Correlation of DUOX2 residual enzymatic activity with phenotype in congenital hypothyroidism caused by biallelic DUOX2 defects

TSHR Variant Screening and Phenotype Analysis in 367 Chinese Patients With Congenital Hypothyroidism

Background

Genetic defects in the human thyroid-stimulating hormone (TSH) receptor (TSHR) gene can cause congenital hypothyroidism (CH). However, the biological functions and comprehensive genotype-phenotype relationships for most TSHR variants associated with CH remain unexplored. We aimed to identify TSHR variants in Chinese patients with CH, analyze the functions of the variants, and explore the relationships between TSHR genotypes and clinical phenotypes.

Methods

In total, 367 patients with CH were recruited for TSHR variant screening using whole-exome sequencing. The effects of the variants were evaluated by in-silico programs such as SIFT and polyphen2. Furthermore, these variants were transfected into 293T cells to detect their Gs/cyclic AMP and Gq/11 signaling activity.

Results

Among the 367 patients with CH, 17 TSHR variants, including three novel variants, were identified in 45 patients, and 18 patients carried biallelic TSHR variants. In vitro experiments showed that 10 variants were associated with Gs/cyclic AMP and Gq/11 signaling pathway impairment to varying degrees. Patients with TSHR biallelic variants had lower serum TSH levels and higher free triiodothyronine and thyroxine levels at diagnosis than those with DUOX2 biallelic variants.

Conclusions

We found a high frequency of TSHR variants in Chinese patients with CH (12.3%), and 4.9% of cases were caused by TSHR biallelic variants. Ten variants were identified as loss-of-function variants. The data suggest that the clinical phenotype of CH patients caused by TSHR biallelic variants is relatively mild. Our study expands the TSHR variant spectrum and provides further evidence for the elucidation of the genetic etiology of CH.

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 function. 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 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 the clinical severity among patients with DUOX2 amorphic/amorphic, amorphic/hypomorphic, and hypomorphic/hypomorphic variants. Conclusions: These results broaden the mutation 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.

Contactin 6, A Novel Causative Gene for Congenital Hypothyroidism, Mediates Thyroid Hormone Biosynthesis Through Notch Signaling

Background: Congenital hypothyroidism (CH) is the most common neonatal metabolic disorder. In patients with CH in China, thyroid dyshormonogenesis is more common than thyroid dysgenesis; however, the genetic causes of CH due to thyroid dyshormonogenesis remain largely unknown. Therefore, we aimed at identifying novel candidate causative genes for CH. Methods: To identify novel CH candidate genes, a total of 599 patients with CH were enrolled and next-generation sequencing was performed. The functions of the identified variants were confirmed using HEK293T and FTC-133 cell lines in vitro and in a mouse model organism in vivo. Results: Three pathogenic contactin 6 (CNTN6) variants were identified in two patients with CH. Pedigree analysis showed that CH caused by CNTN6 variants was inherited in an autosomal recessive pattern. The CNTN6 gene was highly expressed in the thyroid in humans and mice. Cntn6 knockout mice presented with thyroid dyshormonogenesis and CH due to the decreased expression of crucial genes for thyroid hormone biosynthesis (Slc5a5, Tpo, and Duox2). All three CNTN6 variants resulted in the blocking of the release of the Notch intracellular domain, which could not translocate into the nucleus, impaired NOTCH1 transcriptional activity, and decreased expression of SLC5A5, TPO, and DUOX2. Further, we found that DTX1 was required for CNTN6 to promote thyroid hormone biosynthesis through Notch signaling. Conclusions: This study demonstrated that CNTN6 is a novel causative gene for CH through the mediation of thyroid hormone biosynthesis via Notch signaling, which provides new insights into the genetic background and mechanisms involved in CH and thyroid dyshormonogenesis.

Whole exome sequencing reveal 83 novel Mendelian disorders carrier P/LP variants in Chinese adult patients

Carrier screening can identify people at risk of conceiving pregnancies affected with inherited genetic disorders or who have a genetic disorder with late or variable onset. Carrier screening based on whole exome sequencing (WES) data can offer more comprehensive assessment than on-target carrier screening tests. A total of 224 Chinese adult patients WES data was analyzed, except positive variants associated with the patients' major complaint, 378 pathogenic (P) and "likely pathogenic" (LP) variants from 175 adult patients were identified. Whole exome-wide frequency of carriers for Mendelian disorders in Chinese adult patients was about 78.13% in this study, which was lower than the previously reported carrier frequency in healthy population. Contrary to expectations, the number of P or LP variants did not increase with larger chromosome size or decrease with smaller chromosome size. Totally 83 novel P or LP variants were identified which could further expand the carrier variants spectrum of the Chinese population. GJB2: NM_004004.6:c.299_300delAT:p.His100fs*14 and C6:NM_000065.4:c.654T>A:p.Cys218* were found in two or more patients, which might be two underestimated carrier variants in Chinese population. We also found 9 late-onset or atypical symptoms autosomal/X-linked dominant Mendelian disorders causative genes, which were easily overlooked during pathogenicity analysis. These results can provide a strong basis for preventing and avoiding the prevalence rates of birth defects and reducing social and family burdens. By comparing with three different expanded carrier screening gene panels, we further confirmed carrier screening based on WES could offer more comprehensive assessment and WES was applicable for carrier screening.

Gene mutations in children with permanent congenital hypothyroidism in Yunnan, China

OBJECTIVE

To investigate molecular and clinical characteristics of children with permanent congenital hypothyroidism (CH) in Yunnan, China.

METHODS

The clinical data of 40 children with CH diagnosed and treated in the First People's Hospital of Yunnan Province during January 2016 and January 2019 were retrospectively analyzed. All children were followed up to 3 years old, and Gesell intelligent score was evaluated at age of 1, 2 and 3 years, respectively. Developmental status and prognosis were evaluated. Next-generation sequencing (NGS) was used to screen all exons and exon-intron boundary sequences of the 27 known CH associated genes, and the relationship between genotypes and clinical phenotypes was analyzed.

RESULTS

Among the 40 children, the thyroid related pathogenic gene mutations were detected in 23 cases with a rate of 57.5%, and a total of 32 mutations of 8 genes were detected. Mutations in DUOX2, TPO and TSHR genes were the most common ones with mutation frequencies of 65.9%(29/44), 11.4%(5/44) and 9.1%(4/44), respectively. DUOX2 gene mutations were detected in 17 children with CH, and a total of 17 mutation types were detected. p.K530* was the most common mutation in DUOX2 gene, accounting for 20.7%(6/29). There was no significant difference in physical development and intelligence assessment between children with DUOX2 heterozygous mutation and compound heterozygous mutations. None of patients could terminate medication at 3 years of the follow-up and all of them were provisionally assessed as permanent CH. The physical and mental development assessment of children with other gene mutations were also in the normal range.

CONCLUSION

The detection rate of DUOX2, TPO and TSHR pathogenic mutations are high among children with permanent CH in Yunnan area, and no correlation is observed between gene mutation types and prognosis in children with CH.