TSH resistance revisited

A Novel TSH Receptor Gene Variant Associated with Non-Autoimmune Hyperthyrotropinemia: A Case Report

BACKGROUND

Resistance to TSH is defined as reduced sensitivity to normal, biologicallyactive TSH, and abnormally high levels of TSH are needed to achieve normal levels of thyroid hormones.

CASE PRESENTATION

A 15-year-old female patient, having been treated since childhood with levothyroxine for hyperthyrotropinemia was referred to our institution complaining of tachycardia after the levothyroxine therapy had been increased. Thyroid ultrasound features were normal, and thyroid antibodies were negative. The therapy was gradually tapered in light of the symptoms, although subclinical hypothyroidism was evident at thyroid function tests. First-degree relatives were tested for thyroid function, and the father was also found to have a previously-unknown subclinical hypothyroidism. The patient underwent genetic testing for TSH receptor (TSHR) gene mutations, which revealed a gene variant hitherto not described: p.C598R (c.1792T>C). The father was also tested and was found to carry the same mutation, while other first-degree relatives were wild-type for the TSHR gene. An in-silico analysis was performed, which revealed a loss-of-function phenotype corresponding to the described variant, suggesting a novel loss-of-function TSH receptor gene mutation.

CONCLUSION

In this case report, we present a novel loss-of-function gene mutation in the TSH receptor gene associated with a TSH resistance phenotype.

Analysis of risk factors for the development of type 2 diabetes mellitus complicated with Hashimoto's thyroiditis

AIMS

The purpose of this study is to elucidate the correlation between thyroid hormone, glycosylated hemoglobin (HbA1c), vitamin D and type 2 diabetes mellitus (T2DM) with Hashimoto's thyroiditis (HT), and to seek the independent predictors affecting disease development.

METHODS

The study included 44 T2DM with HT, 94 T2DM, and 112 healthy subjects. We investigated some laboratory factors like thyroid hormone and compared the levels. Independent predictors determination by logistic univariate regression analysis were analyzed. The diagnostic value of thyroid-stimulating hormone (TSH) and threshold concentration were determined by ROC curve.

RESULTS

In T2DM with HT group, levels of PTH, HbA1c were lower and levels of TSH were significantly higher, when compared with T2DM group. But there was no significant difference in vitamin D between these two groups. In both logistic univariate regression analysis and multiple logistic regression analysis, TSH, HbA1c were independent predictors for T2DM with HT. Based on the ROC curve, the best cut-off value of the TSH was 4 mIU/L (sensitivity 72.7%, specificity 94.6%, AUC = 0.832) for predicting T2DM with HT in T2DM patients.

CONCLUSIONS

TSH has increased risk for T2DM evolving into T2DM complicated with HT, so it is important to monitor the concentrations of TSH in patients with T2DM. Although vitamin D was not the independent predictor in T2DM with HT development, effect of vitamin D deficiency on the progress of diabetes and its complications should be taken into consideration.

Higher maternal thyroid resistance indices were associated with increased neonatal thyroid-stimulating hormone- analyses based on the Huizhou mother-infant cohort

OBJECTIVES

This study aimed to explore the relationship of maternal thyroid function and thyroid resistance parameters with neonatal thyroid-stimulating hormone (TSH).

METHODS

This work was a longitudinal study. Singleton pregnant women without a history of thyroid disorders were recruited in their first prenatal visit from October 2018 to June 2020. Maternal thyroid markers including TSH, free triiodothyronine (FT3), free thyroxine (FT4), and neonatal TSH were tested in the clinical laboratory of the hospital by electrochemiluminescence immunoassay. Thyroid resistance indices including Thyroid Feedback Quantile-based Index (TFQI), TSH index (TSHI), and thyrotroph T4 resistance index (TT4RI) were estimated in accordance with maternal FT4 and TSH levels. Multivariable linear and logistic regression was applied to explore the associations of maternal thyroid indices with infantile TSH level.

RESULTS

A total of 3,210 mothers and 2,991 newborns with valid TSH data were included for analysis. Multivariable linear regression indicated that maternal thyroid variables were significantly and positively associated with neonatal TSH levels with standardized coefficients of 0.085 for TSH, 0.102 for FT3, 0.100 for FT4, 0.076 for TSHI, 0.087 for TFQI, and 0.089 for TT4RI (all P < 0.001). Compared with the lowest quartile, the highest quartile of TSHI [odds ratio (OR) = 1.590, 95% CI: 0.928-2.724; P_trend = 0.025], TFQI (OR = 1.746, 95% CI: 1.005-3.034; P_trend = 0.016), and TT4RI (OR = 1.730, 95% CI: 1.021-2.934; P_trend = 0.030) were significantly associated with an increased risk of elevated neonatal TSH (>5 mIU/L) in a dose-response manner.

CONCLUSION

The longitudinal data demonstrated that maternal thyroid resistance indices and thyroid hormones in the first half of gestation were positively associated with neonatal TSH levels. The findings offered an additionally practical recommendation to improve the current screening algorithms for congenital hypothyroidism.

The Mysterious Universe of the TSH Receptor

The thyroid-stimulating hormone receptor (TSH-R) is predominantly expressed in the basolateral membrane of thyrocytes, where it stimulates almost every aspect of their metabolism. Several extrathyroidal locations of the receptor have been found including: the pituitary, the hypothalamus, and other areas of the central nervous system; the periorbital tissue; the skin; the kidney; the adrenal; the liver; the immune system cells; blood cells and vascular tissues; the adipose tissue; the cardiac and skeletal muscles, and the bone. Although the functionality of the receptor has been demonstrated in most of these tissues, its physiological importance is still a matter of debate. A contribution to several pathological processes is evident in some cases, as is the case of Grave's disease in its multiple presentations. Conversely, in the context of other thyroid abnormalities, the contribution of the TSH-R and its ligand is still a matter of debate. This article reviews the several different sites of expression of the TSH-R and its potential role in both physiological and pathological processes.

Mild Hypothyroidism in Childhood: Who, When, and How Should Be Treated?

Mild hypothyroidism, also known as subclinical hypothyroidism (SH), is biochemically defined as serum TSH levels above the upper limit of the reference range, in the presence of normal serum concentrations of total T4 and free T4 (FT4). In the neonatal period, mild hypothyroidism can be defined by the presence of a TSH value between 6 and 20 mIU/L and normal FT4 levels. After the neonatal period, SH can be defined mild if TSH ranges between 4.5 and 10 mIU/L. The management of mild hypothyroidism in childhood is challenging. The major concern is to establish whether this condition should always be considered an expression of mild thyroid dysfunction. Indeed, the effects of untreated mild hypothyroidism are still not completely defined. In the neonatal period, concern exists about neurocognitive outcome; in children, although there is no clear evidence of alterations in growth or neurocognitive development, subtle cardiovascular abnormalities have been documented. Therefore, there is still uncertainty about the need of treatment across all ages, and the management should be based on the age of the child, the etiology, and the degree of TSH elevation, as well as on other patient factors. This review updates current evidences on diagnosis and management of mild hypothyroidism in childhood.

Mild TSH resistance: Clinical and hormonal features in childhood and adulthood

OBJECTIVE

Mutations in TSH receptor (TSHR) are associated with TSH resistance, a genetic defect characterized by a heterogeneous phenotype ranging from severe hypothyroidism to subclinical hypothyroidism (SCH). We assessed the clinical and hormonal pattern of TSHR variants in a series of pediatric patients, and the long-term outcome of growth, biochemical measurements of metabolism, and neuropsychological functions in TSHR mutations carriers.

DESIGN

Observational, retrospective study.

PATIENTS

Thirty four children (age 7 days to 11 years) and 18 adult carriers of TSHR variants.

MEASUREMENTS

The TSHR gene was sequenced by PCR-amplified direct sequencing in 111 pediatric patients with slight to moderate elevation of TSH and normal FT4 levels. The study focused on the: auxological and biochemical parameters, thyroid ultrasound, bone age, bone mineral density (BMD), and intellectual outcome (IQ) were collected during the long follow-up (1-15 years).

RESULTS

Seventeen different TSHR variants (eight novel) were identified in 34 of the 111 pediatric patients, with a high prevalence of familial cases (27/34). Neonatal screening for congenital hypothyroidism was positive in half of the TSHR carriers. Growth, IQ, BMD, and biochemical parameters were normal in all subjects. Twenty patients received L-T4 replacement therapy, in all cases before genetic analysis. After re-evaluation, six patients resumed L-T4 therapy: they were compound heterozygous, or single heterozygous and with associated conditions at risk of thyroid impairment (SGA). No adults presented clinical features consistent with impaired thyroid function.

CONCLUSIONS

Children carriers of TSHR variants, regardless of L-T4 treatment, show regular growth and neuropsychological development, with no evident biochemical and US alterations.