Ataxia-telangiectasia breakpoints in chromosome rearrangements reflect genes important to T and B lymphocytes.

The AT cell fails to pause sufficiently after X-ray or similar radiomimetic insults to repair damage. Rather, it launches with undue speed into DNA replication. It may incorporate errors into DNA that lead to the chromatid and chromosome breaks. Breakpoints have been noted at 7p13, 7q33-35, 14q11-12, and 14q32. The regions at 7q33-35, and 14q11-12 are specific to T cells and include T cell receptor genes. The region at 14q11-12 is involved in T-cell malignancies. The region at 14q32 contains immunoglobulin heavy-chain genes and is involved in B-cell malignancies.