It is generally known that untreated congenital thyroid deficiency1 is characterized by lack of statural growth and by marked retardation of dentition, sitting, walking and talking. Mental development is extremely slow, and there are sluggishness and absence of emotional response. Metabolism is markedly reduced; body temperature may be subnormal, and the appearance of carpal development is greatly delayed.
In 1934 we published a preliminary report2 on the influence of thyroid therapy on the mental development of a group of 21 children, 2 who had juvenile hypothyroidism and 19 cretins. At that time the following tentative conclusions were reached: 1. There is evidence that early recognition of the affliction and persistent treatment thereafter are the important factors in ultimate mental development. 2. Not all cretins, if treated, are predestined to a fixed low mental age. Some of them may reach a mental age of at least 12 years. 3.