Thyroxin is the hormone that promotes growth of the brain and other body tissue. Hypothyroidism is the most common endocrine problem in children with Down syndrome. One study showed these individuals to be 28 times more prone to congenital hypothyroidism than the general population. It is estimated that approximately 10 percent of children with Down syndrome have congenital or acquired thyroid disease. Incidence of thyroid disease in adults with this genetic disorder varies from 13 to 50 percent.
Hypothyroidism can occur at any time from infancy through adulthood.
As the thyroid hormone affects normal development of the brain, testing of infants is particularly crucial. The thyroid hormone, thyroxin, is readily replaced through medication. In this case, the thyroid gland is overactive. Symptoms are swelling in the neck, abnormal sweating and rapid pulse rate. No evidence exists as to whether hyperthyroidism is more prevalent in individuals with Down syndrome than in the general population.