Two compound heterozygous mutations (c.215delA/c.2422T-->C and c.387delC/c.1159G-->A) in the thyroid peroxidase gene responsible for congenital goitre and iodide organification defect

The role of DUOXA2 in the clinical diagnosis of paediatric congenital hypothyroidism

Background: Congenital hypothyroidism (CH) is a common metabolic disorder in children that can impact growth and neurodevelopment, particularly during infancy and early childhood. DUOXA2, a DUOX maturation factor, plays a crucial role in the maturation and activation of dual oxidase DUOX2 (a member of the NADPH oxidase family). DUOX2 can correctly migrate to the plasma membrane from the endoplasmic reticulum (ER) with the help of DUOXA2, and the two proteins together form a stable complex that promotes hydrogen peroxide (H2O2) generation in the synthesis of thyroid hormones. Genetic alterations in DUOXA2 lead to defects function of DUOX2 protein causing inherited CH.

Objectives: This review discusses the relationship between DUOXA2 and CH, including the pathogenic mechanisms of CH in children caused by DUOXA2 mutations and the possibility or promise of DUOXA2 gene screening as a diagnostic marker for CH in the clinic.

Methods: The review synthesizes current research on the biological role of DUOXA2 and DUOX2 in thyroid hormone synthesis, the molecular impact of DUOXA2 mutations, and the clinical implications of genetic screening for CH.

Results: Mutations in DUOXA2 disrupt this process of H2O2 generation in the synthesis of thyroid hormones , leading to inherited CH. Early identification through DUOXA2 gene screening could improve diagnostic accuracy, which facilitates early intervention and personalized treatment.

Conclusions: DUOXA2 gene screening holds promise for enhancing diagnostic accuracy in CH. However, it cannot be used as a sole diagnostic indicator, and to optimize diagnostic sensitivity, it should be combined with the screening of other relevant genetic mutations and diagnostic tools. Further research is needed to refine screening protocols and explore therapeutic options.

Genetic Analyses in a Cohort of Pediatric Patients with Congenital Hypothyroidism Based on Congenital Hypothyroidism Consensus Guideline

INTRODUCTION

Pathogenic variants in the genes involved in the formation of thyroid tissue and thyroid hormone secretion have been reported to cause congenital hypothyroidism (CH) in some cases. This study aimed to evaluate the clinical and genetic findings of CH cases thought to be due to genetic variants.

METHODS

The study included cases whose genetic analysis was performed in accordance with the Congenital Hypothyroidism: A 2020-2021 Consensus Guidelines Update Guidelines recommendations criteria and analyzed them using the next-generation sequencing panel.

RESULTS

Sixty one Turkish patients from 45 families were included in the study. The overall frequency of variant detection was 37.7% (out of 45 families, 17 had a positive mutation). Segregation was carried out for all families with positive variants. Variants in the TPO gene are the most frequently encountered, and this situation was identified in 10 families. Variants followed this in the TSHR gene in 7 families, variants in the DUOX2 gene in 5 families, and two variants in the TG and NKX2-1 genes in 2 families each, which are six novel variants. Furthermore, among the NKX2-1 cases, one had thyroid involvement only, while the other had chorea only. We did not find differences between cases with detected mutations and mutation-negative cases regarding gender, neonatal/perinatal parameters, initial thyroid function values, and thyroid morphology.

CONCLUSION

In the current investigation, rare new variations in genes known to be related to CH were discovered, adding to the molecular genetic spectrum. When we compare the overall variant detection frequency, the selection criterion for genetic analysis based on the current guidelines is quite rational, considering the benefits and costs, on the other hand, present in new genes awaiting discovery. Also, TSHR mutations are likely to be common and may account for more than 5% of thyroid dysgenesis cases if we include nonfamilial thyroid dysgenesis.

Frequency of Mutations in the TPO Gene in Patients with Congenital Hypothyroidism Due to Dyshormonogenesis in Chile

Background and Objectives: Congenital thyroid dyshormonogenesis is caused by alterations in the synthesis of thyroid hormones in a newborn. Additionally, 10 to 20% of these cases are hereditary, caused by defects in proteins involved in hormonal synthesis. One of the most common causes is mutations in the thyroid peroxidase (TPO) enzyme gene, an autosomal recessive disease. We aimed to detect mutations of the TPO gene in 12 Chilean patients with congenital hypothyroidism due to dyshormonogenesis (CHD) and to characterize these patients clinically and molecularly. Materials and Methods: Twelve patients under 20 years of age with CHD, controlled at San Juan de Dios Hospital in Santiago, Chile, were selected according to the inclusion criteria: elevated neonatal TSH, persistent hypothyroidism, and thyroid normotopic by imaging study. Those with deafness, Down syndrome, and central or transient congenital hypothyroidism were excluded. Blood samples were taken for DNA extraction, and the 17 exons and exon-intron junctions of the TPO gene were amplified by PCR. The PCR products were sequenced by Sanger. Results: Two possibly pathogenic mutations of the TPO gene were detected: c.2242G>A (p.Val748Met) and c.1103C>T (p.Pro368Leu). These mutations were detected in 2 of 12 patients (16.6%): 1 was compound heterozygous c.1103C>T/c.2242G>A, and the other was heterozygous for c.2242G>A. In the diagnostic confirmation test, both patients presented diffuse hyper-uptake goiter on thyroid scintigraphy and high TSH in venous blood (>190 uIU/mL). Conclusions: The frequency of patients with possibly pathogenic mutations in TPO with CHD was 16.6%. Its study would allow for genetic counseling to be offered to the families of affected patients.

Genetic Screening and Functional Analysis of Thyroid Peroxidase Variants in Chinese Patients with Congenital Hypothyroidism

INTRODUCTION

Congenital hypothyroidism (CH), the most common neonatal endocrine disorder worldwide, can be caused by variants in the thyroid peroxidase (TPO) gene. This study aimed to identify TPO variants in Chinese patients with CH, analyze their impact on TPO function, and establish relationships between TPO genotypes and clinical characteristics.

METHODS

A total of 328 patients with CH were screened for TPO variants by performing whole-exome sequencing. The function of the detected TPO variants was investigated via transfection assays in vitro. The pathogenic effect of five novel variants was further assessed in silico.

RESULTS

Among 328 patients with CH, 19 TPO variants, including six novel ones, were identified in 43 patients. Eighteen patients (5.5%) carried biallelic TPO variants. In vitro experiments showed that TPO activity was impaired to varying degrees in 17 variants. Furthermore, we determined that a residual TPO enzyme activity threshold of 15% may serve as a criterion for differentiating CH severity.

CONCLUSIONS

According to our study, the prevalence of TPO variants among Chinese patients with CH was 13.1%. Five novel variants led to impaired TPO function by altering its structure or by affecting its expression or cellular localization, which should result in impaired thyroid hormone synthesis.

Curating the gnomAD database: Report of novel variants in the thyroid peroxidase gene using in silico bioinformatics algorithms and a literature review

Thyroid peroxidase (TPO) is a membrane-bound glycoprotein located at the apical side of the thyroid follicular cells that catalyzes both iodination and coupling of iodotyrosine residues within the thyroglobulin molecule, leading to the synthesis of thyroid hormone. Variants in TPO cause congenital hypothyroidism (CH) by iodide organification defect and are commonly inherited in an autosomal recessive fashion. In the present work, we report a detailed population analysis and bioinformatic prediction of the TPO variants indexed in the Genome Aggregation Database (gnomAD) v2.1.1. The proportion of missense cysteine variants and nonsense, frameshift, and splice acceptor/donor variants were analyzed in each ethnic group (European (Non-Finnish), European (Finnish), African/African Americans, Latino/Admixed American, East Asian, South Asian, Ashkenazi Jewish, Other). The results showed a clear predominance of frameshift variants in the East Asian (82%) and European (Finnish) (75%) population, whereas the splice site variants predominate in African/African Americans (99.46%), Other (96%), Latino/Admixed American (94%), South Asian (86%), European (Non-Finnish) (56%) and Ashkenazi Jewish (56%) populations. The analysis of the distribution of the variants indexed in gnomAD v2.1.1 database revealed that most missense variants identified in the An peroxidase domain map in exon 8, followed by exons 11, 7 and 9, and finally in descending order by exons 10, 6, 12 and 5. In total, 183 novel TPO variants were described (13 missense cysteine's variants, 158 missense variants involving the An peroxidase domain and 12 splicing acceptor or donor sites variants) which were not reported in the literature and that would have deleterious effects on prediction programs. In the gnomAD v2.1.1 population, the estimated prevalence of heterozygous carriers of the potentially damaging variants was 1:77. In conclusion, we provide an updated and curated reference source of new TPO variants for application in clinical diagnosis and genetic counseling. Also, this work contributes to elucidating the molecular basis of CH associated with TPO defects.

Iodide handling disorders (NIS, TPO, TG, IYD)

Iodide Handling Disorders lead to defects of the biosynthesis of thyroid hormones (thyroid dyshormonogenesis, TD) and thereafter congenital hypothyroidism (CH), the most common endocrine disease characterized by low levels of circulating thyroid hormones. The prevalence of CH is 1 in 2000-3000 live births. Prevention of CH is based on prenatal diagnosis, carrier identification, and genetic counseling. In neonates a complete diagnosis of TD should include clinical examination, biochemical thyroid tests, thyroid ultrasound, radioiodine or technetium scintigraphy and perchlorate discharge test (PDT). Biosynthesis of thyroid hormones requires the presence of iodide, thyroid peroxidase (TPO), a supply of hydrogen peroxide (DUOX system), an iodine acceptor protein, thyroglobulin (TG), and the rescue and recycling of iodide by the action of iodotyrosine deiodinase or iodotyrosine dehalogenase 1 (IYD or DEHAL1). The iodide transport is a two-step process involving transporters located either in the basolateral or apical membranes, sodium iodide symporter (NIS) and pendrin (PDS), respectively. TD has been linked to mutations in the solute carrier family 5, member 5 transporter (SLC5A5, encoding NIS), solute carrier family 26, member 4 transporter (SLC26A4, encoding PDS), TPO, DUOX2, DUOXA2, TG and IYD genes. These mutations produce a heterogeneous spectrum of CH, with an autosomal recessive inheritance. Thereafter, the patients are usually homozygous or compound heterozygous for the gene mutations and the parents, carriers of one mutation. In the last two decades, considerable progress has been made in identifying the genetic and molecular causes of TD. Recent advances in DNA sequencing technology allow the massive screening and facilitate the studies of phenotype variability. In this article we included the most recent data related to disorders caused by mutations in NIS, TPO, TG and IYD.

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.

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.

Cloning of TPO gene and associations of polymorphisms with chicken growth and carcass traits

Thyroid peroxidase (TPO), which located on the apical membrane surface of thyrocytes, is the key enzyme involved in thyroid hormone synthesis, mainly catalyses the iodination of tyrosine residues and the coupling of iodotyrosines on thyroglobulin to form thyroxine and triiodothyronine. The objectives of this study were to identify genetic polymorphisms of the chicken TPO gene and to analyze potential association between single nucleotide polymorphisms (SNPs) and growth and carcass traits in chicken. Partial sequences of TPO gene were cloned firstly. The nucleotide sequence was found to have 72 % identity with that of humans. The chicken TPO amino acid sequence was 71 %. Through polymerase chain reaction-restriction fragment length polymorphism and DNA sequencing methods, three novel mutations of the chicken TPO gene were detected in the F2 resource population from Gushi chickens and Anka broilers. The association analysis indicated that all of the three SNPs showed association with chicken growth at different periods. The g.29996C>T polymorphisms was significantly associated with body weight, breast bone length, pectoral angle at 12 weeks, claw weight and leg muscle weight (P < 0.05). In addition, individuals with the TT genotype had higher value for almost all the traits than CC and CT genotype. Meanwhile for CLW, the additive effects were significant (P < 0.05). Hence, we suggest that genotype TT can be regarded as a potential molecular marker for later growth and carcass traits in chicken.

Molecular screening of the TSH receptor (TSHR) and thyroid peroxidase (TPO) genes in Korean patients with nonsyndromic congenital hypothyroidism

OBJECTIVE

To investigate thyroid-stimulating hormone receptor (TSHR) and thyroid peroxidase (TPO) mutations in Korean patients with primary congenital hypothyroidism (CH).

CONTEXT

Congenital hypothyroidism is a common genetic disorder in which the majority of mutations occur in the TSHR and TPO genes.

DESIGN

We examined the frequencies of TSHR and TPO mutations among Korean patients with primary CH. Furthermore, we explored the relationships between imaging findings and mutation status.

PATIENTS

A total of 193 paediatric patients with nonsyndromic CH were enrolled in the present study.

MEASUREMENTS

Patients with decreased (99m) Tc uptake were screened for TSHR mutations using Sanger sequencing, and those with increased uptake were screened for TPO mutations. The relationships between scintigraphic and ultrasonographic findings and mutation status were analysed.

RESULTS

Thirteen (16·5%) of 79 patients with decreased (99m) Tc uptake were found to harbour TSHR mutations including G132R, G245S, R450H, R519C and F525S. The R450H mutation was present in 13 (72·2%) of 18 disease alleles. Seven (10·3%) of 68 patients with increased (99m) Tc uptake harboured TPO mutations including R189Q, K439E, G493S, C808LfsX72, A863T, R875Hfs and P883S. The TSHR and TPO mutations were observed only in patients with normal to slightly enlarged thyroid glands.

CONCLUSIONS

This study identified underlying TSHR and TPO mutations in Korean patients with CH and revealed a possible relationship between imaging findings and mutation status. In addition, the low rate of mutation positivity suggests significant genetic heterogeneity of CH in the Korean population.

Monoallelic thyroid peroxidase gene mutation in a patient with congenital hypothyroidism with total iodide organification defect

The aim of this study was to identify the genetic defect of a patient with dyshormonogenetic congenital hypothyroidisms (CH) with total iodide organification defect (TIOD). A male child diagnosed with CH during neonatal screening. Laboratory tests confirmed the permanent and severe CH with TIOD (99% perchlorate release). The coding sequence of TPO, DUOX2, and DUOXA2 genes and 2957 base pairs (bp) of the TPO promoter were sequenced. Molecular analysis of patient's DNA identified the heterozygous duplication GGCC (c.1186_1187insGGCC) in exon 8 of the TPO gene. No additional mutation was detected either in the TPO gene, TPO promoter, DUOX2 or DUOXA2 genes. We have described a patient with a clear TIOD causing severe goitrous CH due to a monoallelic TPO mutation. A plausible explanation for the association between an autosomal recessive disorder with a single TPO-mutated allele is the presence of monoallelic TPO expression.

Clinical, biochemical, and molecular findings in Argentinean patients with goitrous congenital hypothyroidism

We describe the clinical, biochemical, and molecular findings of a cohort of Argentinean patients with congenital hypothyroidism (CH) and goiter studied to characterize iodide organification and thyroglobulin (TG) defects. 20 CH patients (16 unrelated) were grouped according to serum TG levels and a perchlorate discharge test (PDT) in: group 1 (G1): nine patients with high TG and PDT > 10% who were studied for tiroperoxidase (TPO), dual oxidase 2 (DUOX2), and dual oxidase A2 (DUOXA2) defects and group 2 (G2): 11 patients with low TG and PDT < 10% studied for TG defects. Goiter characteristics, outcome, and TT₄ and TT₃ levels without treatment were compared between groups. 6/9 G1 patients harbored mutations in TPO gene and 3/9 in DUOX2 gene. In G2, mutations of TG gene were found in 3/11 homozygous, 5/11 compound heterozygous, and 3/11 heterozygous patients. Goiter was only evidenced by thyroid scan in the neonatal period in both groups; was moderately enlarged in patients diagnosed during infancy. In the late detected patients, goiter was big and nodular in G1 while diffuse and moderate in G2. Early detected patients grew and developed normally while those diagnosed late were severely mentally retarded in G1 and only mildly retarded in G2. Thyroid hormone levels of G1 were significantly lower than those of G2 P < 0.01. Molecular approach to characterize defects in organification and TG defects was optimized by TG measurements and PDT. Clinical and biochemical differences based on molecular findings will allow further investigations on genotype-phenotype relationships.