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An intronic SNP in the thyroid hormone receptor ? gene is associated with pituitary cell-specific over-expression of a mutant thyroid hormone receptor ?2 (R338W) in the index case of pituitary-selective resistance to thyroid hormone.

ABSTRACT: The syndrome of resistance to thyroid hormone (RTH) is caused by mutations in the thyroid hormone receptor ? gene (THRB). The syndrome varies from asymptomatic to diffuse hypothyroidism, to pituitary-selective resistance with predominance of hyperthyroid signs and symptoms. The wide spectrum of clinical presentation is not completely attributable to specific THRB mutations. The THRB gene encodes two main isoforms, TR ?1 which is widely distributed, and TR ?2, whose expression is limited to the cochlea, retina, hypothalamus, and pituitary. Recent data demonstrated that in mice an intron enhancer region plays a critical role in the pituitary expression of the ?2 isoform of the receptor. We thus hypothesized that polymorphisms in the human homologous region could modulate the pituitary expression of the mutated gene contributing to the clinical presentation of RTH.Screening and in vitro characterization of polymorphisms of the intron enhancer region of the THRB gene in the index case of pituitary-selective RTH.The index case of pituitary-selective resistance is characterized by the missense R338W exon 9 mutation in cis with two common SNPs, rs2596623T and rs2596622C, located in the intron enhancer region of the THRB gene. Reporter gene assay experiments in GH3 pituitary-derived cells indicate that rs2596623T generates an increased pituitary cell-specific activity of the TR ?2 promoter suggesting that rs2596623T leads to pituitary over-expression of the mutant allele.The combined coding mutation and non-coding SNP therefore generate a tissue-specific dominant-negative condition recapitulating the patient's peculiar phenotype. This case illustrates the role of regulatory regions in modifying the clinical presentation of genetic diseases.

SUBMITTER: Alberobello AT

PROVIDER: S-EPMC3170239 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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An intronic SNP in the thyroid hormone receptor β gene is associated with pituitary cell-specific over-expression of a mutant thyroid hormone receptor β2 (R338W) in the index case of pituitary-selective resistance to thyroid hormone.

Alberobello Anna Teresa AT Congedo Valentina V Liu Hong H Cochran Craig C Skarulis Monica C MC Forrest Douglas D Celi Francesco S FS

Journal of translational medicine 20110826

<h4>Background</h4>The syndrome of resistance to thyroid hormone (RTH) is caused by mutations in the thyroid hormone receptor β gene (THRB). The syndrome varies from asymptomatic to diffuse hypothyroidism, to pituitary-selective resistance with predominance of hyperthyroid signs and symptoms. The wide spectrum of clinical presentation is not completely attributable to specific THRB mutations. The THRB gene encodes two main isoforms, TR β1 which is widely distributed, and TR β2, whose expression ...[more]

PMID: 21871106

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Project description:BackgroundResistance to thyroid hormone alpha (RTHα), a disorder characterized by tissue-selective hypothyroidism and near-normal thyroid function tests due to thyroid receptor alpha gene mutations, is rare but probably under-recognized. This study sought to correlate the clinical characteristics and response to thyroxine (T4) therapy in two adolescent RTHα patients with the properties of the THRA mutation, affecting both TRα1 and TRα2 proteins, they harbored.MethodsClinical, auxological, biochemical, and physiological parameters were assessed in each patient at baseline and after T4 therapy.ResultsHeterozygous THRA mutations occurring de novo were identified in a 17-year-old male (patient P1; c.788C>T, p.A263V mutation) investigated for mild pubertal delay and in a 15-year-old male (patient P2; c.821T>C, p.L274P mutation) with short stature (0.4th centile), skeletal dysplasia, dysmorphic facies, and global developmental delay. Both individuals exhibited macrocephaly, delayed dentition, and constipation, together with a subnormal T4/triiodothyronine (T3) ratio, low reverse T3 levels, and mild anemia. When studied in vitro, A263V mutant TRα1 was transcriptionally impaired and inhibited the function of its wild-type counterpart at low (0.01-10 nM) T3 levels, with higher T3 concentrations (100 nM-1 μM) reversing dysfunction and such dominant negative inhibition. In contrast, L274P mutant TRα1 was transcriptionally inert, exerting significant dominant negative activity, only overcome with 10 μM of T3. Mirroring this, normal expression of KLF9, a TH-responsive target gene, was achieved in A263V mutation-containing peripheral blood mononuclear cells following 1 μM of T3 exposure, but with markedly reduced expression levels in L274P mutation-containing peripheral blood mononuclear cells, even with 10 μM of T3. Following T4 therapy, growth, body composition, dyspraxia, and constipation improved in P1, whereas growth retardation and constipation in P2 were unchanged. Neither A263V nor L274P mutations exhibited gain or loss of function in the TRα2 background, and no additional phenotype attributable to this was discerned.ConclusionsThis study correlates a milder clinical phenotype and favorable response to T4 therapy in a RTHα patient (P1) with heterozygosity for mutant TRα1 exhibiting partial, T3-reversible, loss of function. In contrast, a more severe clinical phenotype refractory to hormone therapy was evident in another case (P2) associated with severe, virtually irreversible, dysfunction of mutant TRα1.

Project description:Domestic chickens are less fearful, have a faster sexual development, grow bigger, and lay more eggs than their primary ancestor, the red junglefowl. Several candidate genetic variants selected during domestication have been identified, but only a few studies have directly linked them with distinct phenotypic traits. Notably, a variant of the thyroid stimulating hormone receptor (TSHR) gene has been under strong positive selection over the past millennium, but it's function and mechanisms of action are still largely unresolved. We therefore assessed the abundance of the domestic TSHR variant and possible genomic selection signatures in an extensive data set comprising multiple commercial and village chicken populations as well as wild-living extant members of the genus Gallus. Furthermore, by mean of extensive backcrossing we introgressed the wild-type TSHR variant from red junglefowl into domestic White Leghorn chickens and investigated gene expression, hormone levels, cold adaptation, and behavior in chickens possessing either the wild-type or domestic TSHR variant. While the domestic TSHR was the most common variant in all studied domestic populations and in one of two red junglefowl population, it was not detected in the other Gallus species. Functionally, the individuals with the domestic TSHR variant had a lower expression of the TSHR in the hypothalamus and marginally higher in the thyroid gland than wild-type TSHR individuals. Expression of TSHB and DIO2, two regulators of sexual maturity and reproduction in birds, was higher in the pituitary gland of the domestic-variant chickens. Furthermore, the domestic variant was associated with higher activity in the open field test. Our findings confirm that the spread of the domestic TSHR variant is limited to domesticated chickens, and to a lesser extent, their wild counterpart, the red junglefowl. Furthermore, we showed that effects of genetic variability in TSHR mirror key differences in gene expression and behavior previously described between the red junglefowl and domestic chicken.

Dataset Information

An intronic SNP in the thyroid hormone receptor ? gene is associated with pituitary cell-specific over-expression of a mutant thyroid hormone receptor ?2 (R338W) in the index case of pituitary-selective resistance to thyroid hormone.

Publications

An intronic SNP in the thyroid hormone receptor β gene is associated with pituitary cell-specific over-expression of a mutant thyroid hormone receptor β2 (R338W) in the index case of pituitary-selective resistance to thyroid hormone.

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