Characterization of a novel loss of function mutation of PAX8 in a familial case of congenital hypothyroidism with in-place, normal-sized thyroid

Identification of a core transcriptional program driving the human renal mesenchymal-to-epithelial transition

During kidney development, nephron epithelia arise de novo from fate-committed mesenchymal progenitors through a mesenchymal-to-epithelial transition (MET). Downstream of fate specification, transcriptional mechanisms that drive establishment of epithelial morphology are poorly understood. We used human iPSC-derived renal organoids, which recapitulate nephrogenesis, to investigate mechanisms controlling renal MET. Multi-ome profiling via snRNA-seq and ATAC-seq of organoids identified dynamic changes in gene expression and chromatin accessibility driven by activators and repressors throughout MET. CRISPR interference identified that paired box 8 (PAX8) is essential for initiation of MET in human renal organoids, contrary to in vivo mouse studies, likely by activating a cell-adhesion program. While Wnt/β-catenin signaling specifies nephron fate, we find that it must be attenuated to allow hepatocyte nuclear factor 1-beta (HNF1B) and TEA-domain (TEAD) transcription factors to drive completion of MET. These results identify the interplay between fate commitment and morphogenesis in the developing human kidney, with implications for understanding both developmental kidney diseases and aberrant epithelial plasticity following adult renal tubular injury.

The PAX Genes: Roles in Development, Cancer, and Other Diseases

Since their 1986 discovery in Drosophila, Paired box (PAX) genes have been shown to play major roles in the early development of the eye, muscle, skeleton, kidney, and other organs. Consistent with their roles as master regulators of tissue formation, the PAX family members are evolutionarily conserved, regulate large transcriptional networks, and in turn can be regulated by a variety of mechanisms. Losses or mutations in these genes can result in developmental disorders or cancers. The precise mechanisms by which PAX genes control disease pathogenesis are well understood in some cases, but much remains to be explored. A deeper understanding of the biology of these genes, therefore, has the potential to aid in the improvement of disease diagnosis and the development of new treatments.

Novel Missense Variants in PAX8 and NKX2-1 Cause Congenital Hypothyroidism

Primary congenital hypothyroidism (CH) is a common neonatal endocrine disorder characterized by elevated concentrations of thyroid stimulating hormone (TSH) and low concentrations of free thyroxine (FT4). PAX8 and NKX2-1 are important transcription factors involved in thyroid development. In this study, we detected three novel variants in PAX8 (c.149A > C and c.329G > A) and NKX2-1 (c.706A > G) by whole exome sequencing (WES) in three unrelated CH patients with variable phenotypes. The results of Western blot and immunofluorescence analysis showed that the three variants had no effect on protein expression and subcellular localization. However, the results of the electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter assay suggested that the three variants in PAX8 and NKX2-1 both affected their DNA-binding ability and reduced their transactivation capacity. Moreover, a dominant-negative effect in K236E−NKX2-1 was identified by dual-luciferase reporter assay. To sum up, our findings extend our knowledge of the current mutation spectrum of PAX8 and NKX2-1 and provide important information for diagnosing, treating, and preventing CH in these families.

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

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

PBRM1 loss in kidney cancer unbalances the proximal tubule master transcription factor hub to repress proximal tubule differentiation

PBRM1, a subunit of the PBAF coactivator complex that transcription factors use to activate target genes, is genetically inactivated in almost all clear cell renal cell cancers (RCCs). Using unbiased proteomic analyses, we find that PAX8, a master transcription factor driver of proximal tubule epithelial fates, recruits PBRM1/PBAF. Reverse analyses of the PAX8 interactome confirm recruitment specifically of PBRM1/PBAF and not functionally similar BAF. More conspicuous in the PAX8 hub in RCC cells, however, are corepressors, which functionally oppose coactivators. Accordingly, key PAX8 target genes are repressed in RCC versus normal kidneys, with the loss of histone lysine-27 acetylation, but intact lysine-4 trimethylation, activation marks. Re-introduction of PBRM1, or depletion of opposing corepressors using siRNA or drugs, redress coregulator imbalance and release RCC cells to terminal epithelial fates. These mechanisms thus explain RCC resemblance to the proximal tubule lineage but with suppression of the late-epithelial program that normally terminates lineage-precursor proliferation.

Gu et al. identify that transcription factor PAX8 needs the PBRM1/PBAF coactivator to activate proximal tubule genes. PBRM1 mutation/deletion thus explains the resemblance of clear cell kidney cancer to proximal tubule tissue but with suppressed terminal epithelial markers. This oncogenic mechanism could be repaired using drugs to inhibit corepressors.

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

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

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.

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

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

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSIONS

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

Mouse Models of Congenital Kidney Anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects, which cause the majority of chronic kidney diseases in children. CAKUT covers a wide range of malformations that derive from deficiencies in embryonic kidney and lower urinary tract development, including renal aplasia, hypodysplasia, hypoplasia, ectopia, and different forms of ureter abnormalities. The majority of the genetic causes of CAKUT remain unknown. Research on mutant mice has identified multiple genes that critically regulate renal differentiation. The data generated from this research have served as an excellent resource to identify the genetic bases of human kidney defects and have led to significantly improved diagnostics. Furthermore, genetic data from human CAKUT studies have also revealed novel genes regulating kidney differentiation.

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.

Impact of next generation sequencing on our understanding of CAKUT

Congenital abnormalities of the kidney and urinary tract (CAKUT) form the leading cause of pediatric end-stage renal disease. Knowledge on the molecular mechanisms that underlie CAKUT leads to the improvement of DNA diagnostics and counseling regarding prognosis and recurrence risk estimation for CAKUT patients and their relatives. Implementation of next generation sequencing in research and diagnostic settings has led to the identification of the molecular basis of many developmental diseases. In this review, we summarize the efforts on next generation sequencing in CAKUT research and we discuss how next generation sequencing added to our understanding of CAKUT genetics. Although next generation sequencing has certainly proven to be a game changer in the field of disease gene identification and novel CAKUT-causing gene variants have been identified, most CAKUT cases still remain unsolved. Occurring with genetic and phenotypic heterogeneity along with incomplete penetrance, the identification of CAKUT etiology poses many challenges. We see great potential for combined -omics approaches that include next generation sequencing in the identification of CAKUT-specific biomarkers, which is necessary to optimize the care for CAKUT patients.

Wnt Signaling in Thyroid Homeostasis and Carcinogenesis

The Wnt pathway is essential for stem cell maintenance, but little is known about its role in thyroid hormone signaling and thyroid stem cell survival and maintenance. In addition, the role of Wnt signaling in thyroid cancer progenitor cells is also unclear. Here, we present emerging evidence for the role of Wnt signaling in somatic thyroid stem cell and thyroid cancer stem cell function. An improved understanding of the role of Wnt signaling in thyroid physiology and carcinogenesis is essential for improving both thyroid disease diagnostics and therapeutics.

Identification and characterization of novel PAX8 mutations in Congenital Hypothyroidism(CH) in a Chinese population

Objective

Based on mutations in PAX8 is associated with thyroid dysgenesis. We aim to identify and characterize PAX8 mutations in a large cohort of congenital hypothyroidism(CH) from thyroid dysgenesis in Chinese population.

Methods

We screened 453 unrelated Chinese patients with CH from thyroid dysgenesis for PAX8 mutations by sequencing the whole coding regions of PAX8 on genomic DNA isolated from blood. Cell transfection assays using various vector constructs and induced mutagenesis as well as electrophoretic mobility shift assays were used to investigate the effects of selected mutations on the transcribing and binding activities of PAX8 at the promoters of target genes for thyroglobulin (TG) and thyroperoxidase (TPO).

Results

Five PAX8 mutations were found, yielding a mutation prevalence of 5/453 (1.1%). We selected two mutations in the critical paired domain of PAX8 and generated mutants D94N and G41V. We demonstrated G41V was unable to bind the specific sequence in the promoters of TG and TPO and activate them. D94N could bind to TG and TPO promoters and normally activate the TG promoter transcription but not the TPO promoter transcription. We also demonstrated a dominant negative role of the PAX8 mutants in impairing the function of the wild-type PAX8.

Conclusion

We for the first time documented the prevalence and characterized the function of PAX8 mutations in CH in Chinese population. The study specifically demonstrated the role of novel mutations D94N and G41V in impairing the function of PAX8, providing further evidence for genetic PAX8 defects as a disease mechanism in CH.

Somatic mutations and increased lymphangiogenesis observed in a rare case of intramucosal gastric carcinoma with lymph node metastasis

BACKGROUND AND AIM

Intramucosal gastric adenocarcinoma of the well-moderately differentiated type only exhibits lymph node metastasis in extremely rare cases. We encountered such case and investigated both the lymphangiogenic properties and somatic mutations in the cancer to understand the prometastatic features of early-stage gastric cancer.

METHODS

We quantitatively measured the density of lymphatic vessels and identified mutations in 412 cancer-associated genes through next-generation target resequencing of DNA extracted from tumor cells in a formalin-fixed and paraffin-embedded tissue. Functional consequence of the identified mutation was examined in vitro by means of gene transfection, immunoblot, and the quantitative real-time polymerase chain reaction assay.

RESULTS

The intramucosal carcinoma was accompanied by abundant lymphatic vessels. The metastatic tumor harbored somatic mutations in NBN, p.P6S, and PAX8, p.R49H. The PAX8R49H showed significantly higher transactivation activity toward E2F1 than the wild-type PAX8 (P< 0.001).

CONCLUSIONS

Our data suggest that increased lymphangiogenesis and somatic mutations of NBN and/or PAX8 could facilitate lymph node metastasis from an intramucosal gastric carcinoma. These findings may potentially inform evaluations of the risk of developing lymph node metastasis in patients with intramucosal gastric cancer.

Development of the thyroid gland

Thyroid hormones are crucial for organismal development and homeostasis. In humans, untreated congenital hypothyroidism due to thyroid agenesis inevitably leads to cretinism, which comprises irreversible brain dysfunction and dwarfism. Elucidating how the thyroid gland - the only source of thyroid hormones in the body - develops is thus key for understanding and treating thyroid dysgenesis, and for generating thyroid cells in vitro that might be used for cell-based therapies. Here, we review the principal mechanisms involved in thyroid organogenesis and functional differentiation, highlighting how the thyroid forerunner evolved from the endostyle in protochordates to the endocrine gland found in vertebrates. New findings on the specification and fate decisions of thyroid progenitors, and the morphogenesis of precursor cells into hormone-producing follicular units, are also discussed.

A Gene Implicated in Activation of Retinoic Acid Receptor Targets Is a Novel Renal Agenesis Gene in Humans

Renal agenesis (RA) is one of the more extreme examples of congenital anomalies of the kidney and urinary tract (CAKUT). Bilateral renal agenesis is almost invariably fatal at birth, and unilateral renal agenesis can lead to future health issues including end-stage renal disease. Genetic investigations have identified several gene variants that cause RA, including EYA1, LHX1, and WT1 However, whereas compound null mutations of genes encoding α and γ retinoic acid receptors (RARs) cause RA in mice, to date there have been no reports of variants in RAR genes causing RA in humans. In this study, we carried out whole exome sequence analysis of two families showing inheritance of an RA phenotype, and in both identified a single candidate gene, GREB1L Analysis of a zebrafish greb1l loss-of-function mutant revealed defects in the pronephric kidney just prior to death, and F0 CRISPR/Cas9 mutagenesis of Greb1l in the mouse revealed kidney agenesis phenotypes, implicating Greb1l in this disorder. GREB1L resides in a chromatin complex with RAR members, and our data implicate GREB1L as a coactivator for RARs. This study is the first to associate a component of the RAR pathway with renal agenesis in humans.

Congenital urogenital abnormalities in children with congenital hypothyroidism

Background: Congenital hypothyroidism (CH), as one of the most common congenital endocrine disorders, may be significantly associated with congenital malformations. This study investigates urogenital abnormalities in children with primary CH (PCH).

Methods: This case-control study was conducted on 200 children aged three months to 1 year, referred to Amir-Kabir Hospital, Arak, Iran. One hundred children with PCH, as the case group, and 100 healthy children, as the control group, were selected using convenient sampling. For all children, demographic data checklists were filled, and physical examination, abdomen and pelvic ultrasound and other diagnostic measures (if necessary) were performed to evaluate the congenital urogenital abnormalities including anomalies of the penis and urethra, and disorders and anomalies of the scrotal contents.

Results: Among 92 (100%) urogenital anomalies diagnosed, highest frequencies with 37 (40.2%), 26(28.2%) and 9 (9.7%) cases including hypospadias, Cryptorchidism, and hydrocele, respectively. The frequency of urogenital abnormalities among 32 children with PCH, with 52 cases (56.5%) was significantly higher than the frequency of abnormalities among the 21 children in the control group, with 40 cases (43.4%). (OR=2.04; 95%CI: 1.1-3.6; p=0.014).

Conclusion: Our study demonstrated that PCH is significantly associated with the congenital urogenital abnormalities. However, due to the lack of evidence in this area, further studies are recommended to determine the necessity of conducting screening programs for abnormalities of the urogenital system in children with CH at birth.

The role of GLIS3 in thyroid disease as part of a multisystem disorder

Congenital hypothyroidism is the most common hereditary endocrine disorder. In a small number of cases, mutations have been identified that are associated with maldevelopment and maldescent of the thyroid. Some of these mutations present as syndromes with a multisystem phenotype such as NKX2-1, PAX8, and FOXE. The association of permanent neonatal diabetes and congenital hypothyroidism was first reported in 2003 and subsequently led to the identification GLIS3 as the mutation responsible for this presentation. GLIS3 is a member of the GLI-similar zinc finger protein family encoding for a nuclear protein with five zinc finger domains and maps to chromosome 9p24. Given the role of GLIS3 in transcriptional activation and repression during embryogenesis, in humans, GLIS3 mutations present with multisystem involvement that also includes renal cystic dysplasia, progressive liver fibrosis and osteopenia. Thyroid findings in GLIS3 patients include thyroid aplasia, diminished colloid with interstitial fibrosis at post-mortem, and apparently normal gross thyroid anatomy on ultrasonography but with temporary TSH resistance on treatment. To date no biological mechanism has explained this variable presentation.

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.

Rtfc (4931414P19Rik) Regulates in vitro Thyroid Differentiation and in vivo Thyroid Function

Thyroid is a one of the most important endocrine organs. Understanding the molecular mechanism underlying thyroid development and function, as well as thyroid diseases, is beneficial for the clinical treatment of thyroid diseases and tumors. Through genetic linkage analysis and exome sequencing, we previously identified an uncharacterized gene C14orf93 (RTFC, mouse homolog: 4931414P19Rik) as a novel susceptibility gene for familial non-medullary thyroid carcinoma, and demonstrated its function in promoting thyroid tumor. However, the role of RTFC in thyroid development and function remains unexplored. In this study, we found that knockout of Rtfc compromises the in vitro thyroid differentiation of mouse embryonic stem cells. In contrast, Rtfc^−/− mice are viable and fertile, and the size and the morphology of thyroid are not affected by Rtfc knockout. However, female Rtfc^−/− mice, but not male Rtfc^−/− mice, display mild hypothyroidism. In summary, our data suggest the roles of Rtfc in in vitro thyroid differentiation of embryonic stem cells, and in vivo thyroid function.

Update of Thyroid Developmental Genes

Thyroid dysgenesis (TD) is the most common cause of congenital hypothyroidism in iodine-sufficient regions and includes a spectrum of developmental anomalies. The genetic components of TD are complex. Although a sporadic disease, advances in developmental biology have revealed monogenetic forms of TD. Inheritance is not based on a simple Mendelian pattern and additional genetic elements might contribute to the phenotypic spectrum. This article summarizes the key steps of normal thyroid development and provides an update on responsible genes and underlying mechanisms of TD. Up-to-date technologies in genetics and biology will allow us to advance in our knowledge of TD.

Analysis of the T354P mutation of the sodium/iodide cotransporter gene in children with congenital hypothyroidism due to dyshormonogenesis

Background:

Congenital hypothyroidism (CH) due to the thyroid dyshormonogenesis is more prevalent in Iran in comparison to other countries. Sodium iodide symporter (NIS) is one of the plasma membrane glycoproteins that is located on the basolateral side of thyroid follicular cells and mediates active I⁻ trapping into these cells. Playing a prominent role in thyroid hormone synthesis, NIS gene mutations can be a cause of permanent CH with the etiology of dyshormonogenesis. The aim of this study was to investigate the occurrence of T354P mutation of the NIS gene, in a group of children affected with permanent CH in Isfahan.

Materials and Methods:

Thirty-five patients with the etiology of dyshormonogenesis, and 35 healthy children, collected between 2002 and 2011 in Isfahan Endocrine and Metabolism Research Center, were examined for T354P mutation of the NIS gene by direct polymerase chain reaction-sequencing method.

Results:

No T354P mutation was detected in any of the studied children.

Conclusions:

More subjects with confirmed iodide transport defects should be screened for detecting the frequency of different reported NIS gene mutations in our population.

A Novel Mutation (S54C) of the PAX8 Gene in a Family with Congenital Hypothyroidism and a High Proportion of Affected Individuals

BACKGROUND

Congenital hypothyroidism (CH) is a common endocrine disorder in newborns. The cause of CH is thyroid dysgenesis in 80-85% of patients. Paired box gene 8 (PAX8) is a thyroid transcription factor that plays an important role in thyroid organogenesis and development. To date, 22 different PAX8 gene mutations have been reported.

METHODS

Four generations of a Hungarian Jewish family were affected, and in the 3 generations studied, 9 males and 4 females were affected and 3 first-degree relatives were unaffected. Six were diagnosed at birth [thyroid-stimulating hormone (TSH) level 59-442 mU/l] and 7 at 2-48 years of age (TSH level 6-223 mU/l). One affected patient had thyroid hemiagenesis on ultrasound.

RESULTS

Direct sequencing of the PAX8 gene revealed a novel single nucleotide substitution (c.162 A>T) in exon 2 that resulted in the substitution of the normal serine 54 with a cysteine (S54C), which segregated with elevated serum TSH levels. Other mutations of the same amino acid (S54G and S54R) have also been shown to produce functional impairment.

CONCLUSION

We report a large family with a novel mutation in the PAX8 gene presenting with variable phenotype and with a high proportion of affected family members.

Congenital anomalies of kidney and upper urinary tract in children with congenital hypothyroidism; a case-control study

INTRODUCTION

Congenital hypothyroidism (CH) may be significantly associated with congenital malformations. However, there is little evidence on the relationship between renal and urinary tract anomalies and CH.

OBJECTIVES

The aim of this study was to compare the renal and upper urinary tract anomalies in children with and without primary CH (PCH).

PATIENTS AND METHODS

This case-control study was conducted on 200 children aged 3 months to 1 year, referring to Amir-Kabir hospital, Arak, Iran. One hundred children with PCH, as the case group, and 100 children without CH, as the control group, were selected. For all children, ultrasonography and other diagnostic measures (if necessary) were performed to evaluate renal and upper urinary tract anomalies (ureter and bladder).

RESULTS

The frequency of renal and upper urinary tract anomalies among 43 children with primary CH, with 83 cases (72.8%), was significantly higher than the frequency of anomalies among the 19 children in the control group, with 31 cases (27.1%) (OR = 3; CI 95%: 1.6-5.4; P = 0.001). Among the anomalies studied, only the differences in frequency of uretero-pelvic junction obstruction (UPJO) (OR = 6; CI 95%: 1.3-28; P = 0.018) and hydronephrosis (OR = 22; CI 95%: 5-95; P = 0.001) was significant between the two groups.

CONCLUSION

Our study demonstrated that PCH is significantly associated with the frequency of congenital anomalies of the kidneys and upper urinary tracts. However, further studies are recommended to determine the necessity of conducting screening programs for anomalies of the kidneys and urinary tract in children with CH at birth.

Genetic, environmental, and epigenetic factors involved in CAKUT

Congenital anomalies of the kidney and urinary tract (CAKUT) refer to a spectrum of structural renal malformations and are the leading cause of end-stage renal disease in children. The genetic diagnosis of CAKUT has proven to be challenging due to genetic and phenotypic heterogeneity and incomplete genetic penetrance. Monogenic causes of CAKUT have been identified using different approaches, including single gene screening, and gene panel and whole exome sequencing. The majority of the identified mutations, however, lack substantial evidence to support a pathogenic role in CAKUT. Copy number variants or single nucleotide variants that are associated with CAKUT have also been identified. Numerous studies support the influence of epigenetic and environmental factors on kidney development and the natural history of CAKUT, suggesting that the pathogenesis of this syndrome is multifactorial. In this Review we describe the current knowledge regarding the genetic susceptibility underlying CAKUT and the approaches used to investigate the genetic basis of CAKUT. We outline the associated environmental risk factors and epigenetic influences on CAKUT and discuss the challenges and strategies used to fully address the involvement and interplay of these factors in the pathogenesis of the disease.

Thyroid transcription factors in development, differentiation and disease

Identification of the thyroid transcription factors (TTFs), NKX2-1, FOXE1, PAX8 and HHEX, has considerably advanced our understanding of thyroid development, congenital thyroid disorders and thyroid cancer. The TTFs are fundamental to proper formation of the thyroid gland and for maintaining the functional differentiated state of the adult thyroid; however, they are not individually required for precursor cell commitment to a thyroid fate. Although knowledge of the mechanisms involved in thyroid development has increased, the full complement of genes involved in thyroid gland specification and the signals that trigger expression of the genes that encode the TTFs remain unknown. The mechanisms involved in thyroid organogenesis and differentiation have provided clues to identifying the genes that are involved in human congenital thyroid disorders and thyroid cancer. Mutations in the genes that encode the TTFs, as well as polymorphisms and epigenetic modifications, have been associated with thyroid pathologies. Here, we summarize the roles of the TTFs in thyroid development and the mechanisms by which they regulate expression of the genes involved in thyroid differentiation. We also address the implications of mutations in TTFs in thyroid diseases and in diseases not related to the thyroid gland.

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.

Pax genes: regulators of lineage specification and progenitor cell maintenance

Pax genes encode a family of transcription factors that orchestrate complex processes of lineage determination in the developing embryo. Their key role is to specify and maintain progenitor cells through use of complex molecular mechanisms such as alternate RNA splice forms and gene activation or inhibition in conjunction with protein co-factors. The significance of Pax genes in development is highlighted by abnormalities that arise from the expression of mutant Pax genes. Here, we review the molecular functions of Pax genes during development and detail the regulatory mechanisms by which they specify and maintain progenitor cells across various tissue lineages. We also discuss mechanistic insights into the roles of Pax genes in regeneration and in adult diseases, including cancer.

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.

A new PAX8 mutation causing congenital hypothyroidism in three generations of a family is associated with abnormalities in the urogenital tract

BACKGROUND

Although thyroid dysgenesis is the most common cause of congenital hypothyroidism (CH), its molecular basis remains largely elusive. Indeed, in only a minority of cases with thyroid dysgenesis (2%-3%) was it possible to identify an underlying genetic defect. The objective of this study was to screen the PAX8 gene and the PAX2 gene in a family with six cases of CH spanning three generations and presenting urogenital malformations. Herein, we report a case series and in vitro characterization of the PAX8 gene mutation.

METHODS

Investigations were conducted at a tertiary care referral center. The index case was diagnosed to have congenital hypothyroidism at 7 months of age when he presented with severe impairment of suckling, constipation, and poor development. Treatment with levothyroxine corrected the symptoms and was associated with catch-up growth. His progeny, including two sons, one daughter, and two granddaughters, were affected by CH, and three of them received the diagnosis at neonatal screening. Ultrasound demonstrated normally located thyroid glands with reduced volumes. Five of the six affected family members, including the index case, had urogenital malformations, including incomplete horseshoe kidney, undescended testicles, hydrocele, and ureterocele. Strabismus was found in three out of six affected patients. No other somatic malformations were found.

RESULTS

Direct sequencing of the PAX8 gene revealed a new heterozygous mutation (c.74C > G) in all affected individuals. This mutation leads to substitution of proline with arginine at codon 25 (P25R). Fluorescence microscopy showed that P25R is normally located in the nucleus. In transient transfection studies, this mutation causes reduced transcriptional activation ability when using a luciferase reporter construct under the control of a thyroglobulin promoter. This diminished transactivation ability is due to loss of DNA binding capability as shown in electrophoresis mobility shift assay. The sequencing analysis of the PAX2 gene was normal.

CONCLUSIONS

We conclude that this novel PAX8 mutation is responsible for a severe form of dominantly inherited CH. The mutation seems to be associated with abnormalities of the urogenital tract.

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.

Thyroid-specific inactivation of KIF3A alters the TSH signaling pathway and leads to hypothyroidism

Kinesins, including the kinesin 2/KIF3 molecular motor, play an important role in intracellular traffic and can deliver vesicles to distal axon terminals, to cilia, to nonpolarized cell surfaces or to epithelial cell basolateral membranes, thus taking part in the establishment of cellular polarity. We report here the consequences of kinesin 2 motor inactivation in the thyroid of 3-week-old Kif3a(Δ)(/flox) Pax8(Cre/)(+) mutant mice. Our results indicate first that 3-week-old Pax8(Cre/)(+) mice used in these experiments present minor thyroid functional defects resulting in a slight increase in circulating bioactive TSH and intracellular cAMP levels, sufficient to maintain blood thyroxine levels in the normal range. Second, Kif3a inactivation in thyrocytes markedly amplified the phenotype observed in Pax8(Cre/)(+) mice, resulting in altered TSH signaling upstream of the second messenger cAMP and mild hypothyroidism. Finally, our results in mouse embryonic fibroblasts indicate that Kif3a inactivation in the absence of any Pax8 gene alteration leads to altered G protein-coupled receptor plasma membrane expression, as shown for the β2 adrenergic receptor, and we suggest that a similar mechanism may explain the altered TSH signaling and mild hypothyroidism detected in Kif3a(Δ)(/flox) Pax8(Cre/)(+) mutant mice.

Screening of PAX8 mutations in Chinese patients with congenital hypothyroidism

BACKGROUND

Congenital hypothyroidism (CH) is a neonatal endocrine disease with an incidence of 1:2000 to 1:4000 worldwide. In about 85% of patients CH is secondary to thyroid dysgenesis, but its pathogenesis remains unclear. Thyroid transcription factors, such as paired box transcription factor 8 (PAX8), play an important role in thyroid organogenesis and development.

AIM

To screen PAX8 mutations in Chinese CH patients and characterize the features of PAX8 mutations in China.

MATERIALS AND METHODS

Blood samples were collected from 300 CH patients in Shandong Province, China, and genomic DNA was extracted from peripheral blood leukocytes. Using PCR and direct sequencing, exon 3 and exon 4 of PAX8 were analyzed.

RESULTS

Analysis of PAX8 in 300 CH patients revealed heterozygous missense mutations or variations in two unrelated patients; one was a known missense mutation G92A, resulting in an arginine to histidine substitution at codon 31, the other was a missense variation G122T, resulting in the substitution of a glycine at position 41 by a valine residue. The patient with the R31H mutation had CH with thyroid hypoplasia, while the patient with the G41V variation had CH with a eutopic and normal-sized thyroid gland.

CONCLUSION

We report a heterozygous missense mutation and a variation in PAX8 in two out of 300 unrelated Chinese CH patients, showing that the PAX8 mutation rate is very low in CH patients in China.

Functional characterization of four novel PAX8 mutations causing congenital hypothyroidism: new evidence for haploinsufficiency as a disease mechanism

BACKGROUND

Individuals carrying a heterozygous inactivating PAX8 mutation are affected by congenital hypothyroidism (CH), although heterozygous Pax8 knockout mice are not. It has remained unclear whether CH in PAX8 mutation carriers is caused by haploinsufficiency or a dominant negative mechanism.

OBJECTIVE

To report clinical and molecular findings of four novel PAX8 mutations, including one early-truncating frameshift mutation.

SUBJECTS AND METHODS

Four probands were CH patients. Two had family history of congenital or childhood hypothyroidism. Three probands were diagnosed in the frame of newborn screening for CH, while one had a negative result in screening but was diagnosed subsequently. Three had thyroid hypoplasia and one had a slightly small thyroid with low echogenicity. For these probands and their family members, we sequenced PAX8 using a standard PCR-based method. Pathogenicity of identified mutations was verified in vitro.

RESULTS

We found four novel heterozygous PAX8 mutations in the four probands: L16P, F20S, D46SfsX24, and R133Q. Family studies showed four additional mutation carriers, who were confirmed to have high serum TSH levels. Expression experiments revealed that three mutations (L16P, F20S, and R133Q) had defects in target DNA binding, while D46fs had protein instability that was rescued by the proteasome inhibitor MG132. All four mutations had reduced transactivation on the thyroglobulin promoter, supporting that they were inactivating mutations.

CONCLUSION

D46fs is the first PAX8 mutation with confirmed protein instability. Our clinical and in vitro findings together suggest that pure PAX8 haploinsufficiency can cause CH in humans.

Newborn screening and renal disease: where we have been; where we are now; where we are going

Newborn screening (NBS) has rapidly changed since its origins in the 1960s. Beginning with a single condition, then a handful in the 1990 s, NBS has expanded in the past decade to allow the detection of many disorders of amino-acid, organic-acid, and fatty-acid metabolism. These conditions often present with recurrent acute attacks of metabolic acidosis, hypoglycemia, liver failure, and hyperammonemia that may be prevented with initiation of early treatment. Renal disease is an important component of these disorders and is a frequent source of morbidity. Hemodialysis is often required for hyperammonemia in the organic acidemias and urea-cycle disorders. Rhabdomyolysis with renal failure is a frequent complication in fatty-acid oxidation disorders. Newer screening methods are under investigation to detect lysosomal storage diseases, primary immunodeficiencies, and primary renal disorders. These advances will present many challenges to nephrologists and pediatricians with respect to closely monitoring and caring for children with such disorders.

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.

Complete activation of thyroid hormone receptor β by T3 is essential for normal cochlear function and morphology in mice

BACKGROUND/AIMS

Thyroid hormones (THs) regulate many developmental processes, including the developmental onset of cochlear differentiation and function. TH action is mediated mostly by triiodothyronine (T3) bound to thyroid hormone nuclear receptors (TRs). At positive regulated genes and in the absence of THs, nuclear co-repressors are bound to TRs and decrease basal transcription rate. Ligand (T(3)) binding results in the dissociation of co-repressors and the recruitment of co-activators to the complex, which results in full transcriptional activation.

METHODS

We measured cochlear function in two knock-in mouse models: TRβ(E457A/E457A), with the TRβ co-activator binding surface (AF-2) disrupted to prevent co-activator binding; and TRβ(Δ337T/Δ337T), which is unable to bind T(3). Cochlear morphology and function were analyzed in 10-week-old normal and mutated mice. Cochlear function was determined by measuring auditory brainstem responses, cochlear tuning and compound action potential (CAP) thresholds.

RESULTS

All TRβ(Δ337T/Δ337T) and 85% of the TRβ(E457A/E457A) mice presented elevated CAP thresholds (P < 0.05 or less). Five percent of the TRβ(E457A/E457A) mice presented normal CAP thresholds with broadened cochlear tuning. TRβ(E457A/E457A) and TRβ(Δ337T/Δ337T) presented developmental defects that led to a decreased width (P < 0.01) and an increased thickness (P<0.01) of the tectorial membrane. In addition, TRβ(Δ337T/Δ337T) animals showed an increased tectorial membrane area (P<0.01).

CONCLUSION

Both mutations were deleterious to tectorial membrane development and led to important alterations in cochlear morphology and loss of cochlear function.

PAX8 mutation disturbing thyroid follicular growth: a case report

CONTEXT

Heterozygous inactivating PAX8 mutations cause congenital hypothyroidism. Although more than 30 mutation carriers have been reported, no histological examination of the thyroid has been conducted.

OBJECTIVE

The objective of this study was to document the histological characteristics of the thyroid tissue harboring a PAX8 mutation.

SUBJECTS AND METHODS

The patient was a 40-yr-old female, whose two children had congenital hypothyroidism and an inactivating PAX8 mutation (p.K80_A84dup). She had normal thyroid function but had a thyroid nodule and received right hemithyroidectomy at age 28 yr. Mutation analyses using DNA derived from multiple sources, namely lymphocytes, nails, and laser capture microdissected thyroid samples, were performed.

RESULTS

The PAX8 mutation was detected in the lymphocytes; however, the level of the mutant allele was significantly lower than that of the wild-type allele. This finding was compatible with her somatic mosaic state. We reviewed the histology of her resected thyroid and found a characteristic lesion in the nonneoplastic tissue: dense aggregates of thyrocytes with absent or very small follicles, resembling a fetal thyroid in the late phase of development. Mutation analyses of laser capture microdissected thyroid samples revealed that the fetal-like tissue carried the PAX8 mutation, whereas surrounding morphologically normal tissue and adenoma tissue did not.

CONCLUSIONS

In our case, the histology of PAX8 mutation-carrying thyroid tissue was characterized by the lack of follicular growth. Our observations provide the first evidence suggesting that the late phase of thyroid development is sensitive to the PAX8 gene dosage and can be disturbed by heterozygous inactivating PAX8 mutations.

Detection and treatment of congenital hypothyroidism

Congenital hypothyroidism is the most frequent endocrine disorder in neonates. Controversy exists regarding the necessity to adjust current screening programs to also diagnose patients with central hypothyroidism or those with mild forms of congenital hypothyroidism, who have high TSH levels but normal T(4) and normal T(3) levels (also known as 'subclinical hypothyroidism'). Thyroid hormone replacement should start as soon as the diagnosis is confirmed by measurement of elevated TSH and low serum thyroid hormone levels. Further diagnostic approaches, such as ultrasonography, scintigraphy and measurement of thyroglobulin levels, to determine the subtype of congenital hypothyroidism, should not delay initiation of treatment. Recommendations regarding the initial dosage of levothyroxine vary considerably, and no general accepted guideline exists with regards to initial dosage or optimal time point for dose adjustment according to biochemical parameters. More than 30 years after the introduction of the first neonatal screening programs, mental retardation can be prevented in the majority of children (>90%) with congenital hypothyroidism if therapy is commenced within the first 2 weeks of life, making neonate screening for this disorder the most successful population-based screening test in pediatrics.

Thyroid dysfunctions in children detected in mass screening for congenital hypothyroidism

BACKGROUND

Congenital hypothyroidism (CH) affects approximately 1:3000-1:4000 infants.

OBJECTIVES

To determine the prevalence of CH and isolated hyperthyrotropinemia (IHT) in newborns selected in mass screening for CH.

METHODS

Mass screening of 233,120 neonates born in southeastern Poland was carried out and CH-suspected children were identified. Serum thyroid-stimulating hormone and free thyroxine levels were determined during first confirmation and diagnosis re-evaluation in 118 and 34 children, respectively. Additionally, the patients were subjected to thyroid ultrasonography (n=53) and/or scintiscan (n=28).

RESULTS

Out of 118 children, first confirmation indicated CH in 58 neonates and IHT in 4 neonates. Out of these, 34 were re-evaluated with regard to diagnosis. A final diagnosis of permanent CH was reported in 34 children with thyroid dysgenesis (n=27) or dyshormonogenesis (n=7), transient CH affected 15 children, and permanent IHT was diagnosed in 6 children. CH prevalence was 1:4570 (permanent 1:6475, transient 1:38,853) and permanent IHT 1:38,853.

CONCLUSIONS

The prevalence of CH and IHT corresponds to the prevalence of the condition in iodine-sufficient and borderline iodine-deficient areas.

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.

A locus on mouse chromosome 2 is involved in susceptibility to congenital hypothyroidism and contains an essential gene expressed in thyroid

We report here the mapping of a chromosomal region responsible for strain-specific development of congenital hypothyroidism in mice heterozygous for null mutations in genes encoding Nkx2-1/Titf1 and Pax8. The two strains showing a differential predisposition to congenital hypothyroidism contain several single-nucleotide polymorphisms in this locus, one of which leads to a nonsynonymous amino acid change in a highly conserved region of Dnajc17, a member of the type III heat-shock protein-40 (Hsp40) family. We demonstrate that Dnajc17 is highly expressed in the thyroid bud and had an essential function in development, suggesting an important role of this protein in organogenesis and/or function of the thyroid gland.

Transcription factor mutations and congenital hypothyroidism: systematic genetic screening of a population-based cohort of Japanese patients

CONTEXT

Gene mutations of transcription factors that are predominantly expressed in the thyroid gland cause congenital hypothyroidism (CH). The prevalence of CH due to transcription factor mutations remains undetermined.

OBJECTIVE

This study was designed to define the prevalence of CH due to mutations of PAX8, NKX2-1 [encoding thyroid transcription factor (TTF)-1], FOXE1 (encoding TTF-2), and NKX2-5 among patients with permanent primary CH and in the general population in Japan.

SUBJECTS AND METHODS

We enrolled 102 CH patients that represent 353,000 newborns born in Kanagawa prefecture from October 1979 to June 2006. We sequenced PAX8, NKX2-1, FOXE1, and NKX2-5 using PCR-based methods. Additionally, deletion/duplication of PAX8, NKX2-1, and FOXE1 was screened by multiplex ligation-dependent probe amplification. Molecular functions of putative mutations were verified in vitro.

RESULTS

We identified a novel small duplication of PAX8 (p.K80_A84dup) in two half-sibling patients with thyroid hypoplasia. We also found a novel NKX2-1 variation (p.H60W) in a sporadic nonsyndromic CH patient. In vitro experiments showed that K80_A84dup PAX8 had impaired transactivation of the thyroglobulin promoter. H60W TTF-1 exhibited a comparable transactivating capacity with wild-type TTF-1, suggesting a benign variation. We estimate the prevalence of PAX8 mutations to be 2.0% (two in 102) among Japanese CH patients and one in 176,000 (two in 353,000) in the general Japanese population.

CONCLUSIONS

Using a population-based sample, we confirmed that a minor subset of CH patients has transcription factor mutations, but they are rare. In our cohort, PAX8 mutations were the leading cause of such a rare condition.