Functional analysis of a variant of the thyrotropin receptor gene in a family with Graves' disease

Utility of systematic TSHR gene testing in adults with hyperthyroidism lacking overt autoimmunity and diffuse uptake on thyroid scintigraphy

OBJECTIVE

Patients with hyperthyroidism lacking autoimmune features but showing diffuse uptake on thyroid scintigram can have either Graves' disease or germline activating TSH receptor (TSHR) mutation. It is important to identify patients with activating TSHR mutation due to treatment implication, but the overlapping clinical features with Graves' disease make it difficult to discriminate these two conditions without genetic testing. Our study aimed to assess the potential of systematic TSHR mutation screening in adults with hyperthyroidism, showing diffuse uptake on thyroid scintigraphy but absence of TSH receptor antibodies (TRAb) and clinical signs of autoimmunity.

DESIGN

A cross-sectional study of Caucasian adults with hyperthyroidism, managed at three endocrine centres in the South West, UK, from January 2006 to April 2017.

METHODS

We recruited 78 adult Caucasian patients with hyperthyroidism showing diffuse uptake on 99m Tc-pertechnetate thyroid scintigraphy but without TRAb and other autoimmune clinical features of Graves' disease (such as thyroid-associated ophthalmopathy or dermopathy). Genomic DNA of these patients was analysed for variants in the TSHR gene.

RESULTS

Genetic analysis identified 11 patients with four variants in TSHR [p.(Glu34Lys), p.(Asp36His), p.(Pro52Thr) and p.(Ile334Thr)]. None of these variants were pathogenic according to the American College of Medical Genetics and Genomics guideline.

CONCLUSIONS

Activating TSHR mutations are a rare cause of nonautoimmune adult hyperthyroidism. Our study does not support the routine genetic testing in adult patients with hyperthyroidism showing diffuse uptake on scintigraphy but negative TRAb and lacking extrathyroidal manifestations of Graves' disease.

Pituitary Diseases and Bone

Neuroendocrinology of bone is a new area of research based on the evidence that pituitary hormones may directly modulate bone remodeling and metabolism. Skeletal fragility associated with high risk of fractures is a common complication of several pituitary diseases such as hypopituitarism, Cushing disease, acromegaly, and hyperprolactinemia. As in other forms of secondary osteoporosis, pituitary diseases generally affect bone quality more than bone quantity, and fractures may occur even in the presence of normal or low-normal bone mineral density as measured by dual-energy X-ray absorptiometry, making difficult the prediction of fractures in these clinical settings. Treatment of pituitary hormone excess and deficiency generally improves skeletal health, although some patients remain at high risk of fractures, and treatment with bone-active drugs may become mandatory. The aim of this review is to discuss the physiological, pathophysiological, and clinical insights of bone involvement in pituitary diseases.

Clinical Significance of Thyroid-Stimulating Hormone Receptor Gene Mutations and/or Sodium-Iodine Symporter Gene Overexpression in Indeterminate Thyroid Fine Needle Biopsies

Objectives: To examine the prevalence of genetic alterations of thyroid-stimulating hormone receptor (TSHR) gene and sodium-iodine symporter (NIS) in a series of thyroid fine needle biopsy (FNB) specimens with indeterminate cytology, and to assess the correlation of the type of genetic changes with clinical features and follow-up results in the target thyroid nodule. Methods: Between February 2015 and September 2017, 388 consecutive FNBs with indeterminate cytology were evaluated for TSHR mutations and NIS gene overexpression using ThyroSeqV.2 next-generation sequencing (NGS) panel. Medical records were reviewed for target nodules. Results: Among 388 indeterminate FNBs, TSHR mutations and/or NIS overexpression were detected in 25 (6.4%) nodules. Ten nodules (2.6%) harbored TSHR mutations only, 7 nodules (1.8%) over-expressed NIS gene only, and 8 nodules (2.1%) had both alterations. The TSHR mutations were located between codons 281 and 640, with codon 453 being the most frequently affected. The allelic frequency of the mutated TSHR ranged from 6 to 36%. One nodule with NIS overexpression was simultaneously detected EIF1AX mutation and GNAS mutation. Nodules with TSHR mutations and/or NIS overexpression presented hyperfunctioning (n = 4), hypofunctioning (n = 5), and isofunctioning (n = 3) on the available thyroid scintigraphies. Eight cases accompanied with hyperthyroidism in which only 1 was caused by the target nodule. Evidence of co-existing autoimmune thyroid disease (AITD) and multinodular goiter were found in 52% and 52% of cases, respectively. Seven nodules underwent surgeries and all were benign on final pathology. None of 9 nodules with follow-up by ultrasound (3~33 mon, median 12 mon) showed grow in size. Conclusions: TSHR mutations and/or NIS overexpression can be detected in pre-operative FNB specimens using the NGS approach. These genetic alterations occurred in 6.4% thyroid nodules in this consecutive series with indeterminate cytology. They present not only in hyperfunctioning nodules but also in hypo- or iso-functional nodules, indicating their prevalence may be higher than previously expected. Co-existing AITD was common in cases with these molecular alterations. None of our patients with TSHR mutations and/or NIS overexpression manifested malignant outcomes. How to use these two molecular markers in thyroid FNBs to guide our clinical practice warrants further investigation.

Refined association of TSH receptor susceptibility locus to Graves' disease in the Chinese Han population

BACKGROUND

Convincing evidence has demonstrated the association of TSH receptor (TSHR) with Graves' disease (GD) in the Chinese Han population.

OBJECTIVE

The aim of this study was to identify the causal variants for GD in the region encompassing TSHR by a refining association study.

DESIGN AND METHODS

GD patients (1536) and 1516 sex-matched controls were recruited in the first stage, and an additional 3832 GD patients and 3426 sex-matched controls were recruited in the replication stage. Genotyping was performed using Illumina Human660-Quad BeadChips or TaqMan single nucleotide polymorphism (SNP) Genotyping Assays and the Fluidigm EP1 platform.

RESULTS

When the results of regression analysis for 74 genotyped SNPs and 922 imputed SNPs in the first-stage cohort were combined, rs179243 and rs3783949 were the probable susceptibility SNPs associated with GD in TSHR. Eleven SNPs, including rs179243 and rs3783949, were selected to further refine the association in the replication study. Finally, rs12101261 and rs179243 were confirmed as independent GD susceptibility variants in the replication and combined populations. Further, we also found that the rate of persistent TSHR autoantibody positivity (pTRAb+) was significantly higher in the GD patients with the susceptible genotypes rs12101261 or rs179243 than in the GD patients carrying the protective genotypes, after the GD patients had been treated for more than 1 year.

CONCLUSIONS

These findings indicate that rs12101261 and rs179243 are the possible causal SNPs for GD susceptibility in the TSHR gene and could serve as genetic markers to predict the outcome of pTRAb+ in GD patients.

The Glu727 Allele of Thyroid Stimulating Hormone Receptor Gene is Associated with Osteoporosis

Background:

Published data indicate that thyroid stimulating hormone receptor (TSHR) activities are associated with osteoporosis in some patients.

Aim:

This study aimed to elucidate whether a given polymorphism of the TSHR gene is associated with osteoporosis.

Materials and Methods:

One hundred and fifty subjects with osteoporosis were recruited in this study. The diagnosis of osteoporosis was performed with quantitative ultrasound system. The TSHR gene polymorphism was examined by polymerase chain reaction–restriction fragment length polymorphism.

Results:

The results showed a nucleotide substitution in the first position of codon 36 of the TSHR gene. The nucleotide substitution was from G to C, leading to a ³⁶D → ³⁶H change (D36H) in the predicted amino acid sequence of the receptor. The change did not show significance between healthy subjects and patients with osteoporosis (P > 0.05). On the other hand, we identified another single nucleotide polymorphism that is a C-to-G substitution at codon 727 (GAC to GAG); its frequency was significantly higher in patients with osteoporosis than that in healthy subjects. Using logistic regression analysis, significant correlation was revealed between the genotype D727E and the serum levels of TSH, or the quantitative ultrasound value of the calcaneal bone.

Conclusions:

The present study suggests that the genotype D727E of the TSHR, but not the genotype D36H, may be a genetic risk factor for osteoporosis.

The genetic basis of graves' disease

The presented comprehensive review of current knowledge about genetic factors predisposing to Graves’ disease (GD) put emphasis on functional significance of observed associations. In particular, we discuss recent efforts aimed at refining diseases associations found within the HLA complex and implicating HLA class I as well as HLA-DPB1 loci. We summarize data regarding non-HLA genes such as PTPN22, CTLA4, CD40, TSHR and TG which have been extensively studied in respect to their role in GD. We review recent findings implicating variants of FCRL3 (gene for FC receptor-like-3 protein), SCGB3A2 (gene for secretory uteroglobin-related protein 1- UGRP1) as well as other unverified possible candidate genes for GD selected through their documented association with type 1 diabetes mellitus: Tenr–IL2–IL21, CAPSL (encoding calcyphosine-like protein), IFIH1(gene for interferon-induced helicase C domain 1), AFF3, CD226 and PTPN2. We also review reports on association of skewed X chromosome inactivation and fetal microchimerism with GD. Finally we discuss issues of genotype-phenotype correlations in GD.

Identification and characterization of new variants of three associated SNPs and a microsatellite in the TSH receptor gene which are useful for genetic studies

The purpose of the present work was to characterize g.IVS5-69C>T, g.IVS6+13C>T and c.561C>T SNPs and the [CT](n) microsatellite in the TSHR gene for genetic analysis. Exons 6 and 7 of the TSHR gene, including the flanking intronic sequences, were screened for the presence of g.IVS5-69C>T, g.IVS6+13C>T and c.561C>T SNPs by SSCP. We found genetic association between the three SNPs and a total of three different haplotypes were observed. Two were homozygous blocks, g.IVS5-69T/g.IVS6+13G/c.561C (Haplotype TGC, 3.3%) and g.IVS5-69C/g.IVS6+13A/c.561T (Haplotype CAT, 75%). Every individual who was heterozygous for g.IVS5-69C>T was equally heterozygous for g.IVS6+13A>G and c.561T>C (Haplotype CAT/TGC, 21.7%). The [CT](n) microsatellite, localized in intron 7 of the TSHR gene was amplified by PCR and the labeled products were separated in a polyacrylamide denaturing sequencing gel. Three variable numbers of CT motif were identified, two previously reported ([CT](6) and [CT](8)) and one previously unreported ([CT](9)). The construction and expression of the hybrid minigenes using pSPL3 and alpha-globin-fibronectin EDB (pTB) vectors showed that the [CT](n) microsatellite itself does not interfere with exon 8 definition and processing in vitro. In conclusion, g.IVS5-69C>T/g.IVS6+13C>T/c.561C>T haplotypes and [CT](n) microsatellite are informative polymorphic markers and can be used in linkage studies in families with germ line TSHR mutations or autoimmunity thyroid diseases.

A new silent germline mutation of the TSH receptor: coexpression in a hyperthyroid family member with a second activating somatic mutation

BACKGROUND

Up to date, three thyroid-stimulating hormone receptor (TSHR) germline variants have been reported for which no functional consequences have been detected by in vitro characterizations. However, familial nonautoimmune hyperthyroidism and hot nodules are clearly associated with constitutively activating TSHR germline mutations. We describe a family with a new TSHR germline mutation that is associated with euthyroidism in 13 family members and hyperthyroidism in 1 family member.

METHODS

Mutation analysis of the TSHR gene was performed by denaturing gradient gel electrophoresis. TSHR constructs were characterized by determination of cell surface expression, 3'-5'-cyclic adenosine monophosphate (cAMP) accumulation, and constitutive cAMP activity.

RESULTS

A novel TSHR germline mutation (N372T) was found in a man who presented with thyrotoxicosis. The mutation was also detected in 13 family members, all of whom were euthyroid. Interestingly, an additional constitutively active somatic mutation (S281N) was identified on the second parental TSHR allele of the hyperthyroid index patient. Linear regression analysis showed a lack of constitutive activity for N372T. Moreover, coexpression studies of N372T with S281N did not reveal any evidence for a functional influence of N372T on the constitutively active mutation (CAM).

CONCLUSIONS

N372T is unlikely to cause altered thyroid function. This is consistent with the finding that only the index patient with the additional somatic mutation S281N was hyperthyroid.

Thyroid-stimulating hormone receptor and its role in Graves' disease

The thyroid-stimulating hormone (TSH, or thyrotropin) receptor (TSHR) mediates the activating action of TSH to the thyroid gland, resulting in the growth and proliferation of thyrocytes and thyroid hormone production. In Graves' disease, thyroid-stimulating autoantibodies can mimic TSH action and stimulate thyroid cells. This leads to hyperthyroidism and abnormal overproduction of thyroid hormone. TSHR-antibodies-binding epitopes on the receptor molecule are well studied. Mechanism of TSHR-autoantibodies production is more or less clear but a susceptibility gene, which is linked to their production, is still unknown. Genetic studies show no linkage between the TSHR gene and Graves' disease. Among three common polymorphisms in the TSHR gene, only the D727E germline polymorphism in the cytoplasmic tail of the receptor showed an association with the disease, and this association is weak. The absence of a strong genetic effect of the TSHR polymorphisms in such a common and complex disorder as Graves' disease may be explained by a high degree of evolutionary conservation in TSHR. This can be shown by naturally existing germline and somatic mutations in the TSHR gene that cause various types of nonautoimmune and hereditary thyroid disease.

Association of Graves' disease with intragenic polymorphism of the thyrotropin receptor gene in a cohort of Singapore patients of multi-ethnic origins

Thyrotropin (TSH) receptor (TSHr) mutations have been investigated in relation to Graves' disease (GD) genetic susceptibility under the hypothesis that a modified antigen may have novel immunogenic properties. The prevalence of three germline polymorphisms--D36H, P52T, and D727E--were studied in a cohort of multiracial GD patients together with their associations with disease state, Graves' ophthalmopathy, and thyroid autoantibodies titers. Polymerase chain reaction products of exon 1 and 10e of the TSHr were generated from 164 GD patients (109 Chinese, 34 Malays, and 21 Indians) and 240 individuals with no thyroid illnesses (74 Chinese, 84 Malays, and 82 Indians). Mutations were detected by single-strand conformational polymorphism and confirmed with direct sequencing. The D36H mutation was absent, while significant ethnic differences in the distribution of the P52T and D727E mutations were found. The levels of thyroid autoantibodies also differed significantly amongst the three ethnic groups, with the Indian cohort having the lowest titer. Both the P52T and D727E mutations were not associated with GD. An intron mutation, C/G+63IVS1, was detected and showed significant association with GD. Overall, it conferred a twofold increase risk of GD, while subgroup analysis showed increased odds ratios of 2.4 for Chinese (p = 0.008) and 2.8 for Indian (p = 0.049) but not for the Malay ethnic group. Together with recent identification of disease susceptibility markers in the region of the TSHr gene, these results are supportive of genetic factors existing in this region that may be in linkage disequilibrium with the inheritance of various TSHr polymorphisms.

Polymorphisms in thyroid hormone pathway genes are associated with plasma TSH and iodothyronine levels in healthy subjects

Single nucleotide polymorphisms (SNPs) in genes involved in thyroid hormone metabolism may affect thyroid hormone bioactivity. We investigated the occurrence and possible effects of SNPs in the deiodinases (D1-D3), the TSH receptor (TSHR), and the T(3) receptor beta (TR beta) genes. SNPs were identified in public databases or by sequencing of genomic DNA from 15 randomly selected subjects (30 alleles). Genotypes for the identified SNPs were determined in 156 healthy blood donors and related to plasma T(4), free T(4), T(3), rT(3), and TSH levels. Eight SNPs of interest were identified, four of which had not yet been published. Three are located in the 3'-untranslated region: D1a-C/T (allele frequencies, C = 66%, T = 34%), D1b-A/G (A = 89.7%, G = 10.3%), and D3-T/G (T = 85.5%, G = 14.2%). Four are missense SNPs: D2-A/G (Thr92Ala, Thr = 61.2%, Ala = 38.8%), TSHRa-G/C (Asp36His, Asp = 99.4%, His = 0.6%), TSHRb-C/A (Pro52Thr, Pro = 94.2%, Thr = 5.8%), and TSHRc-C/G (Asp727Glu, Asp = 90.7%, Glu = 9.3%). One is a silent SNP: TR beta-T/C (T = 96.8%, C = 3.2%). D1a-T was associated in a dose-dependent manner with a higher plasma rT(3) [CC, 0.29 +/- 0.01; CT, 0.32 +/- 0.01; and TT, 0.34 +/- 0.02 nmol/liter (mean +/- SE); P = 0.017], a higher plasma rT(3)/T(4) (P = 0.01), and a lower T(3)/rT(3) (P = 0.003) ratio. The D1b-G allele was associated with lower plasma rT(3)/T(4) (P = 0.024) and with higher T(3)/rT(3) (P = 0.08) ratios. TSHRc-G was associated with a lower plasma TSH (CC, 1.38 +/- 0.07, vs. GC, 1.06 +/- 0.14 mU/liter; P = 0.04), and with lower plasma TSH/free T(4) (P = 0.06), TSH/T(3) (P = 0.06), and TSH/T(4) (P = 0.08) ratios. No associations with TSH and iodothyronine levels were found for the other SNPs. We have analyzed eight SNPs in five thyroid hormone pathway genes and found significant associations of three SNPs in two genes (D1, TSHR) with plasma TSH or iodothyronine levels in a normal population.

Analysis of the genetic variability of the 1st (CCC/ACC, P52T) and the 10th exons (bp 1012-1704) of the TSH receptor gene in Graves' disease

We determined the genetic variability of the 1st (CCC/ACC, P52T polymorphic variant) and 10th exons (bp 1012-1704) of the TSH receptor (TSHR) gene in Graves' disease. A total of 101 Graves' patients and 163 control subjects were screened. The A253 mutant allele was carried by nine patients with Graves' disease (8.91%) and 13 control subjects (7.98%) in heterozygous genotype. No significant difference in the frequency of the mutant allele was found between Graves' patients and control subjects. These results provide evidence that the A253 polymorphism has no genetic relevance in Graves' disease. Moreover, the DNA nucleotide sequence of 693 bp of the 10th exon (bp 1012-1704) of the TSHR gene was determined in 15 Graves' patients. Six patients were homozygous for the wild-type allele and nine were heterozygous for the mutant allele at the 253rd nucleotide of the first exon. No polymorphism was found in the DNA sequences obtained from leukocytes of Graves' patients, similarly to the sequences obtained from the nine control subjects. None of the nine patients carrying the A253 polymorphism in the 1st exon of the TSHR had polymorphism in the examined part of the 10th exon, including two additional patients whose thyroid tissue was directly analysed. In all likelihood, the polymorphisms of the examined regions of either the 1st or the 10th exon of the THSR gene do not contribute to the genetic susceptibility to Graves' disease.

Analysis of mutations in exon 1 of the human thyrotropin receptor gene: high frequency of the D36H and P52T polymorphic variants

The aim of the present study was to investigate the N-terminal part (the translated part of exon 1) of the human thyrotropin receptor (TSHR) for the presence of mutations. Patients with Graves' disease (n = 160) and healthy controls (blood donors; n = 140) were screened using single-stranded conformational polymorphism (SSCP) in combination with restriction enzyme digestion for the two previously known mutations in this part of the receptor, viz. D36H and P52T TSHR-variants. We did not find any novel mutation in this region. However, D36H and P52T variants were found both in the TSHR of Graves' patients and in the healthy controls. The overall frequency of the D36H-receptor variant was 5.0% (15/300) and of the P52T-receptor, 7.3% (22/300). There was no major difference in the frequency for either of the TSHR alleles between the 2 groups. Thus, these 2 polymorphic variants of the TSHR seem to occur in a relatively high frequency in the population.

Functional characteristics of a variant thyrotropin receptor

A claim has been made that a variant of the human thyrotropin receptor in which Pro52 is replaced by Thr ([Thr52]thyrotropin receptor) is associated with autoimmune thyroid diseases and displays increased responsiveness to thyrotropin. We have analysed the functional characteristics of this variant receptor. Equivalent numbers of of the wild type and of the variant thyrotropin receptor, measured both by 125I-thyrotropin binding and by flow cytofluorimetry, were transiently expressed in COS-7 cells. Under these conditions, the two receptors showed the same degree of constitutive activity for the cAMP pathway, the same affinity for bovine thyrotropin, and a virtually identical responsiveness to bovine thyrotropin for activation of both the cAMP and inositol-phosphate regulatory pathways. Our results show that the [Thr52]thyrotropin receptor variant of the human thyrotropin receptor, which is present in the 12% of the population, does not affect receptor function and represents most likely a simple polymorphism.