<prompt> The commonest cause of congenital hypothyroidism: September 2012Thyroid dysgenesisPendred syndromeDefective iodine releaseDeficiency of de-iodinase  <response>: Ans. A i.e. Thyroid dysgenesis Congenital hypothyroidism Large open posterior fontanelle, Absent social smile eyebrows, Growth retardation, Delayed pubey, Cold extremities, Large tongue, Prolongation of physiological jaundice Epiphyseal dysgenesis 