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
A 2-year-old child presented with diarrhoea and failure to thrive, Blood examination shows – Na = 122,K – 6. He is most probably suffering from – 
Select and explain. 
A. Banter syndrome, B. 21–α Hydroxylase deficiency, C. 11–β Hydroxylase deficiency, D. 17–a Hydroxylase deficiency
B: 21–α Hydroxylase deficiency
Answer: B: 21–α Hydroxylase deficiency 
Explanation: Na+ is 122 (hyponatremia). That means, there is salt losing enzyme deficiency, causing hyponatremia and hyperkalemia.
21 hydroxylase deficiency causes hyponatremia and hyperkalemia. 17α -hydroxylase and 11-β -( hydroxylase deficiency cause hypernatremia and hypokalemia.
Butter syndrome causes excessive loss of Na+, K+ and Cl causing severe hypokalemia and hyponatremia.