Which of the following is not an autoimmune disorder?

Options

A. Myasthenia gravis
B. Rheumatoid arthritis
C. Hashimoto's disease
D. Down's syndrome

Answer

To determine which of the following is not an autoimmune disorder, we will analyze each option provided in the question step by step.

### Step 1: Understand Autoimmune Disorders
Autoimmune disorders occur when the immune system mistakenly attacks the body's own tissues. This can lead to various diseases affecting different organs or systems in the body.

### Step 2: Analyze Each Option
1. **Myasthenia Gravis**: This is a neuromuscular disorder characterized by weakness in the skeletal muscles. It is caused by an autoimmune response where the immune system attacks the communication between nerves and muscles. Therefore, Myasthenia Gravis is an autoimmune disorder.

2. **Rheumatoid Arthritis**: This is an inflammatory autoimmune disease that primarily affects the joints. The immune system attacks the synovium (the lining of the membranes that surround the joints), leading to inflammation and pain. Thus, Rheumatoid Arthritis is also an autoimmune disorder.

3. **Hashimoto's Disease**: This is an autoimmune disorder that affects the thyroid gland, leading to hypothyroidism. The immune system attacks the thyroid, causing it to become underactive. Therefore, Hashimoto's Disease is an autoimmune disorder.

4. **Down's Syndrome**: This is a genetic disorder caused by the presence of an extra full or partial copy of chromosome 21. It is not caused by an autoimmune response but rather by abnormal cell division during the formation of reproductive cells. Therefore, Down's Syndrome is not an autoimmune disorder.

### Conclusion
After analyzing all the options, we conclude that the correct answer is **Down's Syndrome**, as it is a genetic disorder and not an autoimmune disorder.

### Final Answer
**Down's Syndrome** is not an autoimmune disorder.

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