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

Molecular and Clinical Features of Congenital Hypothyroidism Due to Multiple DUOX2 Variants

Background: DUOX2 is one of the major causative genes of congenital hypothyroidism (CH). Still, the mutation spectrum and clinical outcomes of biallelic DUOX2 variants are not fully understood. This study aimed to elucidate the molecular features and long-term clinical manifestations of CH caused by multiple pathogenic DUOX2 variants. Methods: A total of 255 patients with CH were screened for rare variants of 11 known causative genes. DUOX2 variants were classified according to their protein structure and residual activity. In vitro assays were performed for several variants of unknown functions. Clinical analyses were conducted for patients with multiple pathogenic variants of DUOX2 but not of other genes. Results: We identified 24 pathogenic variants of DUOX2, together with two benign variants and seven variants of uncertain significance, in 63 patients. The pathogenic variants included three missense substitutions and one frameshift variant that have not yet been linked to CH. Twenty-one patients carried multiple pathogenic DUOX2 variants without any other pathogenic gene variants. Three of the 21 patients harbored homozygous variants. Family analysis, long-read amplicon sequencing, and haplotype phasing confirmed compound heterozygosity of the DUOX2 variants in 14 patients, whereas the allelic positions of the variants in the remaining four patients could not be determined. Of the 21 patients, 19 were treated with levothyroxine; their ages at drug withdrawal ranged from 9 months to 21.4 years. Three patients required retreatment after drug-free intervals of 6 months, 8 months, and 10 years. There were no differences in clinical severity among patients with DUOX2 amorphic/amorphic, amorphic/hypomorphic, and hypomorphic/hypomorphic variants. Conclusions: These results broaden the mutational spectrum of DUOX2. Furthermore, our data imply that patients with multiple pathogenic DUOX2 variants typically exhibit transient CH without significant genotype-phenotype correlations. Most importantly, this study demonstrated for the first time that these patients are at risk of developing recurrent hypothyroidism after a long drug-free interval.

Concurrent THRB and DUOX2 variants in a patient detected via newborn screening for congenital hypothyroidism: a case of resistance to thyroid hormone

Most patients with resistance to thyroid hormone (RTH) test negative in newborn screening (NBS) for congenital hypothyroidism (CH). Here, we present a case of RTH diagnosed through NBS. The patient presented to us after her NBS for CH revealed high TSH (23.4 µIU/mL) and free T4 (FT4) (5.40 ng/dL) levels. Apart from tachycardia, she exhibited no other manifestations related to excess or deficiency of thyroid hormones. A confirmatory test replicated the findings, showing elevated serum TSH levels (35.7 µIU/mL) along with high FT4 levels (5.84 ng/dL). Ultrasonography showed marked thyroid gland enlargement (> +4 SD). Targeted next-generation sequencing of genes associated with genetic thyroid disorders revealed a previously reported THRB variant, p.Gly345Cys. Unexpectedly, two biallelic DUOX2 variants (p.His678Arg and p.Arg1334Trp) were also detected. At her last visit, no significant issues were observed with neurological development, growth, bone maturation, or gastrointestinal symptoms related to thyroid function at the age of 1 year, without treatment for RTH and CH. During follow-up, the TSH and FT4 levels gradually decreased. In conclusion, we report a patient with simultaneous RTH and DUOX2 defects, demonstrating the value of conducting a comprehensive analysis of multiple genes associated with thyroid diseases to better comprehend the pathogenesis in patients with atypical thyroid-related phenotypes.

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.

Identification and analyzes of DUOX2 mutations in two familial congenital hypothyroidism cases

BACKGROUND

Mutations in DUOX2 are the frequent cause of congenital hypothyroidism (CH), a common neonatal metabolic disorder characterized by great phenotypic variability. CH can be traditionally subclassified into two subtypes: thyroid dysgenesis (TD) and thyroid dyshormonogenesis. The objectives of this study were to analyze the genetic data of two familial CH cases, to elucidate the pathogenesis from the perspective of genetics and to review and summarize the previous findings.

METHODS

Targeted regions sequencing (TRS) technology covering all exons and intron-exon boundaries of 35 known and potential CH-related candidate target genes in combination with Sanger sequencing were performed to identify the likely pathogenic mutations of the six patients with familial CH.

RESULTS

In family 1, two DUOX2 missense mutations, namely, c.1060C>T/p.R354W in exon 10 and c.3200C>T/p.S1067L in exon 25, were found. Patient 1 (P1), P2 and P3 were transient CH (TCH) patients with eutopic thyroid glands of normal size and function. In family 2, only the mutation c.3200C>T/p.S1067L was identified. P4, P5, and P6 were diagnosed with permanent CH (PCH), which requires lifelong levothyroxine (L-T4) treatment. Furthermore, both P4 and P5 harbored properly located thyroid glands, whereas P6 had a mildly reduced gland. P1, P3, P6, and other family members carrying monoallelic or biallelic DUOX2 mutations showed no obvious abnormal clinical symptoms or signs, while P2, P4, and P5 showed umbilical hernias.

CONCLUSIONS

The present study suggests that the phenotypic features resulting from DUOX2 mutations vary greatly. The p.R354W and p.S1067L alterations or the combination of the two alterations in DUOX2 are probably only predisposing to CH and DUOX2 may be involved in the morphogenesis of the human thyroid gland. Simultaneously, the compensation of DUOX1 for the loss of DUOX2, undetectable pathogenic mutations, the effects of environmental factors, epigenetic mechanisms and the involvement of multiple genes cannot be excluded in the explanation of these genetic results.

Clinical and genetic investigation of 136 Japanese patients with congenital hypothyroidism

Objectives Congenital hypothyroidism (CH) is the most common congenital endocrine disorder. Recent advances in genetic testing have revealed its causative mutations in some CH patients. However, the underlying etiology remains unknown in most patients. This study aimed to perform clinical and genetic investigation in Japanese CH patients to uncover genotype-phenotype correlations. Methods We enrolled 136 Japanese patients with transient or permanent CH between April 2015 and March 2017, and performed next-generation sequencing of 19 genes implicated in CH. Results We identified potentially pathogenic bi-allelic variants in DUOX2, TSHR, and TPO in 19, 5, and 1 patient, respectively (autosomal recessive), and a potentially pathogenic mono-allelic variant in NKX2-1 (autosomal dominant) in 1 patient. Molecular genetic diagnosis was highly suggested in 26 patients (19%) from 23 families. We also detected a potentially pathogenic mono-allelic variant in five recessive genes (DUOX2, TSHR, TG, DUOXA2, and TPO) in 31 unrelated patients (23%), although the pathogenicity of these variants remains inconclusive. Patients with bi-allelic DUOX2 variants showed a more severe clinical presentation in infancy than those with bi-allelic TSHR variants. However, this trend reversed beyond infancy. There were no statistical differences in initial thyroid stimulating hormone, free thyroxine, thyroglobulin, and levothyroxine dose as of March 2017 between patients with bi-allelic and mono-allelic DUOX2 variants. Conclusions The prevalence of potentially-pathogenic variants in Japanese CH patients was similar to that found by previous reports. Our study demonstrates a genotype-phenotype correlation in Japanese CH patients.

Mutation spectrum analysis of 29 causative genes in 43 Chinese patients with congenital hypothyroidism

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder with a genetic origin. The purpose of the present study was to analyze the mutation spectrum of CH patients in China. A targeted next-generation sequencing panel covering all exons of 29 CH-related causative genes was used in 43 Han Chinese patients with CH [11 dysgenesis and 32 glands in situ (GIS)]. The functional impact and pathogenicity of detected variants were analyzed using a comprehensive bioinformatics approach and co-segregation studies. A total of 47 rare non-polymorphic variants in 9 target genes associated with thyroid hormone synthesis (DUOX2, DUOXA2, TPO, TG, SLC26A4 and SLC5A5), thyroid stimulating hormone resistance (TSHR) and central hypothyroidism (PROP1 and TRHR) were identified in 31 patients (31/43, 72%). Of these variants, 8 were novel, including 3 in DUOX2, 2 in TPO, 3 in TSHR and 1 in SLC5A5. Variants were mostly affected by DUOX2, TG, TPO and TSHR. Approximately 44% of the patients (19/43) carried DUOX2 variants. The mutation detection rates in patients with GIS were higher compared with patients with dysgenesis [25/32 (78%) vs. 6/11 (54%)]. Oligogenic mutations were detected in 25.6% of the total cases and 35% of the mutated cases. Genetic basis was ascertained in 13 patients, reaching a diagnosis detection rate of 30%. In conclusion, genetic defects in dyshormonogenesis, mainly in DUOX2, were the main genetic cause of CH in the Chinese population. Oligogenicity is highly involved in CH pathogenesis and may thus be an important factor in common phenotypic variability observed in patients with CH.

Inhibition of the thyroid hormonogenic H2O2 production by Duox/DuoxA in zebrafish reveals VAS2870 as a new goitrogenic compound

Thyroid hormone (TH) synthesis requires extracellular hydrogen peroxide generated by the NADPH oxidases, DUOX1 and DUOX2, with maturation factors, DUOXA1 and DUOXA2. In zebrafish, only one duox and one duoxa gene are present. Using a thyroid-specific reporter line, we investigated the role of Duox and Duoxa for TH biosynthesis in zebrafish larvae. Analysis of several zebrafish duox and duoxa mutant models consistently recovered hypothyroid phenotypes with hyperplastic goiter caused by impaired TH synthesis. Mutant larvae developed enlarged thyroids and showed increased expression of the EGFP reporter and thyroid functional markers including wild-type and mutated duox and duoxa transcripts. Treatment of zebrafish larvae with the NADPH oxidase inhibitor VAS2870 phenocopied the thyroid effects observed in duox or duoxa mutants. Additional functional in vitro assays corroborated the pharmacological inhibition of Duox activity by VAS2870. These data support the utility of this new experimental model to characterize endocrine disruptors of the thyroid function.

A Novel Homozygous Mutation of Thyroid Peroxidase Gene Abolishes a Disulfide Bond Leading to Congenital Hypothyroidism

Congenital hypothyroidism (CH) is the most prevalent congenital endocrine disorder and causes mental retardation. A male Japanese patient with first cousin marriage parents was diagnosed as CH at 10 months. He was born before introduction of mass screening for CH. With continuous thyroid hormone replacement therapy, normal thyroid hormone status was maintained until adulthood. Genetic screening of next-generation sequencing was performed at the age of 52 years, and we identified a new homozygous thyroid peroxidase (TPO) gene mutation (GRCh38.p13, chromosome 2 at position 1493997, c.1964 G>T, p.Cys655Phe). TPO is an important enzyme to produce thyroid hormone. As demonstrated by a homology analysis of TPO proteins among different species, cysteine 655 residue is highly conserved, suggesting an important role in maintaining TPO function and structure. An in silico study with three-dimensional structure of the novel mutation was performed and suggested that the mutation abolished disulfide bond between cysteines at positions 598 and 655. An in vitro functional analysis using HEK293 cells revealed that TPO activity of the mutant was significantly impaired compared with that of the wild type. Furthermore, study of immunohistochemistry showed that localization of TPO in cells did not differ between the wild type and the mutant. In conclusion, this single disulfide bond loss mutation of a new TPO homozygous mutation, p.Cys655Phe, reduced TPO activity and caused congenital hypothyroidism without affecting subcellular localization of TPO proteins.

DUOX Defects and Their Roles in Congenital Hypothyroidism

Extracellular hydrogen peroxide is required for thyroperoxidase-mediated thyroid hormone synthesis in the follicular lumen of the thyroid gland. Among the NADPH oxidases, dual oxidases, DUOX1 and DUOX2, constitute a distinct subfamily initially identified as thyroid oxidases, based on their level of expression in the thyroid. Despite their high sequence similarity, the two isoforms present distinct regulations, tissue expression, and catalytic functions. Inactivating mutations in many of the genes involved in thyroid hormone synthesis cause thyroid dyshormonogenesis associated with iodide organification defect. This chapter provides an overview of the genetic alterations in DUOX2 and its maturation factor, DUOXA2, causing inherited severe hypothyroidism that clearly demonstrate the physiological implication of this oxidase in thyroid hormonogenesis. Mutations in the DUOX2 gene have been described in permanent but also in transient forms of congenital hypothyroidism. Moreover, accumulating evidence demonstrates that the high phenotypic variability associated with altered DUOX2 function is not directly related to the number of inactivated DUOX2 alleles, suggesting the existence of other pathophysiological factors. The presence of two DUOX isoforms and their corresponding maturation factors in the same organ could certainly constitute an efficient redundant mechanism to maintain sufficient H₂O₂ supply for iodide organification. Many of the reported DUOX2 missense variants have not been functionally characterized, their clinical impact in the observed phenotype remaining unresolved, especially in mild transient congenital hypothyroidism. DUOX2 function should be carefully evaluated using an in vitro assay wherein (1) DUOXA2 is co-expressed, (2) H₂O₂ production is activated, (3) and DUOX2 membrane expression is precisely analyzed.

Mild thyroid peroxidase deficiency caused by TPO mutations with residual activity: Correlation between clinical phenotypes and enzymatic activity

Thyroid peroxidase (TPO) deficiency, caused by biallelic TPO mutations, is a well-established genetic form of congenital hypothyroidism (CH). More than 100 patients have been published, and the patients have been diagnosed mostly in the frame of newborn screening (NBS) programs. Correlation between clinical phenotypes and TPO activity remains unclear. Here, we report clinical and molecular findings of two unrelated TPO mutation-carrying mildly hypothyroid patients. The two patients were born at term after an uneventful pregnancy and delivery, and were NBS negative. They sought medical attention due to goiter at age 8 years. Evaluation of the thyroid showed mild elevation of serum TSH levels, normal or slightly low serum T₄ levels, high serum T₃ to T₄ molar ratio, high serum thyroglobulin levels, and high thyroidal ¹²³I uptake. We performed next-generation sequencing-based genetic screening, and found that one patient was compound heterozygous for two novel TPO mutations (p.Asp224del; c.820-2A>G), and the other was homozygous for a previously known mutation (p.Trp527Cys). In vitro functional analyses using HEK293 cells showed that the two amino acid-altering mutations (p.Asp224del and p.Trp527Cys) caused partial loss of the enzymatic activity. In conclusion, we report that TPO mutations with residual activity are associated with mild TPO deficiency, which is clinically characterized by marked goiter, mild TSH elevation, high serum T₃ to T₄ molar ratio, and high serum thyroglobulin levels. Our findings illuminate the hitherto under-recognized correlation between clinical phenotypes and residual enzymatic activity among patients with TPO deficiency.

Disorders of H2O2 generation

After the identification of thyroid H₂O₂ generation system (DUOX) and of its maturation factors (DUOXA), defects in DUOX2 and/or DUOXA2 were rapidly recognized as the possible cause of congenital hypothyroidism (CH) due to thyroid dyshormonogenesis. The present Review reports data on the prevalence of DUOX2 mutations, which is variable among different series but invariably high, pointing to DUOX2 defects as one of the leading causes of dyshormonogenesis. Differently, DUOXA defects seem to be rarely involved in the pathogenesis of CH. Genotype-phenotype correlations are also reported, highlighting the great intra- and inter-familial phenotype variability which appears to be a constant feature of the defects in the H₂O₂ generation systems. Finally, the hypotheses to explain the phenotypic variability of the DUOX2/A2 mutations are discussed, such as the existence of other H₂O₂ generating systems, the age variability in thyroid hormones requirements, the differences in ethnicity, in iodine intake, and in the methodological approaches.

Exome sequencing identifies SLC26A4, GJB2, SCARB2 and DUOX2 mutations in 2 siblings with Pendred syndrome in a Malaysian family

BACKGROUND

Pendred syndrome (PDS, MIM #274600) is an autosomal recessive disorder characterized by congenital sensorineural hearing loss and goiter. In this study, we describing the possible PDS causal mutations in a Malaysian family with 2 daughters diagnosed with bilateral hearing loss and hypothyroidism.

METHODS AND RESULTS

Whole exome sequencing was performed on 2 sisters with PDS and their unaffected parents. Our results showed that both sisters inherited monoallelic mutations in the 2 known PDS genes, SLC26A4 (ENST00000265715:c.1343C > T, p.Ser448Leu) and GJB2 (ENST00000382844:c.368C > A, p.Thr123Asn) from their father, as well as another deafness-related gene, SCARB2 (ENST00000264896:c.914C > T, p.Thr305Met) from their mother. We postulated that these three heterozygous mutations in combination may be causative to deafness, and warrants further investigation. Furthermore, we also identified a compound heterozygosity involving the DUOX2 gene (ENST00000603300:c.1588A > T:p.Lys530* and c.3329G > A:p.Arg1110Gln) in both sisters which are inherited from both parents and may be correlated with early onset of goiter. All the candidate mutations were predicted deleterious by in silico tools.

CONCLUSIONS

In summary, we proposed that PDS in this family could be a polygenic disorder which possibly arises from a combination of heterozygous mutations in SLC26A4, GJB2 and SCARB2 which associated with deafness, as well as compound heterozygous DUOX2 mutations which associated with thyroid dysfunction.

Natural course of congenital hypothyroidism by dual oxidase 2 mutations from the neonatal period through puberty

AIM

We previously reported that biallelic mutations in dual oxidase 2 (DUOX2) cause transient hypothyroidism. Since then, many cases with DUOX2 mutations have been reported. However, the clinical features and prognosis of individuals with DUOX2 defects have not been clarified.

OBJECTIVE

We investigated the prognosis of patients with congenital hypothyroidism (CH) due to DUOX2 mutations.

PATIENTS

Twenty-five patients were identified by a neonatal screening program and included seven familial cases. Their serum TSH values ranged from 18.9 to 734.6  mU/l. Twenty-two of the patients had low serum free thyroxine (fT4) levels (0.17-1.1  ng/dl). Twenty-four of the patients were treated with L-thyroxine.

METHODS

We analyzed the DUOX2, thyroid peroxidase, Na(+)/I(-) symporter, and dual oxidase maturation factor 2 genes of these 25 patients by PCR-amplified direct sequencing. An additional 11 genes were analyzed in 11 of the 25 patients using next-generation sequencing.

RESULTS

All patients had biallelic DUOX2 mutations, and seven novel alleles were detected. Fourteen of the patients were able to discontinue replacement therapy, and seven were receiving reduced L-thyroxine doses. Normalization of thyroglobulin lagged several years behind the completion of treatment. Two patients showed permanent hypothyroidism. Except for one case of a learning disability, growth and psychomotor development were normal.

CONCLUSION

The prognosis of Japanese patients with DUOX2 defects was usually transient CH. Delayed improvement of thyroglobulin indicates that these patients have subclinical hypothyroidism. Hypothyroidism did not recur in patients during the study period (up to 18 years old).