Bcl-9L is a 1,499 amino acid protein that localizes to the nucleus and contains a specialized C-terminal domain that is important for its overall activity. Expressed in breast tissue, as well as in eye, lung, prostate and various carcinomas, Bcl-9L functions as a transcriptional activator that forms a complex with Parafibromin and β-catenin and is thought promote the transcriptional activity of Parafibromin and enhance the neoplastic transforming activity of β-catenin. Bcl-9L exists as multiple alternatively spliced isoforms and is thought to be involved in tumorigenesis, possibly playing a role in tumor transformation and metastasis. The gene encoding Bcl-9L maps to human chromosome 11, which houses over 1,400 genes and comprises nearly 4% of the human genome. Jervell and Lange-Nielsen syndrome, Jacobsen syndrome, Niemann-Pick disease, hereditary angioedema and Smith-Lemli-Opitz syndrome are associated with defects in genes that maps to chromosome 11.