CD344 is a member of the Frizzled family, known as Frizzled-4 (Fz4, FZD4, hFz4, or FzE4). Ten frizzled member have been identified in humans. Human FZD4 gene has been mapped to chromosome 11q14-q21. FZD4 is a 48-53 kD seven transmembrane G-protein-coupled receptor (GPCR), a receptor for Wnt proteins and norrie. It is involved in the activation of Wnt/beta-catenin pathway (canonic Wnt signaling). FZD4 is a neuronal stem cell marker and is also expressed on fetal neuronal progenitor cells and neuronal intestinal cells. Kidney, lung, brain and liver express abundant of FZD4. It has been reported that FZD4 controls retinal and inner ear angiogenesis, participates in the regulation of embryonic development, tissue and cell polarization and proliferation.