BACKGROUND

In the last couple of years, different genes that play major roles in embryonic thyroid development have been identified. Several mutations, e.g., NKX2.1, FOXE1 and PAX8, were identified in patients with congenital hypothyroidism due to thyroid dysgenesis. However, the pathophysiology of most cases of thyroid dysgenesis remains unknown. Due to the sporadic occurrence and discordance observed in monozygotic twins, a classic genetic hypothesis for thyroid dysgenesis is improbable.

METHODS

We present two pairs of monozygotic twins discordant for thyroid dysgenesis that exemplify these conceptual difficulties.

CONCLUSIONS

Identification of the epigenetic differences observed in monozygotic twins discordant for thyroid dysgenesis may be crucial in discovering the pathogenesis of thyroid dysgenesis.