This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NEET Jan 2020, Subject name: Gynaecology & Obstetrics
13 yr old child visit OPD with complains of not attaining menarche with karyotype 46 XX. O/E there is clitromegaly, which enzyme is likely deficient? 
Select and explain. 
A. 17 alpha hydroxylase, B. 21 alpha hydroxylase, C. 11 alpha hydroxylase, D. 3 beta hydroxyteroid dehydrogenase
B: 21 alpha hydroxylase
Answer: B: 21 alpha hydroxylase 
Explanation: Above history point towards diagnosis of Congenital adrenal hyperplasia: - Due to deficiency of enzyme21-alpha Hydroxylase There is lack of coisol production resulting in excess of Adrenocoicotropic hormone (ACTH) production from pituitary. Features: - Enlarged clitoris Presence of penile urethra or hypospadias Associated metabolic abnormality -Salt wasting (hyponatremia, hyperkalemia) Fusion of Labia majora Lethargic hypoglycemic females. Investigations: - Karyotype is 46 XX Serum estimation Sex chromatin study reveals positive Barr body Sonographic evaluation