FOXE1 and thanatophoric dysplasia: However, the etiology of TD is still unclear but can be explained on a small scale by genetic mutations in 4 transcription factors (FOXE1 [5], NKX2.1 [6], PAX8 [7, 8], and NKX2.5 [9]) and at the thyrotrophin receptor [10], which are genes important in the development and normal function of the thyroid gland [11–13].