A family with congenital hypothyroidism caused by a combination of loss-of-function mutations in the thyrotropin receptor and adenylate cyclase-stimulating G alpha-protein subunit genes

BACKGROUND

Resistance to thyrotropin (TSH) causes congenital hypothyroidism (CH). TSH receptor (TSHR) and adenylate cyclase-stimulating G alpha protein subunit (GNAS) loss-of-function mutations cause TSH resistance. We describe a family with TSH resistance and CH bearing a combination of inactivating mutations in TSHR and GNAS genes. We describe studies to determine the molecular mechanisms involved in TSH resistance in this family.

METHODS

DNA sequencing to identify TSHR and GNAS gene mutations was performed. In vitro effects of the mutations on cAMP production and TSH binding were investigated in COS7 cells. cAMP production was evaluated by transfecting a cAMP response element (CRE)-luciferase reporter with pSVL-TSHR and pSVK3-GNAS vectors. For binding studies, cells transfected with pSVL-TSHR vectors were incubated with iodine-125 bovine TSH ((125)IbTSH).

RESULTS

Family members with and without CH were heterozygous for the TSHR mutant p.E34K or the GNAS mutant c.750_751insA (=GNASMut). The propositus had CH and he was heterozygous for TSHR p.E34K; his mother, also heterozygous for TSHR p.E34K, did not have CH. The euthyroid propositus' wife was heterozygous for GNASMut. The propositus' two daughters had CH, one was heterozygous for GNASMut and the other a compound heterezygous for TSHR p.E34K and GNASMut. Albright's hereditary osteodystrophy phenotype was present in those with GNASMut mutation but only the daughters had pseudohypoparathyroidism type 1a. Cells transfected with TSHRE34K had lower TSH affinity and less CRE-luciferase response than cells transfected with TSHR wild-type (WT). Cells transfected with GNASMut did not stimulate CRE-luciferase activity, but when cells were transfected with GNASMut plus GNASWT, a similar response to GNASWT alone was observed. The combination of TSHRWT and GNASWT showed higher CRE-luciferase response than TSHRWT and TSHRE34K with either GNASWT or GNASWT plus GNASMut.

CONCLUSIONS

CH was caused by loss-of-function mutations in TSHR and/or GNAS. The absence of CH in the propositus' mother argues against a role for TSHR p.E34K being the only cause of CH. The minimal thyroidal phenotypic differences between the sisters with pseudohypoparathyroidism type 1a and TSH resistance, both heterozygous for GNAS c.750_751insA but only one bearing the TSHR p.E34K mutant, suggest that the main cause for CH was preferential expression of the mutated maternal GNAS allele in the thyroid gland.

Benign hereditary chorea

Benign hereditary chorea (BHC) is a hyperkinetic movement disorder that historically has been characterized as a nonprogressive, dominantly inherited, childhood-onset chorea with normal intelligence. However, in some cases, atypical features were described such that controversy arose regarding whether BHC was a single syndrome. In 2002, a candidate gene, thyroid transcription factor (TITF-1), was identified to cause at least some cases of BHC. Since that time, the classical phenotype has expanded further to include "brain-thyroid-lung syndrome," which, in addition to the neurological symptoms, also manifests variable degrees of thyroid and lung abnormalities. Pathophysiologic mechanisms by which symptoms can occur are postulated to include haploinsufficiency (loss of function) and/or dominant negative effect on wild-type protein. However, genotype-phenotype correlations are complex and there is no clear relationship between mutation size, location or type of mutation, and severity of phenotype. Gross and microscopic pathology has been unremarkable, though immunohistochemistry suggests that BHC may manifest as a result of a reduced complement of migratory interneurons to the striatum and cortex. This chapter reviews the historical literature and current understanding regarding this familial, developmental disorder.

Homologs of genes expressed in Caenorhabditis elegans GABAergic neurons are also found in the developing mouse forebrain

BACKGROUND

In an effort to identify genes that specify the mammalian forebrain, we used a comparative approach to identify mouse homologs of transcription factors expressed in developing Caenorhabditis elegans GABAergic neurons. A cell-specific microarray profiling study revealed a set of transcription factors that are highly expressed in embryonic C. elegans GABAergic neurons.

RESULTS

Bioinformatic analyses identified mouse protein homologs of these selected transcripts and their expression pattern was mapped in the mouse embryonic forebrain by in situ hybridization. A review of human homologs indicates several of these genes are potential candidates in neurodevelopmental disorders.

CONCLUSIONS

Our comparative approach has revealed several novel candidates that may serve as future targets for studies of mammalian forebrain development.

Pulmonary pathology in thyroid transcription factor-1 deficiency syndrome

Thyroid transcription factor-1 (TTF-1) deficiency syndrome is characterized by neurologic, thyroidal, and pulmonary dysfunction. Children usually have mild-to-severe respiratory symptoms and occasionally die of respiratory failure. Herein, we describe an infant with a constitutional 14q12-21.3 haploid deletion encompassing the TTF-1 gene locus who had cerebral dysgenesis, thyroidal dysfunction, and respiratory insufficiency. The clinical course was notable for mild hyaline membrane disease, continuous ventilatory support, and symmetrically distributed pulmonary cysts by imaging. He developed pneumonia and respiratory failure and died at 8 months. Pathologically, the lungs had grossly visible emphysematous changes with "cysts" up to 2 mm in diameter. The airway generations and radial alveolar count were diminished. In addition to acute bacterial pneumonia, there was focally alveolar septal fibrosis, pneumocyte hypertrophy, and clusters of airspace macrophages. Ultrastructurally, type II pneumocytes had numerous lamellar bodies, and alveolar spaces contained fragments of type II pneumocytes and extruded lamellar bodies. Although immunoreactivity for surfactant protein SP-A and ABCA3 was diminished, that for SP-B and proSP-C was robust, although irregularly distributed, corresponding to the distribution of type II pneumocytes. Immunoreactivity for TTF-1 protein was readily detected. In summation, we document abnormal airway and alveolar morphogenesis and altered expression of surfactant-associated proteins, which may explain the respiratory difficulties encountered in TTF-1 haploinsufficiency. These findings are consistent with experimental evidence documenting the important role of TTF-1 in pulmonary morphogenesis and surfactant metabolism.

Congenital hypothyroidism

Congenital hypothyroidism (CH) occurs in approximately 1:2,000 to 1:4,000 newborns. The clinical manifestations are often subtle or not present at birth. This likely is due to trans-placental passage of some maternal thyroid hormone, while many infants have some thyroid production of their own. Common symptoms include decreased activity and increased sleep, feeding difficulty, constipation, and prolonged jaundice. On examination, common signs include myxedematous facies, large fontanels, macroglossia, a distended abdomen with umbilical hernia, and hypotonia. CH is classified into permanent and transient forms, which in turn can be divided into primary, secondary, or peripheral etiologies. Thyroid dysgenesis accounts for 85% of permanent, primary CH, while inborn errors of thyroid hormone biosynthesis (dyshormonogeneses) account for 10-15% of cases. Secondary or central CH may occur with isolated TSH deficiency, but more commonly it is associated with congenital hypopitiutarism. Transient CH most commonly occurs in preterm infants born in areas of endemic iodine deficiency. In countries with newborn screening programs in place, infants with CH are diagnosed after detection by screening tests. The diagnosis should be confirmed by finding an elevated serum TSH and low T4 or free T4 level. Other diagnostic tests, such as thyroid radionuclide uptake and scan, thyroid sonography, or serum thyroglobulin determination may help pinpoint the underlying etiology, although treatment may be started without these tests. Levothyroxine is the treatment of choice; the recommended starting dose is 10 to 15 mcg/kg/day. The immediate goals of treatment are to rapidly raise the serum T4 above 130 nmol/L (10 ug/dL) and normalize serum TSH levels. Frequent laboratory monitoring in infancy is essential to ensure optimal neurocognitive outcome. Serum TSH and free T4 should be measured every 1-2 months in the first 6 months of life and every 3-4 months thereafter. In general, the prognosis of infants detected by screening and started on treatment early is excellent, with IQs similar to sibling or classmate controls. Studies show that a lower neurocognitive outcome may occur in those infants started at a later age (> 30 days of age), on lower l-thyroxine doses than currently recommended, and in those infants with more severe hypothyroidism.

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.

Genetic Basis of Children's Interstitial Lung Disease

Specific genetic causes for children's interstitial lung disease (chILD) have been identified within the past decade. These include deletions of or mutations in genes encoding proteins important in surfactant production and function (SP-B, SP-C, and ABCA3), surfactant catabolism (GM-CSF receptor), as well as transcription factors important for surfactant production (TTF1) or lung development (Fox F1), with heterozygous deletions or loss-of-function mutations of the latter resulting in alveolar capillary dysplasia (ACD) with misalignment of the pulmonary veins. Familial pulmonary fibrosis in adults may result from mutations in genes encoding components of telomerase and SP-A2. While not yet reported in children, the expression of these genes in alveolar type II epithelial cells supports a key role for the disruption of normal homeostasis in this cell type in the pathogenesis of interstitial lung disease. The identification of specific genetic causes for chILD now allows for the possibility of non-invasive diagnosis, and provides insight into basic cellular mechanisms that may allow the development of novel therapies.

Morphogenesis of the thyroid gland

Congenital hypothyroidism is mainly due to structural defects of the thyroid gland, collectively known as thyroid dysgenesis. The two most prevalent forms of this condition are abnormal localization of differentiated thyroid tissue (thyroid ectopia) and total absence of the gland (athyreosis). The clinical picture of thyroid dysgenesis suggests that impaired specification, proliferation and survival of thyroid precursor cells and loss of concerted movement of these cells in a distinct spatiotemporal pattern are major causes of malformation. In normal development the thyroid primordium is first distinguished as a thickening of the anterior foregut endoderm at the base of the prospective tongue. Subsequently, this group of progenitors detaches from the endoderm, moves caudally and ultimately differentiates into hormone-producing units, the thyroid follicles, at a distant location from the site of specification. In higher vertebrates later stages of thyroid morphogenesis are characterized by shape remodeling into a bilobed organ and the integration of a second type of progenitors derived from the caudal-most pharyngeal pouches that will differentiate into C-cells. The present knowledge of thyroid developmental dynamics has emerged from embryonic studies mainly in chicken, mouse and more recently also in zebrafish. This review will highlight the key morphogenetic steps of thyroid organogenesis and pinpoint which crucial regulatory mechanisms are yet to be uncovered. Considering the co-incidence of thyroid dysgenesis and congenital heart malformations the possible interactions between thyroid and cardiovascular development will also be discussed.

Characterization of mutations in the FOXE1 gene in a cohort of unrelated Malaysian patients with congenital hypothyroidism and thyroid dysgenesis

The FOXE1 gene was screened for mutations in a cohort of 34 unrelated patients with congenital hypothyroidism, 14 of whom had thyroid dysgenesis and 18 were normal (the thyroid status for 2 patients was unknown). The entire coding region of the FOXE1 gene was PCR-amplified, then analyzed using single-stranded conformational polymorphism, followed by confirmation by direct DNA sequencing. DNA sequencing analysis revealed a heterozygous A>G transition at nucleotide position 394 in one of the patients. The nucleotide transition changed asparagine to aspartate at codon 132 in the highly conserved region of the forkhead DNA binding domain of the FOXE1 gene. This mutation was not detected in a total of 104 normal healthy individuals screened. The binding ability of the mutant FOXE1 protein to the human thyroperoxidase (TPO) promoter was slightly reduced compared with the wild-type FOXE1. The mutation also caused a 5% loss of TPO transcriptional activity.

[New aspects of genetics and molecular mechanisms on thyroid morphogenesis for the understanding of thyroid dysgenesia]

The elucidation of the molecular mechanisms underlying the very early steps of thyroid organogenesis and the etiology of most cases of thyroid dysgenesis are poorly understood. Many genes have been identified as important contributors to survival, proliferation and migration of thyroid cells precursors, acting as an integrated and complex regulatory network. Moreover, by generation of mouse mutants, the studies have provided better knowledge of the role of these genes in the thyroid morphogenesis. In addition, it is likely that a subset of patients has thyroid dysgenesis as a result of mutations in regulatory genes expressed during embryogenesis. This review summarizes molecular aspects of thyroid development, describes the animal models and phenotypes known to date and provides information about novel insights into the ontogeny and pathogenesis of human thyroid dysgenesis.

Thyroid transcription factor-1 (TTF-1/Nkx2.1/TITF1) gene regulation in the lung

TTF-1 [thyroid transcription factor-1; also known as Nkx2.1, T/EBP (thyroid-specific-enhancer-binding protein) or TITF1] is a homeodomain-containing transcription factor essential for the morphogenesis and differentiation of the thyroid, lung and ventral forebrain. TTF-1 controls the expression of select genes in the thyroid, lung and the central nervous system. In the lung, TTF-1 controls the expression of surfactant proteins that are essential for lung stability and lung host defence. Human TTF-1 is encoded by a single gene located on chromosome 14 and is organized into two/three exons and one/two introns. Multiple transcription start sites and alternative splicing produce mRNAs with heterogeneity at the 5' end. The 3' end of the TTF-1 mRNA is characterized by a rather long untranslated region. The amino acid sequences of TTF-1 from human, rat, mouse and other species are very similar, indicating a high degree of sequence conservation. TTF-1 promoter activity is maintained by the combinatorial or co-operative actions of HNF-3 [hepatocyte nuclear factor-3; also known as FOXA (forkhead box A)], Sp (specificity protein) 1, Sp3, GATA-6 and HOXB3 (homeobox B3) transcription factors. There is limited information on the regulation of TTF-1 gene expression by hormones, cytokines and other biological agents. Glucocorticoids, cAMP and TGF-beta (transforming growth factor-beta) have stimulatory effects on TTF-1 expression, whereas TNF-alpha (tumour necrosis factor-alpha) and ceramide have inhibitory effects on TTF-1 DNA-binding activity in lung cells. Haplo-insufficiency of TTF-1 in humans causes hypothyroidism, respiratory dysfunction and recurring pulmonary infections, underlining the importance of optimal TTF-1 levels for the maintenance of thyroid and lung function. Recent studies have implicated TTF-1 as a lineage-specific proto-oncogene for lung cancer.

Lethal respiratory failure and mild primary hypothyroidism in a term girl with a de novo heterozygous mutation in the TITF1/NKX2.1 gene

CONTEXT

Thyroid transcription factor 1 (TITF1/NKX2.1) is expressed in the thyroid, lung, ventral forebrain, and pituitary. In the lung, TITF1/NKX2.1 activates the expression of genes critical for lung development and function. Titf/Nkx2.1(-/-) mice have pituitary and thyroid aplasia but also impairment of pulmonary branching. Humans with heterozygous TITF1/NKX2.1 mutations present with various combinations of primary hypothyroidism, respiratory distress, and neurological disorders.

OBJECTIVE

The objective of the study was to report clinical and molecular studies of the first patient with lethal neonatal respiratory distress from a novel heterozygous TITF1/NKX2.1 mutation.

PARTICIPANT

This girl, the first child of healthy nonconsanguineous French-Canadian parents, was born at 41 wk. Birth weight was 3,460 g and Apgar scores were normal. Soon after birth, she developed acute respiratory failure with pulmonary hypertension. At neonatal screening on the second day of life, TSH was 31 mU/liter (N <15) and total T(4) 245 nmol/liter (N = 120-350). Despite mechanical ventilation, thyroxine, surfactant, and pulmonary vasodilators, the patient died on the 40th day.

RESULTS

Histopathology revealed pulmonary tissue with low alveolar counts. The thyroid was normal. Sequencing of the patient's lymphocyte DNA revealed a novel heterozygous TITF1/NKX2.1 mutation (I207F). This mutation was not found in either parent. In vitro, the mutant TITF-1 had reduced DNA binding and transactivation capacity.

CONCLUSION

This is the first reported case of a heterozygous TITF1/NKX2.1 mutation leading to neonatal death from respiratory failure. The association of severe unexplained respiratory distress in a term neonate with mild primary hypothyroidism is the clue that led to the diagnosis.

The requirement of Nkx2-1 in the temporal specification of cortical interneuron subtypes

Previous work has demonstrated that the character of mouse cortical interneuron subtypes can be directly related to their embryonic temporal and spatial origins. The relationship between embryonic origin and the character of mature interneurons is likely reflected by the developmental expression of genes that direct cell fate. However, a thorough understanding of the early genetic events that specify subtype identity has been hampered by the perinatal lethality resulting from the loss of genes implicated in the determination of cortical interneurons. Here, we employ a conditional loss-of-function approach to demonstrate that the transcription factor Nkx2-1 is required for the proper specification of specific interneuron subtypes. Removal of this gene at distinct neurogenic time points results in a switch in the subtypes of neurons observed at more mature ages. Our strategy reveals a causal link between the embryonic genetic specification by Nkx2-1 in progenitors and the functional attributes of their neuronal progeny in the mature nervous system.

Mutation of a gene for thyroid transcription factor-1 (TITF1) in a patient with clinical features of resistance to thyrotropin

Resistance to TSH (RTSH [MIM 275200]) is a heterogeneous condition defined by variable degree of insensitivity to biologically active TSH. While this condition is classically caused by loss-of-function mutations of the TSH receptor gene (TSHR), several patients have exhibited RTSH-like phenotype in the apparent absence of TSHR mutations, and some of them have mutations of PAX8 or GNAS1. We identified a Japanese boy with congenital hypothyroidism who suffered from recurrent lower respiratory infection during infancy and choreoathetosis at a later age. At 14 years of age, he was diagnosed as having RTSH, on the basis of compensated hypothyroidism (TSH, 30.2 mU/L; FT4, 1.2 ng/dl), disproportionate increments of thyroid hormones and TSH during a TRH test (DeltaFT3, 0.4 pg/ml; DeltaT3, 13 ng/dl; and DeltaTSH, 88.3 mU/L), and normal ultrasound thyroid image and radioactive iodine uptakes. Molecular analysis for TITF1 revealed a novel de novo heterozygous deletion/insertion mutation (c.470_479delinsGCG,) that is predicted to lose the entire homeodomain and the NK2-specific domain. We suggest that a heterozygous loss-of-function TITF1 mutation can also cause RTSH-compatible phenotype.

A novel NKX2.1 mutation in a family with hypothyroidism and benign hereditary chorea

BACKGROUND

We studied a boy with congenital hypothyroidism, benign hereditary chorea, and respiratory distress. His mother and his grandfather were affected by hypothyroidism with a late onset and benign hereditary chorea. The aim of this study was to establish the genetic defects that cause that phenotype and study the molecular mechanisms of the pathology.

METHODS

NKX2.1, PAX8, NKX2.5, and TAZ genes were sequenced.

RESULTS

Direct sequencing of the NKX2.1 gene showed, in all the affected, a new heterozygous mutation from cytosine to adenine in the second base of the triplet encoding for the amino acid at position 145. The mutation (C609A) is responsible for a change from serine to a stop codon (S145X). We also demonstrated that the mutant protein is predominantly in the cytoplasm and unable to translocate into the nucleus. Of note, the S145X mutation produces variable phenotypes in the affected members of the family. No mutations have been identified in the NKX2.5, PAX8, and TAZ genes.

CONCLUSIONS

Our study extends the knowledge of the functional effect of NKX2.1 mutations and further highlights the complexities of genotype-phenotype correlation in the NKX2.1 deficiency syndromes.

Thyrotropin receptor and thyroid transcription factor-1 genes variant in Chinese children with congenital hypothyroidism

The aim of the present study was to investigate the mutation/variant of thyrotropin receptor (TSHR) and thyroid transcription factor-1 (TTF-1) genes in Chinese children with congenital hypothyroidism (CH). Seventy-nine and forty-nine Chinese children with CH were enrolled for molecular analysis of the TSHR gene and TTF-1 gene, respectively. One hundred normal children were evaluated as control. The coding regions of TSHR and TTF-1 genes were amplified by polymerase chain reaction and sequenced. Sequencing of the TSHR gene revealed a compound heterozygous variants (Pro52Thr/Val689Gly) and a heterozygous variant (Gly245Ser) in 2 of 79 patients. In 30 patients and 33 controls the normal cytosine at position 2181 in exon 10 of TSHR gene was replaced by a guanineCresulting in the replacement of Asp (727) by Glu. In 47 patients and 50 controls, the normal thymidine at position 561 in exon 7 of TSHR gene was replaced by a cytosine. This substitution did not change the amino acid in position 187. Sequencing of the TTF-1 gene revealed no mutation or polymorphism in 49 patients and 100 controls. In conclusion, three heterozygous variants (Pro52Thr, Gly245Ser, Val689Gly) of TSHR gene were firstly detected in Chinese children with CH. There were polymorphisms in exon 10 at nucleotide 2181 (C/G) and in exon 7 at nucleotide 561 (T/C) in TSHR gene. No mutation or polymorphism was detected in the coding region of TTF-1 gene. The mutation/variant of TSHR and TTF-1 genes is relatively rare in Chinese children with CH.

Genetic bases of benign thyroid processes

The advances made in the last decade in gene analysis techniques have greatly simplified the study of the genetic bases of disease, hastening identification of the genes causing or involved in disease development. Rapid and low-cost genome sequencing in all individuals may become a reality. The genetic bases of defects in thyroid hormone formation have been well defined, and those of defects in thyroid ontogeny have been partially defined; in the last 4 years, the genes responsible for 2 new syndromes causing reduced sensitivity of the action of thyroid hormone and affecting thyroid hormone transport (MCT8 mutations) and intracellular metabolism (SECISBP2 mutations) have been discovered. The genetic bases of toxic adenomas and toxic multinodular goiters have been determined and several genes involved in the development of follicular thyroid adenomas have been identified. However, not all the genes involved in thyroid ontogeny have been identified and the genetic bases of multinodular hyperplastic goiter, highly prevalent in some regions of Spain, as well as those of most autoimmune thyroid disorders, are unknown. Major challenges remain in the characterization of the genetic bases of benign thyroid processes, which, together with their high prevalence and the current and future potential of technology, suggest a promising and exciting future in this field of research.

Benign hereditary chorea revisited: a journey to understanding

Benign hereditary chorea (BHC) has been characterized as an autosomal dominant disorder manifesting nonprogressive chorea without dementia. However, there has been controversy regarding its existence. Diagnosis has been based solely on clinical criteria with many patients and families demonstrating "atypical" features and until recently, no diagnostic test was available for confirmation. Since 2002, mutations in the thyroid transcription factor (TITF-1) gene have been identified as resulting in some cases of BHC. Additionally, the clinical spectrum has expanded to include abnormalities in thyroid and lung with the putative mechanism of disease resulting from gene haploinsufficiency and reduced protein product. This review summarizes both a historical perspective and our current understanding of BHC.

Homeobox genes in vertebrate forebrain development and disease

Homeobox genes are an evolutionarily conserved class of transcription factors that are key regulators of developmental processes such as regional specification, patterning, migration and differentiation. In both mouse and humans, the developing forebrain is marked by distinct boundaries of homeobox gene expression at different developmental time points. These genes regulate the patterning of the forebrain along the dorsal/ventral and rostral/caudal axes and are also essential for the differentiation of specific neuronal subtypes. Inhibitory interneurons that arise from the ganglionic eminences and migrate tangentially to the neocortex and hippocampus are dramatically affected by mutations in several homeobox genes. In this review, we discuss the identification, expression patterns, loss- and/or gain-of-function models, and confirmed transcriptional targets for a set of homeobox genes required for the correct development of the forebrain in the mouse. In humans, mutations of homeobox genes expressed in the forebrain have been shown to result in mental retardation, epilepsy or movement disorders. The number of homeobox genes currently linked to human nervous system disease is surprisingly low, perhaps reflecting the essential functions of these genes throughout embryogenesis or the degree of functional redundancy during central nervous system development.

Gbetagamma dimers released in response to thyrotropin activate phosphoinositide 3-kinase and regulate gene expression in thyroid cells

Signaling by TSH through its receptor leads to the dissociation of trimeric G proteins into Galpha and Gbetagamma. Galphas activates adenylyl cyclase, which increases cAMP levels that induce several effects in the thyroid cell, including transcription of the sodium-iodide symporter (NIS) gene through a mechanism involving Pax8 binding to the NIS promoter. Much less is known about the function of Gbetagamma in thyroid differentiation, and therefore we studied their role in TSH signaling. Gbetagamma overexpression inhibits NIS promoter activation and reduces NIS protein accumulation in response to TSH and forskolin. Conversely, inhibition of Gbetagamma-dependent pathways increases NIS promoter activity elicited by TSH but does not modify forskolin-induced activation. Gbetagamma dimers are being released from the Gs subfamily of proteins, because cholera toxin mimics the effects elicited by TSH, whereas pertussis toxin has no effect on NIS promoter activity. We also found that TSH stimulates Akt phosphorylation in a phosphoinositide 3-kinase (PI3K)-dependent and cAMP-independent manner. This is mediated by Gbetagamma, because its overexpression or specific sequestration, respectively, increased or reduced phosphorylated Akt levels upon TSH stimulation. Gbetagamma sequestration increases NIS protein levels induced by TSH and Pax8 binding to the NIS promoter, which is also increased by PI3K inhibition. This is, at least in part, caused by Gbetagamma-mediated Pax8 exclusion from the nucleus that is attenuated when PI3K activity is blocked. These data unequivocally demonstrate that Gbetagamma released by TSH action stimulate PI3K, inhibiting NIS gene expression in a cAMP-independent manner due to a decrease in Pax8 binding to the NIS promoter.

Genetic Abnormalities of Surfactant Metabolism

Pulmonary surfactant is the complex mixture of lipids and proteins needed to reduce alveolar surface tension at the air-liquid interface and prevent alveolar collapse at the end of expiration. It has been recognized for almost 50 years that a deficiency in surfactant production due to pulmonary immaturity is the principal cause of the respiratory distress syndrome (RDS) observed in prematurely born infants.1 Secondary surfactant deficiency due to injury to the cells involved in its production and functional inactivation of surfactant is also important in the pathophysiology of acute respiratory distress syndrome (ARDS) observed in older children and adults.2,3 In the past 15 years, it has been recognized that surfactant deficiency may result from genetic mechanisms involving mutations in genes encoding critical components of the surfactant system or proteins involved in surfactant metabolism.4,5 Although rare, these single gene disorders provide important insights into normal surfactant metabolism and into the genes in which frequently occurring allelic variants may be important in more common pulmonary diseases.

Functional characterization of a novel mutation in TITF-1 in a patient with benign hereditary chorea

Benign hereditary chorea (BHC) is an autosomal dominant disorder of early onset characterised by non progressive choreic movements with normal cognitive function occasionally associated with hypothyroidism and respiratory problems. Numerous pieces of evidence link BHC with TITF-1/NKX2.1 gene mutations. We studied a patient with a familial benign hereditary chorea and normal thyroid and respiratory function. Sequence analysis of TITF-1 revealed the presence of a heterozygous C>T substitution at nucleotide 532, predicted to change an arginine (CGA) with a stop codon (TGA) at position 178 (R178X). A functional analysis shows that the mutated TTF-1 is not binding DNA, nor activating the canonical thyroid target gene promoter or interfering with the ability of wild type TTF-1 to activate transcription. In addition, the mutated protein is predominantly cytoplasmic, rather than nuclear as in the case of the wild type TTF-1. Thus, we have identified a new mutation in the TTF-1 coding gene in a patient with benign hereditary chorea. The results show that the mutation leads to a haploinsufficiency of TITF-1 and opens the question of genotype/phenotype correlation.

Polymorphic length of FOXE1 alanine stretch: evidence for genetic susceptibility to thyroid dysgenesis

Familial cases of congenital hypothyroidism from thyroid dysgenesis (TD) (OMIM 218700) occur with a frequency 15-fold higher than by chance, FOXE1 is one of the candidate genes for this genetic predisposition and contains an alanine tract. Our purpose is to assess the influence of length of the alanine tract of FOXE1 on genetic susceptibility to TD. A case-control association study (based on 115 patients affected by TD and 129 controls genotyped by direct sequencing) and transmission disequilibrium testing (TDT) analyses were performed. The transcriptional activities of FOXE1 constructs containing 14 or 16 alanines were also studied. In the case-control association study, the 16/16 and 16/14 genotypes were inversely associated with TD (OR = 0.39, 95%CI = 0.22-0.68, P = 0.0005), strongly suggesting that the presence of 16 alanines in the tract protect against the occurrence of TD. This association was stronger in the subgroup of patients with ectopic thyroid (OR = 0.28, 95%CI = 0.13-0.58, P = 0.00015). The protection was confirmed by the TDT analysis performed in 39 trios (chi(2) = 4.3, P = 0.0374). Alternatively, the presence of the 14/14 genotype is associated with an increase risk of TD (OR = 2.59, 95%CI = 1.56-4.62, P = 0.0005). The expression studies showed that the transcriptional activities of FOXE1 with 16 alanines were significantly higher (1.55-fold) than FOXE1 containing 14 alanines (P < 0.003), while the nuclear localisation of the proteins was not affected. We conclude that FOXE1 through its alanine containing stretch modulates significantly the risk of TD occurrence, enhancing a mechanism linking an alanine containing transcription factor to disease.

A mutation in Tpst2 encoding tyrosylprotein sulfotransferase causes dwarfism associated with hypothyroidism

The growth-retarded (grt) mouse has an autosomal recessive, fetal-onset, severe thyroid hypoplasia related to TSH hyporesponsiveness. Through genetic mapping and complementation experiments, we show that grt is a missense mutation of a highly conserved region of the tyrosylprotein sulfotransferase 2 (Tpst2) gene, encoding one of the two Tpst genes implicated in posttranslational tyrosine O-sulfation. We present evidence that the grt mutation leads to a loss of TPST2 activity, and TPST2 isoform has a high degree of substrate preference for TSH receptor (TSHR). The expression of TPST2 can restore TSH-TSHR-mediated cAMP production in fibroblasts derived from grt mice. Therefore, we propose that the tyrosine sulfation of TSHR by TPST2 is crucial for TSH signaling and resultant thyroid gland function.

GATA and Nkx factors synergistically regulate tissue-specific gene expression and development in vivo

In vitro studies have suggested that members of the GATA and Nkx transcription factor families physically interact, and synergistically activate pulmonary epithelial- and cardiac-gene promoters. However, the relevance of this synergy has not been demonstrated in vivo. We show that Gata6-Titf1 (Gata6-Nkx2.1) double heterozygous (G6-Nkx DH) embryos and mice have severe defects in pulmonary epithelial differentiation and distal airway development, as well as reduced phospholipid production. The defects in G6-Nkx DH embryos and mice are similar to those observed in human neonates with respiratory distress syndromes, including bronchopulmonary dysplasia, and differential gene expression analysis reveals essential developmental pathways requiring synergistic regulation by both Gata6 and Titf1 (Nkx2.1). These studies indicate that Gata6 and Nkx2.1 act in a synergistic manner to direct pulmonary epithelial differentiation and development in vivo, providing direct evidence that interactions between these two transcription factor families are crucial for the development of the tissues in which they are co-expressed.

New syndromic form of benign hereditary chorea is associated with a deletion of TITF-1 and PAX-9 contiguous genes

Benign hereditary chorea is a rare autosomal dominant disorder presenting with a childhood-onset and slowly progressive chorea. The objective of this study was to describe the clinical and genetic features of 3 patients who developed childhood-onset chorea. Three affected patients from three generations of a family with benign hereditary chorea associated with a multisystemic disorder of the basal ganglia, thyroid, lungs, salivary glands, bowels, and teeth. The TITF-1 gene was screened by microsatellite analysis, gene sequencing, and fluorescence in situ hybridization. Genetic analysis revealed a novel 0.9-Mb deletion on chromosome 14, which includes the TITF-1 and PAX9 genes. We have identified a novel deletion responsible for a new syndrome of benign hereditary chorea, including symptoms of brain-thyroid-lung syndrome associated with bowels, salivary glands, and teeth disorders. Associated signs, sometimes of slight expression, remain of high interest for the clinical and genetic diagnosis of benign hereditary chorea.

Human Thyroid Oxidases genes promoter activity in thyrocytes does not appear to be functionally dependent on Thyroid Transcription Factor-1 or Pax8

Thyroid Oxidases (ThOX/DUOX) genes encode proteins that are thought to play a crucial role in the biosynthesis of thyroid hormone by providing the oxidizing agent required to allow the organification of iodine. The expression of these genes is not restricted to the thyroid, but the corresponding mRNAs are found in the thyrocyte more abundantly than in several other cell types. It raises the question whether the same transcription factors, namely Thyroid Transcription Factor-1 (TTF-1) and Pax8, that control the expression of other genes involved in the differentiated thyroid function, also regulate ThOX/DUOX gene transcription in the thyrocyte. We set up a functional co-transfection assay in which fusion proteins composed of the DNA-binding domain of either TTF-1 or Pax8 fused to the repressive domain of the drosophila engrailed protein were used to competitively counteract the activity of endogenous TTF-1 or Pax8 factor in the differentiated thyroid cell line PCCl3. Contrary to the Thyroglobulin or Thyroid Peroxidase promoter, the known regulatory elements of the human ThOX/DUOX genes displayed no reduction in transcriptional activity when either TTF-1 or Pax8 competitor was produced in the cell, indicating that the presently characterized control elements of human ThOX/DUOX genes are not responsive to these thyroid-specific transcription factors.

Molecular advances in thyroglobulin disorders

Synthesis of tri-iodothyronine (T(3)) and thyroxine (T(4)) follows a metabolic pathway that depends on the integrity of the thyroglobulin structure. This large glycoprotein is a homodimer of 660 kDa synthesized and secreted by the thyroid cells into the lumen of thyroid follicle. In humans it is coded by a single copy gene, 270 kb long, that maps on chromosome 8q24 and contains an 8.5 kb coding sequence divided into 48 exons. The preprotein monomer is composed of a 19-amino acid signal peptide followed by a 2749-amino acid polypeptide. In the last decade, several mutations in the thyroglobulin gene were reported. In animals, four of them have been observed in Afrikander cattle (p.R697X), Dutch goats (p.Y296X), cog/cog mouse (p.L2263P) and rdw rats (p.G2300R). Mutations in the human thyroglobulin gene are associated with congenital goiter or endemic and nonendemic simple goiter. Thirty-five inactivating mutations have been identified and characterized in the human thyroglobulin gene: 20 missense mutations (p.C175G, p.Q310P, p.Q851H, p.S971I, p.R989C, p.P993L, p.C1058R, p.C1245R, p.S1447N, p.C1588F, p.C1878Y, p.I1912V, p.C1977S, p.C1987Y, p.C2135Y, p.R2223H, p.G2300D, p.R2317Q, p.G2355V, p.G2356R), 8 splice site mutations (g.IVS3-3C>G, g.IVS5+1G>A, g.IVS10-1G>A, g.IVS24+1G>C, g.IVS30+1G>T, g.IVS30+1G>A, g.IVS34-1G>C, g.IVS45+2T>A) 5 nonsense mutations (p.R277X, p.Q692X, p.W1418X, p.R1511X, p.Q2638X) and 2 single nucleotide deletions (p.G362fsX382, p.D1494fsX1547). The thyroglobulin gene has been also identified as the major susceptibility gene for familial autoimmune thyroid diseases (AITD) by linkage analysis using highly informative polymorphic markers. In conclusion the identification of mutations in the thyrogobulin gene has provided important insights into structure-function relationships.

Thyroid-specific enhancer-binding protein/NKX2.1 is required for the maintenance of ordered architecture and function of the differentiated thyroid

Thyroid-specific enhancer-binding protein (T/ebp)/Nkx2.1-null mouse thyroids degenerate by embryonic day (E) 12-13 through apoptosis whereas T/ebp/Nkx2.1-heterogyzgous mice exhibit hypothyroidism with elevated TSH levels. To understand the role of T/ebp/Nkx2.1 in the adult thyroid, a thyroid follicular cell-specific conditional knockout (KO) mouse line, T/ebp(fl/fl);TPO-Cre, was established that expresses Cre recombinase under the human thyroid peroxidase (TPO) gene promoter. These mice appeared to be healthy and exhibited loss of T/ebp/Nkx2.1 expression in many, but not all, thyroid follicular cells as determined by immunohistochemistry and real-time PCR, thus presenting a T/ebp-thyroid-conditional hypomorphic mice. Detailed analysis of the thyroids from T/ebp(fl/fl), T/ebp(fl/fl);TPO-Cre, and T/ebp(fl/ko) mice, where the latter mouse line is derived from crosses with the original T/ebp/Nkx2.1-heterozygous mice, revealed that T/ebp(fl/fl);TPO-Cre mice can be classified into two groups with different phenotypes: one having atrophic/degenerative thyroid follicles with frequent presence of adenomas and extremely high serum TSH levels, and the other having an altered thyroid structure with reduced numbers of extraordinary dilated follicles consisting of excessive numbers of follicular cells as compared with those usually found in the normal thyroid. The latter phenotype was also observed in aged T/ebp(fl/ko) mouse thyroids. In vitro three-dimensional thyroid primary cultures using thyroids from T/ebp(fl/fl);TPO-Cre, T/ebp(fl/ko), and T/ebp(fl/fl) mice, and the latter treated with recombinant adenovirus with and without Cre expression, demonstrated that only cells from T/ebp(fl/fl) mice without adeno-Cre treatment formed follicular structures. Taken together, these results suggest that T/ebp/Nkx2.1 is required for maintenance of the normal architecture and function of differentiated thyroids.

Genetics, clinical management and natural history of congenital hypothyroidism

Congenital hypothyroidism has an incidence of 1:3000-4000 newborns. In the past, it was a common cause of mental retardation, although newborn screening has improved the prognosis. Several transcription factors are crucial to the early organogenesis of the thyroid, including TITF1, FOXE1, PAX8 and HHEX. Nevertheless, a small minority of humans with congenital hypothyroidism carry mutations in these genes. Long-term follow-up studies show that with appropriate therapy, the mental and physical development of congenital hypothyroidism patients is in the normal range, although somewhat delayed when compared with appropriate controls. Critical issues of treatment include early diagnosis and rapid correction of hypothyroidism by ensuring rapid initiation of treatment and rapid normalization of thyroid-stimulating hormone levels, especially in cases of severe congenital hypothyroidism. There has been recent question of the need to treat premature infants with hypothyroxinemia but no elevation of the thyroid-stimulating hormone concentration. Numerous controlled studies of the short- and long-term effects of thyroid hormone supplementation have not shown a consistent benefit in this group of patients. Future research will investigate further the genetic underpinnings of the condition. There is a worldwide need to prevent congenital hypothyroidism by ensuring adequate dietary iodine and to develop infrastructure to diagnose and treat congenital hypothyroidism in developing countries.

Three Mutations (p.Q36H, p.G418fsX482, and g.IVS19-2A>C) in the Dual Oxidase 2 Gene Responsible for Congenital Goiter and Iodide Organification Defect

Background: Iodide organification defects are associated with mutations in the dual oxidase 2 (DUOX2) gene and are characterized by a positive perchlorate discharge test. These mutations produce a congenital goitrous hypothyroidism, usually transmitted in an autosomal recessive mode.

Methods: We studied the complete coding sequence of the human DUOX2 gene by single-strand conformational polymorphism (SSCP) analysis of DNA from 17 unrelated patients with iodide organification defects. Samples showing an aberrant pattern were directly sequenced. All mutations were validated by SSCP analysis. Finally, the effect of a splicing mutation was studied by construction of minigenes.

Results: Genomic DNA sequencing revealed 3 novel mutations [c.108G&gt;C (p.Q36H), c.1253delG (p.G418fsX482), and g.IVS19-2A&gt;C] and 1 previously reported mutation [c.2895-2898delGTTC (p.S965fsX994)] in 2 families with 1 (family 1) and 2 (family 2) affected members. This implies the inheritance of 2 compound heterozygous mutations, p.Q36H and p.S965fsX994 in family 1 and p.G418fsX482 and g.IVS19-2A&gt;C in family 2. The c.1253delG mutation was associated with a c.1254C&gt;A transversion. In vitro transcription analysis showed that exon 20 is skipped entirely when the g.IVS19-2A&gt;C mutation is present. The wild-type glutamine residue at position 36 is strictly conserved.

Conclusions: Two previously unknown compound heterozygous mutations in the DUOX2 gene, p.Q36H/p.S965fsX994 and p.G418fsX482/g.IVS19-2A&gt;C, are responsible for iodide organification defects in 2 unrelated families. Identification of the molecular basis of this disorder might be helpful for understanding the pathophysiology of this congenital hypothyroidism.

Mutations inTITF1 are not relevant to sporadic and familial chorea of unknown cause

Benign hereditary chorea (BHC; OMIM 118700) is an autosomal dominant movement disorder. Mutations in the thyroid transcription factor 1 (TITF1) gene have been linked with BHC. The phenotype for BHC is highly variable and may include atypical features such as dystonia, slow saccades, and even cognitive deficits. Although BHC is commonly transmitted in a dominant manner, assessment of TITF1 mutations in familial or sporadic patients with late-onset nonprogressive or early-onset progressive chorea is of practical relevance in order to evaluate diagnostic strategies in single patients. In this study, 18 patients with chorea of unknown cause including index patients of three families with autosomal dominantly inherited nonprogressive chorea have been screened for TITF1 mutations by means of denaturating high-pressure liquid chromatography (dHPLC). No sequence variations were detected for the complete open reading frame, suggesting that TITF1 mutations are not a common cause of sporadic or familial chorea of unknown cause. Additionally, linkage analysis excluded TITF1 mutations in a large family with benign hereditary chorea.

A mouse model demonstrates a multigenic origin of congenital hypothyroidism

Congenital hypothyroidism with thyroid dysgenesis (TD) is a frequent human condition characterized by elevated levels of TSH in response to reduced thyroid hormone levels. Congenital hypothyroidism is a genetically heterogeneous disease. In the majority of cases studied, no causative mutations have been identified and very often the disease does not show a Mendelian transmission. However, in approximately 5% of cases, it can be a consequence of mutations in genes encoding the TSH receptor or the transcription factors TITF1, FOXE1, or PAX8. We report here that in mouse models, the combination of partial deficiencies in the Titf1 and Pax8 genes results in an overt TD phenotype that is absent in either of the singly deficient, heterozygous mice. The disease is characterized by a small thyroid gland, elevated levels of TSH, reduced thyroglobulin biosynthesis, and high occurrence of hemiagenesis. The observed phenotype is strain specific, and the pattern of transmission indicates that at least two other genes, in addition to Titf1 and Pax8, are necessary to generate the condition. These results show that TD can be of multigenic origin in mice and strongly suggest that a similar pathogenic mechanism may be observed in humans.

Nonsense mutation in TITF1 in a Portuguese family with benign hereditary chorea

Benign hereditary chorea (BHC) is an autosomaldominant disorder of early onset characterized by a slowly progressing or nonprogressing chorea, without cognitive decline or other progressive neurologic dysfunction, but also by the existence of heterogeneity of the clinical presentation within and among families. The genetic cause of BHC is the presence of either point mutations or deletions in the thyroid transcription factor 1 gene (TITF1). We studied a Portuguese BHC family composed of two probands: a mother and her only son. The patients were identified in a neurology out-patient clinic showing mainly involuntary choreiform movements since childhood, myoclonic jerks, falls, and dysarthria. We performed magnetic resonance imaging (MRI), electroencephalogram (EEG), nerve conduction studies, thyroid ultrasound scan, biochemical thyroid tests, and electrocardiogram (ECG). We excluded Huntington disease by appropriate genetic testing and sequenced the entire TITF1 gene for both patients. The patients showed MRI alterations: (1) in the mother, abnormal hyperintense pallida and cortical cerebral/cerebellar atrophy; and (2) in the son, small hyperintense foci in the cerebellum and subtle enlargement of the fourth ventricle. Sequence analysis of the TITF1 gene in these patients revealed the presence of a heterozygous C > T substitution at nucleotide 745, leading to the replacement of a glutamine at position 249 for a premature stop codon. A previously undescribed nonsense mutation in the TITF1 gene was identified as being the genetic cause of BHC in this family.

Altered parvalbumin-positive neuron distribution in basal ganglia of individuals with Tourette syndrome

Tourette syndrome (TS) is a childhood neuropsychiatric disorder characterized by motor and vocal tics. Imaging studies found alterations in caudate (Cd) and putamen volumes. To investigate possible alterations in cell populations, postmortem basal ganglia tissue from individuals with TS and normal controls was analyzed by using unbiased stereological techniques. A markedly higher total neuron number was found in the globus pallidus pars interna (GPi) of TS. In contrast, a lower neuron number and density was observed in the globus pallidus pars externa and in the Cd. An increased number and proportion of the GPi neurons were positive for the calcium-binding protein parvalbumin in tissue from TS subjects, whereas lower densities of parvalbumin-positive interneurons were observed in both the Cd and putamen of TS subjects. This change is consistent with a developmental defect in tangential migration of some GABAergic neurons. The imbalance in striatal and GPi inhibitory neuron distribution suggests that the functional dynamics of cortico-striato-thalamic circuitry are fundamentally altered in severe, persistent TS.

Linkage and mutational analysis of familial thyroid dysgenesis demonstrate genetic heterogeneity implicating novel genes

The pathophysiology of thyroid dysgenesis (TD) is not elucidated yet in the majority of cases. The unexpected familial clustering of congenital hypothyroidism due to TD suggests a genetically determined disorder. Four genes have been hitherto involved in thyroid development, including migration and growth. Three of these encode transcription factors (the thyroid transcription factors 1 and 2 (TTF1 or NKX2.1 and TTF2 or FOXE1) and PAX8) while the other encodes the thyrotropin hormone receptor (TSHR). Some mutations have been reported in patients affected by thyroid defects, which supports the relevance of these four genes in TD. However, their involvement in the general TD population remains questionable. Therefore, to document their involvement, we performed a linkage analysis followed by mutational analysis in 19 multiplex TD families. The LOD score results failed to prove linkage between any of the four genes and the TD phenotype, whatever the postulated mode of inheritance. Manual extended haplotypes showed allele sharing among affected individuals of at least one of these four genes in the majority of families. Nevertheless, mutational analysis did not identify mutations in these cases, arguing in favor of identity by descent and not identity by state. Furthermore, as a main result of the present study, extended haplotypes confirmed by mutational analysis showed that the four genes were excluded in five out of the 19 investigated families, demonstrating the relevance of other genes. In conclusion, the present study demonstrates genetic heterogeneity in the TD disorder and suggests the involvement of novel genes.

Thyroid Transcription Factor 1 Rescues PAX8/p300 Synergism Impaired by a Natural PAX8 Paired Domain Mutation with Dominant Negative Activity

Mutations in the paired domain transcription factor PAX8 are a rare cause of congenital hypothyroidism due to thyroid dysgenesis. We identified a novel and unique PAX8 mutation segregating in seven affected members of a three-generations family. The mutation replaces an invariant serine residue within helix 2 of the paired DNA-binding domain for phenylalanine. The mutant protein (PAX8-S48F) does not induce the thyroglobulin promoter in nonthyroid cells, but displays almost half of wild-type PAX8 activity in thyroid cells. PAX8-S48F shows no defect in expression, nuclear targeting, or DNA binding and retains the ability to synergize with thyroid transcription factor 1 (TTF-1, NKX2.1). However, we found that in nonthyroid cells, the acetylation-independent synergism with the general transcriptional adaptor p300 is completely abrogated, suggesting that PAX8-S48F may be unable to efficiently recruit p300. Reconstitution experiments in nonthyroid cells reveal that TTF-1 can partially rescue PAX8-S48F/p300 synergism and thus reproduce the situation in thyroid cells. These functional characteristics result in a dominant negative effect of PAX8-S48F on coexpressed wild-type PAX8 activity, which is not observed in paired domain mutations with DNA binding defect. Our results describe the first dominant negative missense mutation in a paired domain and provide evidence for a crucial role of the p300 coactivator in mediating the functional synergism between PAX8 and TTF-1 in thyroid-specific gene expression.

Thyroid hemiagenesis is a rare variant of thyroid dysgenesis with a familial component but without Pax8 mutations in a cohort of 22 cases

Thyroid hemiagenesis is a rare form of thyroid dysgenesis of which some familial cases have been reported, including one associated with a heterozygous mutation in the Pax8 gene. However, the physiopathology remains not well known. The objectives of this study were 1) to describe the clinical features, 2) to look for familial clustering, and 3) to search for Pax8 mutations in a relatively large cohort of affected patients. A family history of thyroid dysgenesis was found in nine patients (40%), whose affected relatives had ectopic thyroid (n = 4), athyreosis (n = 1), thyroid hemiagenesis (n = 2), or thyroglossal duct cysts (n = 2). Screening for Pax8 mutations identified abnormal migration profiles by SSCP analysis in 3 patients, but direct sequencing did not show coding region mutations in any of the 22 patients. In conclusion, this study provides the first evidence that thyroid hemiagenesis can occur as a familial disorder associated with any form of thyroid dysgenesis. This finding supports both a common underlying mechanism to the various abnormalities in thyroid development and a role for genetic factors; however, our results from Pax8 analysis suggest that this gene may not be a key factor.

Brain-Thyroid-Lung syndrome: a patient with a severe multi-system disorder due to a de novo mutation in the thyroid transcription factor 1 gene

A 23-year-old man was diagnosed with pulmonary alveolar proteinosis at the age of 11 months, and primary hypothyroidism gradually developed during infancy. He had delayed developmental milestones and severe hypotonia that evolved into non-progressive chorea during childhood. He died from large cell lung carcinoma at the age of 23 years. A de novo heterozygous insertion mutation 859-860insC in the TITF-1 gene was demonstrated.

CONCLUSION

TITF-1 gene mutations should be considered in paediatric and adult patients with unexplained (combinations of) chorea, mental retardation, primary hypothyroidism, and chronic lung disease. Introduction of a name for the disorder, e.g. Brain-Thyroid-Lung syndrome, would probably facilitate further recognition. Whether the TITF-1 gene mutation in this patient predisposed to the development of lung cancer remains speculative.

TTF-1 and RET promoter SNPs: regulation of RET transcription in Hirschsprung's disease

Single nucleotide polymorphisms (SNPs) of the coding regions of receptor tyrosine kinase gene (RET) are associated with Hirschsprung's disease (HSCR, aganglionic megacolon). These SNPs, individually or combined, may act as a low penetrance susceptibility locus and/or be in linkage disequilibrium (LD) with another susceptibility locus located in RET regulatory regions. Because two RET promoter SNPs have been found associated with HSCR, in LD with HSCR-associated RET coding region haplotypes, their implication in the transcriptional regulation of RET is of major interest. Analysis of 172 sporadic HSCR patients also revealed the presence of HSCR-associated RET promoter SNPs in LD with the main coding region RET haplotype observed in Chinese patients. By using a weighted logistic regression approach, we determined that of all SNPs tested in our study, the promoter SNPs are the most correlated to the disease. Functional analysis of the RET promoter SNPs in the context of additional 5' regulatory regions demonstrated that the HSCR-associated alleles decrease RET transcription. These SNPs overlap a TTF-1 binding site and TTF-1-activated RET transcription is also decreased by the HSCR-associated SNPs. Moreover, we identified an HSCR patient with a Gly322Ser TTF-1 mutation that compromises activation of transcription from HSCR-associated RET promoter haplotypes. Interestingly, we show that the pattern of RET and TTF-1 expression is coincident in developing human gut. We also present a detailed profile of the RET gene in our population, which provides an insight into the higher incidence of the disease in China.

Thyroid development and its disorders: genetics and molecular mechanisms

Thyroid gland organogenesis results in an organ the shape, size, and position of which are largely conserved among adult individuals of the same species, thus suggesting that genetic factors must be involved in controlling these parameters. In humans, the organogenesis of the thyroid gland is often disturbed, leading to a variety of conditions, such as agenesis, ectopy, and hypoplasia, which are collectively called thyroid dysgenesis (TD). The molecular mechanisms leading to TD are largely unknown. Studies in murine models and in a few patients with dysgenesis revealed that mutations in regulatory genes expressed in the developing thyroid are responsible for this condition, thus showing that TD can be a genetic and inheritable disease. These studies open the way to a novel working hypothesis on the molecular and genetic basis of this frequent human condition and render the thyroid an important model in the understanding of molecular mechanisms regulating the size, shape, and position of organs.

Pituitary hypoplasia and respiratory distress syndrome in Prop1 knockout mice

Mutations in Prophet of PIT1 (Prop1), one of several homeodomain transcription factors that are required for the development of the anterior pituitary gland, are the predominant cause of MPHD (multiple pituitary hormone deficiency) in humans. We show that deletion of Prop1 in mice causes severe pituitary hypoplasia with failure of the entire Pit1 lineage and delayed gonadotrope development. The pituitary hormone deficiencies cause secondary endocrine problems and a high rate of perinatal mortality due to respiratory distress. Lung atelectasis in mutants correlates with reduced levels of NKX2.1 and surfactant. Lethality of mice homozygous for either the null allele or a spontaneous hypomorphic allele is strongly influenced by genetic background. Prop1-null mice are an excellent model for MPHD and may be useful for testing the efficacy of pharmaceutical intervention for neonatal respiratory distress.

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

Thyroid dysgenesis is the most common cause of congenital hypothyroidism, a relatively frequent disease affecting 1 in 3000-4000 newborns. Whereas most cases are sporadic, mutations in transcription factors implicated in thyroid development have been shown to cause a minority of cases transmitted as monogenic Mendelian diseases. PAX8 is one of these transcription factors, and so far, five mutations have been identified in its paired domain in patients with thyroid dysgenesis. We have identified a novel mutation of PAX8, in the heterozygous state, in a father and his two children both presenting with congenital hypothyroidism associated with an in-place thyroid of normal size at birth. In addition, one of the affected siblings displayed unilateral kidney agenesis. The mutation substitutes a highly conserved serine in position 54 of the DNA-binding domain of the protein (S54G mutation) by a glycine. Functional analyses of the mutant protein (PAX8-S54G) demonstrated that it is unable to bind a specific cis-element of the thyroperoxidase gene promoter in EMSAs and that it has almost completely lost the ability to act in synergy with Titf1 to transactivate transcription from the thyroglobulin promoter/enhancer. These results indicate that loss of function mutations of the PAX8 gene may cause congenital hypothyroidism in the absence of thyroid hypoplasia.

Autosomal dominant transmission of congenital hypothyroidism, neonatal respiratory distress, and ataxia caused by a mutation of NKX2-1

OBJECTIVE

To study the NKX2-1 gene in two half-siblings with elevated thyroid-stimulating hormone (TSH) on state screen, prolonged neonatal respiratory distress despite term gestations, and persistent ataxia, dysarthria, and developmental delay.

STUDY DESIGN

We amplified and sequenced DNA samples from blood or buccal swab for subjects and their unaffected siblings.

RESULTS

The same mutation that prevents splicing together of exons 2 and 3 of the NKX2-1 gene was present in the affected siblings, their mother, and maternal grandmother but not in their unaffected siblings. The mutation was present in the heterozygous form, thus explaining the disease phenotype.

CONCLUSIONS

Autosomal dominant transmission of mutations of NKX2-1 may cause congenital hypothyroidism, neonatal respiratory distress at term, and persistent neurologic findings such as ataxia, choreoathetosis, and dysarthria in families with affected subjects in multiple generations.

Analysis of the PAX8 gene in congenital hypothyroidism caused by different forms of thyroid dysgenesis in a father and daughter

Thyroid dysgenesis occurs sporadically with only rare familial presentation. We report a father and daughter with congenital hypothyroidism caused by different forms of thyroid dysgenesis. The father had a severely hypoplastic thyroid gland in a normal location, whereas the daughter had an ectopic thyroid gland in a sublingual position. Her brother had a hypoplastic thyroid but was euthyroid. The involvement of the candidate gene, PAX8, as the cause of thyroid dysgenesis in this family was partially excluded by linkage analysis, and the possibility of a de novo mutation excluded by sequencing.

Thyroglobulin gene mutations and other genetic defects associated with congenital hypothyroidism

Congenital hypothyroidism affects about 1:3000-1:4000 infants. Screening programs now permit early recognition and treatment, thus avoiding the disastrous consequences of thyroid hormone deficiency on brain development. In about 85%, congenital hypothyroidism is associated with developmental defects referred to as thyroid dysgenesis. They include thyroid (hemi)agenesis, ectopic tissue and thyroid hypoplasia. Thyroid dysgenesis is usually sporadic; in only 2% it occurs in a familial fashion. It can be caused by mutations in transcription factors that are essential for the development and function of thyroid follicular cells. Thyroid hypoplasia can also result from resistance to TSH at the level of the thyrocytes. Defects in the steps required for thyroid hormone synthesis within thyroid follicular cells are referred to as dyshormonogenesis and account for about 10-15% of congenital hypothyroidism. In contrast to thyroid dysgenesis, affected patients typically present with goitrous enlargement of the thyroid. The defects leading to dyshormonogenesis typically display a recessive mode of inheritance. Careful clinical, biochemical and molecular analyses of patients with syndromic and non-syndromic forms of thyroid dysgenesis and dyshormonogenesis have significantly enhanced our understanding of the wide spectrum of pathogenetic mechanisms underlying congenital hypothyroidism and provide unique insights into the (patho)physiology of thyroid development and hormone synthesis.

Aspectos genéticos do hipotireoidismo congênito

Hipotireoidismo congênito (HC) afeta cerca de 1:3000 a 1:4000 recém-nascidos (RN). Numerosos genes são essenciais, tanto para o desenvolvimento normal do eixo hipotálamo-hipófise-tireóide quanto para a produção hormonal, e estão associados ao HC. Cerca de 85% do hipotireoidismo primário é denominado disgenesia tireoidiana e evidências sugerem que mutações nos fatores de transcrição (TTF2, TTF1 e PAX-8) e no gene do receptor de TSH podem ser responsáveis pela doença. Os defeitos hereditários da síntese hormonal podem ser devidos a mutações nos genes NIS (natrium-iodide symporter), pendrina, tireoglobulina (TG), peroxidase (TPO). Mais recentemente, mutações no gene THOX-2 têm sido descritas para defeitos na organificacão. O hipotireoidismo central afeta cerca de 1:20.000 RN e tem sido associado com mutações nos fatores transcricionais hipofisários (POUIF1, PROP1, LHX3, HESX1). A síndrome de resistência periférica ao hormônio tireoidiano é uma doença rara que cursa com hipotireoidismo em alguns tecidos e, freqüentemente, está associada a mutações autossômicas dominantes no receptor beta (TRß).