Phenylketonuria (PKU) is a rare, inherited, metabolic disorder that can result in mental retardation and other neurological problems. People with this disease have difficulty breaking down and using (metabolizing) the amino acid phenylalanine. PKU is sometimes called Folling's disease in honor of Dr. Asbjorn Folling who first described it in 1934.
Phenylalanine is an essential amino acid. These substances are called "essential" because the body must get them from food to build the proteins that make up its tissues and keep them working. Therefore, phenylalanine is required for normal development. Phenylalanine is a common amino acid and is found in all natural foods. However, natural foods contain more phenylalanine than required for normal development. This level is too high for patients with PKU, making a special low-phenylala-nine diet a requirement.
The incidence of PKU is approximately one in every 15,000 births (1/15,000). There are areas in the world where the incidence is much higher, particularly Ireland and western Scotland. In Ireland the incidence of PKU is 1/4,500 births. This is the highest incidence in the world and supports a theory that the genetic defect is very old and of Celtic origin. Countries with very little immigration from Ireland or western Scotland tend to have low rates of PKU. In Finland, the incidence is less than 1/100,000 births. Caucasians in the United States have a PKU incidence of 1/8,000, whereas Blacks have an incidence of 1/50,000.
John T. Lohr PhD, The Gale Group Inc., Gale, Detroit,