Deficiency of `B_(12)`causes

Options

A. Thalassaemia
B. Beri-beri
C. Perniciuos anaemia
D. Cheilosis

Answer

### Step-by-Step Solution:

1. **Understanding Vitamin B12**: Vitamin B12, also known as cobalamin, is a crucial water-soluble vitamin that plays a significant role in red blood cell formation, neurological function, and DNA synthesis.

2. **Identifying the Deficiency Effects**: A deficiency in vitamin B12 can lead to various health issues, primarily affecting the blood and nervous system.

3. **Exploring Pernicious Anemia**: One of the most notable conditions caused by vitamin B12 deficiency is pernicious anemia. This condition occurs when there is a lack of intrinsic factor, a protein produced in the stomach that is essential for the absorption of vitamin B12 in the intestines.

4. **Mechanism of Pernicious Anemia**: In pernicious anemia, the immune system mistakenly attacks the cells in the stomach that produce intrinsic factor, leading to inadequate absorption of vitamin B12. This results in the production of abnormally large and dysfunctional red blood cells, causing anemia.

5. **Differentiating from Other Conditions**: It is important to note that other conditions mentioned, such as thalassemia and beriberi, are not caused by vitamin B12 deficiency. Thalassemia is related to hemoglobin production, while beriberi is due to a deficiency of vitamin B1 (thiamine).

6. **Conclusion**: Therefore, the primary condition caused by a deficiency of vitamin B12 is pernicious anemia.

### Final Answer:
Deficiency of vitamin B12 causes pernicious anemia.

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