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Resistance to thyroid hormones. A disorder frequently confused with Graves' disease
Abstract:
Five patients from two unrelated families were found to have goiter and elevated serum concentrations of thyroxine (T4) and triiodothyronine (T3) without symptoms or signs of hyperthyroidism. All had measurable concentrations of thyroid stimulating hormone (TSH), and in four who were tested, there was an increase in TSH concentration following thyrotropin releasing hormone (TRH) administration. We believe these five patients have general resistance to the effects of thyroid hormones and need elevated concentrations of T4 and T3 to maintain a eumetabolic state. Study of nuclear T3 receptors from cultured fibroblasts of one patient disclosed a normal equilibrium association constant and a maximal binding capacity that was greater than normal control values. These findings suggest that thyroid hormone resistance in this patient is not due to a decrease in either the affinity or the number of specific nuclear T3 receptors. This disorder can easily be confused with Graves' disease and result in inappropriate treatment for hyperthyroidism, as was the case in three of our patients.
Insights
Patients with general resistance to thyroid hormone have elevated thyroid hormones without hyperthyroidism symptoms. This resistance is not due to issues with thyroid hormone receptors, preventing misdiagnosis and incorrect treatment.
Area of Science:
- Endocrinology
- Genetics
- Molecular Biology
Background:
- Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), regulate metabolism.
- Thyroid stimulating hormone (TSH) controls thyroid hormone production.
- Resistance to thyroid hormone (RTH) is a rare genetic disorder.
Observation:
- Five patients from two families presented with goiter and elevated serum T4 and T3 levels.
- Patients were euthyroid, lacking typical hyperthyroidism signs or symptoms.
- Thyroid stimulating hormone (TSH) levels were measurable, with some showing a TSH increase after TRH administration.
Findings:
- Patients exhibit general resistance to thyroid hormones, requiring higher hormone levels for a eumetabolic state.
- Nuclear T3 receptor analysis in one patient showed normal binding affinity but increased capacity.
- Thyroid hormone resistance in this case is not attributed to reduced receptor affinity or number.
Implications:
- This condition can be misdiagnosed as Graves' disease, leading to inappropriate hyperthyroidism treatment.
- Accurate diagnosis is crucial to avoid unnecessary and potentially harmful interventions.
- Understanding the molecular basis of RTH is vital for developing targeted therapies.