Sabrina is a toddler at a preparatory school. She is a good helper and loves to share with the other children in class. A few months ago, Sabrina developed a persistent cough that has worsened over time. She has also had trouble breathing over the past week or so. Although she loves to eat fruits and vegetables, her mother has noticed that she has been passing very greasy stools when she has her bowel movements. Her parents have also noticed that over the past 6-8 months, Sabrina has not gained much weight. Since birth, she has gained weight at a very slow pace compared to other children her age. They attributed her slow weight gain to their family’s naturally thin frames and Sabrina’s recent enrollment in ballet. Her parents decided it was time she see a doctor and made an appointment with the family physician. The doctor asked her a number of questions about the family’s health history and daily habits. The doctor decided it was necessary to take a biopsy of the cells that line the bronchus (passageway to the lungs). After several days, the biopsy report has come back along with a micrograph of the bronchial cells. Sabrina's cells are producing a very thick mucus.