gland. However, recent studies have shown an increase in the number of cases caused by gland in situ (termed dyshormonogenesis when there is a defect in hormone production). A hypoplastic gland may develop higher in the neck or even in the back of the tongue. A gland in the wrong place is referred to as ectopic, and an ectopic gland at the base or back of the tongue is a lingual thyroid. Some of these cases of developmentally abnormal glands result from genetic defects, and some are "sporadic," with no identifiable cause. One Japanese study found a statistical correlation between certain organochlorine insecticides and dioxin-like chemicals in the milk of mothers who had given birth to infants with congenital hypothyroidism. Neonatal hypothyroidism has been reported in cases of infants exposed to lithium, a mood stabilizer used to treat bipolar disorder, in utero. In some instances, hypothyroidism detected by screening may be transient. One common cause of this is the presence of maternal antibodies that temporarily impair thyroid function for several weeks. The word "cretinism" is an old term for the state of mental and physical retardation resulting from untreated congenital hypothyroidism, usually due to iodine deficiency from birth because of low iodine levels in the soil and local food sources. The term, like so many other 19th century medical terms, acquired pejorative connotations as it became used in lay speech. It is now deprecated; ICD-10 uses "congenital iodine deficiency syndrome" with additional specifiers for the various types. Genetics Congenital hypothyroidism can also occur due to genetic defects of thyroxine or triiodothyronine synthesis within a structurally normal gland. Among specific defects are thyrotropin (TSH) resistance, iodine trapping defect, organification defect, thyroglobulin, and iodotyrosine deiodinase deficiency. In a small proportion of cases of congenital hypothyroidism, the defect is due to a deficiency of thyroid-stimulating hormone, either isolated or as part of congenital hypopituitarism. Genetic types of nongoitrous congenital hypothyroidism include: Nongoitrous congenital hypothyroidism has been described as the "most prevalent inborn endocrine disorder". Diagnosis In the developed world, nearly all cases of congenital hypothyroidism are detected by the newborn screening program. These are based on measurement of TSH or thyroxine (T4) on the second or third day of life (Heel prick). Evaluation If the TSH is high, or the T4 low, the infant's doctor and parents are called and a referral to a pediatric endocrinologist is recommended to confirm the diagnosis and