FREM1 encodes a basement membrane protein which forms a ternary complex with the FRAS1 and FREM2 proteins. FREM1 is required for epidermal adhesion during embryonic development and is thought to be involved in craniofacial and renal development. The latter protein is composed of many functional domains, including a conserved signal sequence, a CALX-b calcium-binding loop, 12 chondroitin sulfate proteoglycan (CSPG) elements, and a C-terminal lectin Type C domain. Four isoforms of the FREM1 protein were identified.