In case of phenylketonuria mental retardation occurs due to

Options

A. Eliminationfo tyrosine from blod
B. Accumulation of tyrosine in blood
C. Accumulation of phenylpyruvic acid in blood
D. Elimination of phenylalanine from blood

Answer

### Step-by-Step Solution:

1. **Understanding Phenylketonuria (PKU)**:
- Phenylketonuria is a genetic disorder that is inherited in an autosomal recessive manner. It results from a mutation in the gene responsible for producing the enzyme phenylalanine hydroxylase.

2. **Role of Phenylalanine Hydroxylase**:
- The enzyme phenylalanine hydroxylase is crucial for the metabolism of the amino acid phenylalanine. This enzyme converts phenylalanine into another amino acid called tyrosine.

3. **Consequences of Enzyme Deficiency**:
- In individuals with PKU, the lack of phenylalanine hydroxylase leads to the accumulation of phenylalanine in the blood. High levels of phenylalanine are toxic and can cause various neurological issues.

4. **Impact on Mental Development**:
- The accumulation of phenylalanine affects brain development and function, leading to mental retardation and other cognitive impairments. This is due to the toxic effects of excess phenylalanine on the brain.

5. **Conclusion**:
- Therefore, in the case of phenylketonuria, mental retardation occurs due to the accumulation of phenylalanine in the blood as a result of the deficiency of the enzyme phenylalanine hydroxylase.