Genetic analysis of the PAX8 gene in children with congenital hypothyroidism and dysgenetic or eutopic thyroid glands: identification of a novel sequence variant

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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 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.

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.

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.

Thyroid hemiagenesis and Hashimoto's thyroditis-diagnostic and treatment pitfalls

Background

Thyroid hemiagenesis (TH) is a rare congenital disease with absence of a thyroid lobe; most patients have no clinical symptoms. The etiology of TH remains unclear. In this paper, we describe a rare case of TH and congenital absence of the ipsilateral parathyroid gland, found during the operation, combined with the autoimmune disease Hashimoto’s thyroiditis, also known as chronic lymphocytic thyroiditis.

Case Presentation

A 31-year-old woman was admitted to our hospital because of a mass in the right neck. Surgical exploration validated the absence of the left lobe of the thyroid and parathyroid glands, and pathological examination of the excised nodules confirmed Hashimoto’s thyroiditis.

Patients with TH might show accompanying absence of the ipsilateral parathyroid gland. The case described here, in which TH was combined with Hashimoto’s thyroiditis, is rare in the medical literature. The operation should be ended at once if Hashimoto’s thyroiditis is diagnosed during surgery.

Conclusions

Absence of thyroid lobe may accompany with a congenital absence of the ipsilateral parathyroid gland and Hashimoto’s thyroiditis. Fine needle aspiration is essential to diagnosis and decision-making of the treatment.

Thyroid Hemiagenesis: Incidence, Clinical Significance, and Genetic Background

CONTEXT

Thyroid hemiagenesis (THA) constitutes a rare, congenital disorder that is characterized by an absence of one thyroid lobe. Because the pathogenesis and clinical significance of this malformation remain undefined, specific clinical recommendations are lacking, especially for asymptomatic cases.

EVIDENCE ACQUISITION

The PubMed database was searched (years 1970 to 2017), and the following terms were used to retrieve the results: "thyroid hemiagenesis," "thyroid hemiaplasia," "one thyroid lobe agenesis," and "one thyroid lobe aplasia." Subsequently, reference sections of the retrieved articles were searched.

EVIDENCE SYNTHESIS

There is a noticeable susceptibility of subjects with THA to develop additional thyroid and nonthyroidal pathologies. In pathogenesis of concomitant thyroid pathologies, a chronic elevation in thyroid-stimulating hormone values may play an important role. Thus far, genetic studies failed to find a common genetic background of the anomaly, and the potential underlying cause was identified in a minority of the cases.

CONCLUSIONS

Patients with THA are prone to develop additional thyroid pathologies and theoretically might benefit from l-thyroxine treatment to lower the thyrotropin levels to those observed in the normal population. However, further research should be done to ascertain whether such intervention early in life would prevent development of associated thyroid conditions. At least, increased vigilance should be maintained to reveal all of the concomitant disorders as soon as possible during follow-up examinations. Application of high-throughput technologies enabling a genome-wide search for novel factors involved in thyroid embryogenesis might be the next step to expand the knowledge on THA pathogenesis.

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.

Does TSH Trigger the Anti-thyroid Autoimmune Processes? Observation on a Large Cohort of Naive Patients with Thyroid Hemiagenesis

Thyroid hemiagenesis (THA) is a rare abnormality characterized by the absence of one thyroid lobe. Elevated thyroid stimulating hormone (TSH) level and higher incidence of thyroid diseases were reported in THA. The aim of the study is to evaluate the thyroid autoimmunity incidence in patients with THA and influence of higher than average TSH level on thyroid volume (TV) and its change with age. The study included a group of naive patients with THA and a control group of subjects with bilobate thyroid. All patients underwent clinical examination, thyroid ultrasound, scintiscan and laboratory tests. In the studied and control group the presence of thyroid autoantibodies (TAb) was evaluated. The THA group consisted of 65 patients. In THA group 53.85 % of patients were positive for TAb. Patients with positive TAb were older (46.0 ± 18.3 years) than those with negative (35.0 ± 19.8 years); p = 0.02. The incidence of TAb was lower in controls (13.85 %, p < 0.0001). In the study group, positive correlation between the age and TV (r = 0.46, p = 0.0001), and negative correlations between the age and TSH level (r = −0.31, p = 0.01), and TSH concentration and TV (r = −0.35, p = 0.004) were found. In a subgroup of 30 patients with THA negative for TAb, even stronger correlations were observed. The median single lobe volume and median TSH level were higher in patients with THA when compared to controls (13.60 vs 8.20 ml, p < 0.0001; 3.23 vs 1.48 µU/ml, p < 0.0001, respectively). Patients with THA constitute an in vivo model of long-term thyroid TSH overstimulation. Further studies are needed to reveal, whether TSH overstimulation may be the trigger for thyroid autoimmunity.

The role of ¹²³I imaging in the evaluation of infants with mild congenital hypothyroidism

BACKGROUND/AIMS

Controversy exists regarding the diagnosis and treatment of mild congenital hypothyroidism (MCH). We studied the value of (123)I imaging in patients with MCH.

METHODS

Retrospective chart review of infants and children <4 years of age who underwent (123)I imaging: group 1 = MCH [thyroid-stimulating hormone (TSH) <25 µIU/ml, normal free T4/T3], group 2 = severe congenital hypothyroidism (TSH ≥25 µIU/ml), and group 3 = MCH in infancy imaged after treatment withdrawal at age 3 years. Data collected included 4- and 24-hour (123)I uptake, TSH, free T4/total T3 at imaging, age at imaging, and levothyroxine (L-T4) dose at 1 year of.

RESULTS

Thirty-six patients underwent (123)I imaging. In group 1 (n = 20, median TSH: 8.49 µIU/ml), 85% had abnormal imaging consistent with dyshormonogenesis. Two patients were referred after 1 year of age. The median age at imaging for the remaining 18 patients was 54 days. Median L-T4 dose at 1 year of age for these 18 patients was 2.8 μg/kg, which is consistent with dyshormonogenesis. Ninety-one percent of group 2 (n = 11, median TSH: 428.03 µIU/ml) had abnormal imaging. The median age at imaging was 13 days. Four patients in group 3 had abnormal (123)I imaging and restarted treatment.

CONCLUSION

(123)I imaging is a valuable tool for evaluation, diagnosis, and treatment of MCH.

Extreme phenotypic variability of thyroid dysgenesis in six new cases of congenital hypothyroidism due to PAX8 gene loss-of-function mutations

CONTEXT

Within the last two decades, heterozygous loss-of-function PAX8 mutations have been reported in patients with a wide degree of thyroid gland dysfunction and growth despite the presence of identical mutations.

OBJECTIVES

To search for PAX8 mutations in a cohort of patients with congenital hypothyroidism (CH) and various types of thyroid gland defects.

DESIGN

A cross-sectional study was conducted in a cohort of patients.

SETTING

The French neonatal screening program was used for recruiting patients.

PATIENTS

A total of 118 patients with CH, including 45 with familial and 73 with sporadic diseases, were included in this study. The thyroid gland was normal in 23 patients had hypoplasia, 25 had hemithyroid agenesis, 21 had athyreosis, and 21 had ectopy.

RESULTS

We found four different PAX8 mutations (p.R31C, p.R31H, p.R108X, and p.I47T) in ten patients (six patients with CH and four family members), two with sporadic and eight with familial diseases. Imaging studies performed in the index cases showed ectopic thyroid gland (n=2), hypoplasia (n=2), eutopic lobar asymmetry (n=1), and eutopic gland compatible with dyshormonogenesis (n=1). The previously reported p.R31C and the novel p.I47T PAX8 mutations are devoid of activity.

CONCLUSION

Four different PAX8 mutations were detected in six index patients with CH (ten total subjects). The p.R31C, p.R31H, and p.R108X mutations have been reported. The novel p.I47T PAX8 mutation presented loss of function leading to CH. Thyroid ectopy was observed in two cases of PAX8 (p.R31H) mutation, a finding that has not been reported previously. We observed a high inter-individual and intra-familial variability of the phenotype in PAX8 mutations, underlining that population genetic studies for CH should include patients with various clinical presentations.

Identification of a novel pax8 gene sequence variant in four members of the same family: from congenital hypothyroidism with thyroid hypoplasia to mild subclinical hypothyroidism

BACKGROUND

Congenital hypothyroidism is often secondary to thyroid dysgenesis, including thyroid agenesis, hypoplasia, ectopic thyroid tissue or cysts. Loss of function mutations in TSHR, PAX8, NKX2.1, NKX2.5 and FOXE1 genes are responsible for some forms of inherited congenital hypothyroidism, with or without hypoplastic thyroid. The aim of this study was to analyse the PAX8 gene sequence in several members of the same family in order to understand whether the variable phenotypic expression, ranging from congenital hypothyroidism with thyroid hypoplasia to mild subclinical hypothyroidism, could be associated to the genetic variant in the PAX8 gene, detected in the proband.

METHODS

We screened a hypothyroid child with thyroid hypoplasia for mutations in PAX8, TSHR, NKX2.1, NKX2.5 and FOXE1 genes. We studied the inheritance of the new variant R133W detected in the PAX8 gene in the proband's family, and we looked for the same substitution in 115 Caucasian European subjects and in 26 hypothyroid children. Functional studies were performed to assess the in vitro effect of the newly identified PAX8 gene variant.

RESULTS

A new heterozygous nucleotide substitution was detected in the PAX8 DNA-binding motif (c.397C/T, R133W) in the proband, affected by congenital hypothyroidism with thyroid hypoplasia, in his older sister, displaying a subclinical hypothyroidism associated with thyroid hypoplasia and thyroid nodules, in his father, affected by hypothyroidism with thyroid hypoplasia and thyroid nodules, and his first cousin as well, who revealed only a subclinical hypothyroidism. Functional studies of R133W-PAX8 in the HEK293 cells showed activation of the TG promoter comparable to the wild-type PAX8.

CONCLUSIONS

In vitro data do not prove that R133W-PAX8 is directly involved in the development of the thyroid phenotypes reported for family members carrying the substitution. However, it is reasonable to conceive that, in the cases of transcriptions factors, such as Pax8, which establish several interactions in different protein complexes, genetic variants could have an impact in vivo.

Bilobar thyroid agenesis with primary hyperparathyroidism: report of a case

Congenital thyroid abnormalities are rarely seen. They mostly include hemiagenesis with or without involving the isthmus. In this report, we present a case of bilateral lobe agenesis with hypertrophied isthmus and high calcium and elevated PTH levels which were detected during routine examinations of a 49-year-old female patient. Some findings consistent with parathyroid pathology on the right side were determined in parathyroid scintigraphy. At thyroid scan and neck ultrasonography there was no sign of bilateral thyroid tissue except a mass localized isthmus. The right lower parathyroidectomy and thyroidectomy for isthmus were performed; the pathology report was shown as parathyroid adenoma and nodular colloidal goiter. This case of bilobar agenesis with incidental primary hyperparathyroidism due to single parathyroid adenoma is the first case reported in literature.

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 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.

Hypothyroxinemia induced by mild iodine deficiency deregulats thyroid proteins during gestation and lactation in dams

The main object of the present study was to explore the effect on thyroidal proteins following mild iodine deficiency (ID)-induced maternal hypothyroxinemia during pregnancy and lactation. In the present study, we established a maternal hypothyroxinemia model in female Wistar rats by using a mild ID diet. Maternal thyroid iodine content and thyroid weight were measured. Expressions of thyroid-associated proteins were analyzed. The results showed that the mild ID diet increased thyroid weight, decreased thyroid iodine content and increased expressions of thyroid transcription factor 1, paired box gene 8 and Na+/I- symporter on gestational day (GD) 19 and postpartum days (PN) 21 in the maternal thyroid. Moreover, the up-regulated expressions of type 1 iodothyronine deiodinase (DIO1) and type 2 iodothyronine deiodinase (DIO2) were detected in the mild ID group on GD19 and PN21. Taken together, our data indicates that during pregnancy and lactation, a maternal mild ID could induce hypothyroxinemia and increase the thyroidal DIO1 and DIO2 levels.

Two cases of thyroid dysgenesis caused by different novel PAX8 mutations in the DNA-binding region: in vitro studies reveal different pathogenic mechanisms

BACKGROUND

Mutations in PAX8, a transcription factor gene, cause thyroid dysgenesis (TD). The extreme variability of the thyroid phenotype makes it difficult to identify individuals harboring PAX8 gene mutations. Here we describe two patients with TD and report two novel PAX8 gene mutations (S54R and R133Q). We performed in vitro studies to functionally characterize these mutations.

METHODS

Using PAX8 expression vectors, we investigated whether the PAX8 mutants localized correctly to the nucleus. To analyze the DNA-binding properties of S54R and R133Q, electrophoretic mobility shift assays were performed. Furthermore, we measured whether the mutant PAX8 proteins were able to activate the thyroglobulin (TG)- and the thyroperoxidase (TPO)-promoters.

RESULTS

S54R had an impaired binding to DNA and a negligible activity on the TG- and the TPO-promoters. The DNA-binding property of R133Q, which is located in the highly conserved terminal portion of the PAX8 DNA-binding domain, was normal. Interestingly, it also exhibited dramatically impaired activation of the TG- and TPO-promoters. However, R133Q has no dominant negative effect on the WT protein in vitro. Thus, the underlying molecular mechanism by which the function of R133Q is impaired remains to be elucidated.

CONCLUSIONS

We identified and functionally characterized two novel mutations of the PAX8 gene that lead to TD by distinct mechanisms. A structural defect of the mutant R133Q leading to a reduced capability for induced fit upon DNA interaction might explain the disparity between its apparently normal binding to DNA, but lack of promoter activation.

Absence of mutations in PAX8, NKX2.5, and TSH receptor genes in patients with thyroid dysgenesis

OBJECTIVES: To precisely classify the various forms of TD, and then to screen for mutations in transcription factor genes active in thyroid development. SUBJECTS AND METHODS: Patients underwent ultrasound, thyroid scan, and serum thyroglobulin measurement to accurately diagnose the form of TD. DNA was extracted from peripheral leukocytes. The PAX8, and NKX2.5 genes were evaluated in all patients, and TSH receptor (TSHR) gene in those with hypoplasia. RESULTS: In 27 nonconsanguineous patients with TD, 13 were diagnosed with ectopia, 11 with hypoplasia, and 3 with athyreosis. No mutations were detected in any of the genes studied. CONCLUSION: Sporadic cases of TD are likely to be caused by epigenetic factors, rather than mutations in thyroid transcription factors or genes involved in thyroid development.

Right-sided hemiagenesis of the thyroid lobe and isthmus: A case report

Unilateral or bilateral hypoplasia or agenesis of one or both thyroid lobes, with or without isthmic agenesis, is a rare developmental anomaly. Hemiagenesis of the left lobe is far commoner than of the right. Clinically, these patients may be euthyroid, hyperthyroid, or hypothyroid. Ultrasonography is usually able to diagnose this condition easily, as we demonstrate in this case report of a 37-year-old lady with an incidentally detected thyroid nodule who was found to have hemiagenesis of the right lobe and isthmus.

Thyroid hypoplasia as a cause of congenital hypothyroidism in monozygotic twins concordant for Rubinstein-Taybi syndrome

Rubinstein-Taybi syndrome (RSTS), a genetic disorder characterized by growth retardation, mental deficiency, dysmorphic face, broad thumbs and large toes, generally affects monozygotic twins concordantly. Thyroid hypoplasia (TH) is a common cause of congenital hypothyroidism (CH) and often accompanies dysmorphic syndromes. A pair of female twins were admitted to our neonatology unit 16 hours after delivery. They were born at 35 weeks of gestation. Both twins had an unusual dysmorphic facial appearance with microcephaly, as well as broad short thumbs and large toes. Based on the presence of characteristic dysmorphic features, the twins were diagnosed as RSTS. Thyroid function tests in the first twin revealed the following results: free thyroxine (T4) 8.4 pg/mL, thyrotropin (TSH) 4.62 mIU/L, thyroglobulin (TG) 213.24 ng/mL and a normal level of urinary iodine excretion (UIE). Thyroid function test results in the second twin in the second week were: free T4 5.9 pg/mL, TSH 9.02 mIU/L, TG 204.87 ng/mL, and normal UIE levels. Thyroid volumes were 0.36 mL and 0.31 mL in the first and second twin, respectively. TH was confirmed by technetium 99 m pertechnetate thyroid scans in both infants. Thyroid function tests normalized with L-thyroxine replacement therapy (10 μg/kg/day) around the end of the 3(rd) week of life. The infants were discharged planning their follow-up by both endocrinology and cardiology units. The rarity of cases of twins with RSTS (concordant) co-existing with CH led us to present this report.

Update on some aspects of neonatal thyroid disease

This article explores the basic development and pathophysiology of the thyroid gland. New factors in the normal development of the thyroid in the neonate are mentioned. The incidence of congenital hypothyroidism continues to increase. We describe congenital hypothyroidism, its possible etiologies, treatment and outcomes. We explore hypothyroxinanemia in pre−term neonates and the risk/benefit of prophylactic thyroid hormone replacement. We discuss the late rise of thyrotropin (TSH) in ill infants and those with very low birth weight. Ill infants or those born premature should have their thyroid function tests routinely monitored. On the occasion of borderline thyroid function test results, TRH testing can be useful in identifying those infants with either persistent or transient hypothyroidism. TRH testing is also helpful in identifying those patients with secondary hypothyroidism. With the early identification and prompt and proper treatment, neonates with congenital hypothyroidism, transient or persistent, should have positive long−term outcomes.

Conflict of interest:None declared.

Mutations in the gene encoding paired box domain (PAX8) are not a frequent cause of congenital hypothyroidism (CH) in Iranian patients with thyroid dysgenesis

OBJECTIVE: Congenital hypothyroidism (CH) may be caused by defects in the thyroid or in one of the stages in the synthesis of thyroid hormones. Thyroid dysgenesis may be associated with mutation in the paired box transcription factor 8 (PAX8) gene. We attempted to screen PAX8 gene mutation in 50 CH patients with thyroid dysgenesis. SUBJECTS AND METHODS: The patients were classified in two groups as agenesis and ectopic based on biochemical and para clinical tests. By employing PCR, Single Strand Conformation Polymorphism (SSCP) and sequencing, exons 3 to 12 of PAX8 gene with their exon-intron boundaries were studied. RESULTS: No mutation was found in these patients in any of the exons. CONCLUSION: Our results, once again, indicate that the PAX8 mutation rate is very low and can only explain a minority of the cases. Therefore, it is highly needed to further investigate the genes controlling development and function of thyroid.

Congenital Hypothyroidism Caused by a PAX8 Gene Mutation Manifested as Sodium/Iodide Symporter Gene Defect

Loss-of-function mutations of the PAX8 gene are considered to mainly cause congenital hypothyroidism (CH) due to thyroid hypoplasia. However, some patients with PAX8 mutation have demonstrated a normal-sized thyroid gland. Here we report a CH patient caused by a PAX8 mutation, which manifested as iodide transport defect (ITD). Hypothyroidism was detected by neonatal screening and L-thyroxine replacement was started immediately. Although ¹²³I scintigraphy at 5 years of age showed that the thyroid gland was in the normal position and of small size, his iodide trapping was low. The ratio of the saliva/plasma radioactive iodide was low. He did not have goiter; however laboratory findings suggested that he had partial ITD. Gene analyses showed that the sodium/iodide symporter (NIS) gene was normal; instead, a mutation in the PAX8 gene causing R31H substitution was identified. The present report demonstrates that individuals with defective PAX8 can have partial ITD, and thus genetic analysis is useful for differential diagnosis.

Identification and characterization of four PAX8 rare sequence variants (p.T225M, p.L233L, p.G336S and p.A439A) in patients with congenital hypothyroidism and dysgenetic thyroid glands

CONTEXT

Thyroid dysgenesis may be associated with mutations in the paired box transcription factor 8 (PAX8) gene and is characterized by congenital hypothyroidism transmitted in an autosomal dominant mode.

OBJECTIVES

The aim of this study was to identify new mutations in the PAX8 gene. Sixty congenital hypothyroidism-affected individuals with dysgenetic (agenesis, ectopia and hypoplasia) and eutopic thyroid glands were studied.

METHODS

The 12 exons of the PAX8 gene along with their exon-intron boundaries were amplified from genomic DNA and a mutational screening was performed by single-strand conformational polymorphism (SSCP) followed by direct sequencing of samples with abnormal migration patterns. The PAX8 mutations were functionally characterized by transient transfection experiments.

RESULTS

Molecular analysis of the PAX8 gene indicated that four affected individuals had four sequence differences: three novel variations [c.699C>T (p.L233L), c.1006G>A (p.G336S) and c.1317A>G (p.A439A)] and one recently reported [c.674C>T (p.T225M)], whereas the 56 remaining patients showed only wild-type alleles of PAX8. p.T225M, p.L233L and p.G336S variants were not detected in 530 chromosomes from 265 subjects randomly selected from the general population, whereas the p.A439A variant was identified in only one of the 530 chromosomes analysed. Functional analysis of the nonsynonymous substitutions showed that the p.T225M and p.G336S proteins had not lost their ability to bind a specific DNA sequence and to activate the transcription of the thyroglobulin (TG) promoter in synergy with thyroid transcription factor 1 (TTF1).

CONCLUSIONS

We report the occurrence of two nonsynonymous substitutions, one recently reported (p.T225M) and one novel (p.G336S), and two novel synonymous substitutions (p.L233L and p.A439A) in the PAX8 gene. p.T225M and p.G336S are rare sequence variants or may act by inhibiting an unknown particular function. Our study also confirms the very low prevalence of PAX8 mutations in thyroid dysgenesis.