Which of the following is true about ataxia telangiectasia?
**Core Concept**
Ataxia telangiectasia (AT) is a rare, autosomal recessive disorder characterized by progressive cerebellar degeneration, impaired immune function, and an increased risk of malignancies. The disease is caused by mutations in the ATM gene, which plays a crucial role in the repair of DNA double-strand breaks.
**Why the Correct Answer is Right**
The ATM gene product is a protein kinase that phosphorylates and activates several key proteins involved in the DNA damage response, including p53 and BRCA1. In the absence of functional ATM protein, cells are unable to properly repair DNA damage, leading to genomic instability and an increased risk of cancer. The cerebellar degeneration in AT is thought to be due to the accumulation of DNA damage in Purkinje cells, leading to their progressive loss.
**Why Each Wrong Option is Incorrect**
**Option A:** While AT is associated with an increased risk of malignancies, it is not primarily a disorder of cell growth and proliferation. The primary defect in AT is in the DNA damage response, not in cell cycle regulation.
**Option B:** AT is characterized by telangiectasias, which are dilated blood vessels, but these are not the primary feature of the disease. The telangiectasias are a secondary consequence of the underlying genetic defect.
**Option C:** AT is not primarily a disorder of the immune system, although immunodeficiency is a feature of the disease. The primary defect in AT is in the DNA damage response, which affects all cell types, not just immune cells.
**Clinical Pearl / High-Yield Fact**
ATM mutations are responsible for a range of clinical disorders, including AT, but also Li-Fraumeni syndrome and breast cancer susceptibility. The ATM gene is a key player in the DNA damage response, and mutations in this gene are associated with an increased risk of cancer.
**Correct Answer: C.**