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. The Kelch domain-containing protein 9 (KLHDC9), also designated Kelch/ankyrin repeat-containing cyclin A1-interacting protein (KARCA1), contains 3 Kelch repeats and interacts with CCNA1. The gene encoding KLHDC9 maps to chromosome 1, the largest human chromosome spanning about 260 million base pairs and making up 8% of the human genome. Notably, the rare aging disease Hutchinson-Gilford progeria is associated with the LMNA gene of human chromosome 1, which encodes lamin A. Aberrations in chromosome 1 are found in a variety of cancers including head and neck cancer, malignant melanoma and multiple myeloma.