Features of cystic fibrosis –a) Lung nornial at birthb) Abnormal sweat chloride testsc) Autosomal dominantd) Defect in Chromosome 11

**Core Concept**
Cystic fibrosis is a genetic disorder characterized by **autosomal recessive** inheritance, primarily affecting the respiratory, digestive, and reproductive systems due to mutations in the **CFTR gene**. It leads to the production of thick, sticky mucus that clogs the airways and traps bacteria, resulting in recurrent respiratory infections and lung damage. The **sweat chloride test** is a key diagnostic tool.

**Why the Correct Answer is Right**
The correct answer involves the understanding that cystic fibrosis is indeed characterized by abnormal sweat chloride tests, which is a diagnostic hallmark. The **CFTR gene**, located on **Chromosome 7**, not 11, encodes for a chloride channel, and its defect leads to the disease's manifestations. Lung function is typically normal at birth but deteriorates over time due to repeated infections and inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while lung function is normal at birth, this option does not encompass the full scope of cystic fibrosis features.
**Option C:** Incorrect because cystic fibrosis is **autosomal recessive**, not autosomal dominant.
**Option D:** Incorrect because the defect is in **Chromosome 7**, not Chromosome 11.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that cystic fibrosis patients often present with respiratory symptoms and malabsorption due to pancreatic insufficiency, and the **sweat chloride test** is crucial for diagnosis.

**Correct Answer:** B. abnormal sweat chloride tests