Phenylketonuria is a metabolic disease that is caused by a buildup of Phenylalanine in the body due to an enzyme deficiency, particularly the hepatic enzyme Phenylalanine Hydroxylase (PAH). People with PKU can not convert the amino acid Phenylalanine to Tyrosine due to a mutation in the gene that codes for PAH. It was discovered by Dr. Asbjorn Folling in 1934. Phenylketonuria can lead to severe brain damage and mental retardation if not treated. The disease is an aurtosomal recessive disorder inherited by offspring from parents if both are carriers, meaning each parent has one defective and one functional gene. It is found on chromosome 12. 

Phenylketonuria 1

The child on the left has PKU.

PKU shows up in 1 out of every 15000 births.


Early diagnosis of the disease is essential, however, this can prove to be difficult because few symptoms are observable in new born infants. One major symptom is Eczema, an irritating and itchy rash on the skin, and a musky odor. Abnormally fair skin and hair as well as hair loss are also very rare symptoms. In extreme cases, the afflicted child will experience seizures. If left untreated this disease can cause severe mental retardation.

Method of DetectionEdit

Phenylketonuria testing

Guthrie Test

In 1962 Robert Guthrie devised a test (Guthrie Test) which is used to detect elevated levels of the amino acid phenylalanine in the bloodstream. The test is a semiquantitative assay that uses a bacterial culture in addition to an inhibitor to test if phenylalanine levels are too high. The test works by adding Bacillus Subtilus and B-2 Thienylalanine, a bacteria and a growth inhibitor respectively, along with a drop of blood obtained from the heel of the newborn at the end of the first week of life. The prescence of a surplus of Phenylalanine represses the inhibitor and allows the bacteria to grow, thus signifying that the affected child has Phenylketonuria.


The most common treatment for Phenylketonuria is a diet low in Phenylalanine. This can prove to be very difficult seeing as Phenylalanine is an essential amino acid found in the majority of meat products. Fortunately, a diet low in Phenylalanine is all that is required to treat the disease as long as it is detected early. Blood tests should be taken two times a month in order to test for Phenylalanine levels. In some cases, special pills are prescribed that contain a balance of vitamins, minerals, and amino acids (except for Phenylalanine) in order to maintain proper nutritional levels and prevent any further medical complications. However, if Phenylketonuria is not diagnosed early, treatment is not as effective and symptoms can appear including brain damage. Kuvan(sapropterin dihydrochloride) is a new medication available that can be used to treat PKU. However, the effectiveness of the drug is unknown for children under age 4 and patients over the age of 65. It is also unknown whether or not the drug actually reduces nervous system damage. A low protein diet is still the recommended treatment for people with PKU.

Life Expectancy/Quality of LifeEdit

People with Phenylketonuria on average live for as long as any other normal person. The biggest factor towards their life expectancy is how well they have kept to their diets. As long as the patient maintains a low-protein diet and tests their blood regularly, they can live just as long as an unaffected person.

The quality of life for people whith PKU is generally better than that of people with other serious genetic diseases. People with PKU can enjoy all the pleasures of life and show little symptoms as long as they abide by their strict diet . 


Types of PhenylketonuriaEdit

Maternal PhenylketonuriaEdit

Maternal Phenylketonuria is caused when the mother of the child has very high levels of Phenylalaine. This causes symptoms similar to that of regular PKU including microcephaly (small head size) and congenital heart disease. lies


Patients have high levels of phenylalanine in their blood, but not as high as seen in patients with classical PKU. There are two forms of hyperphenylalaninemia: mild and severe


This disease is characterized by high levels of Phenylalanine and Tyrosine. Patients with this disease have many of the same symptoms as seen in classical PKU, including mental retardation. Treatment consists of a special diet similar to the diet for PKU. The main difference between the two diets is that patients with tyrosinemia must eat a diet that is low in both phenylalanine and tyrosine.