The BTB (Broad-Complex, Tramtrack and Bric a brac) domain, also known as the POZ (POxvirus and Zinc finger) domain, is an N-terminal homodimerization domain that contains multiple copies of kelch repeats and/or C2H2-type zinc fingers. Proteins that contain BTB domains are thought to be involved in transcriptional regulation via control of chromatin structure and function. KCTD12 (potassium channel tetramerisation domain containing 12), also known as PFET1 or PFETIN, is a 325 amino acid protein that is expressed in fetal organs, with highest levels in the cochlea and brain and extremely low levels in adult organs, such as brain and lung. KCTD12 is considered a prognostic biomarker of gastrointestinal stromal tumors.