Q. A 2-year-old child is brought to the clinic by his parents with concerns of recurrent episodes of dehydration and difficulty in gaining weight despite a good appetite. The child has been experiencing episodes of vomiting and diarrhea, which have led to significant weight loss and muscle weakness. The child's medical history is significant for frequent urination and increased thirst. On physical examination, the child is found to have a low blood pressure, fast heart rate, weak reflexes, and a distended abdomen. Lab results reveal hypokalemia, hypercalciuria and metabolic alkalosis. Which of the following is the most likely diagnosis?