Severe Resistance to Thyroid Hormone Beta in a Patient with Athyreosis

Approach to the Patient With Raised Thyroid Hormones and Nonsuppressed TSH

Measurement of free thyroid hormones (THs) and thyrotropin (TSH) using automated immunoassays is central to the diagnosis of thyroid dysfunction. Using illustrative cases, we describe a diagnostic approach to discordant thyroid function tests, focusing on entities causing elevated free thyroxine and/or free triiodothyronine measurements with nonsuppressed TSH levels. Different types of analytical interference (eg, abnormal thyroid hormone binding proteins, antibodies to iodothyronines or TSH, heterophile antibodies, biotin) or disorders (eg, resistance to thyroid hormone β or α, monocarboxylate transporter 8 or selenoprotein deficiency, TSH-secreting pituitary tumor) that can cause this biochemical pattern will be considered. We show that a structured approach, combining clinical assessment with additional laboratory investigations to exclude assay artifact, followed by genetic testing or specialized imaging, can establish a correct diagnosis, potentially preventing unnecessary investigation or inappropriate therapy.

Concurrent THRB and DUOX2 variants in a patient detected via newborn screening for congenital hypothyroidism: a case of resistance to thyroid hormone

Most patients with resistance to thyroid hormone (RTH) test negative in newborn screening (NBS) for congenital hypothyroidism (CH). Here, we present a case of RTH diagnosed through NBS. The patient presented to us after her NBS for CH revealed high TSH (23.4 µIU/mL) and free T4 (FT4) (5.40 ng/dL) levels. Apart from tachycardia, she exhibited no other manifestations related to excess or deficiency of thyroid hormones. A confirmatory test replicated the findings, showing elevated serum TSH levels (35.7 µIU/mL) along with high FT4 levels (5.84 ng/dL). Ultrasonography showed marked thyroid gland enlargement (> +4 SD). Targeted next-generation sequencing of genes associated with genetic thyroid disorders revealed a previously reported THRB variant, p.Gly345Cys. Unexpectedly, two biallelic DUOX2 variants (p.His678Arg and p.Arg1334Trp) were also detected. At her last visit, no significant issues were observed with neurological development, growth, bone maturation, or gastrointestinal symptoms related to thyroid function at the age of 1 year, without treatment for RTH and CH. During follow-up, the TSH and FT4 levels gradually decreased. In conclusion, we report a patient with simultaneous RTH and DUOX2 defects, demonstrating the value of conducting a comprehensive analysis of multiple genes associated with thyroid diseases to better comprehend the pathogenesis in patients with atypical thyroid-related phenotypes.

Effect of the Fetal THRB Genotype on the Placenta

CONTEXT

Pregnant women with mutations in the thyroid hormone receptor beta (THRB) gene expose their fetuses to high thyroid hormone (TH) levels shown to be detrimental to a normal fetus (NlFe) but not to an affected fetus (AfFe). However, no information is available about differences in placental TH regulators.

OBJECTIVE

To investigate whether there are differences in placentas associated with a NlFe compared with an AfFe, we had the unique opportunity to study placentas from 2 pregnancies of the same woman with THRB mutation G307D. One placenta supported a NlFe while the other an AfFe.

METHODS

Sections of placentas were collected and frozen at -80 °C after term delivery of a NlFe and an AfFe. Two placentas from healthy women of similar gestational age were also obtained. The fetal origin of the placental tissues was established by gDNA quantitation of genes on the X and Y chromosomes and THRB gene. Expression and enzymatic activity of deiodinases 2 and 3 were measured. Expression of following genes was also quantitated: MCT10, MCT8, LAT1, LAT2, THRB, THRA.

RESULTS

The placenta carrying the AfFe exhibited a significant reduction of deiodinase 2 and 3 activities as well as the expression of the TH transporters MCT10, LAT1 and LAT2, and THRA.

CONCLUSION

We present the first study of the effect of the fetal THRB genotype on the placenta. Though limited by virtue of the rarity of THRB mutations and sample availability, we show that the fetal THRB genotype influences the levels of TH regulators in the placenta.

Resistance to Thyroid Hormone Beta in a Patient Born to a Mother With Undiagnosed Graves' Disease

Background/Objective

Graves' disease is an autoimmune disease associated with high levels of circulating thyroid hormones (THs). Resistance to thyroid hormone beta (RTHβ) caused by mutations in the thyroid hormone receptor beta (THRB) gene also can lead to high TH levels. Here, we describe 2 related cases, one of a woman with Graves' disease, and her newborn with RTHβ.

Case Report

The woman was 27 years of age, with free thyroxine (T4) (FT4) >7.7 ng/dL (0.8-1.8), triiodothyronine of 1350 ng/dL (90-180), and undetectable thyrotropin (TSH), but no symptoms of thyrotoxicosis. She also had thyroglobulin antibodies of 65 (2-38). She was treated with methimazole and atenolol. The newborn neonatal screen showed a TSH of 43 mU/L [upper limit of normal 20 mU/L] and total T4 of 21.8 μg/dL (upper limit of normal 15). At 6 days of age, the newborn had a FT4 of 12.3 ng/dL (0.9-2.3), and unsuppressed TSH. The infant, at 3.5 months of age, was identified to harbor a THRB mutation (R438H) inherited from her father, but the brothers and mother had no THRB mutation. The newborn had tachycardia and delayed growth and was treated with atenolol and supplemental feeding, resulting in weight gain and reduced heart rate.

Discussion

The perinatal high FT4 and tachycardia could have been influenced by the elevated TH levels of the mother and the fetal RTHβ.

Conclusion

It is difficult to evaluate the etiology of neonatal hyperthyroidism when fetal RTHβ and maternal Graves' disease are not diagnosed early at birth.

Primary hypothyroidism and quality of life

In the 1970s, treatment with thyroid extract was superseded by levothyroxine, a synthetic L form of tetraiodothyronine. Since then, no major innovation has emerged for the treatment of hypothyroidism. The biochemical definition of subclinical hypothyroidism is a matter of debate. Indiscriminate screening for hypothyroidism has led to overdiagnosis and treatment initiation at lower serum levels of thyroid-stimulating hormone (TSH) than previously. Adverse health effects have been documented in individuals with hypothyroidism or hyperthyroidism, and these adverse effects can affect health-related quality of life (QOL). Levothyroxine substitution improves, but does not always normalize, QOL, especially for individuals with mild hypothyroidism. However, neither studies combining levothyroxine and liothyronine (the synthetic form of tri-iodothyronine) nor the use of desiccated thyroid extract have shown robust improvements in patient satisfaction. Future studies should focus not only on a better understanding of an individual's TSH set point (the innate narrow physiological range of serum concentration of TSH in an individual, before the onset of hypothyroidism) and alternative thyroid hormone combinations and formulations, but also on autoimmunity and comorbidities unrelated to hypothyroidism as drivers of patient dissatisfaction. Attention to the long-term health consequences of hypothyroidism, beyond QOL, and the risks of overtreatment is imperative.