Based on limited published evidence, CYB5RL encodes a cytochrome b5 reductase-like protein with NADH-dependent oxidoreductase activity. UniProt annotations indicate involvement in fatty acid desaturation and elongation, cholesterol biosynthesis, and drug metabolism. The protein localizes to the endoplasmic reticulum membrane. A germline mutation (R51X) in CYB5RL was identified in a canine model of extreme intestinal polyposis, suggesting a role in oxidative stress regulation relevant to tumorigenesis 1.