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Prevalence is estimated at around 1/28,000. Athyreosis and thyroid hypoplasia (see this term) combined account for one-third of cases of thyroid dysgenesis.

Clinical manifestations of athyreosis are often subtle or not present at birth, probably as a result of trans-placental passage of some maternal thyroid hormone. More specific symptoms and signs do not develop until several months of age. Common clinical features and signs include decreased activity and increased sleep, feeding difficulty and constipation, prolonged jaundice, myxedematous facies, large fontanels (especially posterior), macroglossia, a distended abdomen with umbilical hernia, and hypotonia. Goiter is always absent. Slow linear growth and developmental delay are usually apparent by 4-6 months of age.

Around 2% of cases have been shown to be familial and may be caused by mutations in the FOXE1, NKX2-1, NKX2-5 or PAX8 genes (9q22, 14q13, 5q34 and 2q12-q14). Mutations that result in complete inactivation of the TSHR gene (14q31) can present with athyreosis.

Imaging studies are required to confirm the diagnosis of athyreosis.

Athyreosis is generally thought to be sporadic. However, recent evidence points to the possibility of a genetic component.

Without treatment athyreosis results in severe intellectual deficit and short stature.