TSH Receptor Gene Mutations Research Articles

Prevalence of germline mutations in the TSH receptor gene as a cause of juvenile thyrotoxicosis.

To ascertain the prevalence of germline mutations in the TSH receptor gene as a cause of juvenile thyrotoxicosis (JT) in non-autoimmune patients. TSH receptor gene mutations are not seen in autoimmune-active patients. In a nationwide study on JT, 123 patients were re-examined 10 y (range 4 to 21 y) after diagnosis. Two patients with toxic adenoma were excluded. In 25 patients, no TPO, TG or TSH-R antibodies were found. In 17 patients, DNA material was available for TSH receptor gene analysis. The entire TSH receptor gene was sequenced in five patients. TSH receptor "hot spots" for mutations in exon 9 and 10 were sequenced in the remaining 12 patients. A TSH receptor gene germline mutation was identified in only one patient of a total number of 121 patients with JT, of which 17 patients were presumed to have non-autoimmune JT by the lack of thyroid autoantibodies. In Denmark the prevalence of germline mutations in the TSH receptor gene is one in 121 patients with JT (0.8%; 95% CI: 0.02-4.6%) and one in 17 patients with presumed non-autoimmune JT (6%; 95% CI: 5.88% (0.15-28.69)).

Prevalence of germline mutations in the TSH receptor gene as a cause of juvenile thyrotoxicosis

Aim: To ascertain the prevalence of germline mutations in the TSH receptor gene as a cause of juvenile thyrotoxicosis (JT) in non‐autoimmune patients. TSH receptor gene mutations are not seen in autoimmune‐active patients. Methods: In a nationwide study on JT, 123 patients were re‐examined 10 y (range 4 to 21 y) after diagnosis. Two patients with toxic adenoma were excluded. In 25 patients, no TPO, TG or TSH‐R antibodies were found. In 17 patients, DNA material was available for TSH receptor gene analysis. The entire TSH receptor gene was sequenced in five patients. TSH receptor “hot spots” for mutations in exon 9 and 10 were sequenced in the remaining 12 patients. Results: A TSH receptor gene germline mutation was identified in only one patient of a total number of 121 patients with JT, of which 17 patients were presumed to have non‐autoimmune JT by the lack of thyroid autoantibodies. Conclusion: In Denmark the prevalence of germline mutations in the TSH receptor gene is one in 121 patients with JT (0.8%; 95% CI: 0.02–4.6%) and one in 17 patients with presumed non‐autoimmune JT (6%; 95% CI: 5.88% (0.15–28.69)).

TSH receptor and Gs(alpha) genetic analysis in children with Down's syndrome and subclinical hypothyroidism.

The prevalence of thyroid diseases in children with Down's syndrome (DS) is about 3%. The most frequently observed condition is autoimmune subclinical hypothyroidism (SH). Autoimmune SH must be distinguished from defects in the biological activity of the TSH molecule or from the rare inherited condition of thyroid resistance to TSH. To investigate this last aspect we studied 12 patients with DS that had moderately elevated TSH with normal free thyroid hormones without signs of autoimmunity. For the genetic analysis the genomic DNA was extracted from peripheral lymphocytes. All the exons of the TSH receptor (TSHr) and Gs(alpha) genes were sequenced. The genetic analysis of the TSHr gene revealed the presence of four polymorphic variants. In two patients there was an allelic variant in the exon 1 (Pro52Thr--in one patient in the heterozygous state and in the other as a homozygous substitution). In one patient there was an allelic variant in the exon 1 (Asp36His) in the heterozygous state. In 11 patients there was a silent polymorphism in the exon 7 at nucleotide 561. All patients were homozygous for a silent polymorphism in the exon 9 at nucleotide 855. No inactivating mutations of TSHr or Gs(alpha) genes were identified in the 12 patients. In conclusion, our results seem to exclude the role of TSHr or Gs(alpha) gene mutations in the pathogenesis of the non-autoimmune SH observed in some children with DS.

Resistance to thyrotropin.

Resistance to TSH is a syndrome of reduced sensitivity to a biologically active TSH molecule. Subjects have elevated TSH levels but no goiter. However, thyroid hormone concentration may vary from normal to very high, depending on the severity of the resistance. Individuals with very high TSH, low T4 and hypoplastic thyroid glands can be mistakenly diagnosed as having primary hypothyroidism due to a defective development of the thyroid gland. Those with normal or slightly decreased T4 can be misdiagnosed as having central hypothyroidism especially if their serum TSH concentration is only slightly elevated. Mutations in the TSH receptor (TSHr) gene have been reported in 16 families with homozygous or compound heterozygous inheritance. The mutant TSHrs show reduced or no function due to either altered ligand binding or defect in membrane targeting. Some individuals, heretozygous for a TSHr gene mutation can present mild resistance to TSH manifesting as euthyroidism with slight hyperthyrotropinemia. A larger proportion of families express the phenotype of resistance to TSH in the absence of a TSHr defect. In many the inheritance is dominant and the genetic cause has not been yet determined.

Functioning and nonfunctioning thyroid adenomas involve different molecular pathogenetic mechanisms.

The molecular biology of follicular cell growth in thyroid nodules is still poorly understood. Because gain-of-function (activating) mutations of the thyroid-stimulating hormone receptor (TShR) and/or Gs alpha genes may confer TSh-independent growth advantage to neoplastic thyroid cells, we searched for somatic mutations of these genes in a series of hyperfunctioning and nonfunctioning follicular thyroid adenomas specifically selected for their homogeneous gross anatomy (single nodule in an otherwise normal thyroid gland). TShR gene mutations were identified by direct sequencing of exons 9 and 10 of the TShR gene in genomic DNA obtained from surgical specimens. Codons 201 and 227 of the Gs alpha gene were also analyzed. At histology, all hyperfunctioning nodules and 13 of 15 nonfunctioning nodules were diagnosed as follicular adenomas. Two nonfunctioning thyroid nodules, although showing a prevalent microfollicular pattern of growth, had histological features indicating malignant transformation (a minimally invasive follicular carcinoma and a focal papillary carcinoma). Activating mutations of the TShR gene were found in 12 of 15 hyperfunctioning follicular thyroid adenomas. In one hyperfunctioning adenoma, which was negative for TShR mutations, a mutation in codon 227 of the Gs alpha gene was identified. At variance with hyperfunctioning thyroid adenomas, no mutation of the TShR or Gs alpha genes was detected in nonfunctioning thyroid nodules. In conclusion, our findings clearly define a different molecular pathogenetic mechanism in hyperfunctioning and nonfunctioning follicular thyroid adenomas. Activation of the cAMP cascade, which leads to proliferation but maintains differentiation of follicular thyroid cells, typically occurs in hyperfunctioning thyroid adenomas. Oncogenes other than the TShR and Gs alpha genes are probably involved in nonfunctioning follicular adenomas.

Genetic analysis of the TSH receptor gene in differentiated human thyroid carcinomas.

Somatic mutations of the TSH receptor (TSHR) gene have been identified as the major cause of toxic thyroid adenoma. Recently, point mutations of the same gene have also been described in some differentiated thyroid carcinomas. The aim of the present study was to investigate the presence TSHR gene mutations in a series of thyroid specimens obtained from 22 consecutive patients with differentiated thyroid carcinomas (8 follicular and 14 papillary). Genomic DNA was extracted from fresh-frozen or paraffin-embedded tumor and normal surrounding parenchyma. Two fragments corresponding to the entire exon 10 and one fragment corresponding to exon 9 were amplified by PCR using biotinylated primers. PCR products were purified on streptavidin-coated magnetic beads and subjected to direct sequencing with Sequenase and 35(3)-labeled d-ATP-alphaS. Adenyl-cyclase activity in membrane preparations of 10 papillary carcinomas was also determined. No TSHR mutations were detected in these tumors. A polymorphism that encoded a single amino acid change Asp727Glu was identified in two follicular thyroid carcinomas. Adenyl-cyclase activity was normal in the ten papillary thyroid carcinomas we analyzed. In conclusion, our results suggest that clonal somatic mutations of the TSHR gene do not play a role in the pathogenesis of differentiated thyroid carcinoma.

Mutations of thyrotropin receptor gene

Thyrotropin is the primary pituitary hormone which stimulates the growth and differentiation of thyroid cells. TSH binds a specific receptor present in the plasma membrane of thyroid cells and signals the G protein transducers, which activate different effectors, mainly adenyl cyclase and phospholipase C. The TSH receptor belongs to a broad class of receptors known as seven-loop receptors because they contain a long stretch of amino acids which cross the plasma membrane seven times. Mutations in the TSH receptor gene have been found in hyperfunctioning thyroid adenomas. These mutations are: (a) somatic (present only in the tumor), (b) dominant (only one copy of the gene is affected), and (c) lead to the constitutive activation of the cAMP signaling cascade. Most mutations which have been identified occur in the intracellular loop III and in the transmembrane domain VI. Germline mutations in the same regions of the receptor have been found in congenital nonautoimmune hyperthyroidism. In addition, germ line mutations have been described in the extracellular domain of the receptor leading to increased TSH levels. The clinical implications of these findings are discussed.

Thyroid-stimulating hormone receptor gene mutations and polymorphisms in thyroid disease

Since thyroid-stimulating hormone receptor (TSHR) gene mutations were first detected in autonomously hyperfunctioning thyroid adenomas, considerable progress has been made in defining the role of genetic alterations of the TSHR in thyroid diseases regarding the receptor domains and the amino acid residues involved in mutations responsible for the altered (gain or loss) receptor function; the structure-function relationship based on the in vitro assessment of the different signal transduction pathways activated by the TSHR; the involvement of TSHR alterations in the development of thyroid malignancies; and the functional role and the frequency of TSHR mutations occurring in thyroid disorders. This review summarizes recent findings conceming the localization and the functional role of the naturally occurring TSHR gene mutations in thyroid diseases.

Novel mutations of thyrotropin receptor gene in thyroid hyperfunctioning adenomas. Rapid identification by fine needle aspiration biopsy

Novel mutations of thyrotropin receptor gene in thyroid hyperfunctioning adenomas. Rapid identification by fine needle aspiration biopsy

Novel mutations of thyrotropin receptor gene in thyroid hyperfunctioning adenomas. Rapid identification by fine needle aspiration biopsy.

Hyperfunctioning thyroid adenomas are clonal neoplasms with the intrinsic capacity of growing and differentiate independently of thyroid-stimulating hormone (TSH). We analysed the mRNA encoding thyrotropin receptor of 11 adenomas obtained by fine needle aspiration biopsy (FNAB) and found 7 mutants all located in three aminoacids clustered in the sixth transmembrane domain of the receptor. These mutations were somatic and specifically present in the tumour tissue. DNA sequence revealed that 80 to 90% of the mutations can be rapidly screened and identified by restriction enzyme analysis of the amplified cDNA obtained from the FNABs. The mutation Thr->Ile was introduced in the wild type receptor and expressed in mouse fibroblasts. These cells constitutively activate the transcription of a reporter gene under the control of cyclic AMP responsive element.