Diagnosis of Phenylketonuria

Diagnosis is carried out in two different ways as standard. One is the detection of the defective enzyme, the other is the detection of the greatly increased phenylalanine concentration in the blood. The first method is part of newborn screening as so-called tandem mass spectroscopy and indicates the defect without the need to take up penylalanine.

Tandem mass spectroscopy can also be used to diagnose more than twenty other diseases quite reliably. The second method is the guthrie test (also called heel test). However, this test requires that the child must already have ingested phenylalanine – for example, through breast milk. In the test, some blood is then taken from the child’s heel as part of the U2 and examined for its phenylalanine content.

These are the symptoms of phenylketonuria

The symptoms of phenylketonuria depend to a large extent on the residual activity of the enzyme. If there is still a certain percentage of functioning enzymes, the disease is not as pronounced as in a pronounced full-blown Phenylketonuria.Typical symptoms that are noticed early on are the strong and peculiar smell of the urine of affected children and the mental and psychomotoric underdevelopment of the children that develops in the course of the disease. If the disease is not detected and treated early, permanent damage to the development of the brain occurs.

In the worst case, the children with their intelligence quotient can remain below a value of 50 IQ points. In addition to this, there can be motor deficits in the context of phenylketonuria. The important signal substance dopamine is missing, as in Parkinson’s disease. This is why it is also referred to as juvenile Parkinson’s disease in this context. In addition, children with phenylketonuria usually have blonde hair and blue eyes, since their production of the pigment melanin is also disturbed.

Treatment of phenylketonuria

The good news regarding the therapy of phenylketonuria is that the symptoms of mental underdevelopment can be completely prevented if the therapy is started early. The basic element of the therapy is a low-phenylalanine diet that prevents the accumulation of too much phenylalanine. The later the diagnosis is made and the later therapy is started, the greater the resulting mental retardation (underdevelopment).

If the disease is not the full-blown form of phenylketonuria, but a form with reduced enzyme activity, a so-called substitution therapy can also be performed. One supplies the affected persons with the molecule tetrahydrobiopterin. This supports the body in the conversion of phenylalanine.

The measure of success of the therapy is the blood concentration of phenylalanine. It should be kept in the range of 2 to 4 mg/dL in persons with phenylketonuria. As already mentioned, a low-phenylalanine diet is the cornerstone of the treatment of phenylketonuria.

However, since phenylalanine is an essential amino acid, it cannot be completely avoided. Therefore, babies and infants need a special infant milk, because normal breast milk contains too much phenylalanine. It is recommended to continue the diet at least until the age of fourteen to ensure the normal mental development of the child. Since phenylalanine is present in almost every animal protein, it is generally advisable for those affected to follow a diet low in meat to meat-free.