Most common cause of congenital hypothyroidism:
Ref: Nelson s Textbook of Pediatrics. 19th Edition, Page: 1895.Explanation:"Most cases of congenital hypothyroidism results from thyroid dysgenesis"(Ref: Nelson)Thyroid DysgenesisSome form of thyroid dysgenesis (aplasia, hypoplasia, or an ectopic gland) is the most common cause of congenital hypothyroidism, accounting for 80-85% of cases; 15% are caused by an inborn error of thyroxine synthesis (dyshormonogeneses). and 2% are the result of transplacental maternal thyrotropin-receptor blocking antibody (TRBAB).In about 33% of cases of dysgenesis, even sensitive radionuclide scans can find no remnants of thyroid tissue (aplasia).In the other 66%' of infants, rudiments of thyroid tissue are found in an ectopic location, anyw here from the base of the tongue (lingual thyroid) to the normal position in the neck (hypoplasia).The cause of thyroid dysgenesis is unknown in most cases.Thyroid dysgenesis occurs sporadically, but familial cases occasionally have been reported.The finding that thyroid developmental anomalies, such as thvroglossal duct cysts and hemiage- nesis. are present in 8-10% of lst-degree relatives of infants with thyroid dysgenesis supports an underlying genetic component.Causes of Congenital HypothyroidismDefect of fetal thyroid development (dysgenesis)AplasiaHypoplasiaEctopiaDefect in thyroid hormone synthesis (dyshormonogenesis)Iodide transport defect: mutation in sodium- iodide symporter geneThyroid organification, or coupling defect: mutation in thyroid peroxidase geneDefects in H202 generation: mutations in DUOXA2 maturation factor or DU0X2 geneThyroglobulin synthesis defect: mutation in thyroglobulin geneDeiodination defect: mutation in DEHAL1 geneTSH unresponsivenessGsa mutation (e.g.. type IA pseudohypopar-athyroidism)Mutation in TSH receptorDefect in thyroid hormone transport:Mutation in monocarboxylate transporter 8 (MCT8) geneIodine deficiency (endemic goiter)Maternal antibodies:Thyrotropin receptor-blocking antibody (TRBAb, also termed thvrotropin-binding inhibitor immunoglobulin)Maternal medicationsIodides, amiodaronePropylthiouracil, methimazoleRadioiodine
Thyroid dysgenesis
Dvshormonogenesis
Antithyroid antibodies
Maternal Hypothyroidism
Thyroid Gland