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Mild resistance to thyroid hormone with a truncated thyroid hormone receptor beta
M Taniyama1, S Kusano, Y Miyoshi
1Third Dept. of Internal Medicine, School of Medicine, Showa University (Tokyo), Japan.
Summary
A novel mutation in the thyroid hormone receptor beta (TR beta) gene was found in a patient with generalized resistance to thyroid hormone. This mutation resulted in mild resistance, challenging the idea that C-terminal truncations always cause severe symptoms.
Area of Science:
- Endocrinology
- Genetics
- Molecular Biology
Background:
- Mutations in the thyroid hormone receptor beta (TR beta) gene are a primary cause of generalized resistance to thyroid hormone (GRTH).
- Understanding the relationship between specific mutations and the severity of GRTH is crucial for diagnosis and management.
Observation:
- A 16-year-old male with GRTH and familial thyroxine binding globulin deficiency was identified.
- Genetic analysis revealed a novel nonsense mutation in codon 449 of the TR beta gene, leading to a truncated receptor protein lacking 13 amino acids at the C-terminus.
Findings:
- The patient exhibited mild GRTH, remaining eumetabolic despite elevated free thyroid hormone levels.
- Both the pituitary (thyrotrope) and peripheral tissues responded to triiodothyronine (T3) administration.
- This contrasts with previously reported cases of GRTH with C-terminal truncations (11-16 amino acids missing) that resulted in severe resistance.
Implications:
- The C-terminal truncation of the TR beta receptor does not uniformly correlate with the severity of resistance to thyroid hormone.
- This finding suggests that other factors may modulate the clinical phenotype of GRTH.
- Further research is needed to elucidate the mechanisms underlying variable resistance severity in GRTH.