Overexpression of the TCL1 gene in humans has been implicated in the development of mature T cell leukemia, in which chromosomal rearrangements bring the TCL1 gene in close proximity to the T-cell antigen receptor (TCR)-alpha (MIM 186880) or TCR-beta (MIM 186930) regulatory elements (summarized by Virgilio et al. 1998 [PubMed 9520462]). In normal T cells TCL1 is expressed in CD4-/CD8- cells, but not in cells at later stages of differentiation. TCL1 functions as a coactivator of the cell survival kinase AKT (MIM 164730) TCL1A (T-Cell Leukemia/Lymphoma 1A) is a Protein Coding gene. Diseases associated with TCL1A include Precursor T-Cell Acute Lymphoblastic Leukemia and T-Cell Leukemia. Among its related pathways are PI3K-Akt signaling pathway and PI3K / Akt Signaling. An important paralog of TCL1A is MTCP1.