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Phenylketonuria (PKU) is only one of the congenital (inherited) disorders of Protein Metabolism. Besides PKU, other main disorders within this category are:


  • MSUD Maple Syrup Urine Disease
  • Urea Cycle Defects
  • Homocystinuria
  • Tyrosinemia
  • Organic aciduria


The common factor in these disorders is the reduction in the function – or the total absence of the enzyme responsible for the metabolism of one or more amino acids.

This causes an accumulation of amino acid, or amino acids, which unless broken down, transform into toxins.  Another consequence is the lack of the amino acid, metabolite, the product into which amino acid should transform, if the whole process were to work properly.

Two other important aspects, which unite these inherited disorders of protein metabolism, are newborn screening and diet therapy - fundamental pillars for the required treatment.

The testing for metabolic diseases on newborns is, unfortunately, not widespread, neither in Europe nor in the rest of the world. In fact, the situation is rather different from country to country - even in the same geographical area - with countries that guarantee the detection of about 50 disorders, and others that have no screening policy in place at all.

Where it is possible to have a diagnosis, the indicated treatment – in addition to drug therapy or exclusively depending on the pathology - to prevent the onset of the symptoms of these diseases, is nutritional therapy.  

In all these cases, it consists of a low protein diet – naturally reducing the amino acid harmful to the patient – but with the addition of protein substitutes to guarantee the right dose of other amino acids, which cannot be introduced through the diet.

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