Ataxia telangiectasia-like disorder (ATLD) was first recognized as a subset of ataxia telangiectasia which does not have mutations in the ATM gene. It is a very rare genetic disease which exhibits a late-onset slowly progressive variant of ataxia-telangiectasia without microcephaly and no telangiectasia. ATLD is characterized by cerebellar ataxia, increased frequency of chromosomal translocations and hypersensitivity to ionizing radiation. Until present, ATLD and the associated pathological changes in the brain are unclear. Similarly, ophthalmic features of this disease are not well described.

Genetically, ATLD1 is caused by mutation in the MRE11 (meiotic recombination 11, S. cerevisiae, homolog of, A) gene located at 11q21. Mre11 is a member of the Mre11-Rad50-Nbs1 (MRN) complex involved in different responses to cellular damage induced by ionizing radiation and radiomimetic chemicals, including complexing with chromatin and with other damage response proteins, formation of radiation-induced foci, and the induction of different cell cycle checkpoints. Interestingly, alteration in the levels of Mre11 protein level is associated with a reduction in levels of Nbs1 and Rad50 proteins.