<prompt> Commonest cause of hypothyroidism isDefective synthesis of thyroxineDefect of iodide transportDefect of the thyroglobulin synthesisThyroid dysgenesis  <response>: Thyroid dysgenesis 1872-73-Nelson 17th 481-Ghai 7thHYPOTHYROIDISM results from deficient production of thyroid hormone or a defect in thyroid hormone or a defect in thyroid hormonal receptor activity Someform of thyroid dysgenesis aplasia, hypoplasia or an ectopic gland is the most common cause of congenital hypothyroidism, accounting for 85 of cases, 10 are caused by an in bom error of thyroxine synthjesis and 5 are the result of transplacental maternal thyrotropin receptor blocking antibody. Pendred syndrome - congenital hypothyroidism with sensorineural deafness and goiter, also have a positive perchlorate discharge. Sodium L-thyroxine given orally is the treatment of choices side effects are - craniosynostosis and temperature problems pseudotumour cerebri Acquired hypothyroidism - is most commonly caused by auto immune destruction of thyroid as a part of Chronic lymphocytic thyroidits Hashimotos thyroiditis 