This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
The commonest cause of congenital hypothyroidism: September 2012 
Select and explain. 
A. Thyroid dysgenesis, B. Pendred syndrome, C. Defective iodine release, D. Deficiency of de-iodinase
A: Thyroid dysgenesis
Answer: A: Thyroid dysgenesis 
Explanation: 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