A child with phenylketonuria has no particular symptoms at birth. Before the 1960s, when a child was born it was impossible to tell whether or not it was affected by the disease.

During the 1960s, the first screening tests were conducted in the USA by Dr. Robert Guthrie.

Since it is a curable disease, the aim of screening is to predict the disorder and to enable a restricted phenylalanine diet to be introduced very quickly (on the 10th day of life).

In France, screening has been systematic since 1975, and the Guthrie test is carried out on the 3rd day of life.

The Guthrie test

Thanks to this test, about 50 cases are now discovered every year in France.

It is very easy to perform, and simply involves taking a few drops of blood from the baby’s heel or finger and collecting them on filter paper.

The sample is then sent to a laboratory for analysis. In a bacteriological test, if phenylalanine is present in the blood then bacteria will be able to multiply on a gel (agar gel plate) on which they would not develop under normal conditions. A reference range is then used for quantitative analysis.

« Mental retardation, behaviour disorders, epilepsy, psychosis… »

Numerous disorders are associated with phenylalanine toxicity. Generally speaking, phenylketonuria causes severe mental retardation. A number of cerebral disorders can also occur, including epilepsy, psychosis, etc.

If left undiagnosed, patients with phenylketonuria have very pale colouring. What happens is that phenylalanine is not converted into tyrosine, which plays a role in the process that produces melanin, a pigment that gives the skin, hair and eyes their brown colouring. Furthermore, excess phenylalanine is changed into phenylketones, which are excreted in the urine. These phenylketones are responsible for the distinctive smell of the sweat and urine of children with phenylketonuria. They also give the disease its name.