Which of the following is not true about cystic fibrosis?
**Core Concept**
Cystic fibrosis (CF) is a genetic disorder caused by mutations in the CFTR gene, leading to abnormal chloride and sodium transport across epithelial cells, resulting in thickened mucus production and various systemic complications.
**Why the Correct Answer is Right**
CF primarily affects the respiratory, gastrointestinal, and reproductive systems. The defective CFTR protein leads to impaired chloride secretion, causing dehydration of mucus and its subsequent thickening. This results in chronic lung infections, malabsorption, and infertility in individuals with CF. The CFTR protein is a chloride channel that plays a crucial role in maintaining the balance of salt and water across epithelial cells.
**Why Each Wrong Option is Incorrect**
**Option A:** Cystic fibrosis is primarily caused by mutations in the CFTR gene. This is true, as most cases of CF are due to mutations in the CFTR gene on chromosome 7.
**Option B:** Cystic fibrosis is associated with thickened mucus production. This is true, as the defective CFTR protein leads to impaired chloride secretion, causing dehydration of mucus and its subsequent thickening.
**Option C:** Cystic fibrosis is not caused by a viral infection. This statement is true, as CF is a genetic disorder caused by mutations in the CFTR gene, not a result of a viral infection.
**Clinical Pearl / High-Yield Fact**
CF is the most common life-limiting autosomal recessive disorder in the Caucasian population, with a prevalence of approximately 1 in 2,500 births.
**Correct Answer: C. Cystic fibrosis is not caused by a viral infection. Cystic fibrosis is not caused by a viral infection.**