TSH Receptor Gene Research Articles

Next-generation sequencing of NKX2.1, FOXE1, PAX8, NKX2.5, and TSHR in 100 Chinese patients with congenital hypothyroidism and athyreosis

BackgroundThe abnormal expression of certain transcription factors (NKX2.1, FOXE1, NKX2.5, and PAX8) and thyroid stimulating hormone receptor (TSHR) genes has been associated with athyreosis, which is a form of thyroid dysgenesis (TD). We aimed to identify candidate gene mutations in CH patients with athyreosis and to establish the genotype-phenotype correlations in a Chinese population. MethodsThe exons and flanking sequences of NKX2.1, FOXE1, NKX2.5, PAX8, and TSHR were screened by next-generation sequencing and further confirmed by direct Sanger sequencing. The mutation frequencies were calculated and compared against databases. The relationship between genotype and phenotype was also determined. ResultsSeven variants were detected in TSHR—p.P52T, p.G132R, p.M164K, p.R450H, p.C700E, p.A522V, and p.R528S. The p. G132R, p. M164K and p. R528S variants were first identified in public databases. Five variants (p.G44D, p.G360V, p.R401Q, p.L418I, and p.E453Q) were found in NKX2.1 and one variant (p.P243T) was detected in FOXE1. In addition, one variant (p.N291I) was found in NKX2.5 and two variants (p.A355V and c.-26G>A) were detected in PAX8. ConclusionsOur study indicated that TSHR mutations have phenotypic variability and has further expanded the mutation spectrum of TSHR. We also revealed that the rate of NKX2.1, FOXE1, NKX2.5, and PAX8 mutations were low in patients with CH and athyreosis, in contrast to the higher rate of TSHR mutations.

Genetics of Thyroid-Stimulating Hormone Receptor-Relevance for Autoimmune Thyroid Disease.

Production of thyroid-stimulating hormone receptor (TSHR) antibodies represents the hallmark of Graves’ disease (GD) pathogenesis. Thus, for more than two decades the TSHR gene has been at the center of studies intended to elucidate its contribution to disease pathology. The advent of genome-wide association technology allowed to establish a strong association of the TSHR gene with GD. Subsequent fine-mapping studies narrowed the disease-susceptibility region to a 40 kb sequence in intron 1, where at least five GD-associated SNPs in tight linkage disequilibrium were identified. The current challenge is to understand the functional mechanisms by which these polymorphisms modify physiological processes and trigger disease. The aim of this review is to summarize the current knowledge on the role of the TSHR gene in GD pathogenesis, which has been gained through linkage and association studies, as well as to discuss the emerging mechanisms underlying biological implications of TSHR variants in the development of GD.

Compensated hyperthyrotropinaemia due to partial loss-of-function mutation in TSH receptor gene

Compensated hyperthyrotropinaemia due to partial loss-of-function mutation in TSH receptor gene

Thyrotropin receptor gene expression in the association between chronic spontaneous urticaria and Hashimoto's thyroiditis

Chronic spontaneous urticaria (CSU) may be associated with autoimmune thyroid diseases, and the Autologous Serum Skin Test (ASST) is an autoreactivity marker. The thyrotropin (TSH) and TSH receptor (TSHR) could play a role in the pathogenesis of CSU. The aim of this study was to evaluate ASST positivity and TSHR gene expression in healthy skin and ASST wheals in euthyroid women with CSU, with (14 patients) and without (15 patients) Hashimoto's thyroiditis (HT). ASST was performed and TSHR gene expression studied in wheals induced by ASST and in healthy skin. ASST presented greater positivity (86%×40%) and larger diameter (10.8×9.6mm) in the HT group (P<0.05). TSHR gene expression was higher in the ASST area and healthy skin of HT group (P<0.01). Positive correlation of antibodies levels with ASST wheal measurements and TSHR gene expression was seen. Women with CSU and HT presented greater positivity and larger measurements for ASST and higher TSHR expression in the skin, suggesting association between CSU, thyroid autoimmunity, and TSHR.

Novel germline mutation (Leu512Met) in the thyrotropin receptor gene (TSHR) leading to sporadic non-autoimmune hyperthyroidism.

Primary nonautoimmune hyperthyroidism is a rare cause of neonatal hyperthyroidism. This results from an activating mutation in the thyrotropin-receptor (TSHR). It can be inherited in an autosomal dominant manner or occur sporadically as a de novo mutation. Affected individuals display a wide phenotype from severe neonatal to mild subclinical hyperthyroidism. We describe a 6-month-old boy with a de novo mutation in the TSHR gene who presented with accelerated growth, enlarging head circumference, tremor and thyrotoxicosis. Genomic DNA from the patient's and parents' peripheral blood leukocytes was extracted. Exons 9 and 10 of the TSHR gene were amplified by PCR and sequenced. Sequencing exon 10 of the TSHR gene revealed a novel heterozygous missense mutation substituting cytosine to adenine at nucleotide position 1534 in the patient's peripheral blood leukocytes. This leads to a substitution of leucine to methionine at amino acid position 512. The mutation was absent in the parents. In silico modeling by PolyPhen-2 and SIFT predicted the mutation to be deleterious. The p.Leu512Met mutation (c.1534C>A) of the TSHR gene has not been previously described in germline or somatic mutations. This case presentation highlights the possibility of mild thyrotoxicosis in affected individuals and contributes to the understanding of sporadic non-autoimmune primary hyperthyroidism.

Identification and functional characterization of a novel thyrotropin receptor mutation (V87L) in a Chinese woman with subclinical hypothyroidism.

The thyrotropin receptor (TSHR) gene has been defined as a highly mutable gene. Mutations in the TSHR gene result in either gain or loss of the receptor function. Subclinical hypothyroidism (SH) is a clinical condition defined as an elevated serum TSH level associated with normal free thyroxine and free triiodothyronine. Chronic autoimmune thyroiditis is the most frequent cause of subclinical hypothyroidism in adults. In rare cases, a loss-of-function mutation of TSHR is the cause of SH. In the present study, a novel TSHR mutation (V87L; confirmed to be a loss-of-function mutation) was identified in a 59-year-old Chinese woman, as the potential cause of the patient's subclinical hypothyroidism. The case may provide valuable insight into the etiology of SH.

Genetic associations of the thyroid stimulating hormone receptor gene with Graves diseases and Graves ophthalmopathy: A meta-analysis.

Graves’ disease (GD) is a common thyroid disease, and Graves ophthalmopathy(GO) is the most common extra-thyroidal manifestation of GD. Genetic associations of the thyroid stimulating hormone receptor (TSHR) gene with GD and GO have been studied in different population groups for a long time. We aimed to obtain a more precise estimation of the effects of TSHR single nucleotide polymorphisms (SNPs) on GD/GO using a meta-analysis. Publications were searched on Pub Med and EMBASE up to December 30, 2015. Eight studies involving three SNPs (rs179247, rs12101255, and rs2268458), which included 4790 cases and 5350 controls, met the selection criteria. The pooled odds ratios (OR) and the 95% confidence intervals (CI) were estimated. SNPs rs179247 (dominant model [GG + GA vs. AA]: OR = 0.66, 95%CI: 0.61–0.73, P = 0.000, I2 = 0%) and rs12101255 (dominant model [TT + TC vs. CC]: OR = 1.67, 95%CI: 1.53–1.83, P = 0.000, I2 = 0%) were significantly associated with GD in all of the genetic models. TSHR rs12101255 and rs2268458 polymorphisms had no association between GO and GD (GD without GO). The results indicate that rs179247 and rs12101255 are likely to be genetic biomarkers for GD. Further studies with different population groups and larger sample sizes are needed to confirm the genetic associations of the TSHR gene with GD/GO.

Association of TSHR gene intron 1 and 4p14 single-nucleotide polymorphisms and gene-gene interactions with Graves'disease

Objective To identify the association of thyroid stimulating hormone receptor(TSHR)gene intron 1 susceptible loci and 4p14 susceptible locus rs6832151 polymorphisms with Graves' disease(GD)in Han Chinese population in Bengbu, Anhui, China. The gene-gene interaction among TSHR intron 1 susceptible loci and 4p14 susceptible locus rs6832151 was also investigated. Methods The genotypes of the single-nucleotide polymorphisms(SNPs)were analyzed by Taqman probe technique on Fluidigm EP1 platform in 611 patients with GD and 555 control subjects, and linkage analysis, correlation analysis, haplotype analysis, and epistasis analysis with them were performed. Results Six SNPs in two candidate genes(rs12101261, rs4903964, rs179247, rs2284722 and rs17111394 in TSHR, rs6832151 in 4p14)were associated with GD(all P<0.05). The frequency distributions of haplotypes of SNPs in TSHR intron 1(AGTA, GGCG, AATA, and CC)were significantly different between GD and control groups(all P<0.01). There existed the interactions between rs179247 and rs12101261 in TSHR(P=0.001)and among rs179247(TSHR), rs4903964(TSHR)and rs6832151(4p14)(P=0.001). Conclusions rs683215 in 14p14 and rs12101261, rs4903964, rs179247, rs2284722 and rs17111394 in TSHR intron 1 were susceptible loci of GD in the Chinese Han population from Bengbu. The haplotypes in TSHR intron 1 were associated with GD. There exists the interaction between the SNPs in TSHR and 4p14, which may change the risk of GD. (Chin J Endocrinol Metab, 2016, 32: 292-297) Key words: Graves disease; TSHR gene intron 1; 4p14; Polymorphism, single nucleotide

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

Dissecting the Genetic Susceptibility to Graves' Disease in a Cohort of Patients of Italian Origin.

Graves’ disease (GD) is an autoimmune oligogenic disorder with a strong hereditary component. Several GD susceptibility genes have been identified and confirmed during the last two decades. However, there are very few studies that evaluated susceptibility genes for GD in specific geographic subsets. Previously, we mapped a new locus on chromosome 3q that was unique to GD families of Italian origin. In the present study, we used association analysis of single-nucleotide polymorphism (SNPs) at the 3q locus in a cohort of GD patients of Italian origin in order to prioritize the best candidates among the known genes in this locus to choose the one(s) best supported by the association. DNA samples were genotyped using the Illumina GoldenGate genotyping assay analyzing 690 SNP in the linked 3q locus covering all 124 linkage disequilibrium blocks in this locus. Candidate non-HLA (human-leukocyte-antigen) genes previously reported to be associated with GD and/or other autoimmune disorders were analyzed separately. Three SNPs in the 3q locus showed a nominal association (p < 0.05): rs13097181, rs763313, and rs6792646. Albeit these could not be further validated by multiple comparison correction, we were prioritizing candidate genes at a locus already known to harbor a GD-related gene, not hypothesis testing. Moreover, we found significant associations with the thyroid-stimulating hormone receptor (TSHR) gene, the cytotoxic T-lymphocyte antigen-4 (CTLA-4) gene, and the thyroglobulin (TG) gene. In conclusion, we identified three SNPs on chromosome 3q that may map a new GD susceptibility gene in this region which is unique to the Italian population. Furthermore, we confirmed that the TSHR, the CTLA-4, and the TG genes are associated with GD in Italians. Our findings highlight the influence of ethnicity and geographic variations on the genetic susceptibility to GD.

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.

A domestication related mutation in the thyroid stimulating hormone receptor gene (TSHR) modulates photoperiodic response and reproduction in chickens

The thyroid stimulating hormone receptor gene (TSHR) has been suggested to be a “domestication locus” in the chicken. A strong selective sweep over TSHR in domestic breeds together with significant effects of a mutation in the gene on several domestication related traits, indicate that the gene has been important for chicken domestication. TSHR plays a key role in the signal transduction of seasonal reproduction, which is characteristically less strict in domestic animals. We used birds from an advanced intercross line between ancestral Red Junglefowl (RJF) and domesticated White Leghorn (WL) to investigate effects of the mutation on reproductive traits as well as on TSHB, TSHR, DIO2 and DIO3 gene expression during altered day length (photoperiod). We bred chickens homozygous for either the mutation (d/d) or wild type allele (w/w), allowing assessment of the effect of genotype at this locus while also controlling for background variation in the rest of the genome. TSHR gene expression in brain was significantly lower in both d/d females and males and d/d females showed a faster onset of egg laying at sexual maturity than w/w. Furthermore, d/d males showed a reduced testicular size response to decreased day length, and lower levels of TSHB and DIO3 expression. Additionally, purebred White Leghorn females kept under natural short day length in Sweden during December had active ovaries and lower levels of TSHR and DIO3 expression compared to Red Junglefowl females kept under similar conditions. Our study indicates that the TSHR mutation affects photoperiodic response in chicken by reducing dependence of seasonal reproduction, a typical domestication feature, and may therefore have been important for chicken domestication.

Is the TSHR D727E polymorphism a genetic predisposition for multinodular goiter in the Turkish population?

The D727E germline polymorphism in the thyroid-stimulating hormone receptor gene (TSHR) may cause genetic susceptibility to the development of goiter. Therefore, in this study we investigated allele frequencies and genotype distributions of the TSHR D727E polymorphism, their association with clinical parameters, and the development of goiter in the Turkish population. We investigated the TSHR D727E polymorphism in 123 patients and 97 healthy subjects using the polymerase chain reaction-restriction fragment length polymorphism technique. Peripheral blood was used for DNA extraction. Although no significant difference was found in TSHR D727E polymorphism frequencies between the patients with nodular goiters (26/123 patients, 21.1%) and the controls (12/97 patients, 12.4%) (P = 0.107), the frequency of the TSHR D727E polymorphism in the hyperthyroid+subclinical hyperthyroid patient groups (23%) was significantly higher than in the control subjects (12.4%) (P = 0.024). In this study, nodular goiter presented significantly earlier in GC genotype patients (mean age 35 years) than in CC genotype patients (mean age 42 years) in the hyperthyroid group (P = 0.009). More importantly, TSH levels in the GC variant controls were closely significant lower (1.26 ± 0.49) than in the CC variant controls (1.74 ± 0.84) (P = 0.053). The TSHR D727E polymorphism might be involved in the pathogenesis of toxic multinodular goiter (TMNG). Moreover, this polymorphism might be an indication of early-onset TMNG. However, development of MNG is multifactorial. Therefore, further case-control studies with larger populations are required to verify these observations.

Methylation status of TSHr in well-differentiated thyroid cancer by using cytologic material.

BackgroundThe role of methylation status of the thyroid stimulating hormone receptor gene (TSHr) in the discrimination of benign and malignant thyroid nodules has already been studied using paraffin blocks and cell lines. As cytological sampling plays an important role in assessment of thyroidal nodules, we have investigated the potential clinical use of TSHr methylation status of fine needle aspiration specimens reported according to Bethesda System.MethodSixty nine patients who had both cytological and pathological diagnosis of the same nodule were selected. Four groups were composed according to cytological and pathological diagnoses: Benign (B), papillary thyroid carcinoma (PTC), atypia of unknown significance (AUS) and follicular neoplasia (FN). The latter 2 groups were further sub-classified into 2 as benign (AUS-B and FN-B) and malignant (AUS-M and FN-M) according to final pathological diagnosis. DNAs were isolated from the fine needle aspiration cytology specimens and the methylation status of TSHr promotor region was investigated by using methylation specific polymerase chain reaction.ResultsOverall, TSHr methylation was present in 58 % of cases; 71 % of malignant and 46 % of benign nodules. PTC group showed the highest TSHr methylation rate (87 %), followed by 61 % in AUS, 44 % in B, and 30 % in FN (p = 0.016). TSHr methylation rate was significantly higher in PTC group when compared to B (p = 0.013) and FN-B (p = 0.004) groups; but not in FN-M (p = 0.115) or AUS (p = 0.096) groups. All 9 cases of papillary thyroid carcinoma with lymph node metastasis showed TSHr methylation. Positive predictive value, negative predictive value, sensitivity and specificity of TSHr methylation in determination of malignancy were calculated as 60, 66, 71 and 54 %, respectively.ConclusionThe eminent ratio of TSHr methylation in well-differentiated thyroid carcinoma against benign thyroidal nodules adduced that TSHr methylation status can be utilized as a tumor marker for well-differentiated thyroid cancer; however, it has a limited value. The determination of methylation status of TSHr gene had no efficiency on decision of the malignant potential for the nodules which are cytologically classified as atypia of undetermined significance.

Epigenetic profiling in CD4+ and CD8+ T cells from Graves' disease patients reveals changes in genes associated with T cell receptor signaling

In Graves' disease (GD), a combination of genetic, epigenetic and environmental factors causes an autoimmune response to the thyroid gland, characterized by lymphocytic infiltrations and autoantibodies targeting the thyroid stimulating hormone receptor (TSHR) and other thyroid antigens. To identify the epigenetic changes involved in GD, we performed a genome-wide analysis of DNA methylation and enrichment of H3K4me3 and H3K27ac histone marks in sorted CD4+ and CD8+ T cells. We found 365 and 3322 differentially methylated CpG sites in CD4+ and CD8+ T cells, respectively. Among the hypermethylated CpG sites, we specifically found enrichment of genes involved in T cell signaling (CD247, LCK, ZAP70, CD3D, CD3E, CD3G, CTLA4 and CD8A) and decreased expression of CD3 gene family members. The hypermethylation was accompanied with decreased levels of H3K4me3 and H3K27ac marks at several T cell signaling genes in ChIP-seq analysis. In addition, we found hypermethylation of the TSHR gene first intron, where several GD-associated polymorphisms are located. Our results demonstrate an involvement of dysregulated DNA methylation and histone modifications at T cell signaling genes in GD patients.

Association between TSHR gene polymorphism and the risk of Graves' disease: a meta-analysis.

Thyroid stimulating hormone receptor (TSHR) is thought to be a significant candidate for genetic susceptibility to Graves' disease (GD). However, the association between TSHR gene polymorphism and the risk of GD remains controversial. In this study, we investigated the relationship between the two conditions by meta-analysis. We searched all relevant case-control studies in PubMed, Web of Science, CNKI and Wanfang for literature available until May 2015, and chose studies on two single nucleotide polymorphisms (SNPs): rs179247 and rs12101255, within TSHR intron-1. Bias of heterogeneity test among studies was determined by the fixed or random effect pooled measure, and publication bias was examined by modified Begg's and Egger's test. Eight eligible studies with 15 outcomes were involved in this meta-analysis, including 6,976 GD cases and 7,089 controls from China, Japan, Poland, UK and Brazil. Pooled odds ratios (ORs) for allelic comparisons showed that both TSHR rs179247A/G and rs12101255T/C polymorphism had significant association with GD (OR=1.422, 95%CI=1.353–1.495, P<0.001, Pheterogeneity=0.448; OR=1.502, 95%CI: 1.410–1.600, P<0.001, Pheterogeneity=0.642), and the associations were the same under dominant, recessive and co-dominant models. In subgroup analyses, the conclusions are also consistent with all those in Asian, European and South America subgroups (P<0.001). Our meta-analysis revealed a significant association between TSHR rs179247A/G and rs12101255T/C polymorphism with GD in five different populations from Asia, Europe and South America. Further studies are needed in other ethnic backgrounds to independently confirm our findings.

Loss-of-Function Variants in a Hungarian Cohort Reveal Structural Insights on TSH Receptor Maturation and Signaling.

Congenital hypothyroidism (CH) is one of the most common inborn endocrine disorders with genetic background. Despite the well-established newborn CH screening program in Hungary, no systematic examination of the underlying genetic alterations has been performed as yet. We aimed to explore TSH receptor (TSHR) mutations in a cohort of Hungarian patients with CH. Eighty-five unrelated patients with permanent primary CH, all diagnosed at newborn screening, were selected. Coding exons of the TSHR gene were sequenced and evaluated together with the thyroid-specific clinical parameters. Functional features of the novel mutations were experimentally examined, and their comparative molecular models were built. In four patients (one heterozygous and three compound heterozygous), seven TSHR mutations were identified. Among these, N432(1.50)D and P449(2.39)L are novel missense alterations. Importantly, the N432(1.50) residue is highly conserved among G protein-coupled receptors, and its function has not been examined yet in human glycoprotein hormone receptors. Our results indicate that the N432(1.50)D mutation disrupts important, architecture-stabilizing intramolecular interactions and ultimately leads to the complete intracellular retention of the receptor. On the other hand, P449(2.39) is located in the intracellular part of the receptor, which is important in G protein coupling. The P449(2.39)L mutation results in signaling impairment, with a more profound effect on the Gq/11 pathway. TSHR mutations are common among Hungarian patients with CH. The novel genetic alterations revealed an important structural role of the N432(1.50) and the P449(2.39) residues in receptor expression and signaling, respectively.

A case of 3 months old Japanese boy with sporadic congenital none-autoimmune hyperthyroidism

Sporadic congenital none-autoimmune hyperthyroidism is rare disease. It causes the gain of function with TSH receptor gene mutation. We report 3 months old Japanese boy with sporadic congenital none-autoimmune hyperthyroidism. Our case was born in the 34th week of gestation with a birth weight 1830g, his length 42.0cm, his head circumference 29.5 cm as low birth weight baby between non consanguineous parents. Oligohydramnios was pointed out his perinatal period. There was no history of thyroid disease in other family members. He showed failure to thrive after the age of one month in spite of increasing nutrition. At the age of 3 months, His weight was 3.5kg, his length 54.6cm. He presented with tachycardia (170~180/min), severe sweating, mild exophthalmos and no goiter. We examined carefully and found he was suffered from hyperthyroidism. The thyroid function showed TSH A,p.Ser281Asn that had been reported before. The boy was treated with amount of 0.8 mg/kg/day of methimazole, his irritability disappears and his heart rate is down. Now his weight gains slowly and his development is appropriate for his age. We conclude that careful examination and follow up need for his development and growth because the severity of sporadic congenital none-autoimmune hyperthyroidism is variety and most reported case were recurrent. Written informed consent was obtained from the patient's parent or guardian for publication of this abstract and any accompanying images. A copy of the written consent is available for review by the Editor of this journal.

Long-term outcome of loss-of-function mutations in thyrotropin receptor gene.

Loss-of-function mutations in the thyrotropin receptor (TSHR) gene lead to resistance to TSH (RTSH) presenting with either congenital hypothyroidism (CH) or subclinical hypothyroidism (SCH). Despite several reports of patients with TSHR mutations, data on the long-term outcome of this condition are limited, and no consensus exists on the need for hormone replacement therapy. The aim of the present study was to assess the long-term outcome in children and adolescents with RTSH due to TSHR mutations. The TSHR gene was sequenced in 94 subjects (aged 3 days-21 years) with either nonautoimmune SCH or CH with RTSH. Twenty-seven subjects (29%) carried mutations in TSHR. Fifteen infants were identified by neonatal screening, and the other 79 patients were detected in the process of testing for various other conditions or because of family occurrence of thyroid test abnormalities. Six different mutations were identified: c.484C>G (p.P162A), c.202C>T (p.P68S), c.790C>T (p.P264S), c.269A>C (p.Q90P), c.1957C>G (p.L653V), and c.1347C>T (p.R450C). Twelve subjects were homozygous, three were compound heterozygous, and 12 were heterozygous. Mean serum TSH levels at diagnosis and at last visit were significantly higher in patients with TSHR mutations than in those without mutations (29.04 vs. 14.15, p=0.002; 31.73 vs. 6.19, p<0.0001, respectively). Homozygous patients had a more severe phenotype (TSH 53.6 vs. 9.24, p<0.0001). Mean serum free thyroxine (fT4) levels at the last visit were significantly lower than at the first visit in the homozygous individuals (p=0.05) for a follow-up period of as long as 11 years. Heterozygous subjects had only mild hyperthyrotropinemia with stable TSH levels. However, homozygous subjects showed a trend toward increased TSH and decreased fT4 with time. SCH in heterozygotes with TSHR mutations is a stable compensated condition with an appropriately adjusted set point for pituitary-thyroid feedback that does not require replacement therapy. However, homozygous subjects, with incompletely compensated SCH, show reduced fT4 levels over time and may require levothyroxine treatment. Replacement therapy should be considered on an individual basis, and long-term follow up is recommended.

TSH resistance revisited.

Genetic defects of hormone receptors are the most common form of end-organ hormone resistance. One example of such defects is TSH resistance, which is caused by biallelic inactivating mutations in the TSH receptor gene (TSHR). TSH, a master regulator of thyroid functions, affects virtually all cellular processes involving thyroid hormone production, including thyroidal iodine uptake, thyroglobulin iodination, reuptake of iodinated thyroglobulin and thyroid cell growth. Resistance to TSH results in defective thyroid hormone production from the neonatal period, namely congenital hypothyroidism. Classically, clinical phenotypes of TSH resistance due to inactivating TSHR mutations were thought to vary depending on the residual mutant receptor activity. Nonfunctional mutations in the two alleles produce severe thyroid hypoplasia with overt hypothyroidism (uncompensated TSH resistance), while hypomorphic mutations in at least one allele produce normal-sized thyroid gland with preserved hormone-producing capacity (compensated TSH resistance). More recently, a new subgroup of TSH resistance (nonclassic TSH resistance) that is characterized by paradoxically high thyroidal iodine uptake has been reported. In this article, the pathophysiology and clinical features of TSH resistance due to inactivating TSHR mutations are reviewed, with particular attention to the nonclassic form.