Familial hypothyroidism with autosomal dominant inheritance

Adherence to thyroid therapy and depressive status among patients with hypothyroidism in the northern of Jordan: A cross-sectional study

Hypothyroidism is a chronic and progressive medical condition that requires extreme adherence to medication in order to effectively manage the disease. The aim of this study was to examine patients' adherence to their thyroid therapy and their depressive status and their associated predictors. This is a cross-sectional study that was conducted between April and June 2023 using a sample of chronic hypothyroidism patients visiting the Jordan University of Science and Technology Health Center in Irbid, along with the Family Medicine and Endocrine clinic at King Abdullah University Hospital. The 8-item Morisky Medication Adherence Scale (MMAS-8) and Patient Health Questionnaire (PHQ)-2 were used to examine patients' adherence level and mental status. A total of 296 patients were involved in this study. Around 35.5% of the patients found to have high level of adherence. Around 27.4% of the patients demonstrated a low level of adherence. The mean PHQ-2 score for the study sample was 2.00 (SD: 1.7) out of 6. Using a cutoff point of 3, we identified that 29.7% of the patients are at risk of developing major depressive disorder. Patients aged 31 to 50 years and married patients were identified to have higher adherence level compared to other patients (P < .05). This study observed a notable low to moderate level of adherence among patients diagnosed with hypothyroidism in Jordan with regards to their prescribed therapeutic regimen. Furthermore, a significant part of the individuals had a susceptibility to the development of major depressive disorder.

The W520X mutation in the TSHR gene brings on subclinical hypothyroidism through an haploinsufficiency mechanism

BACKGROUND

TSHR is a G-protein-coupled seven transmembrane domain receptor that activates the two major signal transduction pathways: the Gαs/adenylate cyclase and the Gαq/11/phospholipase C pathways. Inactivating mutations in the TSHR gene have been demonstrated to be responsible for subclinical hypothyroidism, a disorder characterized by elevated serum TSH concentrations despite normal thyroid hormones levels.

AIM

We identified in a child a nonsense mutation (W520X) in the third transmembrane domain of the TSHR that causes the lack of the C-terminus portion of the receptor. The functional significance of this variation was assessed in vitro.

MATERIAL/SUBJECT AND METHODS

The W520X mutation was introduced into the pSVL vector containing the wild-type sequence of TSHR gene. Wild-type and mutated vectors were expressed in Chinese Hamster Ovary (CHO) cells, and cAMP, inositol phosphate (IP), immunofluorescence and FACS analyses were performed.

RESULTS

Transfection with pSVL-TSHR vector induced basal cAMP and IP production in the absence of TSH stimulation, indicating a constitutive activity for the TSHR. An impairment of receptor function was demonstrated by the observation that cells expressing the mutant TSHR exhibited a lower second messenger production with respect to the wild-type, despite a normal expression of the receptor at the cell surface.

CONCLUSIONS

The mechanism through which the W520X mutation exerts its effect is more likely haploinsufficiency rather than a dominant-negative effect. This could explain the phenotype of our patient, who has a hormonal pattern in the range of a mild subclinical hypothyroidism, without an overt disease phenotype.

Resistance to thyrotropin

Resistance to TSH is a syndrome of reduced sensitivity to a biologically active TSH molecule. Subjects have elevated TSH levels but no goiter. However, thyroid hormone concentration may vary from normal to very high, depending on the severity of the resistance. Individuals with very high TSH, low T4 and hypoplastic thyroid glands can be mistakenly diagnosed as having primary hypothyroidism due to a defective development of the thyroid gland. Those with normal or slightly decreased T4 can be misdiagnosed as having central hypothyroidism especially if their serum TSH concentration is only slightly elevated. Mutations in the TSH receptor (TSHr) gene have been reported in 16 families with homozygous or compound heterozygous inheritance. The mutant TSHrs show reduced or no function due to either altered ligand binding or defect in membrane targeting. Some individuals, heretozygous for a TSHr gene mutation can present mild resistance to TSH manifesting as euthyroidism with slight hyperthyrotropinemia. A larger proportion of families express the phenotype of resistance to TSH in the absence of a TSHr defect. In many the inheritance is dominant and the genetic cause has not been yet determined.

The hypothyroidism in an inbred kindred with congenital thyroid hormone and glucocorticoid deficiency is due to a mutation producing a truncated thyrotropin receptor

Growth and function of the thyroid and adrenal glands are maintained and controlled by thyrotropin (TSH) and adrenocorticotrophic hormone (ACTH), respectively. The action of these trophic hormones requires the presence of functional TSH and ACTH receptors. We describe a large inbred Bedouin kindred in which profound congenital hypothyroidism and hypoadrenocortisolism occurred alone or together in eight family members belonging to four nuclear families. The high serum TSH and ACTH levels in the presence of normal or hypoplastic thyroid glands and low glucocorticoid, but not mineralocorticoid concentrations, are characteristic of resistance to TSH and ACTH. Linkage analysis, using specific polymorphic markers, excluded the involvement of the ACTH receptor but not thyrotropin receptor (TSHR). A novel point mutation was identified in exon 10 of the TSHR that replaces the normal cytosine in nucleotide 2024 with a thymidine. As a result the normal arginine in codon 609 (CGA) is replaced with a stop codon (TGA). This mutation produces a truncated TSHR lacking the third intracellular and extracellular loops, the sixth and seventh transmembrane segments, and the intracytoplasmic tail. The presence of hypothyroidism did not affect the timing, severity, and manner of clinical manifestation of hypoadrenocortisolism.

Structural analysis of the thyrotropin receptor in four patients with congenital hypothyroidism due to thyroid hypoplasia

Sporadic congenital hypothyroidism is most commonly caused by developmental abnormalities of the thyroid gland. More rarely, it is due to defects in gene products involved in the regulation of the hypothalamic-pituitary-thyroid axis or thyroid hormone synthesis. Loss of function mutations in the thyrotropin (TSH) receptor have been shown to result in resistance to biologically active TSH. In complete resistance to TSH, the thyroid gland is hypoplastic and unable to synthesize and secrete sufficient amounts of thyroid hormones. In partial resistance, referred to as euthyroid hyperthyrotropinemia, the size of the gland and the thyroid hormone levels are normal at the expense of an elevated TSH. Four patients with sporadic congenital hypothyroidism and properly located hypoplastic thyroid glands were included in this study. Serum TSH concentrations were 150 mU/L or higher, serum thyroglobulin levels were within normal limits (6.1 to 8.2 ng/mL; normal range: 2.1 to 32 ng/mL), and thyroid autoantibodies were absent. The coding region of the TSHbeta subunit gene, the TSH receptor gene, and exons 8 and 9 of Gsalpha were analyzed by direct sequencing and found to be normal in all patients. One patient was heterozygous for a G to A transition in the TSHbeta gene resulting in a substitution of alanine by threonine at position -7 of the signal peptide. This substitution was also found in her euthyroid father. In addition, Southern analysis of the TSH receptor gene excluded major structural alterations. These findings support previous reports that indicate that TSH resistance is genetically heterogeneous. In addition to mutations in the TSH receptor or the Gsalpha genes, other genetic defects can lead to an identical phenotype. These observations also suggest that TSH receptor mutations might be a relatively rare cause of congenital thyroid hypoplasia.