Phenylketonuria and Maple syrup Urine are metabolic diseases of the “intoxication” type.

Phenylketonuria is a rare, autosomal recessive genetic disease found in 1 in 16,000 people. It affects the metabolism of phenylalanine. The main cause of the disease is a defect in enzyme activity i.e. phenylalanine hydroxylase which normally turns phenylalanine into tyrosine. As a result, phenylalanine accumulates in body fluids and there is a relative lack of tyrosine. The only known treatment at the present time is diet-based.

It was first described in 1934 by a Norwegian doctor called Dr. Folling. In 1953, Bickel published a case study of a child with phenylketonuria who was successfully treated by a restrictive diet. The publication had a major impact.

Phenylketonuria is diagnosed at birth using the Guthrie test. Testing began in France in 1967 and all babies have been tested at birth since 1975 because of the frequency of the disease, the absence of clinical signs in neonates and, more importantly, because of the effectiveness of early dietary treatment which has completely overturned the prognosis for the disease.

MSUD (Maple syrup urine disease)

This disease is caused by an enzyme blockage in the oxidative decarboxylation of the 3-branches chain amino acids (leucine, isoleucine and valine). The deficit leads to a build-up of the 3 precursor amino acids and corresponding ketacids in the blood, urine and tissues. The increase in the plasma rate of leucine reflects the build-up of leucine in the body. The frequency of this disease is 1 in 150,000 births. The only known treatment at the present time is a dietary treatment.

Coeliac disease

This disease produces a range of very different signs e.g. diarrhoea, bloating, a cessation of weight gain in children etc. The disease causes intolerance to gluten, a protein naturally present in wheat, barley, oats, rye and spelt. The necessity to ensure that the diet is totally gluten-free means that products such as cakes, bread, pasta and numerous processed foods will be excluded from the diet. They can be replaced by special gluten-free products.

Food Allergy

A food allergy is a clinical reaction to a specific component in the diet, mediated immunologically (in the case of intolerance – the reaction follows the ingestion of a foodstuff or one of its ingredients). One of the commonest food allergies among infants and children is allergy to cow’s milk.