# Identification of a novel THRB mutation causing thyroid hormone resistance syndrome

## TL;DR

A new mutation in the THRB gene is identified in a patient with thyroid hormone resistance syndrome, a rare disorder often misdiagnosed as hyperthyroidism.

## Contribution

The discovery of a novel THRB mutation (c.938T>C: p.M313T) not previously reported in the literature.

## Key findings

- A 57-year-old male with elevated thyroid hormone levels and normal TSH was found to have a novel THRB mutation.
- The THRB mutation c.938T>C: p.M313T is a previously unreported cause of resistance to thyroid hormone syndrome.
- Accurate diagnosis of RTHS is essential to avoid mismanagement as hyperthyroidism.

## Abstract

Resistance to thyroid hormone syndrome (RTHS) is a rare disorder caused by
mutations in the thyroid hormone receptor beta (THRB) gene,
resulting in impaired action of thyroid hormones on target tissues and organs.
We report a case of a 57-year-old Chinese male who presented with palpitations
and hand tremors. Laboratory tests revealed elevated serum thyroid hormone
levels, while serum thyroid-stimulating hormone (TSH) levels remained within the
normal range. Enhanced magnetic resonance imaging of the pituitary gland showed
no abnormalities. Through genetic testing, we identified a rare heterozygous
point mutation in the THRB gene, specifically c.938T>C:
p.M313T. To the best of our knowledge, this mutation site has not been
previously reported in the literature. Clinically, RTHS is often misdiagnosed as
hyperthyroidism, leading to inappropriate treatment and potential exacerbation
of thyroid hormone resistance. Therefore, accurate diagnosis of this condition
is crucial. Given the rarity of RTHS, we hope that this case report will enhance
the understanding of its clinical manifestations and management, particularly in
patients with THRB gene mutations.