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PKU (phenylketonuria): a metabolic disease

  1. Phenylketonuria (PKU) is a hereditary condition involving a metabolic disease. In the Netherlands, all babies are given a heel prick within 8 days of birth, which also checks the presence of this disease. PKU is incurable, but it can be treated. The child will have to follow a special low-protein diet for the rest of his life. If not, it will lead to dementia. What exactly is PKU and what is life like with this condition?

What PKU is

  1. Phenylketony, or PKU for short, is a hereditary metabolic disease. The liver cannot or not sufficiently process one component of protein. As a result, the amino acid (part of the protein) called phenylalanine will not be processed and it will accumulate in the blood. This ensures that brain development is stunted. If not treated, it will lead to dementia. It will then lead to a clear delay within a year and eventually serious brain damage will occur. About 1 in 18,000 babies born in the Netherlands have PKU.

The heel prick

  1. All babies born in our country are tested within 8 days by means of the heel prick. By means of a small injection in the heel, a small amount of blood is taken in which the phenylalanine value is determined. If the value of this amino acid is high, more tests will follow to determine whether there is PKU. For most parents it is a big shock, because sometimes they have never heard of it. Once the diagnosis is made, treatment is started immediately. The baby receives a preparation to lower the high value of phenylalanine. This prevents brain damage.


  1. PKU is treated by preventing the build-up of the amino acid phenylalanine in the blood. This amino acid is a natural component that is found in almost all foods. Therefore, someone with PKU has to follow a very strict diet low in protein for the rest of their life. As a result, the patient will not receive enough nutrients. Therefore, he must take a special preparation that contains all the missing amino acids and minerals so that the body and brain can function and grow properly. In addition, constant medical supervision and a dietician are required. The blood must be tested regularly. The patient can prick himself at home for this and send the blood.


  1. Fortunately, PKU is already detected during the heel prick in our country. This was not the case before. If not treated, it will cause serious brain damage. This is already clearly noticeable at the age of one year, because there is a delay in development. Other symptoms to tell if someone has PKU are:

Low protein diet

  1. Foods that contain a lot of protein are, for example, milk (products), meat, chicken, fish, eggs, nuts, legumes and grain products. Proteins are needed in the body for growth, functioning of all kinds of processes and tissue repair. Patients with PKU do need phenylalanine, but only in small amounts. Because the disease makes it difficult for the body to break down proteins, the patient is given a low-protein diet. Someone with PKU should not ingest any meat, fish, cheese, milk, eggs, bread and chocolate. For example, there is also some protein in fruit and vegetables, but to a lesser extent. A PKU patient may eat this in a limited amount. Everything the patient eats must be weighed precisely. Today, diet products are available especially for PKU disease. These products are basic products such as pasta, flour and rice. Whether or not it is tasty depends on how you prepare the meal.

Example of the diet

  1. Below is an example of what a diet of a PKU patient might look like one day.


  1. If both parents are carriers of the PKU gene, the chance that their child will have it is 25 percent. A couple may decide to know if they carry the gene before starting children. To test PKU, there are three main tests: the enzyme test, flake test, or PKU screening. The enzyme test can be used to check whether the parents are carriers of the gene. The villus test is done on a pregnant woman to see if the fetus has the PKU gene. The PKU screening is the heel prick, which is mandatory in most countries.

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