Weaver Syndrome-Associated EZH2 Protein Variants Show Impaired Histone Methyltransferase Function In Vitro.

Weaver syndrome (WS) is a rare congenital disorder characterized by generalized overgrowth, macrocephaly, specific facial features, accelerated bone age, intellectual disability, and susceptibility to cancers. De novo mutations in the enhancer of zeste homolog 2 (EZH2) have been shown to cause WS. EZH2 is a histone methyltransferase that acts as the catalytic agent of the polycomb-repressive complex 2 (PRC2) to maintain gene repression via methylation of lysine 27 on histone H3 (H3K27). Functional studies investigating histone methyltransferase activity of mutant EZH2 from various cancers have been reported, whereas WS-associated mutations remain poorly characterized. To investigate the role of EZH2 in WS, we performed functional studies using artificially assembled PRC2 complexes containing mutagenized human EZH2 that reflected the codon changes predicted from patients with WS. We found that WS-associated amino acid alterations reduce the histone methyltransferase function of EZH2 in this in vitro assay. Our results support the hypothesis that WS is caused by constitutional mutations in EZH2 that alter the histone methyltransferase function of PRC2. However, histone methyltransferase activities of different EZH2 variants do not appear to correlate directly with the phenotypic variability between WS patients and individuals with a common c.553G>C (p.Asp185His) polymorphism in EZH2.

Novel genetic variants in the TPO gene cause congenital hypothyroidism.

BACKGROUND: Mutations in the dual oxidase maturation factor 2 (DUOXA2) and thyroid peroxidase (TPO) genes have been reported to cause goitrous congenital hypothyroidism (GCH). The aim of this study was to determine the genetic basis of GCH in affected children. METHODS: Thirty children with GCH were enrolled for molecular analysis of the DUOXA2 and TPO genes. All subjects underwent clinical examination and laboratory testing. Genomic DNA was extracted from peripheral blood leukocytes, and Sanger sequencing was used to screen for DUOXA2 and TPO gene mutations in the exon fragments amplified from the extracted DNA. Family members of those patients with mutations were also enrolled and evaluated. RESULTS: Analysis of the TPO gene revealed six genetic variants, including two novel heterozygous mutations, c.1970T> C (p.I657T) and c.2665G> T (p.G889X), and four mutations that have been reported previously (c.670_672del, c.2268dup, c.2266T> C and c.2647C> T). Three patients harbored the same mutation c.2268dup. The germline mutations from four unrelated families were consistent with an autosomal recessive inheritance pattern. Conversely, no mutations in the DUOXA2 gene were detected. CONCLUSION: Two novel inactivating mutations (c.1970T> C and c.2665G> T) in the TPO gene were identified. The c.2268dup mutation occurred frequently. No mutations in the DUOXA2 gene were detected in this study.

Dual Oxidase System Genes Defects in Children With Congenital Hypothyroidism.

PURPOSE: The objectives of this study were to analyze the distribution of dual oxidase (DUOX) system genes (containing DUOX2, DUOX1, DUOXA2, and DUOXA1) variants in children with congenital hypothyroidism (CH) and their phenotypes. METHODS: Target region sequencing technology was performed on DUOX system genes among 606 CH subjects covering all the exon and intron regions. Detailed clinical data were collected for statistical analysis. RESULTS: A total of 95 suspected pathogenic variants were detected in the DUOX system genes, showing a 39.11% rate in variant carrying (237/606). DUOX2 had the highest rate in this study. There were statistical differences in maximum adjusted dose and current dose of levothyroxine between the DUOX system genes nonmutated group with the mutated group (both Ps < 0.001). The cases in the DUOX system genes mutated group were more likely to develop into transient CH (χ 2 = 23.155, P < 0.001) and more likely to manifested as goiter or gland-in-situ (χ 2 = 66.139, P < 0.001). In addition, there was no significant difference in clinical characteristics between DUOX system genes monoallelic and non-monoallelic. Although 20% of the variants affected the functional domain regions (EF hand, flavin adenine dinucleotide and nicotinamide adenine dinucleotide binding sites), there was no significant effect on the phenotype severity whether the variation is located in the functional domain regions. CONCLUSIONS: Our results showed the high variation rate of DUOX2 in the DUOX system genes among Chinese CH patients. The complex genotype-phenotype relationship of DUOX system genes broadened the understanding of CH phenotype spectrum.

Compound heterozygosity for a novel hemizygous missense mutation and a partial deletion affecting the catalytic core of the H2O2-generating enzyme DUOX2 associated with transient congenital hypothyroidism.

Dual oxidases (DUOX) 1 and 2 are components of the thyroid H(2)O(2)-generating system. H(2)O(2) is used by thyroperoxidase to oxidize iodide for thyroid hormonogenesis. Mutations in the DUOX2 gene have been described in transient and permanent congenital thyroid dyshormonogenesis. We report here a novel genetic defect causing congenital hypothyroidism in a French-Canadian patient. At neonatal screening, the patient had high TSH and low total T(4) levels. (99m)Tc scan showed a normally shaped orthotopic but mildly enlarged thyroid gland, suggesting dyshormonogenesis. Thyroxine treatment was given from 1 month to 17 years, after which it was stopped for re-evaluation and the patient remained euthyroid. The transient congenital hypothyroidism phenotype prompted us to screen for mutations in DUOX2 and DUOXA2 genes using the PCR-amplified direct sequencing method. We found complete inactivation of DUOX2 caused by a partial genomic deletion of one allele inherited from the mother associated with a paternally inherited missense mutation (c.4552G>A, p.Gly1518Ser). The deleted fragment encompasses the entire COOH-terminal end which is responsible for the NADPH-oxidase activity. The Gly1518Ser DUOX2 protein is expressed at the cell surface of transfected cells albeit at low level, but it is non-functional. This study provides further evidence that the permanent or transient nature of congenital hypothyroidism is not directly related to the number of inactivated DUOX2 alleles, suggesting the existence of other pathophysiological factors.

Maternal thyroid hormone: a strong repressor of neuronal nitric oxide synthase in rat embryonic neocortex.

Understanding of how maternal thyroid inadequacy during early gestation poses a risk for developmental outcomes is still a challenge for the neuroendocrine community. Early neocortical neurogenesis is accompanied by maternal thyroid hormone (TH) transfer to fetal brain, appearance of TH receptors, and absence of antineurogenesis signals, followed by optimization of neuronal numbers through apoptosis. However, the effects of TH deprivation on neurogenesis and neuronal cell death before the onset of fetal thyroid are still not clear. We show that maternal TH deficiency during early gestational period causes massive premature elevation in the expression of neuronal nitric oxide synthase (nNOS) with an associated neuronal death in embryonic rat neocortex. Maternal hypothyroidism was induced by feeding methimazole (0.025% wt/vol) in the drinking water to pregnant Sprague Dawley rats from embryonic d 6. Cerebral cortices from fetuses were harvested at different embryonic stages (embryonic d 14, 16, and 18) of hypothyroid and euthyroid groups. Immunoblotting and real-time PCR results showed that both protein and RNA levels of nNOS were prematurely increased under maternal hypothyroidism, and showed reversibility upon T4 administration. Immunohistochemistry revealed an increased nNOS immunoreactivity in both the cortical plate and proliferative zone of neocortex along with a corroborative decrease in the microtubule associated protein-2 positive neurons under maternal TH insufficiency. Results combined, put forth nNOS as a novel target of maternal TH action in embryonic neocortex, and underscore the importance of prenatal screening and timely rectification of maternal TH insufficiency, even of a moderate degree.

Pseudodominant inheritance of goitrous congenital hypothyroidism caused by TPO mutations: molecular and in silico studies.

CONTEXT AND OBJECTIVE: Most cases of goitrous congenital hypothyroidism (CH) from thyroid dyshormonogenesis 1) follow a recessive mode of inheritance and 2) are due to mutations in the thyroid peroxidase gene (TPO). We report the genetic mechanism underlying the apparently dominant inheritance of goitrous CH in a nonconsanguineous family of French Canadian origin. DESIGN, SETTING, AND PARTICIPANTS: Two brothers identified by newborn TSH screening had severe hypothyroidism and a goiter with increased (99m)Tc uptake. The mother was euthyroid, but the father and two paternal uncles had also been diagnosed with goitrous CH. After having excluded PAX8 gene mutations, we hypothesized that the underlying defect could be TPO mutations. RESULTS: Both compound heterozygous siblings had inherited a mutant TPO allele carried by their mother (c.1496delC; p.Pro499Argfs2X), and from their father, one brother had inherited a missense mutation (c.1978C-->G; p.Gln660Glu) and the other an insertion (c.1955insT; p.Phe653Valfs15X). The thyroid gland of one uncle who is a compound heterozygote for TPO mutations (p.Phe653Valfs15X/p.Gln660Glu) was removed because of concurrent multiple endocrine neoplasia type 2A. Immunohistochemistry revealed normal TPO staining, implying that Gln660Glu TPO is expressed properly. Modeling of this mutant in silico suggests that its three-dimensional structure is conserved, whereas the electrostatic binding energy between the Gln660Glu TPO and its heme group becomes repulsive. CONCLUSION: We report a pedigree presenting with pseudodominant goitrous CH due to segregation of three different TPO mutations. Although goitrous CH generally follows a recessive mode of inheritance, the high frequency of TPO mutations carriers may lead to pseudodominant inheritance.

Molecular characterization of iodotyrosine dehalogenase deficiency in patients with hypothyroidism.

CONTEXT: The recent cloning of the human iodotyrosine deiodinase (IYD) gene enables the investigation of iodotyrosine dehalogenase deficiency, a form a primary hypothyroidism resulting from iodine wasting, at the molecular level. OBJECTIVE: In the current study, we identify the genetic basis of dehalogenase deficiency in a consanguineous family. RESULTS: Using HPLC tandem mass spectrometry, we developed a rapid, selective, and sensitive assay to detect 3-monoiodo-l-tyrosine and 3,5-diodo-l-tyrosine in urine and cell culture medium. Two subjects from a presumed dehalogenase-deficient family showed elevated urinary 3-monoiodo-l-tyrosine and 3,5-diodo-l-tyrosine levels compared with 57 normal subjects without thyroid disease. Subsequent analysis of IYD revealed a homozygous missense mutation in exon 4 (c.658G>A p.Ala220Thr) that co-segregates with the clinical phenotype in the family. Functional characterization of the mutant iodotyrosine dehalogenase protein showed that the mutation completely abolishes dehalogenase enzymatic activity. One of the heterozygous carriers for the inactivating mutation recently presented with overt hypothyroidism indicating dominant inheritance with incomplete penetration. Screening of 100 control alleles identified one allele positive for this mutation, suggesting that the c.658G>A nucleotide substitution might be a functional single nucleotide polymorphism. CONCLUSIONS: This study describes a functional mutation within IYD, demonstrating the molecular basis of the iodine wasting form of congenital hypothyroidism. This familial genetic defect shows a dominant pattern of inheritance with incomplete penetration.

Transient congenital hypothyroidism caused by biallelic mutations of the dual oxidase 2 gene in Japanese patients detected by a neonatal screening program.

CONTEXT: Mutations in dual oxidase (DUOX2) have been proposed as a cause of congenital hypothyroidism. Previous reports suggest that biallelic mutations of DUOX2 cause permanent congenital hypothyroidism and that monoallelic mutations cause transient congenital hypothyroidism. OBJECTIVE: To clarify the inheritance of hypothyroidism, we looked at the DUOX2 gene in patients with transient congenital hypothyroidism. DESIGN: DUOX2, thyroid peroxidase, Na+/I- symporter and dual oxidase maturation factor 2 genes were analyzed in eight patients with transient congenital hypothyroidism, using the PCR-amplified direct sequencing method. PATIENTS: The eight patients were found by a neonatal screening program. Six of these patients belonged to two independent families; the other two were unrelated. Their serum TSH values varied from 24.8-233.0 mU/liter. Six of the eight patients had a low serum freeT4 level (0.19-0.84 ng/dl). Seven of the eight patients were treated with thyroid hormone replacement therapy, which ceased to be necessary by 9 yr of age. RESULTS: Eight novel mutations were detected in the DUOX2 gene. Four patients in one family were compound heterozygous for p.L479SfsX2 and p.K628RfsX10. Two patients in a second family were compound heterozygous for p.K530X and p.[E876K;L1067S]. The two remaining unrelated patients were also compound heterozygous, for p.H678R/p.L1067S and p.A649E/p.R885Q, respectively. CONCLUSION: All eight patients had biallelic mutations in the DUOX2 gene. We find that loss of DUOX2 activity results in transient congenital hypothyroidism and that transient congenital hypothyroidism caused by DUOX2 mutations is inherited as an autosomal recessive trait.

Clinical description of infants with congenital hypothyroidism and iodide organification defects.

AIMS: To describe the phenotype of a large group of children with congenital hypothyroidism (CH) and iodide organification defect (IOD), suspected based on normal thyroid position and abnormal perchlorate discharge test, as first step of a project evaluating correlations between phenotypes and genotypes. METHODS: 71 children born in Paris between 1980 and 2006 were included. Two groups were defined according to perchlorate discharge: total IOD (TIOD) when the release was above 90% and partial IOD (PIOD) between 10 and 90%. Comparisons between groups were performed using SPSS 14.0 for Windows. RESULTS: The incidence of IOD over the 2003-2006 period was 1:20,660. Of the 71 children, 61 had PIOD and 10 TIOD. Compared to PIOD, TIOD was characterized by greater clinical severity. A wide spectrum of clinical features was seen in the PIOD group. Evolution showed transient hypothyroidism in 10/61 patients with PIOD and 1/10 TIOD patients. CONCLUSIONS: Severe presentation in the majority of TIOD patients suggests dysfunction of a key iodide-organification enzyme. In contrast, the variety of clinical features in PIOD group suggests that diverse mechanisms may lead to PIOD, such as delayed or reduced activity of enzymes involved in hormonogenesis or defects in iodine storage and release.

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.

Missense mutations of dual oxidase 2 (DUOX2) implicated in congenital hypothyroidism have impaired trafficking in cells reconstituted with DUOX2 maturation factor.

Dual oxidase 2 (DUOX2), a reduced NAD phosphate:O2 oxidoreductase flavoprotein, is a component of the thyrocyte H2O2 generator required for hormone synthesis at the apical plasma membrane. We recently identified a specific DUOX2 maturation factor (DUOXA2) that is necessary and sufficient for expression of functional DUOX2 in mammalian cell lines. We have now used a DUOXA2 reconstituted system to provide the first characterization of natural DUOX2 missense variants (Q36H, R376W, D506N) at the molecular level, analyzing their impact on H2O2 generation, trafficking, stability, folding, and DUOXA2 interaction. The Q36H and R376W mutations completely prevent routing of DUOX2 to the cell surface. The mutant proteins are predominantly present as core N-glycosylated, thiol-reduced folding intermediates, which are retained by the quality control system within the endoplasmic reticulum (ER) as indicated by increased complexation with the lectin calnexin. D506N displays a partial deficiency phenotype with reduced surface expression of a mutant protein with normal intrinsic activity in generating H2O2. D506N N-glycan moieties are not subject to normal modification in the Golgi apparatus, suggesting that nonnative protein can escape the quality control in the ER. Oxidative folding of DUOX2 in the ER appears to be the rate-limiting step in the maturation of DUOX2, but is not facilitated by DUOXA2. Rather, DUOXA2 allows rapid ER exit of folded DUOX2 or enhanced degradation of mutant DUOX2 proteins not competent for ER exit. DUOXA2 may thus be part of a secondary quality control system specific for DUOX2.

Congenital hypothyroidism, dwarfism, and hearing impairment caused by a missense mutation in the mouse dual oxidase 2 gene, Duox2.

Dual oxidases generate the hydrogen peroxide needed by thyroid peroxidase for the incorporation of iodine into thyroglobulin, an essential step in thyroid hormone synthesis. Mutations in the human dual oxidase 2 gene, DUOX2, have been shown to underlie several cases of congenital hypothyroidism. We report here the first mouse Duox2 mutation, which provides a new genetic model for studying the specific function of DUOX2 in the thyroid gland and in other organ systems where it is hypothesized to play a role. We mapped the new spontaneous mouse mutation to chromosome 2 and identified it as a T>G base pair change in exon 16 of Duox2. The mutation changes a highly conserved valine to glycine at amino acid position 674 (V674G) and was named "thyroid dyshormonogenesis" (symbol thyd) to signify a defect in thyroid hormone synthesis. Thyroid glands of mutant mice are goitrous and contain few normal follicles, and anterior pituitaries are dysplastic. Serum T(4) in homozygotes is about one-tenth the level of controls and is accompanied by a more than 100-fold increase in TSH. The weight of adult mutant mice is approximately half that of littermate controls, and serum IGF-I is reduced. The cochleae of mutant mice exhibit abnormalities characteristic of hypothyroidism, including a delayed formation of the inner sulcus and tunnel of Corti and an abnormally thickened tectorial membrane. Hearing thresholds of adult mutant mice are on average 50-60 decibels (dB) above those of controls.

Female infertility in grt mice is caused by thyroid hormone deficiency, not by insufficient TPST2 activity in the reproductive organs.

The growth-retarded (grt) mouse has an autosomal recessive hypothyroidism and the female shows lifelong infertility. We previously reported that these mutant phenotypes are caused by a deficiency in the enzymatic activity of tyrosylprotein sulfotransferase-2 (TPST2), and severe thyroid hypogenesis and consequent dwarfism are mainly due to the impairment of the tyrosine sulfation of thyroid-stimulating hormone receptor (TSHR) by TPST2. Although TPST2 is ubiquitously expressed and many proteins are predicted to be tyrosine sulfated and involved in many biological processes, the functional roles of tyrosine sulfation in the reproductive organs remain unclear. These findings tempted us to hypothesize two possible mechanisms underlying the infertility; a deficiency in TPST2 activity in the reproductive organs might cause the infertility in grt mice, or a significant decrease in serum thyroid hormones might impair the normal development of reproductive organs. When mutant female mice were fed a diet supplemented with sufficient thyroid powder to correct their growth retardation, the rate of copulation, pregnancy, and parturition was completely restored. Therefore, we concluded that the infertility in grt female is due to a thyroid hormone deficiency.

Experimental hypothyroidism inhibits delta-aminolevulinate dehydratase activity in neonatal rat blood and liver.

The aim of this study was to investigate the potential relationship between hypothyroidism and delta-aminolevulinate dehydratase (delta-ALA-D) activity in rat blood and liver. Experimental hypothyroidism was induced in weanling rats by exposing their mothers to propylthiouracil (PTU) diluted in tap water (0.05% w/ v), ad libitum, during the lactational period (PTU group). Control (euthyroid) group included weanling rats whose mothers received just tap water, ad libitum, during the lactational period. Reverted-hypothyroid group (PTU + 3,3',5-triiodo-L-thyronine [T(3)]) included weanling rats whose mothers were exposed to PTU similarly to those in the hypothyroid group, but pups received daily subcutaneous injections of T(3) (20 microg/kg, from Postnatal Days 2-20). After the treatment, serum T(3) levels were drastically decreased (around 70%) in the PTU group, and this phenomenon was almost reverted by exogenous T(3). PTU decreased blood delta-ALA-D activity by 75%, and T(3) treatment prevented such phenomena. Erythrocytes and hemoglobin levels were increased by 10% in PTU-treated animals and higher increments (around 25%) were observed in these parameters when exogenous T(3) was coadministered. Dithiothreitol did not change blood delta-ALA-D activity of PTU-exposed animals when present in the reaction medium, suggesting no involvement of the enzyme's essential thiol groups in PTU-induced delta-ALA-D inhibition. PTU did not affect blood delta-ALA-D activity in vitro. These results are the first to show a correlation between hypothyroidism and decreased delta-ALA-D activity and point to this enzyme as a potential molecule involved with hypothyroidism-related hematological changes.

Congenital hypothyroidism alters the phosphorylation of ERK1/2 and p38MAPK in the hippocampus of neonatal rats.

Thyroid hormone deficiency during the critical period of neural differentiation produces permanent and severe alterations in the morphology and function of the nervous system leading to cretinism. Perinatal hypothyroidism results in permanent alterations of hippocampal synaptic functions in adult rats consequently causing learning and memory impairment. Mitogen-activated protein kinases (MAPKs) are a family of protein kinases that regulate essential cellular activities ranging from gene expression, mitosis, programmed cell death to plasticity and memory formation, but their involvement in perinatal hypothyroidism is not determined. The present work was designed to investigate MAPKs phosphorylation in hippocampus of congenital neonatal hypothyroid rats. Congenital hypothyroidism promotes an increase in extracellular signal-regulated kinases 1/2 (ERK 1/2) phosphorylation (+50%) and a decrease in p38(MAPK) phosphorylation (-50%) without changing in Jun N-terminal kinases (JNK) phosphorylation. Therefore, the congenital hypothyroidism model disturbs ERK 1/2 and p38(MAPK) phosphorylation pathways causing an important molecular alteration in the hippocampus. This event might be related, at least partially, to the deficits in hippocampal development and cognitive functions due neonatal congenital hypothyroidism.

Thyroid dyshormonogenesis.

Dyshormonogenesis is an uncommon cause of congenital hypothyroidism. The most common abnormality is absent or insufficient thyroid peroxidase enzyme. Perchlorate discharge test can be used to diagnose thyroid peroxidase deficiency. We report three siblings with hypothyroidism due to thyroid dyshormonogenesis. Early institution of therapy in these patients can prevent mental retardation and other features of hypothyroidism.

The Missense Alteration A5T of the Thyroid Peroxidase Gene is Pathogenic and Associated with Mild Congenital Hypothyroidism.

Congenital hypothyroidism (CH) occurs with a prevalence of approximately 1:4000 live births. Defects of thyroid hormone synthesis account for 15-20% of these cases. Thyroid peroxidase (TPO) gene is the most common cause for dyshormonogenesis. So far, more than 60 mutations in the TPO gene have been described, resulting in a variable decrease in TPO bioactivity. We present an 8-day-old male with mild CH who was identified to have a G to A transition in the fifth codon of the TPO gene (c.13G>A; p.Ala5Thr). The unaffected family members were heterozygous carriers of the mutation, whereas 400 healthy individuals of the same ethnic background did not have the mutation. Mutation analysis of 11 known causative CH genes and 4 of our own strong candidate genes with next-generation sequencing revealed no mutations in the patient nor in any other family members. The results of in silico functional analyses indicated partial loss-of-function (LOF) in the resulting enzyme molecule due to mutation. The patient's clinical finding s were consistent with the effect of this partial LOF of the mutation. In conclusion, we strongly believe that A5T alteration in the TPO gene is actually pathogenic and suggest that it should be classified as a mutation.

Prevalence of c.2268dup and detection of two novel alterations, c.670_672del and c.1186C>T, in the TPO gene in a cohort of Malaysian-Chinese with thyroid dyshormonogenesis.

OBJECTIVES: The c.2268dup mutation in the thyroid peroxidase (TPO) gene is the most common TPO alteration reported in Taiwanese patients with thyroid dyshormonogenesis. The ancestors of these patients are believed to originate from the southern province of China. Our previous study showed that this mutation leads to reduced abundance of the TPO protein and loss of TPO enzyme activity in a Malaysian-Chinese family with goitrous hypothyroidism. The aim of our study was to provide further data on the incidence of the c.2268dup mutation in a cohort of Malaysian-Chinese and its possible phenotypic effects. SETTING: Cohort study. PARTICIPANTS: Twelve biologically unrelated Malaysian-Chinese patients with congenital hypothyroidism were recruited in this study. All patients showed high thyrotropin and low free thyroxine levels at the time of diagnosis with proven presence of a thyroid gland. PRIMARY OUTCOME MEASURE: Screening of the c.2268dup mutation in the TPO gene in all patients was carried out using a PCR-direct DNA sequencing method. SECONDARY OUTCOME MEASURE: Further screening for mutations in other exonic regions of the TPO gene was carried out if the patient was a carrier of the c.2268dup mutation. RESULTS: The c.2268dup mutation was detected in 4 of the 12 patients. Apart from the c.2268dup and a previously documented mutation (c.2647C>T), two novel TPO alterations, c.670_672del and c.1186C>T, were also detected in our patients. In silico analyses predicted that the novel alterations affect the structure/function of the TPO protein. CONCLUSIONS: The c.2268dup mutation was detected in approximately one-third of the Malaysian-Chinese patients with thyroid dyshormonogenesis. The detection of the novel c.670_672del and c.1186C>T alterations expand the mutation spectrum of TPO associated with thyroid dyshormonogenesis.

Inhibition of Na(+),K(+)-ATPase in the hypothalamus, pons and cerebellum of the offspring rat due to experimentally-induced maternal hypothyroidism.

Neurodevelopment is known to be particularly susceptible to thyroid hormone insufficiency and can result in extensive structural and functional deficits within the central nervous system (CNS), subsequently leading to the establishment of cognitive impairment and neuropsychiatric symptomatology. The current study evaluated the effects of gestational and/or lactational maternal exposure to propylthiouracil (PTU)-induced hypothyroidism (as a suggestive multilevel experimental approach to the study of hypothyroidism-induced changes that has been developed and characterized by the authors) on crucial brain enzyme activities of 21-day-old Wistar rat offspring in a CNS region-specific manner. The activities of acetylcholinesterase (AChE), Na(+),K(+)-ATPase and Mg(2+)-ATPase in the offspring hypothalamus, cerebellum and pons were assessed. The study demonstrated that maternal exposure to PTU (0.05% w/v in the drinking water) during the critical periods of neurodevelopment can result in an inhibition of hypothalamic, pontine and cerebellar Na(+),K(+)-ATPase; a major marker of neuronal excitability and metabolic energy production as well as an important regulator of important systems of neurotransmission. On the other hand, no significant changes in the activities of the herein offspring CNS regions' AChE and Mg(2+)-ATPase were recorded. The observed Na(+),K(+)-ATPase inhibition: (i) is region-specific (and non-detectable in whole brain homogenetes), (ii) could constitute a central event in the pathophysiology of clinically-relevant hypothyroidism-associated developmental neurotoxicity, (iii) occurs under all examined experimental schemes, and (iv) certainly deserves further clarification at a molecular and histopathological level. As these findings are analyzed and compared to the available literature, they also underline the need for the adoption and further study of Na(+),K(+)-ATPase activity as a consistent neurochemical marker within the context of a systematic comparative study of existing (and novel) simulation approaches to congenital and early age hypothyroidism.

Variable clinical phenotypes in a family with homozygous c.1159G>A mutation in the thyroid peroxidase gene.

BACKGROUND: Defects in the thyroid peroxidase (TPO) gene have been associated with goitrous congenital hypothyroidism (CH). CASE REPORT: In this study, we report 3 siblings possessing a homozygous mutation, c.1159G>A, but exhibiting different clinical phenotypes in a Malaysian-Malay family. The index patient was diagnosed with CH during a routine neonatal screening but the other 2 siblings appeared to be asymptomatic until the ages of 19 and 12.5, respectively, when they started to develop goiter. RESULTS AND CONCLUSION: The mutation was predicted to interrupt the correct splicing of pre-mRNA and also lead to structural alterations in the functional sites of the mutant TPO. The current results suggest the association of goiter development with a homozygous c.1159G>A mutation, but the CH in the index patient could be triggered by other genetic and epigenetic factors distinct from the c.1159G>A mutation.