Search PubMed⌕ Search

Biomedical subjects

S Refetoff

Publications and source records attributed to S Refetoff.

At least 55 records · Page 3Linked to original sources
PubMed1996

Mutation in the thyroid hormone receptor (TR) beta gene (M313T) not previously reported in two unrelated families with resistance to thyroid hormone (RTH).

Two families expressing the RTH phenotype and harboring the same mutation in the TRbeta gene are described. Five and four affected members in each family were investigated as well as a total of 12 unaffected relatives. The mutation, a T to C transition of nucleotide 1223 in one allele of affected individuals, results in the replacement of the normal Met for a Thr. Haplotyping revealed that the same mutation developed in each family independently. Whereas attention deficit hyperactivity disorder was associated with RTH in 7 of the 9 affected individuals, it was also present in 2 family members without RTH.

Alleles↗
PubMed1996

Evaluation of pituitary and peripheral tissue markers of thyroid hormone action in an Iranian family with resistance to thyroid hormone.

Resistance to thyroid hormone (RTH), an inherited syndrome of reduced sensitivity to thyroid hormone, is being detected with increased frequency. We report the first family with RTH identified in Iran. Goiter prompted thyroid evaluation, and nonsuppressed TSH associated with high free T4, suggested RTH as the etiology. The mother and all four of her children expressed the RTH phenotype associated with attention deficit and hyperactivity. Detailed clinical and laboratory studies before and following the administration of graded doses of L-T3 demonstrated relatively severe resistance to the hormone at the level of the thyrotrophs and peripheral tissues. Our data underscore the importance of evaluating the changes of various parameters of thyroid hormone action in response to thyroid hormone rather than their measurement at baseline or assessment of absolute levels.

Adolescent↗
PubMed1996

Thyroxine-binding globulin: organization of the gene and variants.

Thyroxine-binding globulin (TBG), the principal thyroid hormone transport protein in human serum, is synthesized by the liver and secreted into the bloodstream as a 54-kD acidic glycoprotein made up of a single polypeptide chain of 395 amino acids and four heterosaccharide units. The carbohydrate chains are important for the correct posttranslational folding, secretion and degradation of the molecule but are not required for hormone binding. TBG, encoded by a single gene copy located on Xq22, consists of five exons spanning 5.5 kbp. An upstream sequence of 218 nucleotides containing a hepatocyte nuclear factor 1 binding motif imparts to the gene a strong liver-specific transcriptional activity. Inherited TBG defects produce three phenotypes based on the level of TBG in serum of affected hemizygotes: complete TBG deficiency (TBG-CD), partial TBG deficiency (TBG-PD) and TBG excess (TBG-E). The molecular basis of the TBG defect has been identified in 12 of 16 known TBG variants. TBG-CD is caused by either premature termination of translation or an amino acid substitution resulting in failure of secretion. Point mutations resulting in single amino acid substitutions are responsible for the alteration of the properties and/or concentration of TBG-PD variants. Gene duplication and triplication has been recently identified in subjects with TBG-E.

Base Sequence↗
PubMed1996

Response to challenge with gonadotropin-releasing hormone agonist in a mother and her two sons with a constitutively activating mutation of the luteinizing hormone receptor--a clinical research center study.

The pituitary-gonadal axis was evaluated in a mother after two of her sons with familial male-limited pseudoprecocious puberty were found to have a constitutively activating mutation of the LH receptor (LHR). Genotyping demonstrated that all showed a mutation in one of the two alleles, a substitution of Gly for Asp578 in the sixth transmembrane segment of the LHR. Ovarian function was normal in the 36-yr-old mother as assessed by LH dynamics and FSH and androgen levels throughout the menstrual cycle. Hormonal responses to acute GnRH agonist (nafarelin) challenge, chronic GnRH agonist administration, and dexamethasone were also normal. Studies of the boys upon presentation at 2.4 and 3.5 yr of age revealed that acute LH responses to nafarelin were in the hypogonadotropic range, and the FSH responses were prepubertal despite the presence of late pubertal testosterone blood levels. Upon the inception of true puberty at 11 yr of age in the older brother, gonadotropin responses normalized for the state of development. The data show that this activating LHR mutation does not cause functional ovarian hyperandrogenism and causes only incomplete pubertal activation of Leydig cells. The results are compatible with relatively low constitutive activity associated with this structural abnormality of LHR.

Adult↗
PubMed1996

Dominant inheritance of resistance to thyroid hormone not linked to defects in the thyroid hormone receptor alpha or beta genes may be due to a defective cofactor.

Resistance to thyroid hormone (RTH) is an inherited syndrome of reduced tissue responsiveness to thyroid hormone. To date, all individuals expressing the RTH phenotype have been found to harbor mutations in the thyroid hormone receptor beta (TR beta) gene that impair T3-mediated function. We describe a unique family in which the dominantly inherited RTH is not associated with abnormalities in the TR beta or TR alpha genes, as determined by gene sequencing and linkage analysis. However, affected family members manifest a severe form of RTH, with reduced responses of thyrotrophs and peripheral tissues requiring 8- to 10-fold the normal replacement doses of L-T4 and L-T3. No other endocrine abnormalities were detected. The defect developed de novo in the proposita and was transmitted to her two children of unrelated fathers. As cultured fibroblasts from the proposita responded poorly to T3 despite a normal concentration of TR, other abnormalities in the mediation of T3 action were sought. Nucleotide sequences of the TSH beta promoter, containing thyroid hormone response elements, and TR-interacting protein 1 were normal. Nuclear extracts (NE) of cultured skin fibroblasts from affected individuals of this family were tested for their interaction with normal TR beta and thyroid hormone response elements by the electrophoretic mobility shift assay. NE from the proposita showed a strong additional band compared to NEs from normal individuals and patients with RTH caused by TR beta mutations or deletion. Far Western analysis of NE from the affected daughter hybridized with labeled TR beta demonstrated an additional band that was not seen in NEs from a normal control or patients with TR beta gene defects. It is concluded that the etiology of RTH is not confined to abnormalities in the TR beta gene. An abnormal cofactor with a specific function in the regulation of thyroid hormone action is probably involved in the expression of the RTH phenotype in this family.

Child, Preschool↗
PubMed1996

A new family with hyperthyroxinemia caused by transthyretin Val109 misdiagnosed as thyrotoxicosis and resistance to thyroid hormone--a clinical research center study.

Serum transthyretin (TTR) is a protein of liver origin that under normal conditions transports approximately 20% T4. Missense mutations of the TTR gene produce familial amyloidotic polyneuropathy and rarely, euthyroid hyperthyroxinemia (EHT). Of the 3 TTR variants so far identified with increased affinity for T4, Ser6, Thr109, and Met119, only TTR-Thr109 has high enough affinity for T4 to produce consistent hyperthyroxinemia in the heterozygous individuals. Because the mutation GCC-->ACC in codon 109 results in the loss of one Bso FI site in exon 4 of the TTR gene, the use of this enzyme was suggested to screen for TR-Thr109 in subjects with EHT. We investigated a family with dominantly inherited EHT, in which two of eight affected members received ablative thyroid treatment for presumed thyrotoxicosis, and one was misdiagnosed as having resistance to thyroid hormone. All affected individuals had serum reverse T3 concentrations above normal and average T4 50% above the mean of unaffected relatives. Total T3 and TSH levels were within the normal range. Although loss of the Bso FI site in one allele of the two TTR suggested the presence of Thr109, gene sequencing revealed a different mutation in the same codon (GCC-->GTC) producing TTR-Val109. T4-binding to TTR-Val109 was compared to that of the normal TTR-Ala109 and the formerly identified variant TTR-Thr109. Association constants were 1.3, 9.5, and 13.6 X 10(7) M-1 for TTR-Ala109, Val109, and Thr109, respectively. Thus, for equally expressed mutant and normal allele and 20% of serum T4 bound to TTR, the calculated mean serum T4 concentration of heterozygotes for TTR-Val109 should be 50% above the normal mean; the observed value being 55%. These results are in agreement with the observations based on the crystallographic structure of TTR-Thr109 indicating that the extra atoms in Val as in Thr, which are absent in the Ala of the wild type TTR, widen the ligand binding site.

Adolescent↗
PubMed1996

A mouse model of resistance to thyroid hormone produced by somatic gene transfer of a mutant thyroid hormone receptor.

Resistance to thyroid hormone (RTH) is a dominantly inherited syndrome characterized by hyposensitivity to thyroid hormone caused by mutations in the thyroid hormone receptor-beta (TR beta) gene. Replication-defective recombinant adenoviruses were constructed that express the human wild-type (WT) TR beta, a human mutant TR beta identified in a family with RTH, and luciferase under the control of thyroid hormone (Luc). The efficient introduction and expression of these recombinant genes into adult mouse liver were confirmed by immunocytochemistry. Hypothyroid mice were infected with Luc alone and in combination with the WT TR beta or mutant TR beta. Half of the mice from each group were then treated with T3. Compared with mice infected with Luc alone, T3 treatment of mutant TR beta infected mice showed no changes in liver luciferase, weight, or 5'-deiodinase and spot 14 messenger RNA, and the decrease in the serum cholesterol concentration was blunted as in patients with RTH. The effects of T3 in mice infected with WT TR beta were comparable to those in mice infected with Luc alone. However, overexpression of the WT TR beta tended to further increase serum cholesterol in the hypothyroid state and decrease it in response to T3, suggesting that the unliganded TR has a constitutive effect in vivo and that higher TR levels can aggravate the manifestations of hypothyroidism and enhance the action of thyroid hormone. Transient somatic transfer of mutant TR genes provides a model for the study of RTH. It allows evaluation of the effect of genetic factors interacting with mutant TRs that modify the phenotype of RTH, without animal back-crossing.

Animals↗
PubMed1995

Molecular and structural characterization of the heat-resistant thyroxine-binding globulin-Chicago.

Thyroxine-binding globulin (TBG) is the main transport protein for thyroxine (T4) in blood. It shares considerable sequence homology with alpha 1-antitrypsin (AT) and other members of the serine proteinase inhibitor (serpin) superfamily of proteins. The crystallographic structure of AT has been determined and was found to represent the archetype of the serpins. This model has been used for structure-function correlations of TBG. Sequence analysis of the heat-resistant variant TBG-Chicago (TBG-CH) revealed a substitution of the normal tyrosine 309 with phenylalanine. For further analysis, vectors containing the coding regions of normal TBG (TBG-N) and TBG-CH were constructed, transcribed in vitro, and expressed in Xenopus oocytes. Both TBGs were secreted into the culture medium and could not be distinguished by gel electrophoresis. Scatchard analysis of T4 binding to TBG-N and -CH revealed no significant differences in binding affinity. The rate of heat denaturation of TBGs was determined by measurement of residual T4 binding capacity after incubation at 60 degrees C for various periods of time. The half-life values of denaturation of TBG-N and -CH were 7 and 132 min, respectively. The tyrosine 309 to phenylalanine substitution of TBG-CH involves a highly conserved phenylalanine residue of the serpins. The respective phenylalanine 312 of AT ties the alpha-helix hI1 to the molecule, thus stabilizing the tertiary structure. A substitution with tyrosine would disrupt this interaction. Accordingly, stabilization of the TBG molecule by replacement of tyrosine with phenylalanine in position 309 causes the increased heat stability of TBG-CH.

Amino Acid Sequence↗
PubMed1995

Molecular cloning of an orphan G-protein-coupled receptor that constitutively activates adenylate cyclase.

A human gene encoding an orphan G-protein-coupled receptor named ACCA (adenylate cyclase constitutive activator) was isolated from a genomic library using as a probe a DNA fragment obtained by low-stringency PCR. Human ACCA (hACCA) is a protein of 330 amino acids that exhibits all the structural hallmarks of the main family of G-protein-coupled receptors. Expression of hACCA resulted in a dramatic stimulation of adenylate cyclase, similar in amplitude to that obtained with other Gs-coupled receptors fully activated by their respective ligands. This stimulation was obtained in a large variety of stable cell lines derived from various organs, and originating from different mammalian species. hACCA was found to be the human homologue of a recently reported mouse orphan receptor (GPCR21). The mouse ACCA (mACCA) was therefore recloned by PCR, and expression of mACCA in Cos-7 cells demonstrated that the mouse receptor behaved similarly as a constitutive activator of adenylate cyclase. It is not known presently whether the stimulation of adenylate cyclase is the result of a true constitutive activity of the receptor or, alternatively, is the consequence of a permanent stimulation by a ubiquitous ligand. The tissue distribution of mACCA was determined by RNase protection assay. Abundant transcripts were found in the brain, whereas lower amounts were detected in testis, ovary and eye. Various hypotheses concerning the constitutive activity of ACCA and their potential biological significance are discussed.

Adenylyl Cyclases↗
PubMed1995

Sleep deprivation in the rat: XIX. Effects of thyroxine administration.

Chronic total sleep deprivation (TSD) in the rat produces an initial elevation and then declining body temperatures, increasing metabolic rate and eventual death. Because TSD rats will engage in warming behavior, one hypothesis is that the metabolic increase is an unsuccessful attempt at warming to combat a lethal hypothermia. However, TSD rats also undergo weight loss and progressive deterioration of skin and fur, suggesting TSD-induced pathological catabolic activity, possibly secondary to increased metabolic rate, that could be lethal. To evaluate these alternatives, the metabolic rate of rats was increased by thyroxine (T4) treatment while subjecting them to TSD. Compared to TSD rats not given T4, they had higher metabolic rates, higher body temperatures and reduced warming behavior, but their survival period was 37% shorter. Thus, it is unlikely that hypothermia is the cause of death in TSD rats. Weight and appearance declined more rapidly in T4-treated rats, but at the same proportions of survival time, skin pathology and decline in appearance were less evident in T4-treated rats than in TSD rats not given T4. Thus, there is some doubt whether a general pathological catabolic process is the cause of death. It is also possible that a specific morbid process normally reversed by sleep was accelerated by T4 administration.

Animals↗
PubMed1995

Effects of aging on glucose regulation during wakefulness and sleep.

Glucose intolerance, reduced sleep efficiency, and disturbed circadian rhythmicity occur in aging. In normal young subjects, glucose regulation is modulated by sleep and circadian rhythmicity. To examine age-related alterations in the temporal pattern of glucose tolerance and insulin secretion, eight modestly overweight healthy older men, eight weight-matched young men, and six young lean men were studied during constant glucose infusion for 53 h. Levels of glucose, insulin, C-peptide, and growth hormone (GH) were measured every 20 min. Rates of insulin and GH secretion were calculated by deconvolution. In older volunteers, sleep ws shallow and more fragmented than in young subjects but was nevertheless associated with robust glucose elevations. However, postsleep increases of insulin secretion were markedly dampened. During wakefulness, the normal morning-to-evening increase in glucose was preserved in the elderly, but insulin secretion failed to increase proportionately. Thus decreased glucose tolerance in aging is associated with insulin resistance and also with a relative insensitivity of the beta-cell to the modulation of glucose regulation by sleep and circadian rhythmicity.

Adult↗
PubMed1995

Studies on the repression of basal transcription (silencing) by artificial and natural human thyroid hormone receptor-beta mutants.

Thyroid hormone receptors (TRs) are ligand-dependent transcription factors that regulate target gene transcription. Interestingly, in the absence of ligand, TRs also can repress basal transcription of positively regulated target genes, suggesting that unliganded TR may have a distinct role in gene regulation. In this paper, DNA binding, truncation, and natural human TR beta mutants were used in cotransfection and electrophoretic mobility shift assays to study various aspects of TR-mediated basal repression. Presently, little is known about the role(s) of natural human TR beta mutants on basal repression. These results show that: 1) TR binding to DNA likely is required for basal repression; 2) the amino-terminal region of TR is not required for basal repression; 3) TR homodimer binding is not absolutely required for basal repression, as TR mutants that selectively form TR-retinoid X receptor heterodimers can mediate basal repression; and 4) TR mutants with poor T3-binding affinity likely have constitutive basal repression, even in the presence of ligand. These findings provide new insight on the mechanism of basal repression by unliganded TRs.

Base Sequence↗
PubMed1995

Linkage of familial dysalbuminemic hyperthyroxinemia to the albumin gene in a large Amish kindred.

Familial dysalbuminemic hyperthyroxinemia (FDH) is the most common cause of inherited euthyroid hyperthyroxinemia in Caucasians. Transmitted as an autosomal dominant trait, it is always associated with high serum total T4 (TT4) and more rarely with elevated total T3 (TT3) and/or rT3 (TrT3) concentrations. Free T4, by dialysis, and TSH levels are normal, suggesting the presence of a T4-binding protein abnormality. The abnormal serum T4 carrier shares some physical and immunological properties with albumin, suggesting that it may be albumin itself. Here we show linkage between FDH and the albumin gene in a large Amish family of Swiss descent, using as markers a SacI polymorphism in the coding sequence of the albumin gene and the group-specific component (Gc) gene, located less than 1 centimorgan from the albumin gene. Blood samples were obtained from 160 members of this kindred, and 22 had FDH identified by the pattern of T4 binding to serum proteins separated by isoelectric focusing. Serum TT4 values were above the normal range in all subjects expressing the FDH phenotype, and TrT3 levels were above the normal range in only one half. TT4 concentrations correlated positively with TrT3 and TT3. All TT3 values were, however, within the normal range. Free T4 and TSH levels were normal, confirming the euthyroid state in these subjects. FDH was associated with the albumin SacI(+)/Gc 1S haplotype, yielding a LOD (logarithm of the odds ratio) score of 5.53, with a recombination frequency of 0. These data provide strong support that a variant albumin is the cause of FDH in this kindred.

Base Sequence↗
PubMed1995

Do clinical manifestations of resistance to thyroid hormone correlate with the functional alteration of the corresponding mutant thyroid hormone-beta receptors?

Resistance to thyroid hormone (RTH), a syndrome characterized by variable tissue hyposensitivity to thyroid hormone, is linked to mutations in the thyroid hormone receptor-beta (TR beta) gene. The purpose of this study was to determine whether the clinical phenotypes of RTH can be translated in terms of functional impairment of the corresponding mutant TR beta. Data from 124 subjects with RTH representing 18 different mutant TR beta s, showed that serum free T4 levels correlated with the degree of T3-binding impairment of the corresponding TR beta in 12 of these mutant TR beta s (group I), but not in the remaining 6 (group II). In subjects from both groups studied in detail by the administration of incremental doses of T3, the degree of thyrotroph resistance to T3 correlated with the magnitude of endogenous free T4 elevation at baseline, but did not parallel the resistance of peripheral tissues. In transfection studies, all group I mutant TR beta s inhibited positive transactivation by the wild type TR beta s to a similar degree in the presence of 1 nmol/L T3, whereas group II mutant TR beta s exerted a weaker inhibition that was not related to their T3-dependent trans-activation when tested alone. Similar results were obtained with negatively regulated reporter genes. It is concluded that the clinical severity of RTH, determined by thyrotroph resistance, can be predicted from the degree of T3 binding impairment and dominant negative potency of mutant TR beta s, but the degree of peripheral tissue resistance and related clinical manifestations is limited by putative genetic or environmental factors that modulate the effect of thyroid hormone.

Adolescent↗
PubMed1995

Thyroid function tests and characterization of thyroxine-binding globulin in the carbohydrate-deficient glycoprotein syndrome type I.

Carbohydrate-deficient glycoprotein (CDG) syndrome is a newly recognized hereditary disorder that presents with psychomotor retardation, cerebellar ataxia, peripheral sensorimotor neuropathy, and, variably, skeletal abnormalities, lipodystrophy, and retinitis pigmentosa. These abnormalities appear to be produced by a defect that causes reduced carbohydrate content in glycoproteins. We studied seven patients with CDG type I belonging to five unrelated families. The concentration of serum TBG, a glycoprotein of hepatic origin, was measured by RIA and T4 saturation and was found to be below the normal range in three of the seven patients and normal in four of them. More than half of the total serum TBG had reduced sialic acid content and localized on isoelectric focusing (IEF) as two prominent bands cathodal to the three major bands of normal TBG. The latter two bands are responsible for the characteristic IEF pattern or CDG syndrome. TBG in patients with CDG had immunoreactivity indistinguishable from that of normal TBG and had normal affinity for T4, T3, and rT3. Serum total T4, T3, and rT3 were below the normal range in seven, five, and seven patients, respectively. The free T4 index was also below normal in four patients, but the free T4 concentration, measured by equilibrium dialysis at low dilution, and serum TSH were in the midnormal range. The serum total T4 and rT3 levels were disproportionately reduced relative to the serum TBG concentration and compared to the concentrations of these iodothyronines in matched subjects with inherited partial TBG deficiency. Chronic illness cannot explain these changes, because, contrary to patients with nonthyroidal illness, those with CDG had significantly higher serum total T3/T4 and lower rT3/T4 ratios. It is concluded that IEF of TBG is a rapid and simple method for the diagnosis of CDG type I and that the abnormal pattern can be detected as early as 5 days postpartum. Patients with CDG are chemically euthyroid, and it is postulated that the reduction in serum iodothyronine concentrations beyond that explained on the basis of low TBG levels may be due to the interference with binding to TBG by an unidentified substance.

Adolescent↗
PubMed1995

High prevalence of thyroxine-binding globulin deficiency among Bedouin infants in southern Israel.

A high prevalence of thyroxine-binding globulin deficiency was found among Bedouin newborns in the Negev area (southern Israel) during a study lasting 2 years. This prevalence is significantly higher than those reported in other populations. Moreover, thyroxine-binding globulin deficiency was found to be more common than congenital hypothyroidism among the Bedouin. The results of thyroxine-binding globulin analysis in four patients may suggest the coexistence of at least two different mutations among the Bedouin population.

Ethnicity↗