NADH-cytochrome b5 reductases participate in a variety of physiological processes including biosynthesis of cholesterol, methemoglobin reduction of erythrocytes, elongation of fatty acids and metabolism of drugs. CYB5R1 (cytochrome b5 reductase 1), also known as NADH-cytochrome b5 reductase 1, B5R1, NQO3A2, humb5R2 or NAD(P)H:quinone oxidoreductase type 3 polypeptide A2, is a 305 amino acid single-pass membrane protein that contains one FAD-binding FR-type domain and belongs to the flavoprotein pyridine nucleotide cytochrome reductase family. Widely expressed, CYB5R1 binds FAD as a cofactor and is encoded by a gene located on human chromosome 1. Human chromosome 1 spans 260 million base pairs, contains over 3,000 genes, comprises nearly 8% of the human genome and houses a large number of disease-associated genes, including those that are involved in familial adenomatous polyposis, Stickler syndrome, Parkinson's disease, Gaucher disease, schizophrenia and Usher syndrome.