Girls are more often affected than boys. Hypothyroid infants often have a distinctive appearance with a puffy-appearing face, a dull look, and a large tongue that protrudes from the mouth, which is usually kept open. They usually develop this appearance as the disease progresses. They may have dry brittle hair, low hairline and jaundice . Feeding is poor and the infant may choke frequently.
Constipation is common.
Affected children do not cry much, but sleep excessively and are sluggish and inactive. Muscle tone is usually decreased. If untreated, hypothyroidism can lead to severe mental retardation and growth retardation. Development is delayed early on, often indicated by failure to meet normal milestones. The appearance of teeth may be delayed.