Cretinism: deficiency in TH during fetal development and early postnatal development.
It is irreversible and results in mental retardation, changes in neural mitosis, migration, connectivity, myelination. There are large-scale changes in brain morphology.
Displays short extremities, inactivity, puffy face, enlarged tongue, yellowish skin, slow heart rate, low body temperature.
Can be mitigated by early TH replacement during 1st 2 weeks of life.