Most common cause of Mobius syndrome is by use of which of the following drug in pregnancy ?
**Core Concept**
Mobius syndrome is a rare neurological disorder characterized by facial paralysis and abducens nerve palsy, leading to impaired eye movement and facial expression. The etiology of Mobius syndrome is multifactorial, with both genetic and environmental factors contributing to its development.
**Why the Correct Answer is Right**
The use of **valproic acid** during pregnancy has been associated with an increased risk of Mobius syndrome in the developing fetus. Valproic acid is a teratogenic antiepileptic medication that can disrupt fetal neural development, leading to abnormalities in cranial nerve function, including the sixth (abducens) and seventh (facial) cranial nerves.
**Why Each Wrong Option is Incorrect**
* **Option A:** **Phenytoin** is another antiepileptic medication, but it is not typically associated with Mobius syndrome. Although phenytoin can cause fetal abnormalities, such as cleft palate and cardiac defects, it is not the primary cause of Mobius syndrome.
* **Option B:** **Lithium** is a mood stabilizer used in the treatment of bipolar disorder, but it is not commonly linked to Mobius syndrome. Lithium can cause cardiac malformations and thyroid dysfunction in the fetus, but it is not the primary cause of this condition.
* **Option C:** **Tetracycline** is an antibiotic that can cause dental staining and inhibit bone growth in the fetus, but it is not associated with Mobius syndrome.
**Clinical Pearl / High-Yield Fact**
Valproic acid is a teratogenic medication that can cause a range of fetal abnormalities, including neural tube defects, cardiac malformations, and cranial nerve dysfunction.
**Correct Answer:** C. Tetracycline