CONGENITAL HYPOTHYROIDISM - A NEWBORN SCREENING SUCCESS STORY

Congenital hypothyroidism, present in 1:4000 newborns, is one of the m ost common preventable causes of mental retardation. Screening program s, now routine in all 50 states, Canada, and most of the developed wor ld, have been immensely successful in detection and early treatment of affected infants, Diagnostic studies show thyroid dysgenesis to be th e most common etiology worldwide, with ectopic glands accounting for t he majority of dysgenetic cases. Other etiologies include hereditary d efects in thyroxine synthesis, hypopituitary hypothyroidism, and trans placental passage of maternal thyrotropin receptor blocking antibodies ; the latter condition is usually associated with transient hypothyroi dism. Many programs report good psychometric outcomes, with IQs simila r to control groups. Some, however, report slightly lower IQs, particu larly in the most severely affected infants. These IR differences may result from the effects of fetal hypothyroidism, neonatal hypothyroidi sm that occurs between delivery and the restoration of euthyroid ism w ith therapy, or suboptimal treatment in the first 2 years of life. Stu dies show that approximately one-third of maternal thyroid hormone cro sses the placenta and may partially protect the hypothyroid fetus, It is therefore important that hypothyroid women are treated optimally du ring pregnancy. It is equally important that treatment of the newborn raise the serum T-4 > 10 mu g/dL as rapidly as possible, using a start ing dose of 10-15 mcg/kg/day. Careful monitoring to assure proper dosi ng and compliance in the first 2 years is also important to neurologic outcome. The future may include screening of women of child bearing a ge for hypothyroidism and some way to screen and treat the hypothyroid fetus.