A large-scale association analysis of 68 thyroid hormone pathway genes with serum TSH and FT4 levels.

Objective: Minor variation in serum thyroid hormone (TH) levels can have important effects on various clinical endpoints. Although 45-65% of the inter-individual variation in serum TH levels is due to genetic factors, the causative genes are not well established. We therefore studied the effects of genetic variation in 68 TH pathway genes on serum TSH and free thyroxine (FT(4)) levels.

The pituitary-thyroid axis set point in women is uninfluenced by X chromosome inactivation pattern? A twin study.

Objective: The pituitary-thyroid axis (PTA) set point is determined by a combination of genetic and environmental factors. However, despite considerable efforts to characterize the background, the causative genes as well as environmental factors are not well established. Theoretically, as shown for autoimmune thyroid disease, the pattern of X chromosome inactivation (XCI) could offer a novel explanation for the observed variability of the PTA set point in women.

Aggregation of thyroid autoantibodies in twins from opposite-sex pairs suggests that microchimerism may play a role in the early stages of thyroid autoimmunity.

Context: Microchimerism is the presence of small populations of cells from one individual in another genetically distinct individual. This phenomenon can arise from pregnancy, blood transfusion, or bidirectional cell trafficking between twins in utero. Microchimerism has recently been proposed to play a role in the pathogenesis of thyroid autoimmunity.

X Chromosome inactivation pattern is not associated with interindividual variations in thyroid volume: a study of euthyroid Danish female twins.

Ahigher frequency of skewed X chromosome inactivation (XCI) is found in patients with autoimmune thyroid disease (AITD) than in controls. Although goitre is often present in AITD, a recent study failed to show an association between XCI and clinically overt nontoxic goitre. However, the etiology of overt goitre is complex, and the mechanisms influencing thyroid volume may involve fewer factors than the mechanisms underlying overt goitre.

Preliminary evidence of a noncausal association between the X-chromosome inactivation pattern and thyroid autoimmunity: a twin study.

An increased frequency of skewed X-chromosome inactivation (XCI) is found in clinically overt autoimmune thyroid disease (AITD) compared with controls. Whether skewed XCI is involved in the pathogenesis of autoantibodies to thyroid peroxidase (TPOAb) in euthyroid subjects is unknown. To examine the impact of XCI on the serum concentration of TPOAb, we studied whether within-cohort and within-twin-pair differences in XCI are associated with differences in serum concentrations of TPOAb.

No link between X chromosome inactivation pattern and simple goiter in females: evidence from a twin study.

Background: Simple goiter (SG) comprises diffuse (DG) and nodular (NG) benign nonautoimmune nontoxic goiter. In nonendemic goiter areas, the ratio of females to males may exceed 5:1, indicating that gender and/or sex hormones may play a role in the etiology of SG in these areas. Theoretically, as shown for autoimmune thyroid disease, X chromosome inactivation (XCI) and resultant tissue chimerism could offer a novel explanation for the female preponderance of SG.

Identification and consequences of polymorphisms in the thyroid hormone receptor alpha and beta genes.

Objective: Genetic factors exert considerable influence on thyroid function variables. Single nucleotide polymorphisms (SNPs) in thyroid hormone pathway genes have been associated with serum thyroid parameters implying small alterations in the hypothalamus-pituitary-thyroid axis. However, little is known about SNPs in the THRA (17q11.

The effect of genetic variation in the type 1 deiodinase gene on the interindividual variation in serum thyroid hormone levels: an investigation in healthy Danish twins.

Introduction: Genetic factors have a considerable influence on serum thyroid hormone levels. The C785T and A1814G polymorphisms, located in the 3' untranslated region of the type 1 deiodinase (D1) gene have been associated with serum FT4 and rT3 levels.

Objective: In healthy Danish twins, we examined the association of these polymorphisms with serum thyroid hormone levels and determined the proportion of genetic influence explained by these variants.

Thyroid hormone transport and metabolism by organic anion transporter 1C1 and consequences of genetic variation.

Organic anion transporting polypeptide (OATP) 1C1 has been characterized as a specific thyroid hormone transporter. Based on its expression in capillaries in different brain regions, OATP1C1 is thought to play a key role in transporting thyroid hormone across the blood-brain barrier. For this reason, we studied the specificity of iodothyronine transport by OATP1C1 in detail by analysis of thyroid hormone uptake in OATP1C1-transfected COS1 cells.

Too early to dismiss Yersinia enterocolitica infection in the aetiology of Graves' disease: evidence from a twin case-control study.

Background: Yersinia enterocolitica (YE) infection has long been implicated in the pathogenesis of Graves' disease (GD). The association between YE and GD could, however, also be due to common genetic or environmental factors affecting the development of both YE infection and GD. This potential confounding can be minimized by investigation of twin pairs discordant for GD.

The impact of a TSH receptor gene polymorphism on thyroid-related phenotypes in a healthy Danish twin population.

Objectives: The Asp727Glu polymorphism in the TSH receptor (TSHR) gene is associated with serum TSH levels. However, the proportion of genetic variation accounted for by this polymorphism is unknown. In this study, we (1) examined the association of the Asp727Glu polymorphism with thyroid size, serum levels of TSH, thyroid hormones, and thyroid antibodies in 1241 healthy Danish twin individuals and (2) assessed the contribution of the polymorphism to the trait variation and the genetic variance.

Genetic and environmental interrelations between measurements of thyroid function in a healthy Danish twin population.

Serum thyrotropin (TSH), free thyroxine (T4), and free triiodothyronine (T3) levels illustrate the thyroid function set point, but the interrelations between these have never been characterized in detail. The aim of this study was to examine the associations between TSH and thyroid hormone levels in healthy euthyroid twins and to determine the extent to which the same genes influence more than one of these biochemical traits; 1,380 healthy euthyroid Danish twins (284 monozygotic, 286 dizygotic, 120 opposite-sex twin pairs) were recruited. Genetic and environmental associations between thyroid function measurements were examined using quantitative genetic modeling.

Establishment of reference distributions and decision values for thyroid antibodies against thyroid peroxidase (TPOAb), thyroglobulin (TgAb) and the thyrotropin receptor (TRAb).

Background: The National Academy of Clinical Biochemistry (NACB) stresses that the reference intervals for thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb) and thyroid stimulating hormone (TSH)-receptor antibodies (TRAb) should be based on young men who lack certain risk factors and have serum TSH between 0.5 and 2.0 mIU/L.

Low birth weight is not associated with thyroid autoimmunity: a population-based twin study.

Context: Low birth weight has been proposed as a risk factor for the development of antibodies toward thyroid peroxidase (TPOAb) and thyroglobulin (TgAb) in adult life. However, the association could also be due to genetic or environmental factors affecting both birth weight and the development of thyroid autoantibodies. The effect of these confounders can be minimized through investigation of twin pairs.

The relative importance of genetic and environmental effects for the early stages of thyroid autoimmunity: a study of healthy Danish twins.

Objective: In euthyroid individuals, autoantibodies to thyroid peroxidase (TPOab) and thyroglobulin (Tgab) are regarded as early markers of thyroid autoimmunity. Family and twin studies suggest that development of thyroid autoantibodies in first-degree relatives of patients with autoimmune thyroid disease is under genetic influence. We aimed to estimate the relative importance of genetic and environmental effects for the presence of thyroid autoantibodies in euthyroid subjects.

The relative importance of genetic and environmental factors in the aetiology of thyroid nodularity: a study of healthy Danish twins.

Background: A large proportion of healthy, euthyroid, nongoitrous individuals have thyroid nodules. The aetiology of these ultrasonographically detected morphological abnormalities is largely unknown. Factors such as age, gender, iodine intake, smoking and parity are associated with nodularity of the thyroid.

Establishment of a serum thyroid stimulating hormone (TSH) reference interval in healthy adults. The importance of environmental factors, including thyroid antibodies.

It has previously been shown that thyroid antibodies affect thyroid stimulating hormone (TSH) concentrations in men and women and that TSH levels are predictive of future thyroid disease. We investigated the validity of the National Academy of Clinical Biochemistry (NACB) guidelines regarding the TSH reference interval by studying 1512 individuals. Two hundred and fifty had at least one thyroid antibody, 121 were taking medications other than estrogens and occasional analgesics, and 105 reported a family history of thyroid disease.

Genetic and environmental causes of individual differences in thyroid size: a study of healthy Danish twins.

Factors such as iodine intake, serum TSH concentration, gender, age, body mass index, parity, and cigarette smoking are thought to influence thyroid size. The purpose of our study was to determine the relative roles of these environmental and physiological factors compared with genetic factors in euthyroid subjects with a clinically normal thyroid gland. A representative sample of self-reported healthy twin pairs was identified through the Danish Twin Registry.

Aggregation of thyroid autoantibodies in first-degree relatives of patients with autoimmune thyroid disease is mainly due to genes: a twin study.

Background: Family studies have repeatedly shown aggregation of thyroid autoantibodies to thyroid peroxidase (TPOab) and thyroglobulin (Tgab) in first-degree relatives of patients with autoimmune thyroid disease (AITD). This phenomenon has generally been interpreted as evidence of a genetic component in the development of thyroid autoantibodies. However, family studies cannot determine whether the observed familial aggregation of these antibodies is due to shared genes or shared environment.

Major genetic influence on the regulation of the pituitary-thyroid axis: a study of healthy Danish twins.

Intraindividual variation is smaller than the interindividual variation in serum TSH, free T(4), and free T(3) concentrations. This suggests that each individual may have a genetically determined thyroid function set-point. A representative sample of self-reported healthy twin pairs was identified through the Danish Twin Registry.