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Giorgio Radetti Marienklinik, Bolzano, Italy

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Franco Rigon Department of Paediatrics, University of Padua, Padua, Italy

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Alessandro Salvatoni Department of Medicine and Surgery, University of Insubria, Varese, Italy

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Irene Campi Division of Endocrine and Metabolic Diseases and Laboratory of Endocrine and Metabolic Research, Istituto Auxologico Italiano, IRCCS, Milan, Italy

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Tiziana De Filippis Division of Endocrine and Metabolic Diseases and Laboratory of Endocrine and Metabolic Research, Istituto Auxologico Italiano, IRCCS, Milan, Italy

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Valentina Cirello Division of Endocrine and Metabolic Diseases and Laboratory of Endocrine and Metabolic Research, Istituto Auxologico Italiano, IRCCS, Milan, Italy

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Silvia Longhi Department of Paediatrics, Regional Hospital of Bolzano, Bolzano, Italy

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Fabiana Guizzardi Division of Endocrine and Metabolic Diseases and Laboratory of Endocrine and Metabolic Research, Istituto Auxologico Italiano, IRCCS, Milan, Italy

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Marco Bonomi Division of Endocrine and Metabolic Diseases and Laboratory of Endocrine and Metabolic Research, Istituto Auxologico Italiano, IRCCS, Milan, Italy
Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy

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Luca Persani Division of Endocrine and Metabolic Diseases and Laboratory of Endocrine and Metabolic Research, Istituto Auxologico Italiano, IRCCS, Milan, Italy
Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy

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Introduction

Patients with congenital hypothyroidism (CH) may transiently show a certain degree of pituitary resistance to levothyroxine (LT4) which, however, normalizes subsequently. However, in some individuals, thyroid-stimulating hormone (TSH) fails to normalize despite adequate LT4 treatment.

Methods

Nine patients with CH followed in three Academic Centre who developed over time resistance to thyroid hormones underwent extensive biochemical and genetic analyses. These latter were performed by Sanger sequence or targeted next-generation sequencing technique including a panel of candidate genes involved in thyroid hormone actions and congenital hypothyroidism (CH): THRA, THRB, DIO1, DIO2, SLC16A2, SECISBP2, DUOX2, DUOXA2, FOXE1, GLIS3, IYD, JAG1, NKX2-1, NKX2- 5, PAX8, SLC26A4, SLC5A5, TG, TPO, TSHR.

Results

All patients displayed a normal sensitivity to thyroid hormone (TH) in the first years of life but developed variable degrees of resistance to LT4 treatment at later stages. In all cases, TSH normalized only in the presence of high free thyroxine levels. Tri-iodothyronine suppression test followed by thyrotrophin-releasing hormone stimulation was performed in two cases and was compatible with central resistance to THs. This biochemical feature was present independently on the cause of CH, being observed either in patients with an ectopic (n = 2) or eutopic gland (n = 3) or in case of athyreosis (n = 1). None of the patients had genetic variants in genes involved in the regulation of TH actions, while in two cases, we found two double heterozygous missense variants in TSHR and GLIS3 or in DUOX2 and SLC26A4 genes, respectively.

Conclusions

We report CH patients who showed an acquired and unexplainable pituitary refractoriness to TH action.

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