Low Thyroid Hormone Research Articles

Thyroid function in the euthyroid range and adverse outcomes in older adults.

The appropriateness of current reference ranges for thyroid function testing in older adults has been questioned. This study aimed to determine the relationship between thyroid function tests within the euthyroid range and adverse outcomes in older adults not taking thyroid medication. US community-dwelling adults years of older (n = 2843) enrolled onto the Cardiovascular Health Study with TSH, free T4 (FT4), and total T3 concentrations in the euthyroid range. Incidence of atrial fibrillation, coronary heart disease, heart failure, hip fracture, dementia, and all-cause death were measured. No departures from linearity were detected. Higher TSH was negatively associated (P = .03) and higher FT4 was positively associated (P = .007) with mortality. Higher FT4 was associated with atrial fibrillation (P < .001) and heart failure (P = .004). Compared with the first quartile, individuals with TSH in the fourth quartile had a 9.6 per 1000 person-year lower incidence of dementia (P < .05) and those with FT4 in the fourth quartile had higher incidences of atrial fibrillation, coronary heart disease, heart failure, and mortality (11.0, 8.0, 7.8, and 14.3 per 1000 person-years, respectively, all P < .05). Total T3 was not associated with any outcome. Higher TSH and lower FT4 concentrations within the euthyroid range are associated with lower risk of multiple adverse events in older people, including mortality. This suggests tolerance for lower thyroid hormone levels in this age group. Clinical trials are needed to evaluate the risk-benefit profile of new thresholds for initiating treatment and optimal target concentrations for thyroid hormone replacement in older people.

The second wave of the Controlled Antenatal Thyroid Screening (CATS II) study: the cognitive assessment protocol.

BackgroundChildren whose mothers had low thyroid hormone levels during pregnancy have been reported to have decreased cognitive function. The reported research is part of the follow-on study of the Controlled Antenatal Thyroid Screening Study (CATS I), a randomised controlled trial which investigated the impact of treated vs. untreated low thyroid hormone level in women during pregnancy with the primary outcome being the child’s IQ at age 3. No significant differences in IQ were found between the treated and untreated groups. These children are now aged between 7 and 10 years and aspects of their cognitive functioning including their IQ are being reassessed as part of CATS II.Methods/DesignCognitive assessments generate an IQ score and further tests administered will investigate long term memory function and motor coordination. The aim is to complete the assessments with 40% of the children born to mothers either in the treated or untreated low thyroid hormone groups (n = 120 per group). Also children born to mothers who had normal thyroid functioning during CATS I are being assessed for the first time (n = 240) to provide a comparison. Assessments are conducted either in the research facility or the participant’s home.DiscussionThe study is designed to assess the cognitive functioning of children born to mothers with low thyroid hormone levels and normal thyroid functioning during pregnancy. This is the largest study of its type and also is distinguishable in its longitudinal design. The research has the potential to have a significant impact on public health policy in the UK; universal screening of thyroid hormone levels in pregnancy may be the recommendation.

Unusual ratio between free thyroxine and free triiodothyronine in a long-lived mole-rat species with bimodal ageing.

Ansell's mole-rats (Fukomys anselli) are subterranean, long-lived rodents, which live in eusocial families, where the maximum lifespan of breeders is twice as long as that of non-breeders. Their metabolic rate is significantly lower than expected based on allometry, and their retinae show a high density of S-cone opsins. Both features may indicate naturally low thyroid hormone levels. In the present study, we sequenced several major components of the thyroid hormone pathways and analyzed free and total thyroxine and triiodothyronine in serum samples of breeding and non-breeding F. anselli to examine whether a) their thyroid hormone system shows any peculiarities on the genetic level, b) these animals have lower hormone levels compared to euthyroid rodents (rats and guinea pigs), and c) reproductive status, lifespan and free hormone levels are correlated. Genetic analyses confirmed that Ansell's mole-rats have a conserved thyroid hormone system as known from other mammalian species. Interspecific comparisons revealed that free thyroxine levels of F. anselli were about ten times lower than of guinea pigs and rats, whereas the free triiodothyronine levels, the main biologically active form, did not differ significantly amongst species. The resulting fT4:fT3 ratio is unusual for a mammal and potentially represents a case of natural hypothyroxinemia. Comparisons with total thyroxine levels suggest that mole-rats seem to possess two distinct mechanisms that work hand in hand to downregulate fT4 levels reliably. We could not find any correlation between free hormone levels and reproductive status, gender or weight. Free thyroxine may slightly increase with age, based on sub-significant evidence. Hence, thyroid hormones do not seem to explain the different ageing rates of breeders and non-breeders. Further research is required to investigate the regulatory mechanisms responsible for the unusual proportion of free thyroxine and free triiodothyronine.

Restoration of thyroid hormone balance: a game changer in the treatment of heart failure?

The link between low thyroid hormone (TH) function and heart failure is reviewed in the present report. The idea that TH dysfunction may contribute to diseases leading to HF has been discussed for over 60 yr. A growing body of evidence from animal and human studies, particularly in recent years, suggests that TH treatment may improve clinical outcomes. Indeed, if a similar amount of positive information were available for a newly developed heart drug, there is little doubt that large-scale clinical trials would be underway with considerable excitement. THs offer the promise of improving ventricular contraction and relaxation, improving coronary blood flow, and inhibiting atherosclerosis, and new results suggest they may even reduce the incidence of arrhythmias in heart diseases. Are the potential clinical benefits worth the risk of possible overdosing? After so many years, why has this question not been answered? Clearly, the concept has not been disproven. This review explores the body of clinical evidence related to TH dysfunction and heart failure, discuss insights into pathophysiological, cellular, and molecular mechanisms provided by animal research, and discuss what is needed to resolve this long-standing issue in cardiology and move forward.

Strain and sex effects on ascites development in commercial broiler chickens

Summary The objective of this study was to assess the importance of strain and sex and their interaction effect on broiler chickens’ performance and susceptibility to ascites. Chicks from three strains (Ross 308, Cobb 500 and Arian, labeled as A, B and C respectively) were obtained from the same age breeder and sexed when one-day-old. Each crosses’ sex was assigned to four pens of 60 broilers each. Body weight gain (BWG), feed intake, feed conversion ratio (FCR) and ascites mortality were determined. At the age of 28 and 49 d haematocrit values, arterial pressure index (API = right ventricular/total ventricular weight ratio), the values of plasma thyroid hormone concentration (thyroxin, T4 and triiodothyronine, T3) and metabolic lung weight (lung weight/body weight (0.75) ) were determined. Strain B had the highest BWG but an equal incidence of ascites as strain A, which had low BWG and ascites mortality. Ascites mortality was not correlated with BWG and FCR. A significant strain interaction by sex on feed conversion (P<0.01) and final weight (P<0.05) was found. The sex effect was significant only in strain C on feed conversion and final weight. Strains B and C had lower thyroid hormones and reduced metabolic lung weights compared with strain A. The sex effect was not significant on the parameters associated with ascites syndrome and its incidence.

Non-thyroidal illness in the ICU: a syndrome with different faces.

Critically ill patients typically present with low or low-normal plasma thyroxine, low plasma triiodothyronine (T3), increased plasma reverse T3 (rT3) concentrations, in the absence of a rise in thyrotropin (TSH). This constellation is referred to as nonthyroidal illness syndrome (NTI). Although it is long known that the severity of NTI is associated with risk of poor outcomes of critical illness, the causality in this association has not been well investigated. In this narrative review, the different faces of NTI during critical illness are highlighted. Acute alterations are dominated by changes in thyroid hormone binding, peripheral thyroid hormone uptake, and alterations in the expression and activity of the type-1 and type-3 deiodinases. It was recently shown that at least part of these acute changes are brought about by concomitant macronutrient restriction, and this part appears adaptive and beneficial. However, the face of the NTI in the prolonged phase of critical illness is different, when patients are fully fed but continue to depend on intensive medical care. In that prolonged phase of illness, hypothalamic thyrotropin releasing hormone (TRH) expression is suppressed and explains reduced TSH secretion and whereby reduced thyroidal hormone release. During prolonged critical illness, and in the presence of adequate nutrition, several tissue responses could be interpreted as compensatory to low thyroid hormone availability, such as increased expression of monocarboxylate transporters, upregulation of type-2 deiodinase activity, and increased sensitivity at the receptor level. Infusing hypothalamic releasing factors in these prolonged critically ill patients can reactivate the thyroid axis and induce an anabolic response. It is clear that the name "NTI" during critical illness refers to a syndrome with different faces. Tolerating the early "fasting response" to critical illness and its concomitant changes in thyroid hormone parameters appears to be wise and beneficial. This thus applies to the NTI present in the majority of the patients treated in intensive care units. However, the NTI that occurs in prolonged critically ill patients appears different with regard to both its causes and consequences. Future studies should specifically target this selected population of prolonged critically ill patients, and, after excluding iatrogic drug interferences, investigate the effect on outcome of treatment with hypothalamic releasing factors in adequately powered randomized controlled trials.

A clue to diagnosis in a boy with short stature: Testicular enlargement.

A clue to diagnosis in a boy with short stature: Testicular enlargement.

ROLE OF YOGA IN PREVENTION OF HYPOTHYROIDISM

Hypothyroidism is a condition characterized by abnormally low thyroid hormone production. There are many disorders that resul t in hypothyroidism. These disord ers may directly or indirectly involve the thyroid gland. Because thyroid horm one affects growth, development and many cellular processes, inadequate thyroid hormone has widespread consequences for the body. Since hypothyroidism develops from a shortage of thyroid hormone, the most effective treatment is generally thyroid hormone supplementation. Although treatment provides the necessary hormone control, hypothyroidism often continues throughout life, and the patient may require lifelong follow - up and medic ation to control the condition. Yoga is one of the few natural remedies that have shown promise as prevention and treatment for hypothyroidism. By stimulating the function of the thyroid, pituita ry, pineal and adrenal glands, y oga prevents its damage. Ther e are certain asanas , pranayamas and bandhas which shows tremendous effects on thyroid gland which will be discussed in full paper.

Thyroid functional disease: an under-recognized cardiovascular risk factor in kidney disease patients.

Thyroid functional disease, and in particular hypothyroidism, is highly prevalent among chronic kidney disease (CKD) and end-stage renal disease (ESRD) patients. In the general population, hypothyroidism is associated with impaired cardiac contractility, endothelial dysfunction, atherosclerosis and possibly higher cardiovascular mortality. It has been hypothesized that hypothyroidism is an under-recognized, modifiable risk factor for the enormous burden of cardiovascular disease and death in CKD and ESRD, but this has been difficult to test due to the challenge of accurate thyroid functional assessment in uremia. Low thyroid hormone levels (i.e. triiodothyronine) have been associated with adverse cardiovascular sequelae in CKD and ESRD patients, but these metrics are confounded by malnutrition, inflammation and comorbid states, and hence may signify nonthyroidal illness (i.e. thyroid functional test derangements associated with underlying ill health in the absence of thyroid pathology). Thyrotropin is considered a sensitive and specific thyroid function measure that may more accurately classify hypothyroidism, but few studies have examined the clinical significance of thyrotropin-defined hypothyroidism in CKD and ESRD. Of even greater uncertainty are the risks and benefits of thyroid hormone replacement, which bear a narrow therapeutic-to-toxic window and are frequently prescribed to CKD and ESRD patients. In this review, we discuss mechanisms by which hypothyroidism adversely affects cardiovascular health; examine the prognostic implications of hypothyroidism, thyroid hormone alterations and exogenous thyroid hormone replacement in CKD and ESRD; and identify areas of uncertainty related to the interplay between hypothyroidism, cardiovascular disease and kidney disease requiring further investigation.

Effect of low thyroid hormone bioavailability on childhood cognitive development: data from the Avon Longitudinal Study of Parents and Children birth cohort

BackgroundHypothyroidism is associated with impaired cognitive development. Whether free thyroxine (T4) concentrations at the lower end of the reference range also have a negative effect is less clear. A common genetic variant, the Thr92Ala substitution in deiodinase-2 can exacerbate low free T4 concentrations by reducing intracellular conversion of free T4 to free tri-iodothyronine. We aimed to see whether low thyroid hormone bioavailability (free T4 in the lowest quartile and the Thr92Ala substitution in deiodinase-2) in childhood adversely affects cognitive development. MethodsThe data from this study come from a retrospective cross-sectional analysis in a population-based birth cohort study, the Avon Longitudinal Study of Parents and Children. Children had thyroid function tested at age 7 years and extensive cognitive assessments at age 8 years. We assessed the odds of having a lower end intelligence quotient (IQ) (<85) if an individual had low thyroid hormone bioavailability. Analyses were adjusted for age, sex, other thyroid hormone variables, and social class. Findings422 (13·5%) of 3127 children had the Thr92Ala substitution, with 116 children (3·71%) having the combination of free T4 in the lowest quartile and the Thr92Ala substitution. We noted a strong association between children with free T4 in the lowest quartile and the Thr92Ala substitution and lower mean IQ (p=0·008, t test). Individuals with free T4 in the lowest quartile and the Thr92Ala substitution were more likely to have a total IQ score below 85 than individuals with free T4 above the lowest quartile without the substitution (odds ratio 3·03, 95% CI 1·38–6·67; p=0·006). There was no association with IQ below 85 in individuals with free T4 in the lowest quartile without the substitution (1·07, 0·82–1·39; p=0·59). When we considered total IQ as a continuous variable, children with free T4 in the lowest quartile and the Thr92Ala substitution had a lower IQ than did those with free T4 above the lowest quartile without the substitution (β=−0·34, −0·64 to −0·04, p=0·03). InterpretationCommon genetic variation in the intracellular thyroid hormone action pathway seems to substantially modify the effect of low serum thyroid hormone concentrations on IQ. This finding suggests that thyroid hormone concentrations alone do not entirely reflect thyroid status and raises the possibility that thyroxine supplementation in at-risk children might improve cognitive outcomes. FundingBupa Research Foundation, British Thyroid Foundation.

Patients infected with avian influenza A H7N9 virus have abnormally low thyroid hormone levels.

In March 2013, the novel avian influenza A H7N9 virus spread throughout China. This study evaluated whether thyroid function was altered in patients infected with H7N9 virus. We analyzed thyroid-stimulating hormone (TSH), total triiodothyronine (TT3), total tetraiodothyronine (TT4), free triiodothyronine (FT3), and free tetraiodothyronine (FT4) levels in 17 patients infected with H7N9 on admission to our hospital and compared the values to the reference ranges for these thyroid hormones. Of the 17 patients, 12 (70.6%) patients had abnormally low TT3 levels, 10 (58.8%) patients had abnormally low FT3 and TSH levels, and 5 (29.4%) patients had abnormally low TT4 and FT4 levels (below the lower limit of the reference ranges for each hormone). Abnormally low thyroid hormone levels was common in patients infected with H7N9.

A pilot study: Subclinical hypothyroidism and free thyroid hormone measurement by immunoassay and mass spectrometry

BackgroundThe diagnosis of subclinical hypothyroidism is defined as the presence of an elevated thyroid stimulating hormone (TSH) with a normal free thyroxine (FT4) level. The commonly used direct analogue immunoassays for the measurement of FT4 have been shown to have poor performance at the upper and lower limits of the FT4 reference interval. PurposeThe purpose of this pilot study was to investigate the percentage of individuals classified as having subclinical hypothyroidism with a standard immunoassay, that actually have low free thyroid hormone levels by mass spectrometry measurements. DesignOutpatient samples with elevated TSH values and normal FT4 concentrations as per standard immunoassay methods were collected. FT4 and free triiodothyronine (FT3) analyses were performed on these samples using liquid chromatography–tandem mass spectrometry (LC–MS/MS). ResultsSixty five percent (n=26) of patients (n=40) had (LC–MS/MS) FT4 or FT3 or both FT4 and FT3 values below mass spectrometry reference limits. ConclusionsOur findings indicate that the direct analogue immunoassay method for FT4 measurement results in a significant proportion of patients being misclassified as having subclinical hypothyroidism.

Free triiodothyronine level indicates the degree of myocardial injury in patients with acute ST-elevation myocardial infarction

Background Previous studies have suggested that hypothyroidism correlated with coronary heart diseases (CHD) mortality in long-term cohort, but whether the thyroid function status is associated with myocardial injury in acute ST-elevation myocardial infarction (STEMI) has not been investigated sufficiently. Methods Five hundred and eighty-two hospitalized patients from January 2010 to December 2011, with the diagnosis of STEMI, were enrolled in this study. All patients underwent testing for thyroid function status, cardiac troponin I (cTnI), cardiac enzymes, C-reactive protein (CRP). We investigated the association between thyroid hormone levels and cardiac markers (creatine kinase-MB and cTnI), and thus evaluated the potential role of thyroid function status in predicting the myocardial injury. Results There were 76 patients (13.06%) who had hypothyroidism including low-T3-syndrome (34 patients, 5.84%), subclinical hypothyroidism (28 patients, 4.81%) and clinical hypothyroidism (14 patients, 2.41%). After adjusting for conventional risk factors (age, gender, smoking, diabetes mellitus, dyslipidemia, hypertension), free triiodothyronine (FT3) was significantly and negatively correlated with log-CKMB (r=-0.244, P &lt;0.001) and log-cTnI (r=-0.290, P &lt;0.001), indicating that the lower thyroid hormone level correlates with the severer cardiac injury in STEMI patients. FT3 also had a moderate negative correlation with CRP (r=-0.475, P &lt;0.001), which might indicate that hypothyroidism may activate the inflammation response. No significant correlation was found between other thyroid parameters (TSH, FT4) and cardiac markers. Conclusions As the lower FT3 level correlates with higher level of cardiac markers and lower left ventricular ejection fraction (LVEF), the hypothyroidism may be a predictor for myocardial injury in STEMI. And these results may warrant further study to investigate whether reversing the hypothyroidism could benefit the STEMI patients.

Clinical significance of low triiodothyronine syndrome in critical patients and triiodothyronine impact on evaluation of prognosis

Objective To identify the clinical significance of low triiodothyronine syndrome and the potential impact of triiodothyronine (T3) on prognosis in critical patients.Methods A total of 150 critically ill patients enrolled from October 2012 to April 2013 were divided into two groups,namely low thyroidhormone group (n =38,group A) and normal T3 group (n =112,group B).APACHE Ⅱ scores of patients were recorded at admission and thyroid hormone levels were measured on the first and the third day after admission.Then the survival state of 28-day in each group was observed and then the relationship between prognosis and T3 levels was analyzed by receiver operating characteristic (ROC) curve.Results About 25.3％ of 150 critical patients were suffered from low thyroidhormone syndrome and the mortality rate in this group was 42.1％,which was much higher than 29.5％ in normal T3 group.There was no difference in prediction of death rate analyzed by ROC curve between the T3 level and APACHE Ⅱ scores.The area under curve of T3 level was 0.768 (95％ CI:0.701-0.835) and APACHE Ⅱ was 0.783 (95％CI:0.719-0.846).Best cut-off value of T3 level was 0.41 ng/mL resulting in 76.6％ sensitivity and 78.4％ specificity.Conclusions Critically ill patients complicated with low thyroidhormone syndrome has poor prognosis and T3 may be a predictive marker in evaluating the prognosis of critically ill patients. Key words: Critical; Low triiodothyronine syndrome; Prognosis; ROC curves; APACHE Ⅱ score; Intensive care unit; Euthyroid sick syndrome

Therapeutic exploration of betulinic acid in chemically induced hypothyroidism

Hypothyroidism is a chronic condition characterized by abnormally low thyroid hormone production. The decreased serum level (>5.1mIU/l) of thyroid-stimulating hormone (TSH) in blood indicates hypothyroidism. The study was an attempt to access the effect of betulinic acid on chemically induced hypothyroidism in female albino rats. Betulinic acid is a naturally occurring pentacyclic triterpenoid, which has antiretroviral, antimalarial, and anti-inflammatory properties, as well as anticancer potential, by inhibiting topoisomerase. Hypothyroidism was induced in female albino rats using propylthiouracil (PTU) at a dose of 60μg/kg body weight orally for 1month. Induction of hypothyroidism was confirmed by increased TSH level. At the end of second month, blood was collected, centrifuged and serum was analyzed for TSH, T3, and T4 level and protocol was terminated by killing of animals. The animals exposed to PTU were treated with pure standard drug thyroxine at a dose of 10μg/kg of body weight by oral route and the test drug betulinic acid 20mg/kg by oral route through force feeding in their respective groups. Treatment was carried out for a period of 2months. Group with PTU-induced hypothyroidism showed an elevation in serum TSH and reduction level, which was restored by the betulinic acid in treated female albino rats. Betulinic acid also reduced the damage caused in the thyroid tissues by PTU, thus minimizing the symptoms of hypothyroidism. Histopathological examinations of the thyroid tissue showed changes in the thyrocytes of PTU-treated group while thyroxine group showed normal thyroid follicles cell architecture and the group treated with betulinic acid also showed marked improvement in the follicles integrity which shows that betulinic acid has some protective activity. This study shows that the betulinic acid has thyroid-enhancing potential by lowering down the TSH levels and reducing the damage caused in the thyroid tissues, thus minimizing the symptoms of hypothyroidism when used anaphylactically in rats.

Late-onset Sheehan’s syndrome presenting with rhabdomyolysis and hyponatremia: a case report

IntroductionHyponatremia associated with rhabdomyolysis is a rare event and a correct diagnostic approach is required to rule out this or other diseases as a primary cause and to avoid other complications resulting from a lack of appropriate treatment.Case presentationA 64-year-old Caucasian woman presented to our facility with worsening fatigue, slurred speech, nausea and vomiting, and high serum levels of creatine kinase and myoglobin together with hyponatremia. Normal arterial blood gas analysis results, normal serum potassium levels, increased urine sodium levels, urine specific gravity of >1003N/m3 and low urine volume suggested an endocrine etiology. Her low cortisol and thyroid hormone serum levels suggested a pituitary disorder. A magnetic resonance imaging study showed atrophy of her pituitary gland. A more detailed study of our patient’s obstetric history revealed a post-partum hemorrhage 30 years earlier. She was diagnosed as having late-onset Sheehan’s syndrome and treated with hormone replacement therapy, which normalized her clinical picture.ConclusionsThis case report shows that, in hyponatremia-associated rhabdomyolysis, an endocrinological origin should always be considered. This should include Sheehan’s syndrome as it can occur with late onset.

Exercise training induced myosin heavy chain isoform alteration in the infarcted heart

The myosin heavy chain isoform MHC-α has 3-fold higher ATPase activity than MHC-β. After myocardial infarction (MI), MHC-α expression is profoundly downregulated and MHC-β expression is reciprocally upregulated. This shift, which is attributed to low thyroid hormone (TH), contributes to myocardial systolic dysfunction. We investigated the effect of post-MI exercise training on MHC isoforms, TH, and cardiac function. MI was surgically induced in 7-week-old rats by ligation of the coronary artery. The survivors were assigned to 3 groups (n = 10/group): Sham (no MI, no exercise), MISed (MI, no exercise), and MIEx (MI, exercise). Treadmill exercise training began 1 week post-MI and lasted for 8 weeks. Echocardiogram measurements were taken on the day prior to initiation of exercise training and at the end of exercise training. Tissue and blood samples were collected at the end of the experiment. MHC isoform gene and protein expression and TH were measured. Our results illustrated that MHC-α gene expression was higher and MHC-β gene expression was lower in the MIEx group than in the MISed group. Resting serum TH concentrations (T3 and T4) were similar between the 2 MI groups. The MIEx group had higher fractional shortening than the MISed group. In conclusion, post-MI exercise training beneficially altered MHC isoforms and improved cardiac function without changing TH.

Altered magnetic resonance images of brain and social behaviors of hatchling, and expression of thyroid hormone receptor βmRNA in cerebellum of embryos after Methimazole administration

The effects of low thyroid hormone level during embryogenesis on MRI of the brain and social behaviors of hatchlings were examined using "fertilized hen's egg-embryo-chick" system. Control and hatchlings treated with methimazole (20 μmol/egg), which hatched 3 days later than controls were examined. The results are as follows: 1. The MRI examination of the midsagittal section of the brain on hatch day showed that the sizes, by T1- and ADC values by diffusion-weighted images, of the optic lobe and cerebellum of the MMI-hatchlings were significantly bigger than those of the controls. 2. The social behaviors on post-hatch day 3 were based on the following tests: (a) Aggregation test: The speed of four chicks, individually isolated by cardboard barriers in a box, to make a group upon the removal of barriers. (b) Belongingness tests: The speed of a chick isolated at a corner to join the group of three chicks placed at the opposite corner. (c) Vocalization test: The number of decibel produced by a chick isolated at a corner using a sound meter. These tests demonstrated that MMI-hatchlings took longer times and had weaker vocalization than the controls, significantly. 3. Upregulation of THRβ mRNA after MMI treatment suggested that THR was necessary for cerebellum development. The MMI exposure during the last week of embryogenesis possibly delayed the myelination of certain brain regions and impaired the social behaviors of hatchlings. The chick embryos can be easily induced with hypothyroidism without maternal influences, and the hatchling's behaviors were analyzed using a video camera. The present method will be useful for assessing the effects of unfavorable influences during embryogenesis on social behaviors in later life.

Thyrotoxic Periodic Paralysis in Chinese Patients

Thyrotoxic periodic paralysis (TPP) is a complication of thyrotoxicosis mainly observed in male Asian patients. It was proposed that patients with TPP tend to have lower thyroid hormone levels. We aimed to prove this observation and to assess whether a lower I dose is feasible for prompt control of TPP. A total of 123 male TPP patients were enrolled in this study in a 7-year period. Baseline characteristics were compared with 70 thyrotoxic patients without periodic paralysis (nTPP). Different I doses were given to 90 TPP patients with a median follow-up of 11 months, and the outcome was evaluated. The serum thyroid hormone levels, including total T3 and T4, and free T3 and T4, in TPP patients were slightly less elevated compared with those in nTPP patients. Patients who received lower radioactivity of I had an unsatisfactory overall remission rate of 28.6%. Longer time to remission (P = 0.004; hazard ratio, 1.846; 95% confidence interval, 1.216-2.798) was also observed in patients with lower dose. The serum thyroid hormone levels of TPP patients are lower than those of nTPP patients. Median/high dose of I is necessary to achieve rapid control of thyrotoxicosis.

Combined effects of perchlorate, thiocyanate, and iodine on thyroid function in the National Health and Nutrition Examination Survey 2007–08

Perchlorate, thiocyanate, and low iodine intake can all decrease iodide intake into the thyroid gland. This can reduce thyroid hormone production since iodide is a key component of thyroid hormone. Previous research has suggested that each of these factors alone may decrease thyroid hormone levels, but effect sizes are small. We hypothesized that people who have all three factors at the same time have substantially lower thyroid hormone levels than people who do not, and the effect of this combined exposure is substantially larger than the effects seen in analyses focused on only one factor at a time. Using data from the 2007–2008 National Health and Nutrition Examination Survey, subjects were categorized into exposure groups based on their urinary perchlorate, iodine, and thiocyanate concentrations, and mean serum thyroxine concentrations were compared between groups. Subjects with high perchlorate (n=1939) had thyroxine concentrations that were 5.0% lower (mean difference=0.40μg/dl, 95% confidence interval=0.14–0.65) than subjects with low perchlorate (n=2084). The individual effects of iodine and thiocyanate were even smaller. Subjects with high perchlorate, high thiocyanate, and low iodine combined (n=62) had thyroxine concentrations 12.9% lower (mean difference=1.07μg/dl, 95% confidence interval=0.55–1.59) than subjects with low perchlorate, low thiocyanate, and adequate iodine (n=376). Potential confounders had little impact on results. Overall, these results suggest that concomitant exposure to perchlorate, thiocyanate, and low iodine markedly reduces thyroxine production. This highlights the potential importance of examining the combined effects of multiple agents when evaluating the toxicity of thyroid-disrupting agents.