Phenylketonuria (fen-ul-ke-ton-U-ree-a), or PKU, is an inherited metabolic disease in which the body cannot change one essential amino acid, phenylalanine (fen-ul-AL-a-neen), into another needed amino acid, tyrosine (TΎ-ro-seen). Untreated, PKU often results in severe intellectual disabilities, but if it is detected at birth and these children are put on a special diet, they can lead normal lives.
In 1934 a mother with two children with intellectual disabilities went to a Norwegian medical doctor, Asbjθrn Felling (1888–1973). Felling became interested in the children's condition when the mother described the children's odd musty odor. The children, four and six years of age, had severe intellectual disabilities. The younger child could not speak or walk and still wore diapers. The older child could speak only a few words and had problems walking.
FØlling examined the children's urine and found no protein or glucose in it, but he was puzzled when their urine turned a deep green, instead of staying brownish, after he added the chemical compound ferric chloride to it. Felling expanded his study to other children whose urine produced the same kind of reaction and concluded that the unusual quality of the urine seemed to be connected with intellectual disabilities. Thus, he discovered PKU, which he concluded was a genetic error in the children's metabolism * .
PKU is a disruption in normal metabolism. Normally, an enzyme * in the body called phenylalanine hydroxylase (fen-ul-AL-a-neen hyDROK-silase) changes the essential amino acid * phenylalanine to another needed amino acid called tyrosine. If phenylalanine hydroxylase is missing, as it is in PKU, phenylalanine builds up in the blood and passes out of the body in urine.
PKU affects on average 1 out of every 10,000 to 15,000 babies in the United States. Because PKU is an inherited disorder, there is considerable variation among different ethnic and racial groups. The condition is found less often in people of African descent (1 in every 50,000 babies) and in Ashkenazi Jews.
Infants with PKU usually have lighter skin, hair, and eyes than the rest of their families, but symptoms do not appear until they are about three to six months old. These may include the following:
Almost all babies born in hospitals in the United States are screened for PKU within 48 hours of birth with a blood test that measures their levels of phenylalanine. In families with a history of PKU, the disease can usually be diagnosed in the fetus during pregnancy. A pregnant woman who has untreated PKU herself has a much greater chance of having a baby with (often severe) birth defects.
Jennifer is a happy 12-year-old with fair skin, blue eyes, and a very normal life except for her diet. Jennifer has PKU, which was diagnosed at birth through hospital screening. She cannot go out for pizza, drink diet sodas, or eat many of the common foods that most people take for granted.
Infants with PKU must begin treatment within days of being born to prevent intellectual disabilities. They must eat a special diet that restricts their intake of phenylalanine and provides the tyrosine that the body cannot make. Babies drink special formula * that is low in phenylalanine. People with PKU cannot have high-protein foods such as meat, poultry, fish, milk, eggs, and cheese or products containing the artificial sweetener aspartame (also known by the brand name NutraSweet). They can eat low-protein foods such as fruits, vegetables, and certain cereals.
Not adhering to the diet may cause serious problems such as a drop in IQ and problems with learning and behavior. Experts are not sure whether and at what age it is safe to stop treatment. Most recommend that people with PKU stay on the special diet for life.
See also Birth Defects: Overview • Genetic Diseases: Overview • Intellectual Disability • Metabolic Disease • Seizures • Skin Conditions: Overview
Paul, Diane B., and Jeffrey P. Brosco. The PKU Paradox: A Short History of a Genetic Disease. Baltimore, MD: Johns Hopkins University Press, 2013.
Genetics Home Reference. “Phenylketonuria.” National Institutes of Health. http://ghr.nlm.nih.gov/condition/phenylketonuria (accessed November 11, 2015).
March of Dimes. “PKU (Phenylketonuria) in Your Baby.” http://www.marchofdimes.org/baby/phenylketonuria-in-your-baby.aspx (accessed August 11, 2015).
MedlinePlus. “Phenylketonuria.” U.S. National Library of Medicine, National Institutes of Health. https://www.nlm.nih.gov/medlineplus/phenylketonuria.html (accessed November 11, 2015).
Children's PKU Network. 3306 Bumann Rd., Encinitas, CA 92024. Telephone: 858-756-0079. Website: http://www.pkunetwork.org/Childrens_PKU_Network/Home.html (accessed August 11, 2015).
March of Dimes. 1275 Mamaroneck Ave., White Plains, NY 10605. Telephone: 914-997-4488. Website: http://www.marchofdimes.org (accessed November 11, 2015).
National PKU Alliance. PO Box 501, Tomahawk, WI 54487. Telephone: 715-437-0477. Website: http://npkua.org/Home.aspx (accessed August 11, 2015).
* metabolism (meh-TAB-o-liz-um) is the process in the body that converts food into the energy necessary for body functions.
* enzyme (EN-zime) is a protein that helps speed up a chemical reaction in cells or organisms.
* amino acids (a-MEE-no acids) are the chief building blocks of proteins. In humans, certain amino acids are required to sustain life.
* eczema (EG-ze-mah) is an inflammatory skin condition characterized by redness, itchiness, and oozing blisters that become crusty and hard.
* seizures (SEE-zhurs), also called convulsions, are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.
* hyperactivity (hy-per-ak-TI-vi-tee) is overly active behavior, which makes it hard for a person to sit still.
* formula is a prepared, nutritious drink or a dry drink mix designed