Fgfrl1, or fibroblast growth factor receptor like 1, is the fifth member of the FGFR family. It contains three extracellular Ig-like domains, lacks the protein tyrosine kinase domain, and has a short intracellular tail with a histidine-rich motif. Fgfrl1 binds to FGF ligands and heparin, and is involved in the FGF signaling system, playing important roles in cell proliferation (negative effect), cell differentiation (positive effect), and is crucial for organ development [1].

Gene-targeted deletion in mice shows that Fgfrl1-deficient mice die perinatally due to diaphragm alterations and bilateral kidney agenesis, suggesting its essential role in kidney development [1]. Mice lacking the Ig2 or Ig3 domain of Fgfrl1 die within 24 hours after birth, with Ig3-deficient mice completely lacking metanephric kidneys, indicating these domains' importance in nephrogenesis [2]. In a human patient, a frameshift mutation in Fgfrl1 led to craniosynostosis, highlighting its role in bone formation [1].

In conclusion, Fgfrl1 is essential for kidney development and bone formation as revealed by mouse models and human case. The study of Fgfrl1 in KO mouse models contributes to our understanding of congenital kidney and bone-related diseases, providing insights into the underlying molecular mechanisms and potential therapeutic targets.