Medicine & USMLE


DNA Repair
  1. Lynch Syndrome
  2. Xeroderma Pigmentosum
  3. Ataxia-Telangiectasia
  4. Bloom Syndrome

Ataxia-Telangiectasia is an autosomal recessive disease that is characterized by impaired balance or coordination (ataxia) and the presence of dilated superficial blood vessel structures calledtelangiectasias.

The disease is caused by mutations in the ATM gene, which impairs non-homologous end-joining (NHEJ), a mechanism used to fix double-stranded DNA breaks.

The inability to repair double-strand breaks impairs the development of B- and T-cells, resulting in immunodeficiency. Patients classically present with recurring infections, and labs will reveal decreased immunoglobulins levels of all classes.

Ataxia results from cerebellar dysfunction, so brain imaging may reveal cerebellar atrophy. Telangiectasias (spider veins) may be observed on the sclera and the surface of the skin. Additionally, patients may have elevated AFP levels, although the cause of this finding is not well understood.

Lastly, the inability to repair double-strand DNA breaks makes patients particularly susceptible to radiation, which can induce such DNA damage. Therefore, exposure to radiation should be avoided to reduce the risk of cancer.

Find this mnemonic on Ataxia-Telangiectasia and more mnemonics on DNA repair among Pixorize's visual mnemonics for the USMLE Step 1 and NBME Shelf Exams.