SCID occurs due to deficiency of :-

Options

A. Adenosine deaminase
B. Tyrosin oxidase
C. Phenylalanine hydroxylase
D. One X-chromosome

Answer

**Step-by-Step Solution:**

1. **Understanding SCID**: SCID stands for Severe Combined Immunodeficiency. It is a genetic disorder characterized by the disturbed development of functional T cells and B cells caused by numerous genetic mutations.

2. **Identifying the Cause**: SCID can be caused by various genetic mutations, but one of the most common causes is the deficiency of the enzyme adenosine deaminase (ADA). This enzyme is crucial for the survival of T cells, which are essential for the immune response.

3. **Analyzing Options**: The question provides several options. We need to identify which of these is specifically linked to SCID:
- **Adenosine Deaminase (ADA)**: Deficiency leads to SCID due to impaired T cell function.
- **Tyrosinase**: Related to melanin production, not SCID.
- **Phenylalanine Hydroxylase**: Involved in phenylketonuria, not SCID.
- **X Chromosome**: Refers to genetic conditions like Turner’s syndrome, not SCID.

4. **Conclusion**: Based on the analysis, the deficiency of adenosine deaminase (ADA) is the primary cause of SCID. Therefore, the correct answer is ADA deficiency.

**Final Answer**: SCID occurs due to deficiency of **Adenosine Deaminase (ADA)**.

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