Which one is a hereditary disease?

Options

A. Cataract
B. Leprosy
C. Blindness
D. Phenylketonuria

Explanation

**Step-by-Step Solution:**

1. **Understanding Hereditary Diseases:**
- Hereditary diseases are genetic disorders that are passed down from parents to offspring through genes. They are often caused by mutations in specific genes.

2. **Analyzing the Options:**
- The question provides several options to identify which one is a hereditary disease.

3. **Option 1: Catarrhid**
- Catarrhid is described as a condition where the lens of the eye becomes opaque, leading to blindness. This condition is not hereditary; it is typically acquired and can be treated surgically.

4. **Option 2: Leprosy**
- Leprosy is caused by the bacterium Mycobacterium leprae. It is an infectious disease that occurs after birth and is not inherited genetically. Therefore, it is not a hereditary disease.

5. **Option 3: Blindness**
- Blindness can result from various causes, including environmental factors, injuries, or diseases, but it is not specifically a genetic disorder. Thus, it is not classified as a hereditary disease.

6. **Option 4: Phenylketonuria (PKU)**
- Phenylketonuria is a genetic disorder caused by a defect in the gene responsible for producing the enzyme phenylalanine hydroxylase. This condition leads to an accumulation of phenylalanine in the body, which can cause serious health issues if not managed. PKU is inherited in an autosomal recessive manner, meaning it is indeed a hereditary disease.

7. **Conclusion:**
- Among the options provided, the only hereditary disease is **Phenylketonuria (PKU)**.

**Final Answer: Phenylketonuria (PKU) is a hereditary disease.**

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