Pendred’s syndrome is due to a defect in
**Core Concept**
Pendred's syndrome is a genetic disorder characterized by congenital bilateral sensorineural hearing loss and thyroid dyshormonogenesis. It is caused by mutations in the SLC26A4 gene, which encodes the pendrin protein. This protein plays a crucial role in the transport of iodide into the thyroid gland and chloride ions in the inner ear.
**Why the Correct Answer is Right**
Mutations in the SLC26A4 gene lead to the pendrin protein being truncated or misfolded, resulting in its defective function. This affects the transport of iodide into the thyroid gland, leading to hypothyroidism and goiter. In the inner ear, the defective pendrin protein impairs the endolymph production, causing a disturbance in the ion balance and leading to congenital bilateral sensorineural hearing loss. The SLC26A4 gene is specifically expressed in the thyroid gland and the inner ear, making it a key factor in the pathogenesis of Pendred's syndrome.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Pendred's syndrome is not caused by a defect in the SLC26A4 gene, but rather mutations in this gene are the underlying cause.
* **Option B:** This option is incorrect because Pendred's syndrome is not associated with a defect in the sodium-iodide symporter (NIS), which is a different protein involved in thyroid iodide uptake.
* **Option C:** This option is incorrect because Pendred's syndrome is not caused by a defect in the thyrotropin-releasing hormone (TRH) receptor, which is involved in the regulation of thyroid function.
**Clinical Pearl / High-Yield Fact**
Pendred's syndrome is an important cause of congenital hearing loss, and it is essential for clinicians to consider this diagnosis in patients with bilateral sensorineural hearing loss and thyroid dyshormonogenesis. A family history of hearing loss and thyroid problems can also suggest Pendred's syndrome.
**Correct Answer: D. SLC26A4 gene**