Maturation of human hypothalamic-pituitary-thyroid function and control

A strike to the head: Parallels between the pediatric and adult human and the rodent in traumatic brain injury

Traumatic brain injury (TBI) is a condition that occurs commonly in children from infancy through adolescence and is a global health concern. Pediatric TBI presents with a bimodal age distribution, with very young children (0-4 years) and adolescents (15-19 years) more commonly injured. Because children's brains are still developing, there is increased vulnerability to the effects of head trauma, which results in entirely different patterns of injury than in adults. Pediatric TBI has a profound and lasting impact on a child's development and quality of life, resulting in long-lasting consequences to physical, cognitive, and emotional development. Chronic issues like learning disabilities, behavioral problems, and emotional disturbances can develop. Early intervention and ongoing support are critical for minimizing these long-term deficits. Many animal models of TBI exist, and each varies significantly, displaying different characteristics of clinical TBI. The neurodevelopment differs in the rodent from the human in timing and effect, so TBI outcomes in the juvenile rodent can thus vary from the human child. The current review compares findings from preclinical TBI work in juvenile and adult rodents to clinical TBI research in pediatric and adult humans. We focus on the four brain regions most affected by TBI: the prefrontal cortex, corpus callosum, hippocampus, and hypothalamus. Each has its unique developmental projections and thus is impacted by TBI differently. This review aims to compare the healthy neurodevelopment of these four brain regions in humans to the developmental processes in rodents.

Analysis of Serum Free Thyroxine Concentrations in Healthy Term Neonates Underlines Need for Local and Laboratory-Specific Reference Interval: A Systematic Review and Meta-Analysis of Individual Participant Data

Background: Initial evaluation of the hypothalamus-pituitary-thyroid axis is done by measuring serum free thyroxine (fT4) and thyrotropin concentrations. For correct interpretation of these measurements, reliable age-specific reference intervals (RIs) are fundamental. Since neonatal fT4 RIs conforming to the Clinical and Laboratory Standards Institute guidelines are not available for all assays, we set out to create literature-based uniform age-specific neonatal fT4 RIs that may be used for every assay. Methods: For meta-analysis of individual participant fT4 concentrations, we systematically searched MEDLINE and Embase (search date December 6, 2023; PROSPERO registration CRD42016041871). We searched for studies reporting fT4 concentrations in healthy term newborns aged 2-27 days, born to mothers without thyroid disease in iodine-sufficient regions. Authors were invited to supply data. Due to standardization differences between assays, data could not be combined for meta-analysis directly, and we attempted to normalize the data using two distinct methods. Results: We obtained 4206 fT4 concentrations from 20 studies that used 13 different assays from 6 manufacturers. First, we set out to normalize fT4 data using the mean and standard deviation of (assay-specific) adult RIs. fT4 concentrations were transformed into Z-scores, assuming a normal distribution. Using a linear mixed-effects model (LMM), we still found a significant difference between fT4 concentration across studies (p < 0.001), after this normalization. As a second approach, we normalized the fT4 concentrations using data from a method/assay comparison study. We used the relationship between the Cobas assay and the other assays as a reference point to convert all values to Cobas values. However, this method also failed to produce consistent results, with significant differences between the normalized data (LMM p < 0.001). Conclusions: We conclude that our attempts at normalizing fT4 assay results were unsuccessful. Confounders related to our unsuccessful analysis may be assay related and/or biological. These findings have significant implications for patient care, since relying on RIs from literature may result in erroneous interpretation of results. Therefore, we strongly recommend to establish local RIs for accurate interpretation of serum fT4 concentrations in neonates.

Possible Association Between Thyroid Nodule Formation and Developmental Alterations in the Pituitary-Thyroid Hormone Axis in Children and Adolescents: The Fukushima Health Management Survey

Background: We previously found low thyrotropin (TSH) levels in children and adolescents with thyroid nodules, including papillary thyroid cancer, although it is generally accepted that high TSH levels are a risk factor for formation and growth of thyroid nodules in adults. To clarify the reasons for the discrepancy, we precisely analyzed the features of pituitary-thyroid hormone (TH) actions in children and adolescents with or without nodules at different ages. Methods: Among the 4955 participants who participated in a second screening by thyroid ultrasound examination in the Fukushima Health Management Survey, 721 and 2849 euthyroid participants aged 6-20 years without or with nodules, including thyroid cancer, were selected for evaluation of TH regulation. The responsivity of TSH to THs was assessed by two thyroid feedback quantile-based indices (T4FQI and T3FQI). Logistic regression analyses were conducted to calculate the odds ratios (ORs) of serum concentrations related to thyroid functions for positive thyroid nodules compared with negative nodules. Results: The feedback indices declined in a sex-specific manner with aging. In particular, T3FQI, the index for TSH response to free triiodothyronine (fT3), started to decline after ∼10 and 15 years of age in female and male participants, respectively. Compared with the absence of nodules, the age- and sex-adjusted ORs (confidence intervals) for logTSH, free thyroxine (fT4), fT3, T4FQI, T3FQI, and thyroglobulin levels were 0.586 (0.501-0.685), 1.036 (0.595-1.805), 1.059 (0.842-1.332), 0.569 (0.454-0.715), 0.564 (0.443-0.719), and 1.01 (1.005-1.014), respectively. Associations between the presence of nodules and either low logTSH or low feedback indices were observed in participants aged between 12 and 17 years among the total cohort. Conclusions: The relationships between the levels of TSH and THs changed in a sex-dependent manner in children and adolescents. The age-dependent shift in the pituitary-TH set point may be associated with age-dependent nodule formation during restricted periods of growth and maturation in both young female and male participants.

Research into the Association of Cadmium and Manganese Excretion with Thyroid Function and Behavioral Areas in Adolescents with Autism Spectrum Disorders

Thyroid dysfunction and toxic metal exposure have been linked to the increased risk of autism spectrum disorders (ASD); however, the relationship between those factors remains unclear. We aimed to evaluate the relationship between the serum level of hormones, namely thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), and urinary cadmium (U-Cd) and urinary manganese (U-Mn), in patients with ASD. The study group consisted of 129 adolescents with ASD, and the control group consisted of 86 healthy persons. Ion chromatography with spectrophotometric detection (IC-UV/ViS) was used to quantitatively determine Cd and Mn in all 24-h urine samples. These results indicate that severity of certain symptoms in autism is associated with thyroid function. Correlation analysis between Childhood Autism Rating Scale (CARS) results and the content of both U-Mn and U-Cd as well as fT3, fT4 and TSH values in ASD patients showed significantly positive correlation of CARS7 (visual reaction) with fT3 and fT4 and a negative correlation with TSH for the whole study group. In the group of adolescents over 14 years of age, it was also observed that CARS10 (anxiety reaction) negatively correlates with serum TSH levels, and among younger individuals, CARS9 (near receptor responsiveness, taste, smell) positively correlates with TSH.

Association between the use of allopurinol and risk of increased thyroid-stimulating hormone level

Allopurinol is the first-line agent for patients with gout, including those with moderate-to-severe chronic kidney disease. However, increased thyroid-stimulating hormone (TSH) levels are observed in patients with long-term allopurinol treatment. This large-scale, nested case-control, retrospective observational study analysed the association between allopurinol use and increased TSH levels. A common data model based on an electronic medical record database of 19,200,973 patients from seven hospitals between January 1997 and September 2020 was used. Individuals aged > 19 years in South Korea with at least one record of a blood TSH test were included. Data of 59,307 cases with TSH levels > 4.5 mIU/L and 236,508 controls matched for sex, age (± 5), and cohort registration date (± 30 days) were analysed. An association between the risk of increased TSH and allopurinol use in participants from five hospitals was observed. A meta-analysis (I² = 0) showed that the OR was 1.51 (95% confidence interval: 1.32-1.72) in both the fixed and random effects models. The allopurinol intake group demonstrated that increased TSH did not significantly affect free thyroxine and thyroxine levels. After the index date, some diseases were likely to occur in patients with subclinical hypothyroidism and hypothyroidism. Allopurinol administration may induce subclinical hypothyroidism.

Thyroid function and dysfunction in preterm infants-Challenges in evaluation, diagnosis and therapy

Thyroid hormone levels have a crucial role for optimal brain development from gestation through the first 2 postnatal years. However, thyroid hormones vary with gestational age, and their levels vary between term and preterm infants. Preterm newborns are prone to thyroid dysfunction which is now more frequently observed with the advances of neonatal care and improved survival of extremely premature infants. Thus, hypothyroxinaemia of prematurity associated with delayed TSH elevation is very common in low birth weight premature infants most likely due to the immaturity of the hypothalamic-pituitary thyroid axis. Furthermore, postnatal illness, medications and iodine status may contribute to the thyroid dysfunction or affect the interpretation of the thyroid function tests. Despite available guidelines, timing of screening and optimal treatment of thyroid dysfunction in premature infants remains controversial. Furthermore, it is unknown whether untreated thyroid dysfunction in premature babies affects neurodevelopmental outcome. In the vast majority of preterm infants, hypothyroxinaemia is transient; however, permanent hypothyroidism due to thyroid dysgenesis or enzyme defects might also occur. Therefore, careful monitoring of thyroid function and long-term follow-up is needed to assess an appropriate therapeutic approach. This article reviews thyroid physiology in preterm infants, the influences of gestation and other neonatal conditions on thyroid function tests, optimal timing of screening and possible predictors to differentiate transient hypothyroxinaemia from permanent hypothyroidism.

Delivery factors and neonatal thyroid hormone levels: a systematic review

Postnatal thyroid hormone changes enable the neonate to be adapted for postnatal life. Several factors can affect this adaption. In this review, we summarized the studies that reported the association among the delivery factors and neonatal thyroid hormones and thyroid stimulating hormone. A comprehensive literature search was performed in PubMed, Web of Science, and Scopus up to March 2020, to identify the studies investigating the relationship between delivery factors, especially the mode of delivery and labor pain, and neonatal thyroid hormones and TSH. Finally, in this review study, of 157 articles obtained in the initial search, 25 eligible studies were reviewed. Various maternal, fetal/neonatal, and obstetric factors affected neonatal TSH and thyroid hormones. Among various influencing factors, mode of delivery, labor pains, and duration of labor have a strong relationship with neonatal thyroid hormones and need to be considered for interpretation of neonatal thyroid status. The majority of the studies revealed that vaginal deliveries (instrumental or natural) lead to higher levels of cord TSH compared to elective cesarean section. This can be explained by the increased secretion of catecholamine during labor. It has been suggested that blood TSH and thyroid hormone levels are affected by perinatal stress events such as maternal anxiety, labor pains, fetal distress, and other stimulants of the catecholamine response. These changes may act as the trigger to increase thyroid hormone levels for adapting of neonates in the first hours after birth. This assumption needs to be re-evaluated by performing comprehensive and well-designed studies.

Transcriptomic Signature of Human Embryonic Thyroid Reveals Transition From Differentiation to Functional Maturation

The human thyroid gland acquires a differentiation program as early as weeks 3-4 of embryonic development. The onset of functional differentiation, which manifests by the appearance of colloid in thyroid follicles, takes place during gestation weeks 10-11. By 12-13 weeks functional differentiation is accomplished and the thyroid is capable of producing thyroid hormones although at a low level. During maturation, thyroid hormones yield increases and physiological mechanisms of thyroid hormone synthesis regulation are established. In the present work we traced the process of thyroid functional differentiation and maturation in the course of human development by performing transcriptomic analysis of human thyroids covering the period of gestation weeks 7-11 and comparing it to adult human thyroid. We obtained specific transcriptomic signatures of embryonic and adult human thyroids by comparing them to non-thyroid tissues from human embryos and adults. We defined a non-TSH (thyroid stimulating hormone) dependent transition from differentiation to maturation of thyroid. The study also sought to shed light on possible factors that could replace TSH, which is absent in this window of gestational age, to trigger transition to the emergence of thyroid function. We propose a list of possible genes that may also be involved in abnormalities in thyroid differentiation and/or maturation, hence leading to congenital hypothyroidism. To our knowledge, this study represent the first transcriptomic analysis of human embryonic thyroid and its comparison to adult thyroid.

Improving the Dutch Newborn Screening for Central Congenital Hypothyroidism by Using 95% Reference Intervals for Thyroxine-Binding Globulin

INTRODUCTION

Newborn screening (NBS) for congenital hypothyroidism (CH) in the Netherlands consists of thyroxine (T4), thyroid-stimulating hormone (TSH), and T4-binding globulin (TBG) measurements to detect thyroidal CH and central CH (CH-C). CH-C is detected by T4 or a calculated T4/TBG ratio, which serves as an indirect measure of free T4. TSH and TBG are only measured in the lowest 20 and 5% of daily T4 values, respectively. A recent evaluation of the Dutch NBS for CH showed that the T4 and T4/TBG ratio contribute to the detection of CH-C but also lead to a low positive predictive value (PPV). Dried blood spot (DBS) reference intervals (RIs) are currently unknown and may contribute to improvement of our NBS algorithm.

MATERIALS AND METHODS

RIs of T4, TSH, TBG, and the T4/TBG ratio were determined according to Clinical & Laboratory Standards Institute guidelines in heel puncture cards from routine NBS in both sexes and at the common NBS sampling ages. Scatter plots were used to compare the healthy reference population to previously published data of CH-C patients and false positives.

RESULTS

Analyses of 1,670 heel puncture cards showed small differences between subgroups and led to the formulation of total sample DBS RIs for T4 (56-118 nmol/L), TSH (<2.6 mIU/L), TBG (116-271 nmol/L), and the T4/TBG ratio (>20). 46% of false-positive referrals based on T4 alone had a TBG below the RI, indicating preventable referral due to partial TBG deficiency. One case of CH-C also had partial TBG deficiency (TBG 59 and T4 12 nmol/L blood).

DISCUSSION/CONCLUSION

Established DBS RIs provided possibilities to improve the PPV of the Dutch CH NBS algorithm. We conclude that by taking partial TBG deficiency into account, approximately half of T4 false-positive referrals may be prevented while maintaining NBS sensitivity at the current level.

Response of preterm infants with transient hypothyroxinaemia of prematurity to the thyrotropin-releasing hormone stimulation test is characterized by a delayed decrease in thyroid-stimulating hormone after the peak

OBJECTIVES

We evaluated the response to the thyrotropin-releasing hormone (TRH) stimulation test in very low-birth weight (VLBW) infants to elucidate the aetiology of transient hypothyroxinaemia of prematurity (THOP).

DESIGN AND METHODS

We performed TRH stimulation tests on 43 VLBW infants. Subjects were divided into two groups; a THOP group (N = 11; basal TSH < 15 mU/L and basal FT4 ≤ 0.8 ng/dL) and a non-THOP group (N = 32; basal TSH < 15 mU/L and basal FT4 > 0.8 ng/dL). Basal FT4 and FT3 were measured before, and TSH (0, 30, 60, 90, 120 and 180 minutes) was measured after, the administration of TRH (7 µg/kg). We calculated the ratio of TSH 180 minutes to THS 0 minute as the primary outcome. We also collected data on T3 and rT3 in this study.

RESULTS

In both groups, TSH 30 minutes values were the highest. However, the ratios of TSH 180 minutes to THS 0 minutes in the non-THOP group and the THOP group were (median [IQR]) 1.3 [1.0-1.7] and 3.0 [1.5-5.3] (P < .01). No significant differences were observed in T3 (1.0 [0.8-1.3] and 0.7 [0.4-0.7] ng/mL, P = .06). However, in the THOP group, rT3 was significantly lower than that of the non-THOP group (168.0 [148.1-197.0] and 92.9 [74.7-101.6] pg/mL, P < .01).

CONCLUSIONS

The delayed decrease in the TSH concentration after the peak for the TRH tests and decreased levels of rT3 suggest that the main aetiology for THOP is suppression at the level of the hypothalamus, but not inactivation of peripheral thyroid hormone metabolism.

Congenital Hypothyroidism

Congenital hypothyroidism (CH) is the commonest preventable cause of mental retardation in human species. It is so important for clinician to know its etiology epidemiology, clinical manifestation and treatment strategies. Since it is one of the rare serious diseases that should not be diagnosed clinically because late clinical features corresponds to advanced mental retardation, the neonatal screening detection is the best and preferable way of early diagnosis of this congenital disease. Confirmatory laboratory and radiological diagnostic tests should be performed immediately after the positive neonatal screening test. In order to prevent mental defects and to maintain long term clinical as well as biochemical euthyroidism in affected children its diagnosis approach, medical treatment and follow-up should be well established knowledge to all pediatricians during the childhood period and later on to general practitioners when these individuals grow up as adults. Congenital hypothyroidism is a potentially serious disease that we need to emphasize on early detection, using proper diagnostic tools and early and planned therapeutic approach.

Individualized Therapy for Hypothyroidism: Is T4 Enough for Everyone?

CONTEXT

It is well recognized that some hypothyroid patients on levothyroxine (LT4) remain symptomatic, but why patients are susceptible to this condition, why symptoms persist, and what is the role of combination therapy with LT4 and liothyronine (LT3), are questions that remain unclear. Here we explore evidence of abnormal thyroid hormone (TH) metabolism in LT4-treated patients, and offer a rationale for why some patients perceive LT4 therapy as a failure.

EVIDENCE ACQUISITION

This review is based on a collection of primary and review literature gathered from a PubMed search of "hypothyroidism," "levothyroxine," "liothyronine," and "desiccated thyroid extract," among other keywords. PubMed searches were supplemented by Google Scholar and the authors' prior knowledge of the subject.

EVIDENCE SYNTHESIS

In most LT4-treated patients, normalization of serum thyrotropin levels results in decreased serum T3/T4 ratio, with relatively lower serum T3 levels; in at least 15% of the cases, serum T3 levels are below normal. These changes can lead to a reduction in TH action, which would explain the slower rate of metabolism and elevated serum cholesterol levels. A small percentage of patients might also experience persistent symptoms of hypothyroidism, with impaired cognition and tiredness. We propose that such patients carry a key clinical factor, for example, specific genetic and/or immunologic makeup, that is well compensated while the thyroid function is normal but might become apparent when compounded with relatively lower serum T3 levels.

CONCLUSIONS

After excluding other explanations, physicians should openly discuss and consider therapy with LT4 and LT3 with those hypothyroid patients who have persistent symptoms or metabolic abnormalities despite normalization of serum thyrotropin level. New clinical trials focused on symptomatic patients, genetic makeup, and comorbidities, with the statistical power to identify differences between monotherapy and combination therapy, are needed.

Thyroid Function in Monozygotic Twins with Intra-twin Birth Weight Differences: A Prospective Longitudinal Cohort Study

OBJECTIVE

To analyze the long-term impact of birth weight (BW) on thyroid function in genetically identical twins with intra-twin BW differences from birth to adolescence.

STUDY DESIGN

In total, 52 monozygotic twin pairs underwent at least one analysis of thyroid function at mean ages of 10.1 years (27 pairs), 15.1 years (35 pairs), and 17.4 years (36 pairs); 18 pairs donated blood at all time points. BW difference of <1 SDS was defined as concordant, BW difference ≥1 SDS as discordant.

RESULTS

In concordant twins, no significant differences were observed. In the discordant group, smaller twins had higher mean thyroid-stimulating hormone (TSH) than their larger co-twins at 10.1 years (3.6 vs 2.5 μU/mL; P = .04) and 15.1 years (2.6 vs 2.2 μU/mL; P = .08). Smaller twins showed lower mean thyroxine than larger co-twins at 10.1 years (7.8 vs 8.2 μg/dL P = .05) and 17.4 years (7.7 vs 8.4 μg/dL; P = .03), and a tendency at 15.1 years (6.9 vs 7.4 μg/dL; P = .09). Calculation of TSH-thyroxine ratio revealed significant differences in the discordant group, with greater ratios in the smaller twin at 10.1 years (0.5 vs 0.3; P = .006) and 15.1 years (0.4 vs 0.3; P = .04).

CONCLUSIONS

In this group of monozygotic twins with intra-twin BW differences, BW seemed to exert a long-lasting impact on thyroid function. This may be due to a delay in hypothalamic-pituitary-thyroid axis maturation, with TSH resistance during childhood and early adolescence in children with low BW.

Thyroid-stimulating hormone is not the primary regulator of thyroid development in euthyroid children and adolescents living in an iodine-replete area

OBJECTIVES

It is known that there are multiple factors which can affect thyroid gland development during childhood and adolescence. Our aim was to investigate this issue by examining the relationships between age, sex, several anthropometric parameters, pubertal status, thyroid function tests, and iodine intake status with thyroid volume (TV) in children and adolescents.

STUDY DESIGN

This was a cross-sectional field study conducted in 11 representative cities and villages of Uzbekistan. Six hundred and ten children and adolescents participated. Anthropometric indices and TV were estimated. In addition, thyroid function tests (TFTs) and urinary iodine excretion (UIE) measures were obtained.

RESULTS

Median UIE was 151 μg/L, thus the studied areas were iodine-sufficient. TFTs fluctuated in both genders during childhood and adolescence and the thyroid growth spurt was observed, in both sexes, at the ages of 12 and 13 years, which coincided with the age of menarche in girls. Thyroid volume was positively correlated with body surface area (BSA) (r = 0.800, p < 0.001), age (r = 0.780, p < 0.001), fat-free mass (FFM) (r = 0.797, p < 0.001) and negatively correlated with serum TSH (r = -0.154, p = 0.05). No association between thyroid volume and UIE was observed.

CONCLUSIONS

In euthyroid children and adolescents living in iodine-replete areas, thyroid gland development appears to follow the pattern of linear growth and displays a growth spurt at the onset of puberty, probably due to the abrupt increase of circulating sex steroids. At this age, TSH does not appear to be the main regulator of thyroid gland development.

Polybrominated diphenyl ether (PBDE) exposures and thyroid hormones in children at age 3 years

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) reduce serum thyroid hormone concentrations in animal studies, but few studies have examined the impact of early-life PBDE exposures on thyroid hormone disruption in childhood.

METHODS

We used data from 162 mother-child pairs from the Health Outcomes and Measures of the Environment Study (2003-2006, Cincinnati, OH). We measured PBDEs in maternal serum at 16 ± 3 weeks gestation and in child serum at 1-3 years. Thyroid hormones were measured in serum at 3 years. We used multiple informant models to investigate associations between prenatal and early-life PBDE exposures and thyroid hormone levels at age 3 years.

RESULTS

Prenatal PBDEs were associated with decreased thyroid stimulating hormone (TSH) levels at age 3 years. A 10-fold increase in prenatal ∑PBDEs (BDE-28, -47, -99, -100, and -153) was associated with a 27.6% decrease (95% CI -40.8%, -11.3%) in TSH. A ten-fold increase in prenatal ∑PBDEs was associated with a 0.25 pg/mL (0.07, 0.43) increase in free triiodothyronine (FT3). Child sex modified associations between prenatal PBDEs and thyroid hormones, with significant decrements in TSH among females and decreased free T4 (FT4) in males. Prenatal ∑PBDEs were not associated with TT4, FT4, or total T3.

CONCLUSIONS

These findings suggest an inverse relationship between prenatal ∑PBDEs and TSH at 3 years. Associations may be sexually dimorphic, with an inverse relationship between prenatal BDE-47 and -99 and TSH in females and null associations among males.

Associations of early life urinary triclosan concentrations with maternal, neonatal, and child thyroid hormone levels

BACKGROUND

Triclosan, an antimicrobial agent used in some consumer products, reduces endogenous thyroid hormone concentrations in rodents. Despite ubiquitous triclosan exposure and the importance of thyroid hormones for normal fetal development, few human studies have examined the impact of triclosan exposure on maternal, neonatal, or child thyroid hormones.

METHODS

In the HOME Study, a prospective cohort from Cincinnati, OH, we measured urinary triclosan concentrations up to three times in pregnant women between 16weeks and delivery, and up to three times in children between age 1-3years. We quantified serum concentrations of thyroid stimulating hormone and total and free thyroxine and triiodothyronine in mothers at 16-weeks gestation (n=202), neonates at delivery (n=274), and children at age 3years (n=153). We estimated covariate-adjusted differences in thyroid hormones with a 10-fold increase in triclosan using linear regression and multiple informants models.

RESULTS

Triclosan was not associated with thyroid hormones during pregnancy. We observed a few associations of triclosan concentrations with thyroid hormone concentrations in neonates at delivery and children at age 3years. Higher gestational triclosan, particularly around the time of delivery, was associated with lower cord serum total thyroxine (β: 0.3μg/dL; 95% CI: -0.6, -0.0). Childhood triclosan, particularly at age 1year, was positively associated with total thyroxine at age 3years (β: 0.7μg/dL; 95% CI: 0.3, 1.2).

CONCLUSION

Our findings suggest that triclosan exposure may influence some features of neonatal and early child thyroid function. Given the large number of comparisons we made, these findings should be replicated in other cohorts.

Maternal hypothyroidism in the perinatal period and childhood asthma in the offspring

BACKGROUND

There is increasing interest in the possible link between maternal hypothyroidism in the perinatal period and childhood asthma risk. We explored this in this study while accounting for the timing of hypothyroidism diagnosis. Further, we evaluated whether the risk was moderated by thyroid hormone treatment during pregnancy.

METHODS

We conducted a population-based cohort study using Danish national registers. All live-born singletons in Denmark from 1998 to 2007 were identified. Maternal hypothyroidism and asthma in the children were defined by data from the Patient Register and Prescription Registry. We estimated incidence rate ratios (IRRs) of asthma among children born to hypothyroid mothers versus children born to mothers with no recorded thyroid dysfunction using Poisson regression models.

RESULTS

Of 595 669 children, 3524 children were born to mothers with hypothyroidism diagnosed before delivery and 4664 diagnosed after delivery. Overall, 48 990 children received treatment for asthma. The IRRs of asthma was 1.16 (95% confidence interval (CI): 1.03-1.30) and 1.12 (95% CI: 1.02-1.24) for children born to mothers with hypothyroidism diagnosed before and after delivery, compared to children born to mothers with no thyroid dysfunction. The highest risk was observed among children born to mothers with hypothyroidism diagnosed before delivery who did not receive thyroid hormone treatment during pregnancy (IRR=1.37, 95% CI: 1.04-1.80).

CONCLUSION

Our findings suggest that maternal hypothyroidism, especially when it is untreated, increases childhood asthma risk. Early detection and appropriate treatment of hypothyroidism in pregnant women may be an area for possible prevention of childhood asthma.

Current knowledge of transient hypothyroxinemia of prematurity: to treat or not to treat?

BACKGROUND

Thyroid hormones (THs) play a critical role in normal maturation of the developing brain in the fetus and infant. Continuing advances in neonatal medicine have contributed to an increased survival of extremely premature infants with neonatal morbidities. In these infants, thyroid system immaturities, as well as morbidity-related thyroid dysfunction, contribute to transient hypothyroxinemia of prematurity (THOP), which is characterized by very low total and free thyroxine and normal or low thyroid-stimulating hormone (TSH) levels.

REVIEW

Undoubtedly, low levels of THs with elevated TSH are associated with poor neurodevelopmental outcome. However, continuing debate exists regarding whether THOP is harmful to the developing brain. Moreover, no clear effects of TH treatment on neurodevelopmental outcome in preterm infants with THOP have been demonstrated. THs could have unpredictable effects if given unnecessarily.

CONCLUSION

The current recommendation is to treat THOP with TH only if THOP is accompanied with TSH elevation.

Relationship between thyroid hormone levels and transient tachypnea of the newborn in late-preterm, early-term, and term infants

PURPOSE

We aimed to investigate the association between thyroid hormone levels and transient tachypnea of the newborn (TTN) among late-preterm, early-term, and term infants admitted to neonatal intensive care unit (NICU).

MATERIALS AND METHOD

In the current retrospective study, neonates admitted to the NICU due to TTN were assigned to the TTN group (n = 404). Healthy neonates who were followed up in the well-baby nursery comprised the control group (n = 7335). Infants were grouped by gestational age into late-preterm (34-36⁶ weeks), early-term (37-38⁶ weeks), and term subgroups (39-41⁶ weeks). Serum levels of thyroid-stimulating hormone (TSH) and thyroxin (T₄) were determined from venipuncture samples taken at least 48 hours after birth. The relationship between thyroid hormone levels and the need for NICU admission for TTN was compared between groups.

RESULTS

Compared to control infants, term neonates with TTN had significantly higher TSH levels, whereas late-preterm and early-term neonates with TTN had significantly lower T₄ levels. Birth weight and mode of delivery had no effect on NICU admission for TTN.

CONCLUSIONS

Infants admitted to NICU due to TTN had significantly different thyroid hormone levels with differences depending on gestational age.

Thyroid hormone levels in late preterm, early term and term infants: a study with healthy neonates revealing reference values and factors affecting thyroid hormones

BACKGROUND

Thyroid function tests in neonates have been challenging to interpret because their levels are affected by several neonatal and delivery-related factors. The aim of the study was to evaluate reference values of thyroxine (T4) and thyrotropin (TSH) levels in different gestational age groups and to demonstrate the affect of perinatal factors on thyroid hormones.

METHODS

Medical records of 7616 neonates whose gestational age ranges between 34 and 42 weeks were analyzed retrospectively. Gender, mode of delivery, gestational age, postnatal age and birth weight were noted together with TSH and T4 levels.

RESULTS

Gestational age (r=0.14, p<0.001) and birth weight (r=0.12, p<0.001) had positive correlation with T4 levels, whereas they had no effect on TSH levels. Males had higher TSH and lower T4 levels (p=0.001 for both) compared with females. T4 levels of babies born via vaginal delivery were lower than the ones born via cesarean section (p=0.01). Multivariable analysis yielded gestational age as the only factor affecting T4 levels (p<0.001). T4 and TSH levels based on 2.5-97.5 percentile cutoffs according to gestational age were presented.

CONCLUSIONS

The thyroid hormone ranges given in this study can help pediatricians to interpret the thyroid hormone results with ease.

Early thyroxine treatment in Down syndrome and thyroid function later in life

OBJECTIVE

The hypothalamus-pituitary-thyroid (HPT) axis set point develops during the fetal period and first two years of life. We hypothesized that thyroxine treatment during these first two years, in the context of a randomized controlled trial (RCT) in children with Down syndrome, may have influenced the HPT axis set point and may also have influenced the development of Down syndrome-associated autoimmune thyroiditis.

METHODS

We included 123 children with Down syndrome 8.7 years after the end of an RCT comparing thyroxine treatment vs placebo and performed thyroid function tests and thyroid ultrasound. We analyzed TSH and FT4 concentrations in the subgroup of 71 children who were currently not on thyroid medication and had no evidence of autoimmune thyroiditis.

RESULTS

TSH concentrations did not differ, but FT4 was significantly higher in the thyroxine-treated group than that in the placebo group (14.1 vs 13.0 pmol/L; P = 0.02). There was an increase in anti-TPO positivity, from 1% at age 12 months to 6% at age 24 months and 25% at age 10.7 years with a greater percentage of children with anti-TPO positivity in the placebo group (32%) compared with the thyroxine-treated group (18.5%) (P = 0.12). Thyroid volume at age 10.7 years (mean: 3.4 mL; range: 0.5-7.5 mL) was significantly lower (P < 0.01) compared with reference values (5.5 mL; range: 3-9 mL) and was similar in the thyroxine and placebo group.

CONCLUSION

Thyroxine treatment during the first two years of life led to a mild increase in FT4 almost 9 years later on and may point to an interesting new mechanism influencing the maturing HPT axis set point. Furthermore, there was a trend toward less development of thyroid autoimmunity in the thyroxine treatment group, suggesting a protective effect of the early thyroxine treatment. Lastly, thyroid volume was low possibly reflecting Down-specific thyroid hypoplasia.

Biochemical Hyperthyroidism in a Newborn Baby Caused by Assay Interaction from Biotin Intake

We describe a case of biochemical neonatal thyrotoxicosis caused by biotin supplementation. Biotin may interact with thyroid function testing to imitate thyrotoxicosis with low thyroid-stimulating hormone and elevated triiodothyronine and thyroxine levels.

Neonatal Screening for Congenital Hypothyroidism with Focus on Developing an Indian Screening Programme

Neonatal screening for congenital hypothyroidism, along with eradication of iodine deficiency in large parts of the world, has made it possible to prevent the development of permanent neurological impairment due to thyroid hormone deficiency in the developing brain. The first successful screening programme was demonstrated in Canada in 1973 and since then it has been standard of care in most developed societies. In India there is no national programme for neonatal screening, and screening is only done in selected larger hospitals on newborns whose parents fund it. This review summarises the current understanding of the various strategies for newborn screening that could potentially be employed in India with resource constraints. Once a case is detected, the further evaluation and determination of etiology is summarised. Treatment and long term follow-up with levothyroxine replacement is also described in detail as per current understanding.

Maternal hyperthyroidism increases the susceptibility of rat adult offspring to cardiovascular disorders

Suboptimal intrauterine conditions as changed hormone levels during critical periods of the development are considered an insult and implicate in physiological adaptations which may result in pathological outcomes in later life. This study evaluated the effect of maternal hyperthyroidism (hyper) on cardiac function in adult offspring and the possible involvement of cardiac Renin-Angiotensin System (RAS) in this process. Wistar dams received orally thyroxin (12 mg/L) from gestational day 9 (GD9) until GD18. Adult offspring at postnatal day 90 (PND90) from hyper dams presented increased SBP evaluated by plethysmography and worse recovery after ischemia-reperfusion (I/R), as evidenced by decreased LVDP, +dP/dT and -dP/dT at 25 min of reperfusion and by increased infarct size. Increased cardiac Angiotensin I/II levels and AT1R in hyper offspring were verified. Herein, we provide evidences that maternal hyperthyroidism leads to altered expression of RAS components in adult offspring, which may be correlated with worse recovery of the cardiac performance after ischemic insults and hypertension.

Congenital hypothyroidism

Congenital hypothyroidism (CH) is the one of the most common preventable cause of mental retardation. In the majority of patients, CH is caused by an abnormal development of the thyroid gland (thyroid dysgenesis) that is a sporadic disorder and accounts for 85% of cases and the remaining 15% of cases are caused by dyshormonogenesis. The clinical features of congenital hypothyroidism are so subtle that many newborn infants remain undiagnosed at birth and delayed diagnosis leads to the most severe outcome of CH, mental retardation, emphasizing the importance of neonatal screening. Dried capillary blood is used for screening and it is taken from heel prick optimally between 2 and 5 days of age. Blood spot TSH or thyroxine (T4) or both are being used for CH screening in different programs around the world. Neonates with abnormal thyroid screening tests should be recalled immediately for examination and a venipuncture blood sample should be drawn for confirmatory serum testing. Confirmatory serum should be tested for TSH and free T4, or total T4. Serum TSH and T4 undergo dynamic changes in the first weeks of life; it is important to compare serum results with age-normal reference ranges. Treatment should be started promptly and infant should be rendered euthyroid as early as possible, as there is an inverse relationship between intelligence quotient (IQ) and the age at diagnosis. Levothyroxine (l-thyroxine) is the treatment of choice and American academy of pediatrics and European society of pediatric endocrinology recommend 10-15μgm/kg/day as initial dose. The immediate goal of therapy is to normalize T4 within 2 weeks and TSH within one month. The overall goal of treatment is to ensure growth and neurodevelopmental outcomes as close as possible to their genetic potential.

Altered thyroid hormone profile in offspring after exposure to high estradiol environment during the first trimester of pregnancy: a cross-sectional study

BACKGROUND

The increasing number of babies conceived by in vitro fertilization and embryo transfer (IVF-ET) shifts concern from pregnancy outcomes to long-time health of offspring. Maternal high estradiol (E2) is a major characteristic of IVF-ET and lasts throughout the first trimester of pregnancy. The fetal thyroid develops during this period and may thus be affected by exposure to the supra-physiological E2. The aim of this study is to investigate whether the high E2 maternal environment in the first trimester increases the risk of thyroid dysfunction in children born following IVF-ET.

METHODS

A cross-sectional survey design was used to carry out face-to-face interviews with consecutive children attending the hospital. A total of 949 singletons born after fresh embryo transfer (ET) (n=357), frozen ET (n=212), and natural conception (NC) (n=380), aged 3 to 10 years old, were included. All children were thoroughly examined. Meanwhile, another 183 newborns, including 55 fresh ET, 48 frozen ET, and 80 NC were studied. Levels of serum T3, FT3, T4, FT4, and TSH and levels of maternal E2 at different stages of the first trimester were examined.

RESULTS

The mean serum E2 levels of women undergoing fresh ET during the first trimester of pregnancy were significantly higher than those of the women undergoing frozen ET or following NC. The thyroid hormone profile, especially the levels of T4, FT4, and TSH, were significantly increased in 3- to 10-year-old children conceived by fresh ET compared to NC. The same tendency was confirmed in newborns. However, levels of T4 and TSH in the frozen ET group were nearer to that of the NC group. Furthermore, levels of T4 and FT4 in fresh ET were positively correlated with maternal serum levels of E2 during early pregnancy.

CONCLUSIONS

The maternal high E2 environment in the first trimester is correlated with increased risk of thyroid dysfunction. Frozen ET could reduce risks of thyroid damage in children conceived by IVF. Further studies are needed to confirm these findings and to better determine the underlying molecular mechanisms and clinical significance.

TRIAL REGISTRATION

ChicCTR-OCC-14004682 (22-05-2014).

Thyroid hormone does not induce maturation of embryonic chicken cardiomyocytes in vitro

Fetal cardiac growth in mammalian models occurs primarily by cell proliferation (hyperplasia). However, most cardiomyocytes lose the ability to proliferate close to term and heart growth continues by increasing cell size (hypertrophy). In mammals, the thyroid hormone triiodothyronine (T₃) is an important driver of this process. Chicken cardiomyocytes, however, keep their proliferating ability long after hatching but little information is available on the mechanisms controlling cell growth and myocyte maturation in the chicken heart. Our aim was to study the role of T₃ on proliferation and differentiation of embryonic chicken cardiomyocytes (ECCM), enzymatically isolated from 19‐day‐old embryos and to compare the effects to those of insulin‐like growth factor‐1 (IGF‐1) and phenylephrine (PE). Hyperplasia was measured using a proliferation assay (MTS) and hypertrophy/multinucleation was analyzed morphologically by phalloidin staining of F‐actin and nuclear staining with DAPI. We show that IGF‐1 induces a significant increase in ECCM proliferation (30%) which is absent with T₃ and PE. PE induced both hypertrophy (61%) and multinucleation (41%) but IGF‐1 or T₃ did not. In conclusion, we show that T₃ does not induce maturation or proliferation of cardiomyocytes, while IGF‐1 induces cardiomyocyte proliferation and PE induces maturation of cardiomyocytes.

Our main findings in the study show that T₃ does not affect proliferation or maturation of embryonic chicken cardiomyocytes (ECCMs). Furthermore, phenylephrine induces maturation of ECCMs and IGF‐1 act as a pro‐proliferative mediator.

Adrenal and thyroid function in the fetus and preterm infant

Adrenal and thyroid hormones are essential for the regulation of intrauterine homeostasis, and for the timely differentiation and maturation of fetal organs. These hormones play complex roles during fetal life, and are believed to underlie the cellular communication that coordinates maternal-fetal interactions. They serve to modulate the functional adaptation for extrauterine life during the perinatal period. The pathophysiology of systemic vasopressor-resistant hypotension is associated with low levels of circulating cortisol, a result of immaturity of hypothalamic-pituitary-adrenal axis in preterm infants under stress. Over the past few decades, studies in preterm infants have shown abnormal clinical findings that suggest adrenal or thyroid dysfunction, yet the criteria used to diagnose adrenal insufficiency in preterm infants continue to be arbitrary. In addition, although hypothyroidism is frequently observed in extremely low gestational age infants, the benefits of thyroid hormone replacement therapy remain controversial. Screening methods for congenital hypothyroidism or congenital adrenal hyperplasia in the preterm neonate are inconclusive. Thus, further understanding of fetal and perinatal adrenal and thyroid function will provide an insight into the management of adrenal and thyroid function in the preterm infant.

Pituitary tumors and pregnancy: the interplay between a pathologic condition and a physiologic status

Pregnancy is becoming a relatively common event in patients with pituitary tumors (PT), due to the increasing availability of medical treatments, which control pituitary diseases associated with the development of PT. However, the presence of PT and its treatment may be a disturbing factor for pregnancy, and pregnancy significantly influences the course and the management of PT. This review summarizes the knowledge about the management of PT during pregnancy and the occurrence of pregnancy in patients with pre-existent PT, focusing on secreting PT characterized by hormonal excess and on clinically non-functioning PT often associated to hormone deficiency, which configure the hypopituitaric syndrome.

Thyroid hormone concentrations in foals affected by perinatal asphyxia syndrome

The hypothalamus-pituitary-thyroid axis has specific functions, mostly related to metabolic activities, cell differentiation, and development. To the authors' knowledge, there are no studies about thyroid hormone (TH) concentrations in foals affected by perinatal asphyxia syndrome (PAS). Hence, the aims of the study are (1) to evaluate plasma TH concentrations (T3 and T4) in healthy foals during the first 7 days of life; (2) to evaluate plasma TH concentration (T3 and T4) in critically ill foals affected by PAS during the first 7 days of hospitalization; and (3) to compare TH concentrations between surviving and nonsurviving critically ill foals. Forty-five Standardbred foals were enrolled in this prospective observational study: 21 healthy foals (group 1) and 24 foals affected by PAS (group 2). Jugular blood samples were collected within 10 minutes from birth/admission and every 24 hours for 7 days (t0-t7). TH concentrations were analyzed by RIA. In both groups, T3 concentration was significantly lower at t4, t5, t6, and t7 compared with t1 (P < 0.05), and T4 concentration was significantly higher at birth than at all other time points (P < 0.01). No differences were found in TH concentrations at admission between surviving (n = 20) and nonsurviving (n = 4) foals. Statistical comparison between healthy and PAS foals divided into age groups showed significantly lower TH concentrations at t0 in PAS foals <12 hours old at admission (P < 0.01). In conclusion, PAS may cause lower T3 and T4 concentrations in affected foals than in age-matched healthy foals, as reported for other systemic illnesses, such as sepsis and prematurity. TH concentrations showed no prognostic value, which maybe due to the small number of nonsurviving foals in this study. Further studies are needed to find out if thyroid replacement therapy could be useful in the treatment of critically ill foals affected by PAS.

Fetal endocrinology

Successful outcome of pregnancy depends upon genetic, cellular, and hormonal interactions, which lead to implantation, placentation, embryonic, and fetal development, parturition and fetal adaptation to extrauterine life. The fetal endocrine system commences development early in gestation and plays a modulating role on the various physiological organ systems and prepares the fetus for life after birth. Our current article provides an overview of the current knowledge of several aspects of this vast field of fetal endocrinology and the role of endocrine system on transition to extrauterine life. We also provide an insight into fetal endocrine adaptations pertinent to various clinically important situations like placental insufficiency and maternal malnutrition.

Congenital hypothyroidism: Screening dilemma

Primary sporadic congenital hypothyroidism (CH) is the most common cause of hypothyroidism infancy early childhood in iodine sufficient region. Screening for neonatal CH began in 1970s. The rationale and reason for neonatal screening for CH (NSCH) are well established. It is mandatory in most developed countries along with the screen for metabolic disorder. The possibility of measuring TSH and thyroid hormones in cord blood paved the way for newborn screening (NS) for CH. Worldwide it is estimated that 25% of the live born population of 130 million babies undergo NSCH. Klein et al., by 1972 had shown improved CNS prognosis in CH treated by age 3 months. NSCH has largely eradicated the severe irreversible neurodevelopmental damage and reversed the chances of growth failure in infancy and early childhood.

Long term exposure to organochlorine pesticides and thyroid function in children from Cidade dos Meninos, Rio de Janeiro, Brazil

A pesticide factory in Cidade dos Meninos village, Duque de Caxias County, Rio de Janeiro, Brazil, ended its activity in 1961, leading to widespread contamination of the environment by several organochlorine pesticides. The aim of this study was to investigate the effects of chronic exposure to organochlorine pesticides on thyroid hormone levels in children residing in Cidade dos Meninos. In a population-based survey carried out between 2003 and 2004, serum concentration of 19 pesticides and levels of free thyroxine (T4), total triiodothyronine (T3) and thyroid-stimulating hormone (TSH) were determined in 193 children younger than 15 years old. Multivariate linear regression was conducted to examine thyroid hormone levels according to quintiles of organochlorine exposure, controlling for age, gender and serum lipid content. Free T4 and TSH levels were within reference values (0.7-1.8 ng/dl and 0.35-5.5 mU/l), whereas total T3 was above the reference range (80-180 ng/dl) in 28% of children. More than 60% of the children had detectable levels of most organochlorine pesticides. With the exception of heptachlor and methoxychlor, total T3 levels showed a significant increasing linear trend regardless of pesticide type to which children were exposed. Free T4 levels were positively and significantly associated only with exposure to p,p'-DDD, endosulfan 1, and dieldrin. No significant trend was found for TSH. Data showed that exposure of children to organochlorine pesticides produced a significant increase in serum total T3 concentrations. The clinical implications of such a total T3 elevation and subsequent development are uncertain and warrant the need for health monitoring of these children.

Simulation of post-thyroidectomy treatment alternatives for triiodothyronine or thyroxine replacement in pediatric thyroid cancer patients

BACKGROUND

As in adults, thyroidectomy in pediatric patients with differentiated thyroid cancer is often followed by (131)I remnant ablation. A standard protocol is to give normalizing oral thyroxine (T(4)) or triiodothyronine (T(3)) after surgery and then withdraw it for 2 to 6 weeks. Thyroid remnants or metastases are treated most effectively when serum thyrotropin (TSH) is high, but prolonged withdrawals should be avoided to minimize hypothyroid morbidity.

METHODS

A published feedback control system model of adult human thyroid hormone regulation was modified for children using pediatric T(4) kinetic data. The child model was developed from data for patients ranging from 3 to 9 years old. We simulated a range of T(4) and T(3) replacement protocols for children, exploring alternative regimens for minimizing the withdrawal period, while maintaining normal or suppressed TSH during replacement. The results are presented with the intent of providing a quantitative basis to guide further studies of pediatric treatment options. Replacement was simulated for up to 3 weeks post-thyroidectomy, followed by various withdrawal periods. T(4) vs. T(3) replacement, remnant size, dose size, and dose frequency were tested for effects on the time for TSH to reach 25 mU/L (withdrawal period).

RESULTS

For both T(3) and T(4) replacement, higher doses were associated with longer withdrawal periods. T(3) replacement yielded shorter withdrawal periods than T(4) replacement (up to 3.5 days versus 7-10 days). Higher than normal serum T(3) concentrations were required to normalize or suppress TSH during T(3) monotherapy, but not T(4) monotherapy. Larger remnant sizes resulted in longer withdrawal periods if T(4) replacement was used, but had little effect for T(3) replacement.

CONCLUSIONS

T(3) replacement yielded withdrawal periods about half those for T(4) replacement. Higher than normal hormone levels under T(3) monotherapy can be partially alleviated by more frequent, smaller doses (e.g., twice a day). LT(4) may be the preferred option for most children, given the convenience of single daily dosing and familiarity of pediatric endocrinologists with its administration. Remnant effects on withdrawal period highlight the importance of minimizing remnant size.

Congenital disorders of the thyroid: hypo/hyper

This article summarizes the ontogenesis and genetics of the thyroid with regards to its possible congenital dysfunction and briefly refers to the roles of the mother-placenta-fetal unit, iodine effect, and organic and functional changes of the negative feedback mechanism, as well as maturity and illness, in some forms of congenital hypo- and hyperthyroidism. This article also describes the published literature and the authors' data on the clinical aspects of congenital hypothyroidism, on the alternating hypo- and hyperthyroidism in the neonatal period, and on neonatal hyperthyroidism.

[Endocrinological abnormalities in 1,105 children and adolescents with Down syndrome]

BACKGROUND AND OBJECTIVE

Children and adolescents with Down syndrome (DS) show a greater prevalence of endocrinological abnormalities when compared with the general population. Our aim is to analyze endocrinological abnormalities in 1,105 patients with DS.

PATIENTS AND METHODS

A review of 1,105 cases of children and adolescents with DS under care in our Department (ages between 0 and 18 years) analyzed retrospectively the presence of thyroid pathology and diabetes mellitus throughout development.

RESULTS

Our data indicate the presence of endocrinological abnormalities in 222 patients [216 with thyroid pathology (19.5%) and 6 cases with diabetes mellitus type 1 (0.45%)]. Subclinical primary hypothyroidism was present in 168 cases, congenital primary hypothyroidism in 15 cases, clinical primary hypothyroidism in 24 cases and 5 cases had hyperthyroidism. In addition, 16.9% of these patients exhibit criteria of obesity and 28.2% had overweight. The prevalence of endocrinological comorbidities in children and adolescents with DS is higher than in the general population.

CONCLUSION

Subclinical primary hypothyroidism, due to autoimmune causes in most of the patients, without a higher incidence in females, is the most common endocrinological pathology associated with DS. The high frequency of thyroid pathology and diabetes mellitus type 1 in these patients should induce us to have a closer clinical control of children and adolescents with DS.

The measurement, definition, aetiology and clinical consequences of neonatal transient hypothyroxinaemia

This review focuses on neonatal transient hypothyroxinaemia, a condition characterized by temporary postnatal reductions in concentrations of Total T4 or Free T4, with normal or low concentrations of thyroid stimulating hormone (TSH). There is neither an agreed quantitative definition, nor an agreed mode of measurement for the condition. Transient hypothyroxinaemia is not routinely monitored yet it is thought to affect about 50% of preterm infants; it was thought to be without long-term sequelae but observational studies indicate that neurodevelopment may be compromised. The aetiology of transient hypothyroxinaemia is complex. There are significant contributions from the withdrawal of maternal-placental thyroxine transfer, hypothalamic-pituitary-thyroid immaturity, developmental constraints on the synthesis and peripheral metabolism of iodothyronines and iodine deficiency. It is not possible to distinguish clinically, or from laboratory measurements, whether transient hypothyroxinaemia is an independent condition or simply a consequence of non-thyroidal illness and/or drug usage. An answer to this question is important because studies of thyroid hormone replacement have been instigated, with mixed results. Until the aetiology of transient hypothyroxinaemia is better understood it would seem prudent not to routinely supplement preterm infants with thyroid hormones. Iodine deficiency, non-thyroidal illness and drug usage are the most modifiable risk factors for transient hypothyroxinaemia and are the clear choices for attempts at reducing its incidence. We suggest that transient hypothyroxinaemia in preterm infants is defined as a normal or low TSH concentration in conjunction with a concentration of Total T4, that is ≤10th percentile of cord Total T4 of the equivalent gestational age had the infant remained in utero.

Prevalence and functional significance of thyrotropin receptor blocking antibodies in children and adolescents with chronic lymphocytic thyroiditis

CONTEXT

TSH receptor (TSHR) blocking antibodies (Abs) inhibit TSH-induced thyroid growth and function in some adults with chronic lymphocytic thyroiditis (CLT), but their role in the pediatric age range is unknown.

OBJECTIVES

Our objectives were: 1) to determine the prevalence of TSHR blocking Abs in children and adolescents with CLT and 2) assess their functional significance both in vivo and in vitro.

DESIGN AND SETTING

This was a retrospective study in a referral outpatient setting.

PATIENTS

Sera from a total of 87 CLT patients and 33 controls were studied.

MAIN OUTCOME MEASURES

TSHR Abs were measured by both ELISA and bioassay.

RESULTS

Eight of 87 children and adolescents with CLT (9.2%), including one as young as 4 yr of age, had TSHR Abs in serum as measured by ELISA. The prevalence was significantly higher in individuals whose serum TSH concentration was 20 mU/liter or greater within 3 months of study than in less hypothyroid patients (eight of 45 vs. none of 42, P < 0.005). Conversely, TSHR Ab-positive patients were significantly more hypothyroid at diagnosis but only when the analysis was restricted to those with severe hypothyroidism was a decreased prevalence of goiter observed. IgG purified from TSHR Ab sera retained the TSH binding-inhibitory activity and TSHR Ab-positive sera inhibited TSH-induced stimulation of cAMP significantly more than normal.

CONCLUSIONS

TSHR-blocking Abs contribute significantly to the severity of the hypothyroidism in some children with CLT, but as compared with adults, they appear to play less of a role in determining the presence or absence of a goiter.

Congenital disorders of the thyroid: hypo/hyper

This article summarizes the ontogenesis and genetics of the thyroid with regards to its possible congenital dysfunction and briefly refers to the roles of the mother-placenta-fetal unit, iodine effect, and organic and functional changes of the negative feedback mechanism, as well as maturity and illness, in some forms of congenital hypo- and hyperthyroidism. This article also describes the published literature and the authors' data on the clinical aspects of congenital hypothyroidism, on the alternating hypo- and hyperthyroidism in the neonatal period, and on neonatal hyperthyroidism.

Thyroid system immaturities in very low birth weight premature infants

Continuing advances in the care of premature infants has contributed to the increased survival of very low birth weight premature infants. These infants are characterized by a variety of organ and physiological systems immaturities predisposing to deficiencies of postnatal adaptation and a high prevalence of neonatal morbidities. These morbidities have a major impact on postnatal mental and neurological outcomes. Thyroid hormones play a critical role in central nervous system development and function, and thyroid system immaturities as well as morbidity-related thyroid dysfunction (the nonthyroidal illness syndrome) contribute to the transient hypothyroxinemia of premature infants (THOP). Several studies have demonstrated a correlation of THOP with subsequent low IQ and neurologic sequelae in very low birth weight premature infants, and there is suggestive evidence that thyroid hormone supplementation in very low birth weight infants can improve mental outcome. Here, we review normal fetal thyroid system development and the system immaturities contributing to THOP and predisposing to nonthyroidal illness in very low birth weight infants.

Plasma amino-terminal pro C-type natriuretic Peptide in the neonate: relation to gestational age and postnatal linear growth

CONTEXT

C-type natriuretic peptide (CNP) plays an essential role in endochondral bone growth. Insight into CNP's paracrine actions is possible using plasma measurements of the amino-terminal pro C-type natriuretic peptide (NTproCNP). Whether correlations of NTproCNP with linear growth, as found in children and lambs, apply in neonates is unknown.

OBJECTIVES

Our objective was to determine the effects of prematurity, gender, and antenatal steroids on plasma NTproCNP at birth, and serial changes in hormone concentrations, linear growth, and markers of bone turnover in the first month of postnatal life.

DESIGN AND SETTING

This is a prospective study of newborn infants admitted to an intensive care unit.

SUBJECTS

A total of 48 infants (four gestation groups) were enrolled. Umbilical cord samples were also obtained from 39 healthy term infants.

MAIN OUTCOME MEASURES

Plasma NTproCNP and CNP were measured in cord plasma. In enrolled neonates, serial measurements of hormone concentrations and markers of bone turnover were related to tibial growth velocity as measured by knemometry.

RESULTS

Cord plasma NTproCNP was inversely related to gestational age (r = -0.35; P = 0.003) and was higher in males (P < 0.001). Plasma NTproCNP (P = 0.016) and CNP (P < 0.001) increased within the first week of life, the increase relating inversely to gestational age (r = -0.64; P < 0.001). Plasma NTproCNP at 1 wk was strongly correlated with linear growth velocity (r = 0.49; P < 0.001), and also at 2-4 wk, the relation being stronger than observed between bone turnover markers and growth velocity.

CONCLUSIONS

In neonates with diverse disorders affecting growth and nutrition, plasma NTproCNP was strongly correlated with linear growth during the first 4 wk of postnatal life and may prove to be a novel marker of growth plate activity in neonates.

Effects of maternal levels of thyroid hormone (TH) on the hypothalamus-pituitary-thyroid set point: studies in TH receptor beta knockout mice

A level of thyroid hormone (TH) in agreement with the tissue requirements is essential for vertebrate embryogenesis and fetal maturation. In this study we evaluate the immediate and long-term effects of incongruent intrauterine TH levels between mother and fetus using the TH receptor (TR) beta(-/-) knockout mouse as a model. We took advantage of the fact that the TRbeta(-/-) females have elevated serum TH but are not thyrotoxic due to resistance to TH. We used crosses between heterozygotes with wild-type phenotype (TRbeta(+/-)) males and TRbeta(-/-) females, with a hyperiodothyroninemic (high T(4) and T(3) levels) intrauterine environment (TH congruent with the TRbeta(-/-) fetus and excessive for the TRbeta(+/-) fetus), and reciprocal crosses between TRbeta(-/-) males and TRbeta(+/-) females, providing a euiodothyroninemic intrauterine environment. We found that TRbeta(-/-) dams had reduced litter sizes and pups with lower birth weight but preserved the mendelian TRbeta(-/-) to TRbeta(+/-) ratio at birth, indicating that the incongruous TH levels did not decrease intrauterine survival of a specific genotype. The results of studies in newborns demonstrate that TRbeta(+/-) pups born to TRbeta(-/-) dams have persistent suppression of serum TSH without a peak. On the other hand, TRbeta(-/-) pups born to TRbeta(+/-) dams have lower serum TSH at birth and a tendency to peak higher, compared with TRbeta(-/-) pups born to TRbeta(-/-) dams. The studies in the adult progeny demonstrate that TRbeta(+/-) mice born to TRbeta(-/-) dams and, thus, exposed to higher intrauterine TH levels, have greater resistance to TH at the level of the pituitary when stimulated with TRH. On the other hand, TRbeta(-/-) mice born to TRbeta(+/-) dams and, thus, deprived of TH in uterine life, were more sensitive to TH when similarly stimulated with TRH. Thus, TH exposure in utero has an effect on the regulatory set point of the hypothalamus-pituitary-thyroid axis, which can be seen early in life and persists into adulthood.

Serum free T4 and thyroid stimulating hormone levels in preterm infants and relationship between these levels and respiratory distress syndrome

BACKGROUND

There have been few studies of the thyroid stimulating hormone (TSH) surge in extremely low-birthweight (ELBW) infants, and the relationship between thyroid hormones and respiratory distress syndrome (RDS) has yet to be clarified. The present study sought to determine the serum levels of free T4 (fT4) and TSH in ELBW infants and to examine the relationship between these levels and the development of RDS.

METHODS

The authors measured serum fT4 and TSH levels soon after birth in 449 preterm infants, who were born at 22-36 weeks of gestation, and determined the associations between these levels, the incidence of RDS, and the recognized clinical factors associated with RDS.

RESULTS

Serum fT4 and TSH levels, and the fT4/TSH ratio, in the group at 22-24 weeks of gestation were significantly lower than those in the group at 28-36 weeks. The levels and ratio increased significantly with increasing gestational age. There were significant correlations between the serum fT4 level and the birthweight, Apgar score, and gender, and between the serum TSH level and the gestational age, mode of delivery, and birthweight. No significant relationship between the incidence of RDS and the serum levels of fT4 and TSH was observed.

CONCLUSION

The authors' results suggest that the serum levels of fT4 and TSH in ELBW infants are very low, and that these levels are not correlated with the occurrence of RDS.

Nutritional Epidemiology and Thyroid Hormone Metabolism

Severe iodine deficiency was the main cause of endemic goiter and cretinism. Most of the previously iodine-deficient areas are now supplemented, mainly with iodized salt. The geographical distribution of severe endemic areas has been progressively reduced, and at present, approximately 200 million people living in remote places are still at risk of severe iodine deficiency. International public health programs should be focused first on reaching these populations, and second on auditing and monitoring the operational work of supplementation programs. This second point is essential to prevent iodine-induced hyperthyroidism or interruptions of iodine supplement distribution, which could be catastrophic for the fetus and the young infant. Echography brings a complementary tool to clinical assessment of goiter by palpation. Inductively coupled plasma-mass spectrometry brings at least a definitive gold standard for iodine measurement and thyroid hormone measurement. Thiocyanate overload has been clearly documented as a goitrogen in Central Africa, and when associated with selenium deficiency, it may be included as risk factor for endemic myxedematous cretinism. Variable exposure to different environmental risk factors is likely the explanation of the variable distribution of two types of endemic cretinism (neurological and myxedematous), and the clinical overlap of the pathogeny of both syndromes is more important than previously described. It is possible that Kashin-Beck osteoarthropathy is another evanescent endemic disease that will disappear with the correction of iodine deficiency.

Thyroid dysfunction in the offspring of mothers with autoimmune thyroid diseases

An integrated three-compartment thyroid model exists during gestation: pregnancy influences thyroid function in several ways, the placenta plays an active role in TRH-thyroid and iodide transport and metabolism, and the fetus develops its own hypothalamic-pituitary-thyroid axis. This commentary reviews some basic and new data, especially in the maternal-offspring relationship in the case of maternal autoimmune thyroid diseases.

CONCLUSION

The careful control of maternal autoimmune thyroid disease is essential in order to avoid pathological changes in the offspring.