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A common feature of cystic fibrosis in a child is the increased viscosity of mucus. This condition is caused by a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which results in the production of thick and sticky mucus in various organs, particularly the lungs and pancreas. This excessive mucus can obstruct airways, lead to recurrent respiratory infections, and interfere with normal pancreatic function, ultimately affecting digestion and nutrient absorption.

The presence of thick mucus obstructs airways, making it difficult for children with cystic fibrosis to clear secretions, which can lead to chronic lung issues and reduced respiratory function. Each mucus-obstructed airway can become a breeding ground for bacteria, resulting in frequent infections that can further hinder respiratory health.

While failure to gain weight can be associated with cystic fibrosis due to malabsorption from pancreatic issues, it is primarily the increased viscosity of mucus that defines the pathophysiology of the disease. Absence of liver enzymes is not characteristic of cystic fibrosis; instead, liver dysfunction can occur due to biliary obstructions. Muscle weakness is not specifically linked to cystic fibrosis, as the condition primarily affects the lungs and digestive system. Thus, the increased viscosity of mucus is a hallmark of cyst