A monosaccharide sugar that is less sweet in taste than both glucose and fructose, galactose is a C-4 epimer of glucose. It is found in dairy products, sugar beets, gums, mucilages, and is even synthesized by the human body to form parts of glycolipids and glycoproteins in several tissues. When galactose is combined with glucose via a condensation reaction, it results in disaccharide lactose. In nature, lactose is found primarily in milk and milk products, and many dairy-derived ingredient foods can also contain lactose. As with lactose, the inability to break down galactose is also a condition that results from a genetically inherited mutation in Leloir pathway enzymes. This condition, called galactosemia, means that even consuming tiny quantities of galactose can be harmful to galactosemics. A component of antigens present in blood cells that determine blood type within the ABO blood group system, both A and O type antigens contain two monomers of galactose, and B antigens possess three monomers of galactose.