Genetics of congenital hypothyroidism

The defense and signaling role of NADPH oxidases in eukaryotic cells : Review

This short review article summarizes what is known clinically and biochemically about the seven human NADPH oxidases. Emphasis is put on the connection between mutations in the catalytic and regulatory subunits of Nox2, the phagocyte defense enzyme, with syndromes like chronic granulomatous disease, as well as a number of chronic inflammatory diseases. These arise paradoxically from a lack of reactive oxygen species production needed as second messengers for immune regulation. Both Nox2 and the six other human NADPH oxidases display signaling functions in addition to the functions of these enzymes in specialized biochemical reactions, for instance, synthesis of the hormone thyroxine. NADPH oxidases are also needed by Saccharomyces cerevisiae cells for the regulation of the actin cytoskeleton in times of stress or developmental changes, such as pseudohyphae formation. The article shows that in certain cancer cells Nox4 is also involved in the re-structuring of the actin cytoskeleton, which is required for cell mobility and therefore for metastasis.

Genetics and management of congenital hypothyroidism

Several evidences support a relevant genetic origin for Congenital Hypothyroidism (CH), however familial forms are uncommon. CH can be due to morphogenetic or functional defects and several genes have been originally associated either with thyroid dysgenesis or dyshormonogenesis, with a highly variable expressivity and a frequently incomplete penetrance of the genetic defects. The phenotype-driven genetic analyses rarely yielded positive results in more than 10% of cases, thus raising doubts on the genetic origin of CH. However, more recent unsupervised approaches with systematic Next Generation Sequencing (NGS) analysis revealed the existence of hypomorphic alleles of these candidate genes whose combination can explain a significant portion of CH cases. The co-segregation studies of the hypothyroid phenotype with multiple gene variants in pedigrees confirmed the potential oligogenic origin of CH, which finally represents a suitable explanation for the frequent sporadic occurrence of this disease.

The genetic characteristics of congenital hypothyroidism in China by comprehensive screening of 21 candidate genes

OBJECTIVE

Congenital hypothyroidism (CH), the most common neonatal metabolic disorder, is characterized by impaired neurodevelopment. Although several candidate genes have been associated with CH, comprehensive screening of causative genes has been limited.

DESIGN AND METHODS

One hundred ten patients with primary CH were recruited in this study. All exons and exon-intron boundaries of 21 candidate genes for CH were analyzed by next-generation sequencing. And the inheritance pattern of causative genes was analyzed by the study of family pedigrees.

RESULTS

Our results showed that 57 patients (51.82%) carried biallelic mutations (containing compound heterozygous mutations and homozygous mutations) in six genes (DUOX2, DUOXA2, DUOXA1, TG, TPO and TSHR) involved in thyroid hormone synthesis. Autosomal recessive inheritance of CH caused by mutations in DUOX2, DUOXA2, TG and TPO was confirmed by analysis of 22 family pedigrees. Notably, eight mutations in four genes (FOXE1, NKX2-1, PAX8 and HHEX) that lead to thyroid dysgenesis were identified in eight probands. These mutations were heterozygous in all cases and hypothyroidism was not observed in parents of these probands.

CONCLUSIONS

Most cases of congenital hypothyroidism in China were caused by thyroid dyshormonogenesis rather than thyroid dysgenesis. This study identified previously reported causative genes for 57/110 Chinese patients and revealed DUOX2 was the most frequently mutated gene in these patients. Our study expanded the mutation spectrum of CH in Chinese patients, which was significantly different from Western countries.

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

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

A frequent oligogenic involvement in congenital hypothyroidism

Congenital hypothyroidism (CH), the most frequent form of preventable mental retardation, is predicted to have a relevant genetic origin. However, CH is frequently reported to be sporadic and candidate gene variations were found in <10% of the investigated patients. Here, we characterize the involvement of 11 candidate genes through a systematic Next Generation Sequencing (NGS) analysis. The NGS was performed in 177 unrelated CH patients (94 gland-in-situ; 83 dysgenesis) and in 3,538 control subjects. Non-synonymous or splicing rare variants (MAF < 0.01) were accepted, and their functional impact was predicted by a comprehensive bioinformatic approach and co-segregation studies. The frequency of variations in cases and controls was extended to 18 CH-unrelated genes. At least one rare variant was accepted in 103/177 patients. Monogenic recessive forms of the disease were found in five cases, but oligogenic involvement was detected in 39 patients. The 167 variations were found to affect all genes independently of the CH phenotype. These findings were replicated in an independent cohort of additional 145 CH cases. When compared to 3,538 controls, the CH population was significantly enriched with disrupting variants in the candidate genes (P = 5.5 × 10-7), but not with rare variations in CH-unrelated genes. Co-segregation studies of the hypothyroid phenotype with multiple gene variants in several pedigrees confirmed the potential oligogenic origin of CH. The systematic NGS approach reveals the frequent combination of rare variations in morphogenetic or functional candidate genes in CH patients independently of phenotype. The oligogenic origin represents a suitable explanation for the frequent sporadic CH occurrence.

DUOX2 Mutations Are Associated With Congenital Hypothyroidism With Ectopic Thyroid Gland

CONTEXT

Thyroid dysgenesis (TD) is the leading cause of congenital hypothyroidism (CH). The etiology of TD remains unknown in ∼90% of cases, the most common form being thyroid ectopia (TE) (48% to 61%).

OBJECTIVE

To search for candidate genes in hypothyroid children with TE.

DESIGN, SETTING, AND PARTICIPANTS

We followed a cohort of 268 children with TD and performed whole-exome sequencing (WES) in three children with CH with TE (CHTE) and compared them with 18 thyroid-healthy controls. We then screened an additional 41 children with CHTE by Sanger sequencing and correlated the WES and Sanger molecular findings with in vitro functional analysis.

MAIN OUTCOME MEASURES

Genotyping, mutation prediction analysis, and in vitro functional analysis.

RESULTS

We identified seven variants in the DUOX2 gene, namely G201E, L264CfsX57, P609S, M650T, E810X, M822V, and E1017G, and eight known variations. All children carrying DUOX2 variations had high thyroid-stimulating hormone levels at neonatal diagnosis. All mutations were localized in the N-terminal segment, and three of them led to effects on cell surface targeting and reactive oxygen species generation. The DUOX2 mutants also altered the interaction with the maturation factor DUOXA2 and the formation of a stable DUOX2/DUOXA2 complex at the cell surface, thereby impairing functional enzymatic activity. We observed no mutations in the classic genes related to TD or in the DUOX1 gene.

CONCLUSION

Our findings suggest that, in addition to thyroid hormonogenesis, the DUOX2 N-terminal domain may play a role in thyroid development.

The Sodium/Iodide Symporter (NIS): Molecular Physiology and Preclinical and Clinical Applications

Active iodide (I^-) transport in both the thyroid and some extrathyroidal tissues is mediated by the Na⁺/I^- symporter (NIS). In the thyroid, NIS-mediated I^- uptake plays a pivotal role in thyroid hormone (TH) biosynthesis. THs are key during embryonic and postembryonic development and critical for cell metabolism at all stages of life. The molecular characterization of NIS in 1996 and the use of radioactive I^- isotopes have led to significant advances in the diagnosis and treatment of thyroid cancer and provide the molecular basis for studies aimed at extending the use of radioiodide treatment in extrathyroidal malignancies. This review focuses on the most recent findings on I^- homeostasis and I^- transport deficiency-causing NIS mutations, as well as current knowledge of the structure/function properties of NIS and NIS regulatory mechanisms. We also discuss employing NIS as a reporter gene using viral vectors and stem cells in imaging, diagnostic, and therapeutic procedures.

Thyroid Hemiagenesis: Incidence, Clinical Significance, and Genetic Background

CONTEXT

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

EVIDENCE ACQUISITION

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

EVIDENCE SYNTHESIS

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

CONCLUSIONS

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

Single nucleotide polymorphism 1623 A/G (rs180195) in the promoter of the Thyroglobulin gene is associated with autoimmune thyroid disease but not with thyroid ophthalmopathy

Background

Our studies over recent years have focused on some new ideas concerning the pathogenesis for the orbital reaction that characterizes Graves’ ophthalmopathy namely, that there are antigens expressed by thyroid tissue and orbital tissue where they are targeted by autoantibodies and/or sensitized T cells, leading to orbital inflammation. While this has been well studied for the thyroid stimulating hormone-receptor, the possible role of another major thyroid antigen, Thyroglobulin (TG), has been largely ignored.

Methods

We identified novel variant 1623 A/G single nucleotide polymorphism (SNP) (rs180195) in the promoter of TG gene associated with autoimmune thyroid disorders. We genotyped the TG SNPs rs2069566, rs2076739, rs121912646, rs121912647, rs121912648, rs121912649, rs121912650, rs137854433, rs137854434, and rs180195 by MassARRAY SNP analysis using iPLEX technology in a cohort of 529 patients with thyroid autoimmunity with and without ophthalmopathy, and controls.

Results

We showed that variant 1623 A/G SNP (rs180195) in the promoter of TG gene is a marker for thyroid autoimmunity, but not for ophthalmopathy. We showed that there was a significant difference in the distribution of the major allele (G) vs minor allele (A) in patients with Hashimoto’s thyroiditis (HT). In HT the wild-type (GG) genotype was less common. We showed that the genotypes homozygous AA and heterozygous GA rs180195 SNP in the promoter of TG gene were more closely associated with thyroid autoimmunity than the wild-type (GG) polymorphism, and are thus, markers of autoimmunity.

Conclusion

rs180195 SNP was previously identified by Stefan et al independently of us, who showed that this TG SNP predisposed to autoimmune thyroid diseases. However, this is the first study to explore the association between TG SNPs and HT. Our findings support the notion that the thyroid and orbital disorders are not part of the same disease, ie, “Graves’ disease” or “Hashimoto’s disease”, but separate autoimmune disorders.

Defects of Thyroid Hormone Synthesis and Action

Congenital hypothyroidism (CH) is the most common inborn endocrine disorder and causes significant morbidity. To date, we are only aware of the molecular basis responsible for the defects in a small portion of patients with CH. A better understanding of the pathophysiology of these cases at the genetic and molecular basis provides useful information for proper counseling to patients and their families a well as for the development of better targeted therapies. This article provides a succinct outline of the pathophysiology and genetics of the known causes of thyroid dysgenesis, dyshormonogenesis, and syndrome of impaired sensitivity to thyroid hormone.

The role of season and climate in the incidence of congenital hypothyroidism in Kerman province, Southeastern Iran

BACKGROUND

Congenital hypothyroidism (CH) is a common endocrine disease and an important cause of mental retardation. The purpose of this study was to investigate the probable role of season and climatic factors in the incidence of CH in Kerman province, Iran.

METHODS

Incidence data were collected from the CH screening program files from 2005 to 2011 in Kerman province, a number of 288,437 infants were included in the study. Climate data were collected from the Meteorological Office. The relations were tested by χ2-test, Pearson correlation, and negative binomial regression.

RESULTS

The overall incidence of CH in Kerman province was 2.68 per 1000 births. There was a significant difference in both the monthly and seasonal incidence of CH (p<0.05). There were a few significant, but weak correlation between some climatic factors and the incidence of CH in some regions, but the results were inconsistent.

CONCLUSIONS

It seems like there is no clear relation between CH incidence and climate factors, in Kerman Province. However, CH incidence was highest in October (Autumn) and lowest in June (Summer).

Congenital Hypothyroidism: Role of Nuclear Medicine

Thyroid scintigraphy holds a key place in the etiologic workup of neonatal hypothyroidism. Routine screening for this disorder in maternity hospitals in industrialized countries, for nearly 40 years, has permitted early treatment and thereby helped to prevent its physical and mental complications. Neonatal hypothyroidism affects approximately 1 in 3000 births. The most common causes are abnormal thyroid gland development and defective hormone synthesis by an eutopic thyroid gland. The incidence of the latter has risen in recent years, for reasons that remain unclear. A thorough etiologic workup helps to determine the disease type. Current guidelines recommend thyroid imaging by means of ultrasound and scintigraphy. Ultrasound should be done by a practitioner trained to examine the cervical region of newborns, as the thyroid is very small and must be distinguished from the particular aspect of the "thyroid empty lodge." Ultrasound lacks sensitivity for detecting small ectopic glands but is the gold standard for measuring thyroid dimensions. Scintigraphy provides an etiologic diagnosis in most cases. The two isotopes used in this setting are technetium-99m and iodine-123. The latter isotope gives more contrast and allows the perchlorate discharge test to be performed to detect abnormal iodide organification in the neonate with an eutopic thyroid. If scintigraphy cannot be performed during the neonatal period, a postponed procedure can be achieved after 3 years of age. Close cooperation between the nuclear medicine physician and the pediatric endocrinologist is crucial for timely and optimized scintigraphy.

Genotype-phenotype correlations of dyshormonogenetic goiter in children and adolescents from South India

BACKGROUND

Dyshormonogenetic goiter is one of the most common causes of hypothyroidism in children and adolescents in iodine nonendemic areas. The exact genotype-phenotypic correlations (GPCs) and risk categorization of hypothyroid phenotypes of dyshormonogenetic mutations are largely speculative. The genetic studies in pediatric dyshormonogenesis are very sparse from Indian sub-continent. In this context, we analyzed the implications of TPO, NIS, and DUOX2 gene mutations in hypothyroid children with dyshormonogenetic hypothyroidism (DH) from South India.

MATERIALS AND METHODS

This is interdisciplinary prospective study, we employed eight sets of primers and screened for 142 known single nucleotide polymorphisms in TPO, NIS, and DUOX2 genes. The subjects were children and adolescents with hypothyroidism due to dyshormonogenetic goiter. Congenital hypothyroidism, iodine deficiency, and Hashimoto's thyroiditis cases were excluded.

RESULTS

We detected nine mutations in 8/22 (36%) children. All the mutations were observed in the intronic regions of NIS gene and none in TPO or DUOX2 genes. Except for bi-allelic, synonymous polymorphism of TPO gene in child number 14, all other mutations were heterozygous in nature. GPCs show that our mutations significantly expressed the phenotypic traits such as overt hypothyroidism, goiter, and existence of family history. Other phenotypic characters such as sex predilection, the age of onset and transitory nature of hypothyroidism were not significantly affected by these mutations.

CONCLUSION

NIS gene mutations alone appears to be most prevalent mutations in DH among South Indian children and these mutations significantly influenced phenotypic expressions such as severity of hypothyroidism, goiter rates, and familial clustering.

A Homozygous TPO Gene Duplication (c.1184_1187dup4) Causes Congenital Hypothyroidism in Three Siblings Born to a Consanguineous Family

Congenital hypothyroidism (CH) is the most common neonatal endocrine disease, and germ-line mutations in the TPO gene cause the inherited form of the disease. Our aim in this study was to determine the genetic basis of congenital hypothyroidism in three affected children coming from a consanguineous Turkish family. Because CH is usually inherited in autosomal recessive manner in consanguineous/multicase families, we adopted a two-stage strategy of genetic linkage studies and targeted sequencing of the candidate genes. First, we investigated the potential genetic linkage of the family to any known CH locus, using microsatellite markers, and then screened for mutations in linked-gene by conventional sequencing. The family showed potential linkage to the TPO gene and we detected a homozygous duplication (c.1184_1187dup4) in all cases. The mutation segregated with disease status in the family. This study confirms the pathogenicity of the c.1184_1187dup4 mutation in the TPO gene and helps establish a genotype/phenotype correlation associated with this mutation. It also highlights the importance of molecular genetic studies in the definitive diagnosis and accurate classification of CH.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Detection of Novel Gene Variants Associated with Congenital Hypothyroidism in a Finnish Patient Cohort

BACKGROUND

Congenital hypothyroidism (CH) is defined as the lack of thyroid hormones at birth. Mutations in at least 15 different genes have been associated with this disease. While up to 20% of CH cases are hereditary, the majority of cases are sporadic with unknown etiology. Apart from a monogenic pattern of inheritance, multigenic mechanisms have been suggested to play a role in CH. The genetics of CH has not been studied in Finland so far. Therefore, multigenic sequencing of CH candidate genes was performed in a Finnish patient cohort with both familial and sporadic CH.

METHODS

A targeted next-generation sequencing (NGS) panel, covering all exons of the major CH genes, was applied for 15 patients with sporadic and 11 index cases with familial CH.

RESULTS

Among the familial cases, six pathogenic mutations were found in the TPO, PAX8, and TSHR genes. Furthermore, pathogenic NKX2.1 and TG mutations were identified from sporadic cases, together with likely pathogenic variants in the TG, NKX2.5, SLC26A4, and DUOX2 genes. All identified novel pathogenic mutations were confirmed by Sanger-sequencing and characterized in silico and/or in vitro.

CONCLUSION

In summary, the CH panel provides an efficient, cost-effective, and multigenic screening tool for both known and novel CH gene mutations. Hence, it may be a useful method to identify accurately the genetic etiology for dyshormogenic, familial, or syndromic forms of CH.

High prevalence of DUOX2 gene mutations among children with congenital hypothyroidism in central China

Congenial hypothyroidism (CH) is the most common congenital endocrine disease and is treatable when recognized early enough. We investigated the genetic variants in 12 children diagnosed with CH by newborn screening in Huangshi area central China. Twelve genes commonly involved in CH development were studied. Genomic DNA from peripheral blood was used to amplify all exons of the selected genes, and the constructed sequencing libraries were subjected to next generation high throughput DNA sequencing (NGS). Analysis of the sequencing results identified rare genetic variants in 11 of the 12 patients (91.7%), and two novel rare variants were found in DUOX2 gene and two in TPO gene. Mutations in DUOX2 gene were identified in 10 patients (83.3%), and all these patients were found to carry bi-allelic, tri-allelic mutations or compound mutations with other genes. Recurrent DUOX2 mutations include K530X, R683L, R1110Q, and L1343F. Truncating, splicing, and proven deleterious DUOX2 missense mutations were detected in 50% of the patients. Mutations in TG gene were identified in four patients, and mutations in TPO, THSR, SLC26A4 genes were identified, one in each patient, respectively. The high prevalence of DUOX2 mutations in this cohort of children with CH appears striking and surprising. The clinical implications were discussed.

Pendred Syndrome in a Newborn with Neck Swelling: A Case Report

BACKGROUND

Pendred syndrome is a rare autosomal recessive condition, characterized by functional impairment of thyroid gland and sensorineural hearing loss. The syndrome presents in patients with homozygous or compound heterozygous mutation. The presentation in the form of neck mass in a newborn is rare.

CASE CHARACTERISTICS

A 1 month old baby presented to us with neck mass, which was found to be an enlarged thyroid gland. Thyroid function tests were consistent with hypothyroidism. Further evaluation revealed moderate sensorineural hearing loss; genetic analysis showed that baby was homozygous for the known mutations causing the disease.

INTERVENTION

Thyroid hormone replacement and hearing habilitation were done. Follow up showed regression of the neck mass and normalization of thyroid function tests. Genetic counseling of the family was done.

MESSAGE

Identification of the exact cause of congenital hypothyroidism can prevent grave consequences later on for the patient as well as for the family.

Neonatal Screening for Congenital Hypothyroidism with Focus on Developing an Indian Screening Programme

Neonatal screening for congenital hypothyroidism, along with eradication of iodine deficiency in large parts of the world, has made it possible to prevent the development of permanent neurological impairment due to thyroid hormone deficiency in the developing brain. The first successful screening programme was demonstrated in Canada in 1973 and since then it has been standard of care in most developed societies. In India there is no national programme for neonatal screening, and screening is only done in selected larger hospitals on newborns whose parents fund it. This review summarises the current understanding of the various strategies for newborn screening that could potentially be employed in India with resource constraints. Once a case is detected, the further evaluation and determination of etiology is summarised. Treatment and long term follow-up with levothyroxine replacement is also described in detail as per current understanding.

Genetic and functional analysis of two missense DUOX2 mutations in congenital hypothyroidism and goiter

Mutations in the dual oxidase 2 gene (DUOX2) impair hydrogen peroxide (H₂O₂) production and cause dyshormonogenesis. In addition, these mutations have been implicated in autosomal recessive congenital hypothyroidism (CH) with goiter. In this study, we identified DUOX2 mutations that were causative for CH and explored the effects of these mutations on DUOX2 function. Blood samples were collected from 10 infants born with CH and goiter to unrelated parents. We extracted genomic DNA and sequenced all exons by polymerase chain reaction direct sequencing. The effects of DUOX2 mutations were characterized by H₂O₂ production assays and cycloheximide (CHX) chase experiments. Sequence analysis revealed one novel DUOX2 mutation and one known DUOX2 mutation in unrelated families: c.1060C>T (p.R354W) and c.3616 G>A (p.A1206T). Both mutations impaired H₂O₂ production. CHX chase experiments demonstrated the DUOX2 mutants had shorter half-lives and degraded more rapidly than wild-type DUOX2. Our study identified two novel DUOX2 mutations in Chinese patients with CH and goiter, which were responsible for the deficit in the organification process.

High prevalence of DUOX2 mutations in Japanese patients with permanent congenital hypothyroidism or transient hypothyroidism

BACKGROUND

Dual oxidase 2 (DUOX2) mutations are a cause of dyshormonogenesis (DH) and have been identified in patients with permanent congenital hypothyroidism (PH) and with transient hypothyroidism (TH). We aimed to elucidate the prevalence and phenotypical variations of DUOX2 mutations.

METHODS

Forty-eight Japanese DH patients were enroled and analysed for sequence variants of DUOX2, DUOXA2, and TPO using polymerase chain reaction-amplified direct sequencing.

RESULTS

Fourteen sequence variants of DUOX2, including 10 novel variants, were identified in 11 patients. DUOX2 variants were more prevalent (11/48, 22.9%) than TPO (3/48, 6.3%) (p=0.020). The prevalence of DUOX2 variants in TH was slightly, but not significantly, higher than in PH. Furthermore, one patient had digenic heterozygous sequence variants of both DUOX2 and TPO.

CONCLUSIONS

Our results suggest that DUOX2 mutations might be the most common cause of both PH and TH, and that phenotypes of these mutations might be milder than those of other causes.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Hypothalamus-Pituitary-Thyroid Axis

The hypothalamus-pituitary-thyroid (HPT) axis determines the set point of thyroid hormone (TH) production. Hypothalamic thyrotropin-releasing hormone (TRH) stimulates the synthesis and secretion of pituitary thyrotropin (thyroid-stimulating hormone, TSH), which acts at the thyroid to stimulate all steps of TH biosynthesis and secretion. The THs thyroxine (T4) and triiodothyronine (T3) control the secretion of TRH and TSH by negative feedback to maintain physiological levels of the main hormones of the HPT axis. Reduction of circulating TH levels due to primary thyroid failure results in increased TRH and TSH production, whereas the opposite occurs when circulating THs are in excess. Other neural, humoral, and local factors modulate the HPT axis and, in specific situations, determine alterations in the physiological function of the axis. The roles of THs are vital to nervous system development, linear growth, energetic metabolism, and thermogenesis. THs also regulate the hepatic metabolism of nutrients, fluid balance and the cardiovascular system. In cells, TH actions are mediated mainly by nuclear TH receptors (210), which modify gene expression. T3 is the preferred ligand of THR, whereas T4, the serum concentration of which is 100-fold higher than that of T3, undergoes extra-thyroidal conversion to T3. This conversion is catalyzed by 5'-deiodinases (D1 and D2), which are TH-activating enzymes. T4 can also be inactivated by conversion to reverse T3, which has very low affinity for THR, by 5-deiodinase (D3). The regulation of deiodinases, particularly D2, and TH transporters at the cell membrane control T3 availability, which is fundamental for TH action. © 2016 American Physiological Society. Compr Physiol 6:1387-1428, 2016.

Etiologies of uterine malformations

Ranging from aplastic uterus (including Mayer-Rokitansky-Kuster-Hauser syndrome) to incomplete septate uterus, uterine malformations as a group are relatively frequent in the general population. Specific causes remain largely unknown. Although most occurrences ostensibly seem sporadic, familial recurrences have been observed, which strongly implicate genetic factors. Through the study of animal models, human syndromes, and structural chromosomal variation, several candidate genes have been proposed and subsequently tested with targeted methods in series of individuals with isolated, non-isolated, or syndromic uterine malformations. To date, a few genes have garnered strong evidence of causality, mainly in syndromic presentations (HNF1B, WNT4, WNT7A, HOXA13). Sequencing of candidate genes in series of individuals with isolated uterine abnormalities has been able to suggest an association for several genes, but confirmation of a strong causative effect is still lacking for the majority of them. We review the current state of knowledge about the developmental origins of uterine malformations, with a focus on the genetic variants that have been implicated or associated with these conditions in humans, and we discuss potential reasons for the high rate of negative results. The evidence for various environmental and epigenetic factors is also reviewed. © 2016 Wiley Periodicals, Inc.

Poorly Controlled Congenital Hypothyroidism due to an Underlying Allgrove Syndrome

BACKGROUND

Congenital hypothyroidism of thyroidal origin (CHT) is a common disorder in pediatric endocrinology practices, which can be difficult to manage. Elevated thyrotropin (TSH) concentrations are in the great majority of cases explained by poor compliance to levothyroxine therapy.

METHODS

Case description.

RESULTS

We present a boy with CHT, with 2 heterozygous mutations in the TSH receptor gene, who showed persistently elevated TSH concentrations and psychomotor retardation, initially misinterpreted as malcompliance. At the age of 4 years, he was diagnosed with adrenal insufficiency, wherefore a broad diagnostic search was initiated. After the start of glucocorticoid replacement therapy, his TSH normalized and the levothyroxine could be lowered. At the age of 6 years, his TSH increased again, this time caused by malabsorption of levothyroxine due to esophageal achalasia. In retrospect, alacrima was also present and the diagnosis of Allgrove syndrome was genetically confirmed. The CHT was considered a separate disease entity.

CONCLUSIONS

In case of persistently elevated TSH levels in children with CHT, causes other than noncompliance must be considered. Second, in establishing the cause of adrenal insufficiency, specific symptoms, such as alacrima, are easily overlooked. Third, Allgrove syndrome is a rare disorder, in which diagnostic delay can lead to potentially life-threatening complications.

A Novel Mutation in Thyroid Peroxidase Gene Causing Congenital Goitrous Hypothyroidism in a German-Thai Patient

Thyroid dyshormonogenesis is responsible for 10-15% of all cases of congenital hypothyroidism and is usually inherited. We report a 26-year-old German-Thai male with congenital hypothyroidism caused by a compound heterozygous mutation in the thyroid peroxidase (TPO) gene. He was diagnosed with congenital goitrous hypothyroidism at 4 months of age and had been treated with levothyroxine replacement therapy. His goiter size had increased due to poor compliance to treatment. Ultrasonography of the thyroid gland showed a pattern suspicious for malignancy. The patient later underwent near-total thyroidectomy. Pathologic examination results were consistent with a multinodular goiter and no malignancy. Genetic analyses by direct sequencing of the entire exons and flanking regions of the TPO gene were performed in the index case and family members. The analyses revealed a compound heterozygote of novel TPO mutation of c.1727C>T in exon 10 resulting in amino acid substitution (p.Ala576Val) and c.2268_2269insT in exon 13 causing a frameshift mutation which introduced a stop codon after the insertion site. The latter has been reported in Chinese subjects. However, there is no previous report of c.1727C>T mutation in the literature. We found the allele contained a novel exon 10 mutation inherited from the patient's German mother and an exon 13 mutation from his Thai father. Analysis using two bioinformatic software programs indicated that this variant was likely to cause damage in the resulting protein molecule. The present report emphasizes the importance of regular follow-up and patient compliance to levothyroxine replacement in patients with goitrous congenital hypothyroidism to avoid prolonged stimulation of thyroid tissue by thyroid-stimulating hormone.

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

Background:

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

Materials and Methods:

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

Results:

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

Conclusions:

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

Mutation screening of the TPO gene in a cohort of 192 Chinese patients with congenital hypothyroidism

OBJECTIVES

Defects in the human thyroid peroxidase (TPO) gene are reported to be one of the causes of congenital hypothyroidism (CH) due to dyshormonogenesis. The aim of this study was to examine the TPO mutation spectrum and prevalence among patients with CH in the Guangxi Zhuang Autonomous Region of China and to define the relationships between TPO genotypes and clinical phenotypes.

METHODS

Blood samples were collected from 192 patients with CH in the Guangxi Zhuang Autonomous Region, China and genomic DNA was extracted from peripheral blood leucocytes. All exons of the 10 common CH-associated genes including TPO together with their exon-intron boundaries were screened by next-generation sequencing (NGS). The effect of the novel TPO mutation was investigated by 'in silico' studies.

RESULTS

NGS analysis of TPO in 192 patients with CH revealed 3 different variations in 2 individuals (2/192, 1%). Sequencing other CH candidate genes in the patients with TPO variants revealed that patient 1 was homozygous for c.2422delT TPO mutation combined with double heterozygous DUOX2 pathogenic variants (p.R683L/p.L1343F) and patient 2 was triallelic for TPO pathogenic variants (p.R648Q/p.T561M/p.T561M). The present study identified a novel TPO variation c.1682C>T/p.T561M; and four known mutations: c.2422delT/p.C808Afs×24 and c.1943C>T/p.R648Q in TPO, c.2048G>T/p.R683L and c.4027C>T/p.L1343F in DUOX2.

CONCLUSIONS

Our study indicated that the prevalence of TPO mutations was 1% among studied Chinese patients with CH. More than two variations in one or more CH-associated genes can be found in a single patient, and may, in combination, affect the phenotype of the individual. A novel TPO variation c.1682C>T/p.T561M was found, thereby expanding the mutational spectrum of the gene.

Next-generation sequencing analysis of DUOX2 in 192 Chinese subclinical congenital hypothyroidism (SCH) and CH patients

BACKGROUND

Defects in the human dual oxidase 2 (DUOX2) gene are reported to be one of the major causes of congenital hypothyroidism (CH). This study was set to examine the DUOX2 mutation spectrum and prevalence among Chinese CH and subclinical congenital hypothyroidism (SCH) patients and to define the relationships between DUOX2 genotypes and clinical phenotypes.

METHODS

Peripheral venous blood samples were collected from 192 CH/SCH patients in Guangxi Zhuang Autonomous Region of China. All exons and their exon-intron boundary sequences of the 11 known CH associated genes including DUOX2 were screened by next-generation sequencing (NGS).

RESULTS

NGS analysis of DUOX2 revealed 18 rare non-polymorphic variants in 57 CH/SCH patients. Sequencing of other CH candidate genes in the 57 patients revealed 2 thyroglobulin (TG) variants. All variants included 11 known mutations, 8 novel variants in DUOX2 and one novel variant in TG, among which three variants p.K530X, p.L1343F and p.R683L are highly recurrent in our patient cohort. 35 (83%) of the 42 patients with one or two DUOX2 pathogenic variants turned out to be SCH or transient congenital hypothyroidism (TCH), whereas 13 (87%) of the 15 patients with three or more DUOX2 pathogenic variants are associated with permanent congenital hypothyroidism (PCH). The accumulation of defects in DUOX2 contribute to the more severe disease regarding thyroid stimulating hormone (TSH) levels, free thyroxine (FT4) levels and initial dose of l-thyroxine (L-T4).

CONCLUSION

Our study expanded the mutational spectrum of the DUOX2 and TG genes and provided the best estimation of the DUOX2 mutation rate (29%) for CH/SCH patients in Guangxi Zhuang Autonomous Region of China. Most one or two DUOX2 pathogenic variants turned out to be SCH or TCH, whereas patients with three or more DUOX2 pathogenic variants were mostly associated with PCH. The coexistence of multiple pathogenic variants may have contributed to the severity of the hypothyroid condition.

Thyroglobulin gene mutations in Chinese patients with congenital hypothyroidism

Mutations in Thyroglobulin (TG) are common genetic causes of congenital hypothyroidism (CH). But the TG mutation spectrum and its frequency in Chinese CH patients have not been investigated. Here we conducted a genetic screening of TG gene in a cohort of 382 Chinese CH patients. We identified 22 rare non-polymorphic variants including six truncating variants and 16 missense variants of unknown significance (VUS). Seven patients carried homozygous pathogenic variants, and three patients carried homozygous or compound heterozygous VUS. 48 out of 382 patients carried one of 18 heterozygous VUS which is significantly more often than their occurrences in control cohort (P < 0.0001). Unique to Asian population, the c.274+2T>G variant is the most common pathogenic variant with an allele frequency of 0.021. The prevalence of CH due to TG gene defect in Chinese population was estimated to be approximately 1/101,000. Our study uncovered ethnicity specific TG mutation spectrum and frequency.

Transient congenital hypothyroidism caused by compound heterozygous mutations affecting the NADPH-oxidase domain of DUOX2

Here, we describe three cases of loss-of-function mutations in the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase (NOX) domain of dual oxidase 2 (DUOX2) occurring along with concurrent missense mutations in thyroid peroxidase (TPO), leading to transient congenital hypothyroidism (CH). Three Japanese boys with nonconsanguineous parents were diagnosed with CH during their neonatal screenings. All patients presented with moderate-to-severe neonatal hypothyroidism and were diagnosed with transient CH after re-evaluation of thyroid function. Two siblings were compound heterozygous for p.[R1110Q]+[Y1180X] in DUOX2; one of them was also heterozygous for p.[R361L] in TPO. The third patient was compound heterozygous for p.[L1160del]+[R1334W] in DUOX2 and heterozygous for p.[P883S] in TPO. This is the first report of a de novo L1160del mutation affecting the DUOX2 gene and of the novel mutations Y1180X in DUOX2 and R361L in TPO. R1110Q and L1160del were found to reduce H2O2 production (5%-9%, p<0.01), while Y1180X, which introduces a premature stop codon, did not confer detectable H2O2 production (-0.7%±0.6%, p<0.01). Moreover, R1334W, a missense mutation possibly affecting electron transfer, led to reduced H2O2 production (24%±0.9%, p<0.01) in vitro, and R1110Q and R1334W resulted in reduced protein expression. Y1180X was detected in a 120 kDa truncated form, whereas L1160del expression was maintained. Further, R361L, a novel missense mutation in TPO, caused partial reduction in peroxidase activity (20.6%±0.8%, p=0.01), whereas P883S, a missense variant, increased it (133.7%±2.8%, p=0.02). The protein expression levels in the case of R361L and P883S were maintained. In conclusion, we provide clinical and in vitro demonstrations of different functional defects and phenotypic heterogeneity in the same thyroid hormonogenesis pathway.

Quintuplets: 5 Cases of NEC. Are There Other Risk Factors?

OBJECTIVE

To review a case of quintuplets with all babies developing necrotizing enterocolitis.

METHODS

A retrospective study of preterm quintuplets all developing necrotizing enterocolitis. Clinical outcomes were reviewed.

RESULTS

Quintuplets were born at 24 weeks gestation. Each baby developed NEC and was treated. One baby died. Currently the remaining 4 infants are on full enteral nutrition.

CONCLUSION

Further studies are needed to better understand this emerging population of multiple birth pregnancy and the frequency of NEC development.

Increased incidence of congenital hypothyroidism in France from 1982 to 2012: a nationwide multicenter analysis

PURPOSE

Recent studies have shown an increased incidence of congenital hypothyroidism over the past 2 or 3 decades. The etiology of this change is unknown, but it has been related by several authors to lowering of cutoffs. We sought to determine whether the incidence of congenital hypothyroidism (CH) in France has changed.

METHODS

We analyzed data from the nationwide neonatal screening program for CH during the period 1982-2012. We included all children having thyroid-stimulating hormone values above the threshold and for whom diagnosis of CH confirmed by the pediatrician. We estimated multicentric temporal trends in the annual incidence rates adjusted for screening methods for thyroid dysgenesis and eutopic gland.

RESULTS

We found 6622 cases of CH (28.0 per 100,000 newborns); 1895 had a eutopic gland, and 4727 had thyroid dysgenesis. The incidence of eutopic glands showed a significant annual average increase of (5.1%; 95% confidence interval: 4.3-5.9) regardless of the screening method or screening center. This increase was confirmed in severe cases (thyroid-stimulating hormone ≥ 50: 2.1%; 95% confidence interval, 1.4-2.9). The incidence of dysgenesis remained constant.

CONCLUSIONS

The incidence of eutopic glands increased in France, not only in mild forms but also in severe cases.

Genetic disorders coupled to ROS deficiency

Maintaining the redox balance between generation and elimination of reactive oxygen species (ROS) is critical for health. Disturbances such as continuously elevated ROS levels will result in oxidative stress and development of disease, but likewise, insufficient ROS production will be detrimental to health. Reduced or even complete loss of ROS generation originates mainly from inactivating variants in genes encoding for NADPH oxidase complexes. In particular, deficiency in phagocyte Nox2 oxidase function due to genetic variants (CYBB, CYBA, NCF1, NCF2, NCF4) has been recognized as a direct cause of chronic granulomatous disease (CGD), an inherited immune disorder. More recently, additional diseases have been linked to functionally altered variants in genes encoding for other NADPH oxidases, such as for DUOX2/DUOXA2 in congenital hypothyroidism, or for the Nox2 complex, NOX1 and DUOX2 as risk factors for inflammatory bowel disease. A comprehensive overview of novel developments in terms of Nox/Duox-deficiency disorders is presented, combined with insights gained from structure-function studies that will aid in predicting functional defects of clinical variants.

A Homozygous Nonsense Thyroid Peroxidase Mutation (R540X) Consistently Causes Congenital Hypothyroidism in Two Siblings Born to a Consanguineous Family

OBJECTIVE

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder, and mutations in the thyroid peroxidase (TPO) gene have been reported to cause the disease. Our aim in this study was to determine the genetic basis of CH in two affected children coming from a consanguineous family.

METHODS

First, we investigated the potential genetic linkage of the family to any known CH locus using microsatellite markers and then screened for mutations in the linked gene by Sanger sequencing. By using next-generation sequencing, we also checked if any other mutation was present in the remaining 10 causative CH genes.

RESULTS

The family showed potential linkage to the TPO gene, and we detected a homozygous nonsense mutation (R540X) in both cases. The two patients had total iodide organification defect (TIOD). Both the microsatellite marker haplotypes and the mutation segregated with the disease status in the family, i.e. all healthy subjects were either heterozygous carriers or homozygous wild-type, confirming the pathogenic nature of the mutation. Neither was the mutation present in any of the 400 control chromosomes nor were there any other mutations in the remaining causative CH genes.

CONCLUSION

This study proves the pathogenicity of R540X mutation and demonstrates the strong genotype/phenotype correlation associated with this mutation. It also highlights the power of working with familial cases in revealing the molecular basis of CH and in establishing accurate genotype/phenotype relationships associated with disease causing mutations.

Segregation of S292F TPO gene mutation in three large Tunisian families with thyroid dyshormonogenesis: evidence of a founder effect

We aimed to identify causal mutation(s) in 13 patients with thyroid dyshormonogenesis (TD) from three consanguineous Tunisian families. A 12-year clinical follow-up showed phenotypic variability ranging from the presence to the absence of goiter, sensorineural deafness, and mental retardation. Genetic analysis using microsatellite markers within two candidate genes (TPO and PDS) gave evidence of linkage with the TPO gene. Sequencing of its 17 exons and their flanking intron-exon junctions revealed the previously described c.875C>T (p.S292F) mutation in homozygous state. No additional mutations were found in either a 900 bp of the TPO gene promoter or PDS gene. In silico analysis showed that p.S292F mutation might reduce the catalytic cavity of the TPO which would restrict access of a potential substrate to the catalytic pocket. Using 4SNPs and one microsatellite marker in the TPO gene, an associated haplotype: G-C-G-G-214 was found, giving evidence of a founder mutation.

CONCLUSION

This is the first description of a TD causing mutation in Tunisia and thus may help to develop a genetic screening protocol for congenital hypothyroidism in the studied region. Although structural modeling suggested a pathogenic effect of this mutation, functional studies are needed. Additional causing and/or modifier genes, together with late diagnosis could explain the clinical variability observed in our patients.

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.

Pseudodominant inheritance in a family with nonautoimmune hypothyroidism due to biallelic DUOX2 mutations

OBJECTIVES

Mutations in the dual oxidase 2 gene (DUOX2) is the most common genetic cause of congenital hypothyroidism (CH) in Japan. All previously described DUOX2 mutation-carrying families have followed autosomal recessive inheritance. We report a nonconsanguineous Japanese family harbouring biallelic DUOX2 mutations, which presented an apparently dominant inheritance of nonautoimmune hypothyroidism.

DESIGN AND METHODS

The proband and her two sisters had been diagnosed as having CH on newborn screening and were treated with levothyroxine. Their mother had subclinical hypothyroidism. We sequenced DUOX2 in the proband and her family members. Pathogenicity of the identified novel mutation (p.Y1347C) was verified in vitro.

RESULTS

We found that the proband and her sisters were compound heterozygous for a novel DUOX2 mutation p.Y1347C and a previously reported functional variant p.H678R. Unexpectedly, we found that the mother was homozygous for p.H678R. Expression experiments showed that the p.Y1347C mutant had reduced H2 O2 -producing activity, although there was no significant difference in the level of protein expression or localization, between wild type and p.Y1347C.

CONCLUSIONS

We report a DUOX2 mutation-carrying pedigree presenting pseudodominant inheritance of nonautoimmune hypothyroidism. We speculate that the relatively high frequency of DUOX2 mutations could lead to pseudodominant inheritance in Japan.

A De novo PAX8 mutation in a Chinese child with congenital thyroid dysgenesis

BACKGROUND

Thyroid dysgenesis (TD) is the most frequent cause of congenital hypothyroidism (CH), but its pathogenesis remains unclear. As a thyroid transcription factor, paired box transcription factor 8 (PAX8) is essential for thyroid organogenesis and development.

AIM

To screen PAX8 mutations and characterize the features of these mutations in Chinese TD patients.

MATERIALS AND METHODS

Blood samples were collected from 63 TD patients in Shandong Province, China, and genomic DNA was extracted from peripheral blood leukocytes. Exon 3~4 of PAX8 were analyzed by PCR and direct sequencing.

RESULTS

Direct sequencing of PAX8 revealed a heterozygous missense mutation (c.155G/C, P.Arg52Pro) in one child with agenesis. Genetic screening of the child's family revealed that the clinically unaffected parents do not carry the mutation, suggesting that the identified sequence change is a de novo mutation.

CONCLUSION

We report a heterozygous missense de novo mutation in PAX8 in one out of 63 unrelated Chinese TD patients, showing that the PAX8 mutation rate is very low in TD patients in China. However, de novo mutation and epigenetic mechanisms need to be considered in the future study.

Genetic analysis of the paired box transcription factor (PAX8) gene in a cohort of Polish patients with primary congenital hypothyroidism and dysgenetic thyroid glands

BACKGROUND

The morphological and biochemical phenotype of PAX8 mutation in patients with congenital hypothyroidism (CH) is variable. The contribution of mutations in PAX8 gene in children with CH and dysgenetic thyroid glands still remains a subject of interest for researchers.

PATIENTS AND METHODS

Some 48 children (37 girls and 11 boys) with CH associated with thyroid ectopy (n=22), agenesis (n=10), hypoplasia (n=6), or thyroid dysgenesis of unknown cause (n=10) were enrolled. The study participants were born in south-eastern Poland in the years 1993-2012 and were selected for neonatal mass screening for CH. DNA was extracted from peripheral blood samples using Master Pure DNA Purification Kit (Epicentre Biotechnologies, Madison, WI, USA). The 12 exons of the PAX8 gene along with their exon-intron boundaries were amplified and sequenced by the Sanger method. Capillary electrophoresis was run on ABI 3500 (Applied Biosystems, Carlsbad, CA, USA).

RESULTS

Novel heterozygous transition in exon 3 (c.68G>A) was detected in a 3-year-old girl with a thyroid hypoplasia. This substitution was not identified in the patient's parents (de novo event). Additionally, a novel genetic variant in 3'UTR region of exon 12 (c.*416C>T) occurred in a 3-year-old boy with ectopic thyroid tissue and concomitant congenital urogenital malformation. This heterozygous variant was also detected in other healthy family members. Thirteen well-described single nucleotide polymorphisms were revealed in the PAX8 gene.

CONCLUSIONS

The study reports on the occurrence of two novel heterozygous substitutions in the PAX8 gene. Estimation of the contribution of the revealed c.68G>A variant to the etiology of CH in a girl with hypoplastic thyroid requires further functional analysis.

High frequency of DUOX2 mutations in transient or permanent congenital hypothyroidism with eutopic thyroid glands

BACKGROUND/AIMS

This study aimed to clarify the frequency, phenotypes, and molecular spectrum of DUOX2, TPO, TSHR, and TG mutations in patients with congenital hypothyroidism (CH) with enlarged or normal-sized eutopic thyroid glands.

METHODS

The study cohort included 43 subjects from 41 unrelated families who had CH with eutopic thyroid glands. Mutation analyses of DUOX2, TPO, and TSHR were performed. The functional capacities of novel missense variants of DUOX2 were verified by measuring H2O2 generation in vitro.

RESULTS

Of the 43 subjects, 23 (53.5%) had sequence variants in at least one gene. Twelve different DUOX2 variants, including seven novel variants, were identified in 20 subjects. A functional analysis of the DUOX2 variants revealed that most variants, other than p.G206V and p.H678R, caused a significant reduction in H2O2 generation. Therefore, 15 subjects harbored functionally deleterious DUOX2 variants. Of these, 5 subjects had transient CH, and 10 were found to have permanent CH. Sequence variants in TSHR were identified in 5 subjects. One of the 43 subjects (2.3%) had sequence variants in two different genes.

CONCLUSIONS

DUOX2 variants are a relatively common cause of CH with normal-sized or enlarged eutopic thyroid glands. Variable phenotypes were associated with partial loss of the functional activity of DUOX2 variants.

Genetic determination of the hypothalamic-pituitary-thyroid axis: where do we stand?

For a long time it has been known that both hypo- and hyperthyroidism are associated with an increased risk of morbidity and mortality. In recent years, it has also become clear that minor variations in thyroid function, including subclinical dysfunction and variation in thyroid function within the reference range, can have important effects on clinical endpoints, such as bone mineral density, depression, metabolic syndrome, and cardiovascular mortality. Serum thyroid parameters show substantial interindividual variability, whereas the intraindividual variability lies within a narrow range. This suggests that every individual has a unique hypothalamus-pituitary-thyroid axis setpoint that is mainly determined by genetic factors, and this heritability has been estimated to be 40-60%. Various mutations in thyroid hormone pathway genes have been identified in persons with thyroid dysfunction or altered thyroid function tests. Because these causes are rare, many candidate gene and linkage studies have been performed over the years to identify more common variants (polymorphisms) associated with thyroid (dys)function, but only a limited number of consistent associations have been found. However, in the past 5 years, advances in genetic research have led to the identification of a large number of new candidate genes. In this review, we provide an overview of the current knowledge about the polygenic basis of thyroid (dys)function. This includes new candidate genes identified by genome-wide approaches, what insights these genes provide into the genetic basis of thyroid (dys)function, and which new techniques will help to further decipher the genetic basis of thyroid (dys)function in the near future.

Kinetic characterization of human thyroperoxidase. Normal and pathological enzyme expression in Baculovirus system: a molecular model of functional expression

BACKGROUND

Human thyroperoxidase (hTPO) is a membrane-bound glycoprotein located at the apical membrane of the thyroid follicular cells which catalyzes iodide oxidation and organification in the thyroglobulin (TG) tyrosine residues, leading to the thyroid hormone synthesis by coupling of iodotyrosine residues. Mutations in hTPO gene are the main cause of iodine organification defects (IOD) in infants.

METHODS

We investigated the functional impact of hTPO gene missense mutations previously identified in our laboratory (p.C808R, p.G387R and p.P499L). In order to obtain the whole wild-type (WT) coding sequence of hTPO, sequential cloning strategy in pGEMT vector was carried out. Then, site-directed mutagenesis was performed. WT and mutant hTPOs were cloned into the pAcGP67B transfer vector and the recombinant proteins were expressed in Baculovirus System, purified and characterized by SDS-PAGE and Western blot. Moreover, we report for the first time the kinetic constants of hTPO, of both WT and mutant enzymes.

RESULTS

The functional evaluation of the recombinant hTPOs showed decreased activity in the three mutants with respect to WT. Regarding to the affinity for the substrate, the mutants showed higher Km values with respect to the WT. Additionally, the three mutants showed lower reaction efficiencies (Vmax/Km) with respect to WT hTPO.

CONCLUSIONS

We optimize the expression and purification of recombinant hTPOs using the Baculovirus System and we report for the first time the kinetic characterization of hTPOs.

Thyroid dyshormonogenesis and associated non-thyroidal anomalies in a tertiary care hospital in India

BACKGROUND

Dyshormonogenetic goiter refers to familial goiters owing to an inherited defect in the metabolism of thyroid hormones.

METHODS

19 patients with clinical and biochemically proven hypothyroidism (low T3, FT4 and high TSH) were recruited for the study. All patients were subjected to (i) ultrasound of the neck to rule out thyroid dysgenesis and (ii) technetium-99m radionuclide thyroid scintigraphy and a perchlorate discharge test (PDT). Extrathyroidal malformations were identified by clinical ultrasound (USG) examination of the abdomen and pelvis and by echocardiography.

RESULTS

Out of 19 patients with elevated thyroid uptakes on technetium-99m thyroid scintigraphy, 12 (63%) had a positive PDT and 7 patients (37%) had a negative PDT. All patients were subjected to abdominopelvic USG and echocardiography. Out of 12 patients with a positive PDT, 5 (42%) had associated extrathyroid malformations, 2 had urogenital malformations, and cardiac abnormalities on echocardiography were present in 2 patients (17%). One patient (8%) had features of dysmorphism in the form of a high-arched palate, low-set ears and microcephaly.

CONCLUSION

Congenital hypothyroidism due to dyshormogenesis is associated with a high prevalence of extrathyroidal malformations and needs to be managed as early as possible to ensure normal neurocognitive development of the children affected.

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.

European Society for Paediatric Endocrinology consensus guidelines on screening, diagnosis, and management of congenital hypothyroidism

OBJECTIVE

The aim was to formulate practice guidelines for the diagnosis and management of congenital hypothyroidism (CH).

EVIDENCE

A systematic literature search was conducted to identify key articles relating to the screening, diagnosis, and management of CH. The evidence-based guidelines were developed with the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system, describing both the strength of recommendations and the quality of evidence. In the absence of sufficient evidence, conclusions were based on expert opinion.

CONSENSUS PROCESS

Thirty-two participants drawn from the European Society for Paediatric Endocrinology and five other major scientific societies in the field of pediatric endocrinology were allocated to working groups with assigned topics and specific questions. Each group searched the literature, evaluated the evidence, and developed a draft document. These papers were debated and finalized by each group before presentation to the full assembly for further discussion and agreement.

RECOMMENDATIONS

The recommendations include: worldwide neonatal screening, approaches to assess the cause (including genotyping) and the severity of the disorder, the immediate initiation of appropriate L-T4 supplementation and frequent monitoring to ensure dose adjustments to keep thyroid hormone levels in the target ranges, a trial of treatment in patients suspected of transient CH, regular assessments of developmental and neurosensory functions, consulting health professionals as appropriate, and education about CH. The harmonization of diagnosis, management, and routine health surveillance would not only optimize patient outcomes, but should also facilitate epidemiological studies of the disorder. Individuals with CH require monitoring throughout their lives, particularly during early childhood and pregnancy.