Mutations In TSHR Gene Research Articles

Familial Non-autoimmune Hyperthyroidism in Family Members Across Four Generations Due To a Novel Disease-causing Variant in The Thyrotropin Receptor Gene.

Activating disease-causing variants in the thyrotropin-receptor (TSHR) gene are associated with familial or sporadic congenital non-autoimmune hyperthyroidism. Familial non-autoimmune hyperthyroidism (FNAH) is a rare form of hyperthyroidism with 41 families reported so far in the TSHR gene mutation database. We present clinical and genetic features of 11 patients with FNAH across four generations of a Slovenian family. They all developed clinical features of hyperthyroidism but did not show characteristics of autoimmune hyperthyroidism. Members of the initially diagnosed generation were diagnosed as hyperthyrotic after they developed cardiac complications (rhythm disorders, thromboembolic events, cardiac insufficiency), while patients in the younger generations were diagnosed earlier, and consequently, early cardiovascular complications were less frequent. All patients had a novel heterozygous TSHR variant NP_ 000360.2: p.Met453Val (NM_000369.2: c.1357A>G) predicted to be pathogenic. Therefore, besides expending the mutational spectrum of the activating TSHR variants in FNAH, our experience with this multi-generation family confirms the need for early diagnosis and appropriate treatment of FNAH.

Genetic study of TSHR, PAX8 and NKX2-5 genes in Tunisian patients with congenital hypothyroidism

Introduction Thyroid dysgenesis is reported to be associated to mutations in TSHR, PAX8 and NKX2-5 genes. In fact, mutation in TSHR gene is responsible for non-syndromic thyroid dysgenesis while mutations in PAX8 and NKX2-5 generate thyroid dysgenesis, which could be associated to renal abnormality and congenital heart disease respectively. Patients and methods The aim of the current study is to present the clinical features of eleven Tunisian patients with congenital hypothyroidism and thyroid dysgenesis, and to search for mutations or variants in TSHR, PAX8 and NKX2-5 genes. The clinical, molecular and bioinformatics investigation were performed in the eleven recruited patients. Results According to clinical data, eight patients were diagnosed with non-syndromic thyroid dysgenesis and three Tunisian patients with syndromic thyroid dysgenesis. The mutational analyses of the three candidate genes showed only known polymorphisms and we noticed that polymorphisms in PAX8 and NKX2-5 genes are especially associated with syndromic thyroid dysgenesis in our patients. Bioinformatic tools showed the putative impact of the identified polymorphisms on ESE elements and on mRNA structure. Conclusions The obtained results are suggestive of potential effects of the described polymorphisms on thyroid dysgenesis in our studied patients and are highlighted the utility of the bioinformatics tools.

Progress in the correlation between thyroid stimulating hormone receptor gene and hyperthyroidism

The cause of hyperthyroidism is still not clear.Thyroid stimulating hormone receptor(TSHR) gene is one of the hot topic genes in the etiology of hyperthyroidism.In this review paper, the progress of correlation between TSHR gene and hyperthyroidism was summarized.Results suggested that TSHR gene germline mutations could cause familial non-autoimmune autosomal dominant hyperthyroidism and persistent sporadic congenital non-autoimmune hyperthyroidism.In addition, TSHR gene mutation may also undermine the stability of the TSHR and then become the autoantigens to make producing TSHR antibodies.Which can stimulate thyroid follicular to secrete excessive thyroid hormone and then cause Graves' disease.However, the relationship between TSHR gene and the pathogenesis of Graves' disease still needs further study. Key words: Thyroid stimulating hormone receptor; Gene; Hyperthyroidism

Two novel TSHR gene mutations (p.R528C and c.392+4del4) associated with congenital hypothyroidism

ABSTRACTInactivating mutations of the thyrotropin receptor (TSHR) gene are responsible for non-goitrogenic congenital hypothyroidism (CHNG). This study aimed to investigate mutations in the TSHR gene in 20 children with CHNG. Genomic DNA was extracted from peripheral blood leukocytes and was used for mutation screening by direct sequencing. Analyses of the TSHR gene revealed two novel variants in a 2-year-old boy with thyroid hypoplasia: a missense mutation c.1582C>T (p.R528C) and a splice-site deletion c.392+4del4. Bioinformatics analysis demonstrated that both variants are capable of causing disease. Family members of the patient with two mutations and normal controls were also recruited and investigated. Germline mutations from the proband’s family were consistent with an autosomal recessive inheritance pattern. These findings indicate that two novel inactivating mutations (p.R528C and c.392+4del4) in the TSHR gene can cause CHNG.

Resistance to thyrotropin: familial case report

Two female dizygotic twins with subclinical primary hypothyroidism due to homozygous p.R450H mutation in TSHR gene are presented. A 5-year follow-up in both cases showed no progression of thyroid dysfunction. Indications for levothyroxine replacement in subclinical hypothyroidism are discussed.

Frequency and effect on serum TSH of phosphodiesterase 8B (PDE8B) gene polymorphisms in patients with sporadic nonautoimmune subclinical hypothyroidism

Nonautoimmune subclinical hypothyroidism (NSH) is characterized by elevated serum TSH in presence of normal thyroid hormone levels and absence of anti-thyroid antibodies. As result of a genomic-wide study, a strong association between three polymorphic variants in intron 1 of human PDE8B gene (rs4704397, rs6885099, rs2046045) and serum TSH has been reported in euthyroid subjects. The aim of this study was to evaluate frequency and effects on serum TSH of PDE8B gene polymorphisms in patients with sporadic NSH and verify if differences in serum TSH levels are associated to these polymorphic variants. A total of 58 Italian selected patients affected by NSH, with elevated serum TSH, normal FT3 and FT4 and without TSHr gene mutations, were subjected to genotyping for specific single nucleotide polymorphism of PDE8B gene. In all patients, the integrity of TSH receptor gene was attested. The ancestral allele associated with increased serum TSH was present in 42/58 patients (72.4%) for rs4704397, in 42/58 patients (72.4%) for rs6885099 and in 44/58 patients (75.9%) for rs2046045. However, similar values of serum TSH were detected in patients with minor or major allele for each polymorphism. A prevalence of the minor allele of PDE8B gene polymorphism associated with elevated serum levels of TSH was demonstrated in patients affected by sporadic NSH; however, significant differences in circulating TSH in patients with minor or major alleles for each polymorphism were not identified demonstrating the lack of association between the polymorphisms and serum TSH levels in these patients.

The W520X mutation in the TSHR gene brings on subclinical hypothyroidism through an haploinsufficiency mechanism.

TSHR is a G-protein-coupled seven transmembrane domain receptor that activates the two major signal transduction pathways: the Gαs/adenylate cyclase and the Gαq/11/phospholipase C pathways. Inactivating mutations in the TSHR gene have been demonstrated to be responsible for subclinical hypothyroidism, a disorder characterized by elevated serum TSH concentrations despite normal thyroid hormones levels. We identified in a child a nonsense mutation (W520X) in the third transmembrane domain of the TSHR that causes the lack of the C-terminus portion of the receptor. The functional significance of this variation was assessed in vitro. The W520X mutation was introduced into the pSVL vector containing the wild-type sequence of TSHR gene. Wild-type and mutated vectors were expressed in Chinese Hamster Ovary (CHO) cells, and cAMP, inositol phosphate (IP), immunofluorescence and FACS analyses were performed. Transfection with pSVL-TSHR vector induced basal cAMP and IP production in the absence of TSH stimulation, indicating a constitutive activity for the TSHR. An impairment of receptor function was demonstrated by the observation that cells expressing the mutant TSHR exhibited a lower second messenger production with respect to the wild-type, despite a normal expression of the receptor at the cell surface. The mechanism through which the W520X mutation exerts its effect is more likely haploinsufficiency rather than a dominant-negative effect. This could explain the phenotype of our patient, who has a hormonal pattern in the range of a mild subclinical hypothyroidism, without an overt disease phenotype.

Thyroid hormones – obesity and metabolic syndrome

Recently there has been increased interest in the association between thyroid function and obesity. Based on the notion that triiodothyronine (T3) controls metabolic and energy homeostasis and influences body weight, thermogenesis, lipolysis and metabolism of cholesterol, and that thyroid-stimulating hormone (TSH) via receptors in fat tissue, induces differentiation of preadipocytes in to adipocites and expansion of adipose tissue (adipogenesis), thyroid function has been extensively investigated in obese adults. An elevated level of TSH with normal peripheral thyroid hormone concentration suggesting sub-clinical hypothyroidism has been consistently found in obese subjects. Several mechanisms leading to hyperthyrotropinemia have hypothesis including sub clinical hypothyroidism caused by iodine deficiency, autoimmune thyroiditis or mutations in TSH-R gene. TSH production is also regulated by neurotransmitters and hormones that influence body weight such as neuropeptide Y and alfa-melanocyte-stimulating hormone related peptide, that innervate hypophysiotropic TRH neurons. These neurotransmitters and hormones are also influenced by leptin. Thyrotropin also directly induces the synthesis and release of adipokines. Some of them control appetite by acting on the brain. Metabolic syndrome (MS) is clustering obesity, hypertension, dyslipidemia and insulin resistance. MS is a status where most features of hypothyroidism can be seen. TSH increase was shown to be associated with increased cholesterol and triglycerides and with decreased HDL-C. Thyroid hormones are important determinants of glucose homeostasis. Increased thyroid hormone levels impair the ability of insulin to suppress hepatic glucose production and increase glucose uptake in muscles. An association between TSH and fasting insulin and insulin sensitivity has been reported in adults with obesity. The increased TSH and peripheral hormone levels, which are usually in the upper normal range in obese subjects may be adaptation process to increase energy expenditure in order to reduce further weight gain. The changes of thyroid hormones concentration may be regarded as a consequence rather than a cause of obesity. MS is cluster of metabolic abnormalities with insulin resistance as a major component. The patients with MS have significantly increased thyroid volume and nodule prevalence and insulin resistance is an independent risk factor for nodule formation. The prevalence of insulin resistance would be an important risk factor for developing thyroid cancer and some other non-thyroid cancers.

Consecutive Mutational Events in a TSHR Allele of Arab Families with Resistance to Thyroid Stimulating Hormone

Our laboratory identified six distinct inactivating TSHR gene mutations in Arab tribes living in Israel. We recently reported three nucleotide substitutions in exon 3 producing p.[L89L;Q90P] and one in exon 9 of the same allele producing p.P264S in Family A. Family B, reported herein, harbors the identical mutation in exon 3 only. We set to determine whether the mutations have common ancestral origin. Coding regions of the TSHR were sequenced and flanking microsatellite markers spanning 5.3 cM were used for haplotyping. Two siblings of Family B were compound heterozygous for TSHR gene mutations. The paternal allele contained the exon 3 mutation and the maternal allele harbored a mutation in exon 10 (p.L653V). We investigated the possibility of a founder effect with subsequent mutational events for the presence of the same exon 3 mutation in different families. The haplotype of the allele harboring the exon 3 mutation in Family B was identical to that of Family A, also harboring the exon 9 mutation on the same allele, indicating that the latter occurred subsequently. The ancestral wild-type TSHR was present in Family B, suggesting that the mutation in exon 3 was also new in the history of that population. It is more likely that two consecutive mutational events occurred on the ancestral wild-type allele instead of a recombination bringing exon 3 and exon 9 mutations together on the same allele. New mutational events contribute to the high prevalence of TSHR mutations in this population in addition to a founder effect and limited gene pool due to inbreeding.

The gene for the thyrotropin receptor (TSHR) as a candidate gene for congenital hypothyroidism with thyroid dysgenesis.

According to the central role of the TSH receptor for thyroid function and growth the gene for the TSH receptor is a possible candidate gene for mutations which result in an impairment of thyroid growth and function (Vassart and Dumont 1992). First evidence for the role of TSH receptor defects in the pathogenesis of congenital thyroid disorders was elucidated by the presence of activating germline mutations leading to congenital hyperthyroidism (Duprez et al., 1994). After the finding of partial loss-of-function mutations leading to hyperthyrotropinemia (Sunthornthepvarakul et al., 1995) it was speculated that a more severe phenotype with hypothyroidism and hypoplasia of the gland (thyroid dysgenesis) would be the result, if complete loss-of-function mutations like the isoleucine167 to asparagine mutation would occur in a homozygote or compound heterozygote state. The screening of TSHR gene mutations by SSCP in a well defined cohort of 100 children with congenital hypothyroidism (CH), diagnosed and followed since 1978 in the Childrens Hospital of Berlin, revealed one patient with hypoplasia of the thyroid to be positive for two compound heterozygote inactivating mutations of the TSHR gene, indicating thereby that the clinical approach to define phenotypes of interest could be helpful to understand the fundamental process of thyroid development.

A Somatic Gain-of-Function Mutation in the Thyrotropin Receptor Gene Producing a Toxic Adenoma in an Infant

Activating mutations of the thyroid stimulating hormone receptor gene (TSHR) are rare in the neonate and in the pediatric population. They are usually present in the germline, and are either inherited or occur de novo. Somatic mutations in TSHR are unusual in the pediatric population. We describe a nine-month-old infant with thyrotoxicosis who harbored an activating somatic mutation in TSHR that was not present in the germline. As genomic DNA analysis failed to show a TSHR gene mutation, a radioiodide scan was performed to reveal a unilateral localization of uptake suppressing the remaining thyroid tissue. Genomic and complementary DNA analyses of the active thyroid tissue, removed surgically, identified a missense mutation (D633Y) located in the sixth transmembrane domain of the TSHR. The absence of this TSHR mutation in circulating mononuclear cells and in unaffected thyroid tissue confirmed the somatic nature of this genetic alteration. To the authors' knowledge, this is the youngest patient to receive definitive treatment for hyperthyroidism due to an activating mutation of TSHR.

Autosomal Dominant Resistance to Thyrotropin as a Distinct Entity in Five Multigenerational Kindreds: Clinical Characterization and Exclusion of Candidate Loci

Resistance to TSH (RTSH) is an inherited disorder of variable hyposensitivity to TSH. The metabolic consequences can range from euthyroid hyperthyrotropinemia to severe congenital hypothyroidism with thyroid hypoplasia. Although subclinical and mild hypothyroidism fitting the RTSH phenotype is common in the population, the role of genetic factors is far from being understood. Only in rare cases has RTSH been attributed to TSHR or PAX8 gene mutations. OBJECTIVE, SETTING, AND PARTICIPANTS: Toward the identification of novel RTSH genes, we studied five large, unrelated families comprising 102 individuals, 56 of whom were affected. Inheritance of RTSH in these families followed an autosomal dominant pattern without evidence for incomplete penetrance, yet expressivity was variable. Considering only fully phenotyped generations, 64% of the progeny was affected, with a 1:1.4 male-to-female ratio. Of 18 affected individuals tested in the neonatal period, two were undetected because of borderline results. The thyroid phenotype was indistinguishable from that observed with PAX8 and TSHR defects. In four families, untreated affected subjects of all ages had elevated serum thyroglobulin levels, consistent with a defect in the thyroid follicle cells. Linkage of RTSH to TSHR and PAX8 was excluded in all five families. For the largest families, we likewise excluded a contribution of genes previously only associated with syndromic forms of RTSH, namely TITF1, GNAS, and FOXE1. These kindreds represent a distinct etiological entity of autosomal dominant RTSH. According to the clinical presentation of these families, genetic causes of mild hyperthyrotropinemia in the general population may be more common than currently appreciated.

Genetic alterations in N-bis(2-hydroxypropyl)nitrosamine-induced rat transplantable thyroid carcinoma lines: analysis of the TSH-R, G(alpha)s, ras and p53 genes.

It has recently been shown that point mutations of the TSH-R or G(alpha)s genes are associated with autonomous hyperfunctioning thyroid adenomas and differentiated carcinomas. We therefore screened for mutations in the TSH-R, G(alpha)s, ras and p53 genes in nine rat transplantable thyroid carcinoma lines derived from tumors induced by DHPN as a chemical carcinogen. Mutations were identified using single-strand conformation polymorphism and DNA sequencing analysis. Point mutations in G(alpha)s codon 201 (CGC-->CAC) were detected in three lines (33%), resulting in a heterozygous alteration (Arg-->His) in the expressed G(alpha)s protein. The mean intracellular cAMP level (2.30 +/- 0.27 nmol/mg) of the three mutated cell lines was significantly increased as compared with that of the lines (1.54 +/- 0.32 nmol/mg) without the G(alpha)s mutation (P < 0.01, by paired t-test). Also, these three cell lines had an activating mutation in Ki-ras codon 12 (GGT-->GAT). One TSH-R gene mutation was found with a base substitution in codon 636 (TGC-->TGT) but no amino acid change. No p53 gene (exons 5-8) mutations were detected in any of the cell lines analyzed. The results suggest that mutational activation of the G(alpha)s gene may play a tumorigenic role through constitutive activation of the cAMP pathway and that G-->A point mutations in the G(alpha)s and ras genes in thyroid carcinomas directly reflect interaction of the chemical carcinogen with guanine residues in DNA.