Q. A 24-month-old female is brought to the emergency department by her parents with a primary complaint of respiratory distress and failure to thrive. They report she has experienced recurrent respiratory infections since birth, wheezes constantly, and has a chronic, persistent cough with thick sputum production. Her stools are described as clay-colored, and reportedly float on top of the water. Upon review of her medical records, it is noted that she was a term delivery and required supplemental oxygen resuscitation secondary to a 5 minute APGAR score of 4. A recent sweat chloride test ordered by her pediatrician came back at 62 mmol/L. On physical examination, she appears frail and has labored breathing. She is 80 cm (31.5 inches) tall and weighs 9 kg (19.8 lb). Her temperature is 38.4 degrees Celsius (101.1degrees Fahrenheit), heart rate is 90/min, respiratory rate is 32/min, oxygen saturation is 91 percent on 2L of oxygen via nasal cannula, and blood pressure is 95/60 mm Hg. Ausculation of her chest demonstrates coarse crackles and expiratory wheezing throughout both lung fields with marked use of the accessory muscles. What is the most likely underlying genetic cause of her condition?