t(12;21)(p13;q22)

**Semantic type:** Cell or Molecular Dysfunction

**Definition:** t(12;21) is a chromosomal translocation, involved in TEL-AML1 oncogene formation, that produces a chimeric gene encoding a protein consisting of the N-terminal HLH domain of the TEL ETS-like transcription factor fused with a nearly complete AML1 protein. t(12;21) is the most frequent translocation causing ALL, accounting for 20% of ALL cases.