiveness may have compensated or overt hypothyroidism with a wide spectrum of clinical and morphological alterations depending on the degree of impairment of TSH-receptor (TSH-R) function. We describe the case of two brothers with non autoimmune SH carrying the same heterozygous mutation in the extracellular domain of TSH-R and presenting with different clinical, biochemical and morphological features. The first one had only a slight persistent elevation of TSH, a normal thyroid ultrasound and did never require l- thyroxine (L-T4) replacement treatment. The second one had a neonatal persistent moderate TSH levels increase associated with a thyroid gland hypoplasia and was treated with L-T4 since the first months of life.

These two cases support the recent association of TSH-R mutations inheritance as an autosomal dominant pattern with variable expressivity and suggest that the decision to start replacement therapy in patients with persistent SH due to TSH resistance should be individualized.

A Cohort Historical Analysis of the Relationship between Thyroid Hormone Malady and Alpha-Human Herpesvirus Activation

Background

A number of physiological factors have been suggested to participate in the alpha- Human Herpesvirus (αHHV) reactivation, such as hormonal aberration. Thyroid hormone (TH) was shown to play a suppressive role in Herpes Simplex Virus Type-1 (HSV-1) gene expression and replication in cell culture and animal models. We hypothesize that reactivation of αHHV in humans may be due to, at least in part, by TH status.

Methods

Prior to implementing a full-scale population-based prospective inquiry into this hypothesis, a pilot study using a medical claims data base and a case-controlled, retrospective cohort investigation was conducted to develop a hypothetical link between TH complication and αHHV reactivation. Using diagnostic codes for treating thyroid disorders and αHHV infections as proxies for biologic/clinic outcomes, we queried a large, comprehensive hospital data base to construct two patient cohorts: Cohort 1 was comprised of patients receiving TH diagnoses over a twelve-year period, and Cohort 2 was composed of patients not receiving TH diagnoses during this period. Diagnoses of αHHV were recorded for each cohort and the difference in the frequency was examined for statistical significance. Demographic analyses such as age, gender, etc were also performed.

Results

Using 2×2 contingency table analyses and Statistical Analysis Software (SAS), an Odds Ratio (OR) of 2.83 was observed for the total population of 21 years old and above with a chi-square of 61.55 and p < 0.001, confirming that a severe significant difference was found between these two cohorts. This result suggested that patients with αHHV diagnosis have higher chances to have TH disorders. Additional investigation revealed that female were at higher/significant probability to have both TH and αHHV diagnosis, indicating a link of αHHV reactivation to a complex hormonal profile difference between genders. Our observation indicated that female patients of 21 years of age and above exhibited a very high incidence (OR of 3.40, p < 0.001) compared to the male groups (OR of 1.91, p < 0.05), indicating the possibility that hormonal alteration in females maybe transient but robust and can lead to αHHV reactivation more often than the males.

Conclusion

These results indicated that TH dysfunction may have implication in αHHV pathogenesis and females exhibited much higher probability to suffer αHHV reactivation due to TH disruption. Although the results from this pilot study have limitations and require additional controlled clinical examination such as more detailed patient records, lab data, therapeutic outcome, etc, it provides a tool to assess the effects of hormone imbalance on virus reactivation by retrospective analyses using existing large scale data base.

Subclinical hypothyroidism in children

The prevalence of SH in the pediatric population is < 2%, the caveat being the limited number of studies addressing SCH in the pediatric population. congenital deveolopental anamolies. Mutations in the several proteins are important causes of this condition. Despite the limited data available, SCH in children and adolescents appears to be a benign and remitting disease with a low risk of evolution to OH. It appears that thyroid hormones appear to be functioning well despite elevated TSH. Predictors of progression include, goiter, celiac disease, and positive anti TPO.

Consecutive mutational events in a TSHR allele of Arab families with resistance to thyroid stimulating hormone

BACKGROUND

Our laboratory identified six distinct inactivating TSHR gene mutations in Arab tribes living in Israel. We recently reported three nucleotide substitutions in exon 3 producing p.[L89L;Q90P] and one in exon 9 of the same allele producing p.P264S in Family A. Family B, reported herein, harbors the identical mutation in exon 3 only. We set to determine whether the mutations have common ancestral origin.

METHODS

Coding regions of the TSHR were sequenced and flanking microsatellite markers spanning 5.3 cM were used for haplotyping.

RESULTS

Two siblings of Family B were compound heterozygous for TSHR gene mutations. The paternal allele contained the exon 3 mutation and the maternal allele harbored a mutation in exon 10 (p.L653V). We investigated the possibility of a founder effect with subsequent mutational events for the presence of the same exon 3 mutation in different families. The haplotype of the allele harboring the exon 3 mutation in Family B was identical to that of Family A, also harboring the exon 9 mutation on the same allele, indicating that the latter occurred subsequently. The ancestral wild-type TSHR was present in Family B, suggesting that the mutation in exon 3 was also new in the history of that population.

CONCLUSIONS

It is more likely that two consecutive mutational events occurred on the ancestral wild-type allele instead of a recombination bringing exon 3 and exon 9 mutations together on the same allele. New mutational events contribute to the high prevalence of TSHR mutations in this population in addition to a founder effect and limited gene pool due to inbreeding.

Thyroid function in childhood obesity and metabolic comorbidity

Childhood obesity is a worldwide health problem and its prevalence is increasing steadily and dramatically all over the world. Obese subjects have a much greater likelihood than normal-weight children of acquiring dyslipidemia, elevated blood pressure, and impaired glucose metabolism, which significantly increase their risk of cardiovascular and metabolic diseases. Elevated TSH concentrations in association with normal or slightly elevated free T4 and/or free T3 levels have been consistently found in obese subjects, but the mechanisms underlying these thyroid hormonal changes are still unclear. Whether higher TSH in childhood obesity is adaptive, increasing metabolic rate in an attempt to reduce further weight gain, or indicates subclinical hypothyroidism or resistance and thereby contributes to lipid and/or glucose dysmetabolism, remains controversial. This review highlights current evidence on thyroid involvement in obese children and discusses the current controversy regarding the relationship between thyroid hormonal derangements and obesity-related metabolic changes (hypertension, dyslipidemia, hyperglycemia and insulin resistance, nonalcoholic fatty liver disease) in such population. Moreover, the possible mechanisms linking thyroid dysfunction and pediatric obesity are reviewed. Finally, the potential role of lifestyle intervention as well as of therapy with thyroid hormone in the treatment of thyroid abnormalities in childhood obesity is discussed.

Molecular screening of the TSH receptor (TSHR) and thyroid peroxidase (TPO) genes in Korean patients with nonsyndromic congenital hypothyroidism

OBJECTIVE

To investigate thyroid-stimulating hormone receptor (TSHR) and thyroid peroxidase (TPO) mutations in Korean patients with primary congenital hypothyroidism (CH).

CONTEXT

Congenital hypothyroidism is a common genetic disorder in which the majority of mutations occur in the TSHR and TPO genes.

DESIGN

We examined the frequencies of TSHR and TPO mutations among Korean patients with primary CH. Furthermore, we explored the relationships between imaging findings and mutation status.

PATIENTS

A total of 193 paediatric patients with nonsyndromic CH were enrolled in the present study.

MEASUREMENTS

Patients with decreased (99m) Tc uptake were screened for TSHR mutations using Sanger sequencing, and those with increased uptake were screened for TPO mutations. The relationships between scintigraphic and ultrasonographic findings and mutation status were analysed.

RESULTS

Thirteen (16·5%) of 79 patients with decreased (99m) Tc uptake were found to harbour TSHR mutations including G132R, G245S, R450H, R519C and F525S. The R450H mutation was present in 13 (72·2%) of 18 disease alleles. Seven (10·3%) of 68 patients with increased (99m) Tc uptake harboured TPO mutations including R189Q, K439E, G493S, C808LfsX72, A863T, R875Hfs and P883S. The TSHR and TPO mutations were observed only in patients with normal to slightly enlarged thyroid glands.

CONCLUSIONS

This study identified underlying TSHR and TPO mutations in Korean patients with CH and revealed a possible relationship between imaging findings and mutation status. In addition, the low rate of mutation positivity suggests significant genetic heterogeneity of CH in the Korean population.

Injections of Clostridium botulinum neurotoxin A may cause thyroid complications in predisposed persons based on molecular mimicry with thyroid autoantigens

A woman with Hashimoto's thyroiditis, under replacement L-T4, repeatedly experienced, over a 10-year period, elevations of serum TSH after eyelid injections of Clostridium botulinum neurotoxin A (Btx). We hypothesized a link between Btx injections and TSH elevations via molecular mimicry, and aimed to verify our hypothesis. Using an in silico approach, we searched first for amino acid sequence homology between Btx and thyroid autoantigens, and next for HLA binding motifs within homologous segments. We found that (i) Btx and thyroid autoantigens share amino acid sequence homology; (ii) some homologous regions contain epitopes of both Btx and thyroid autoantigens; (iii) some of such regions contain HLA-DR3 and/or HLA-DR7 binding motifs, which predominate over other HLA-DRs. This is relevant because the patient's HLA-DR haplotype was DR3/DR7. In conclusion, clinical and bioinformatics data suggest a possible pathogenetic link between Btx and autoimmune thyroid diseases. Considering the wide and increasing medical and dermocosmetic use of Btx, and the frequently subclinical course of autoimmune thyroid diseases, we think that thyroid "complications" may pass frequently undetected in Btx-treated persons.

Subclinical hypothyroidism in children: normal variation or sign of a failing thyroid gland?

Subclinical hypothyroidism (SCH), defined by a normal total or free T4 level and a mildly elevated TSH (typically 5–10 mU/L), is common in children, but there is currently no consensus on management. Several recent pediatric studies indicate that progression of SCH to overt hypothyroidism (OH) is uncommon and that over a period of several years, elevated TSH usually either normalizes or persists but does not increase. The etiology appears to be multifactorial, with some cases representing minor developmental abnormalities, some related to obesity, some to mild autoimmune thyroiditis, and some associated with mutations in the gene for the TSH-receptor. There are no pediatric studies showing clinical benefit of treating these children with thyroid hormone, but additional studies in this area are needed. Since few cases of pediatric SCH progress to OH, treatment can be deferred, and periodic follow-up testing may be the preferred strategy, with elevated thyroid antibodies or a goiter being considered risk factors for eventual OH.