Congenital hypothyroidism (CH) is the most common congenital endocrine disorder in childhood and is one of the most common preventable causes of mental retardation. In majority of patients, CH is caused by an abnormal development of the thyroid gland (thyroid dysgenesis) that is a sporadic disorder and accounts for 85% of cases and the remaining 15% of cases are caused by dyshormonogenesis.
The clinical features of congenital hypothyroidism are so subtle that many newborn infants remain undiagnosed at birth and delayed diagnosis leads to the most severe outcome of CH, mental retardation, emphasizing the importance of neonatal screening.
The overall incidence of CH ranges from 1 in 3000 to 1 in 4000 newborn infants. The incidence of CH is higher in Hispanic and Asian individuals and lower in black individuals. There is a 2:1 greater incidence in females compared with males and there is an increased risk in infants with Down’s syndrome.