Phenylketonuria (PKU) is an inherited metabolic disorder which prevents the normal breakdown of protein foods. The amino acid, phenylalanine is naturally found in most protein foods.

In PKU there is a defect in the enzyme phenylalanine hydroxylase, leading to the body being unable to break-down phenylalanine and convert it to another essential amino acid, tyrosine. If phenylalanine is allowed to accumulate in body tissues, brain development is affected, causing learning difficulties.

PKU can be treated very successfully if diagnosed soon after birth. The heel prick test ( guthrie test ) is done on all newborn babies shortly after birth to identify PKU at an early age. The treatment is based on a restricted phenylalanine diet. A small quantity is required to ensure normal growth, so only small amounts are given in a controlled diet.

History of PKU

Since the discovery of PKU as a new disease in 1934, scientific interest in the disease has advanced at an astonishing pace, taking PKU from obscurity to the forefront of cutting-edge biotechnology research—from an unidentified syndrome with devastating and permanent consequences to a condition whose management promises to help people live productive and fulfilling lives. At this pace, it is hard to imagine what discoveries lie ahead in the first years of the 21st century.
1934: PKU is discovered

In 1934, a Norwegian doctor named Asbjorn Folling described a group of mentally retarded patients who had a strange odor. We learned that this smell was caused by phenylacetic acid and that the patients' urine had large amounts of a phenylketone called phenylpyruvic acid. Hence, the condition was given the name phenylketon-uria. Not only was Folling the first to understand the disease and its relationship with phenylalanine, he was also the first to suggest its genetic nature and advise a form of management through dietary restriction.
1951: PKU management combines dietary restriction and protein replacement

Less than 20 years after its discovery, PKU was well known in the scientific community as a disease of protein digestion that could be controlled by a special diet. However, it wasn’t until Horst Bickel, a German professor, developed a protein supplement that people with PKU had any hope of living a somewhat normal life. Bickel’s first protein drink was unflavored.
1966: A simple diagnostic test becomes the international standard for newborn screening

In 1958, the guthrie test, named after its discoverer, Robert Guthrie of Minnesota, was the first affordable test for screening hyper Phe in newborns. It gained recognition rapidly due to its simplicity, which made its widespread implementation cost-effective. In 1966, newborn screening with the test became the standard in hospitals.

The test, still widely used today, requires only a drop of blood, compared with about 4 teaspoons of blood in previous tests.
This simple test made it possible to catch virtually every PKU case in infancy, assuring that the disease could be properly managed from the outset and that mental retardation due to PKU could be avoided. The pioneering efforts of Guthrie played a pivotal role in helping diagnose the majority of people living with PKU today.

References

http://www.nhsdirect.nhs.uk/articles...articleid=283#

http://www.pku.com/AboutPKU/AboutPKU.aspx