Mutation screening of the sodium iodide symporter gene in a cohort of 105 China patients with congenital hypothyroidism

Metabolic features of orbital adipose tissue in patients with thyroid eye disease

Background

Thyroid eye disease (TED) is the most frequent orbital disease in adults and is characterized by the accumulation of orbital adipose tissue (OAT). It can lead to eyelid retraction or even vision loss. Orbital decompression surgery serves as the primary treatment for inactive TED by removing the excess OAT. However, there is a lack of alternative treatments to surgery due to the unclear understanding of the pathogenesis, particularly the metabolic features. Accordingly, our study was implemented to explore the content and features of metabolites of OATs from TED patients.

Method

The OATs used in the current study were obtained from the orbital decompression surgery of seven patients with inactive TED. We also collected control OATs from eye surgical samples of five individuals with no history of autoimmune thyroid diseases, TED, or under non-inflammatory conditions. The liquid chromatography mass spectrometer was used for the measurements of the targeted metabolites. Afterwards, we performed differential metabolite assay analysis and related pathway enrichment analysis.

Results

In our study, a total of 149 metabolite profiles were detected in all participants. There were significant differences in several metabolite profiles between the TED group and the control group, mainly including uric acid, oxidized glutathione, taurine, dGMP, oxidized glutathione 2, uracil, hexose-phosphate, 1-methylnicotinamide, D-sedoheptulose 1,7-bisphosphate, and uridine 5'-monophosphate (all p-value < 0.05). The TED-related pathways identified included purine metabolism, beta-alanine metabolism, glutathione metabolism (p-values < 0.05). Our study found overlaps and differences including uric acid and uracil, which are in accordance with metabolites found in blood of patients with TED from previous study and several newly discovered metabolite by our study such as hexose-phosphate, 1-methylnicotinamide, D-sedoheptulose 1,7-bisphosphate, compared to those tested from blood, OAT, or urine samples reported in previous studies.

Conclusion

The findings of our study shed light on the metabolic features of OAT in individuals with TED. These results may help identify new treatment targets for TED, providing potential avenues for developing alternative treatments beyond ophthalmic surgery.

Mapping of Ion and Substrate Binding Sites in Human Sodium Iodide Symporter (hNIS)

The human sodium iodide symporter (hNIS) is a theranostic reporter gene which concentrates several clinically approved SPECT and PET radiotracers and plays an essential role for the synthesis of thyroid hormones as an iodide transporter in the thyroid gland. Development of hNIS mutants which could enhance translocation of the desired imaging ions is currently underway. Unfortunately, it is hindered by lack of understanding of the 3D organization of hNIS and its relation to anion transport. There are no known crystal structures of hNIS in any of its conformational states. Homology modeling can be very effective in such situations; however, the low sequence identity between hNIS and relevant secondary transporters with available experimental structures makes the choice of a template and the generation of 3D models nontrivial. Here, we report a combined application of homology modeling and molecular dynamics refining of the hNIS structure in its semioccluded state. The modeling was based on templates from the LeuT-fold protein family and was done with emphasis on the refinement of the substrate-ion binding pocket. The consensus model developed in this work is compared to available biophysical and biochemical experimental data for a number of different LeuT-fold proteins. Some functionally important residues contributing to the formation of putative binding sites and permeation pathways for the cotransported Na⁺ ions and I^- substrate were identified. The model predictions were experimentally tested by generation of mutant versions of hNIS and measurement of relative (to WT hNIS) ¹²⁵I^- uptake of 35 hNIS variants.

Mutational Spectrum Analysis of Seven Genes Associated with Thyroid Dyshormonogenesis

OBJECTIVE

Thyroid dyshormonogenesis (DH) is a genetically heterogeneous inherited disorder caused by thyroid hormone synthesis abnormalities. This study aims at comprehensively characterizing the mutation spectrum in Chinese patients with DH.

SUBJECTS AND METHODS

We utilized next-generation sequencing to screen for mutations in seven DH-associated genes (TPO, DUOX2, TG, DUOXA2, SLC26A4, SLC5A5, and IYD) in 21 Chinese Han patients with DH from Xinjiang Province.

RESULTS

Twenty-eight rare nonpolymorphic variants were found in 19 patients (90.5%), including 19, 5, 3, and 1 variants in DUOX2, TG, DUOXA2, and SLC26A4, respectively. Thirteen (62%) patients carried monogenic mutations, and six (28.5%) carried oligogenic mutations. Fifteen (71%) patients carried 2 or more DUOX2 (14) or DUOXA2 (1) variants. The genetic basis of DH in nine (43%) patients harboring biallelic or triallelic pathogenic variants was resolved. Seventeen patients (81%) carried DUOX2 mutations, most commonly p.R1110Q or p.K530X. No correlations were found between DUOX2 mutation types or numbers and clinical phenotypes.

CONCLUSIONS

DUOX2 mutations were the most predominant genetic alterations of DH in the study cohort. Oligogenicity may explain the genetic basis of disease in many DH patients. Functional studies and further clinical studies with larger DH patient cohorts are needed to validate the roles of the mutations identified in this study.

Comprehensive Screening of Eight Known Causative Genes in Congenital Hypothyroidism With Gland-in-Situ

CONTEXT

Lower TSH screening cutoffs have doubled the ascertainment of congenital hypothyroidism (CH), particularly cases with a eutopically located gland-in-situ (GIS). Although mutations in known dyshormonogenesis genes or TSHR underlie some cases of CH with GIS, systematic screening of these eight genes has not previously been undertaken.

OBJECTIVE

Our objective was to evaluate the contribution and molecular spectrum of mutations in eight known causative genes (TG, TPO, DUOX2, DUOXA2, SLC5A5, SLC26A4, IYD, and TSHR) in CH cases with GIS. Patients, Design, and Setting: We screened 49 CH cases with GIS from 34 ethnically diverse families, using next-generation sequencing. Pathogenicity of novel mutations was assessed in silico.

PATIENTS, DESIGN, AND SETTING

We screened 49 CH cases with GIS from 34 ethnically diverse families, using next-generation sequencing. Pathogenicity of novel mutations was assessed in silico.

RESULTS

Twenty-nine cases harbored likely disease-causing mutations. Monogenic defects (19 cases) most commonly involved TG (12), TPO (four), DUOX2 (two), and TSHR (one). Ten cases harbored triallelic (digenic) mutations: TG and TPO (one); SLC26A4 and TPO (three), and DUOX2 and TG (six cases). Novel variants overall included 15 TG, six TPO, and three DUOX2 mutations. Genetic basis was not ascertained in 20 patients, including 14 familial cases.

CONCLUSIONS

The etiology of CH with GIS remains elusive, with only 59% attributable to mutations in TSHR or known dyshormonogenesis-associated genes in a cohort enriched for familial cases. Biallelic TG or TPO mutations most commonly underlie severe CH. Triallelic defects are frequent, mandating future segregation studies in larger kindreds to assess their contribution to variable phenotype. A high proportion (∼41%) of unsolved or ambiguous cases suggests novel genetic etiologies that remain to be elucidated.

Compound heterozygous mutations (p.T561M and c.2422delT) in the TPO gene associated with congenital hypothyroidism

BACKGROUND

The objective of the study was to determine the genetic basis of goitrous congenital hypothyroidism (GCH) in Chinese siblings.

METHODS

The proband and her younger brother with GCH were enrolled for molecular analysis of the dual oxidase 2 (DUOX2), dual oxidase maturation factor 2 (DUOXA2), and thyroid peroxidase (TPO) genes. Mutation screening was performed by Sanger sequencing the fragments amplified from genomic DNA. The detected mutations were verified among the close relatives of the patients and 105 controls. All participants underwent clinical examination and laboratory tests.

RESULTS

Analysis of the TPO gene revealed two heterozygous mutations, the frameshift mutation c.2422delT in the exon14 of the TPO gene, that has been reported previously, and a novel missense mutation c.1682C>T (p.T561M) in the exon10 of the TPO gene. Nine family members of the patients were enrolled for mutation screening. The patients' parents and grandfathers harbored a single heterozygous mutation. The germline mutations from this family were consistent with an autosomal recessive inheritance pattern. No mutations in the DUOXA2 and DUOX2 genes were observed.

CONCLUSIONS

The inactivating mutations (c.2422delT and p.T561M) in the TPO gene were identified in the Chinese siblings with GCH. The compound heterozygous mutations can cause GCH.