Which of the following is a condition in which macroglossia is commonly seen?

Macroglossia, which is an abnormal enlargement of the tongue, is most commonly associated with Down's syndrome. In individuals with Down's syndrome, macroglossia can occur due to genetic and developmental factors associated with the condition. The enlarged tongue can affect speech, eating, and oral hygiene, which are important aspects to consider in the management of patients with Down's syndrome.

This condition is not typically associated with the other options provided. For instance, while Cushing's syndrome may present with various other symptoms related to hormone imbalance, macroglossia is not a characteristic feature. Similarly, pernicious anemia primarily affects the absorption of vitamin B12 and presents with anemia and neurological symptoms, but it does not commonly lead to macroglossia. Thyroid disorders may influence various bodily systems and impact oral health but do not specifically result in an enlarged tongue. Thus, Down's syndrome is the primary condition where macroglossia is notably observed.