Congenital iodine deficiency syndrome is a disease marked by arrested physical and mental development and thyroid dysfunction, caused by a deficiency of iodine. It may (more rarely) occur as hypothyroidism, often associated with dwarfism in an individual, in areas with high intake of cassava (myxedematous or classical cretinism). The nervous or neurological type of congenital iodine deficiency more commonly occurs, which is caused by nutritional deficiency of iodine as a foetus and/or during early childhood, and is preventable by dietary iodine supplements. Unlike hypothroidism, the neurological form of congenital iodine deficiency cannot be reversed by the administration of thyroid hormones.
People who have congenital iodine deficiencies have physical deformities as well as impaired metabolism and low body temperature. Poor hearing is marked and permanent (often manifest as deaf mutism), and intellectual disability is often severe. Other characteristics of people with congenital iodine deficiency syndrome can be slow movement, sleepiness, and the halting of speech; the acquisition of knowledge and skills is a difficult and time-consuming process. The height of people who have congenital iodine deficiency syndrome is well below average (146.7 cm for males and 140 cm for females).
The major cause of congenital iodine deficiency is foetal iodine deficiency. It is widely prevalent in populations living in severely iodine-deficient areas in India, China and Indonesia, where it affects up to 10% of the population. In 1996 in China, 10 million cases of intellectual disability were ascribed to congenital iodine deficiency. Other places where congenital iodine deficiency occurs is Zaire (mainly myxedematous type), Papua New Guinea, and the Andean region of South America (Ecuador, Peru, Bolivia and Argentina). In Zaire, rates of 10% of chemical hypothyroidism have been found among neonates.