Which of the following is a dominant autosomal mutation ?

Options

A. Phenylketonuria
B. Huntington's disease
C. Cystic fibrosis
D. Alzheimer's disease

Answer

To determine which of the following is a dominant autosomal mutation, we will analyze each option provided:

1. **Phenylketonuria (PKU)**:
- This condition is caused by a mutation in the PAH gene and is classified as an autosomal recessive disorder. This means that an individual must inherit two copies of the mutated gene (one from each parent) to express the disease. Therefore, this option is incorrect.

2. **Huntington's Disease**:
- Huntington's disease is caused by a mutation in the HTT gene located on chromosome 4. It is classified as an autosomal dominant disorder. This means that only one copy of the mutated gene is sufficient for an individual to express the disease. Therefore, this option is correct.

3. **Cystic Fibrosis**:
- Cystic fibrosis is caused by mutations in the CFTR gene and is also classified as an autosomal recessive disorder. Similar to PKU, an individual must inherit two copies of the mutated gene to express the disease. Therefore, this option is incorrect.

4. **Alzheimer's Disease**:
- Alzheimer's disease can have both familial (early-onset) and sporadic forms. The familial form is associated with mutations in certain genes and is considered to be autosomal dominant. However, the sporadic form is more common and is influenced by multiple factors. For the purpose of this question, we can classify it as an autosomal dominant condition. Therefore, this option is correct.

**Conclusion**:
The only option that is a dominant autosomal mutation is **Huntington's disease**.