According to WHO, there are close to 7,000 rare diseases that affect 7% of the global population, and one of these groups is made up of Congenital metabolic disorders (CMDs).
Congenital metabolic disorders are caused by alterations in the metabolic routes that are in charge of digesting, absorbing or breaking down nutrients. These alterations can affect any groups of nutrients, such as vitamins, carbohydrates, fats and proteins.
Alteration of a metabolic route can give rise to two situations can occur in parallel. On the one hand, there can be an accumulation of one or many metabolites, which can cause toxicity. And, on the other hand, there could be a low production of a nutrient that can cause a deficit for the organism.
For many of these alterations, there is currently no specific treatment, and while studies are making progress, intervention in diet is key to preventing consequences to health.
Carbohydrate metabolism disorders include GLUT1 glucose transporter and deficiency syndrome and galactosemia. In these cases, treatment consists of following a carbohydrate-restricted diet. In other words, reducing the consumption of carbohydrates in general for the first case, and of galactose (a carbohydrate found in milk and milk derivatives) in the second. This restriction must be maintained for life, under dietary management.
In aminoacidopathies, illnesses related to a deficit in breaking down amino acids, it is essential to be careful with foods containing protein to prevent the accumulation of a certain metabolite. Phenylketonuria (PKU) is the most common aminoacidopathy in Spain. It occurs in one in every 10,000 people and is a consequence of a deficit of activity in the enzyme that metabolises the amino acid phenylalanine. This enzyme’s low activity causes an increase in the concentration of phenylalanine in the blood and the brain, which has neurotoxic effects that can lead to a deterioration of cognitive development. That is why it is so important to implement dietary treatment from the first days of life.
The PKU diet consists of restricting consumption of foods containing protein, as they are a source of phenylalanine. in this way, plasma phenylalanine levels can be kept within the range recommended for each age. Furthermore, people with PKU need to take vitamin supplements, fatty acids, carnitine and other trace elements to prevent protein deficits. They also eat foods specially modified to achieve a very low protein content (under 0.5%), which substitute frequently consumed foods such as pasta, rice and bread. In addition, to prevent nutritional deficits people with PKU must eat dietary formulas that provide all the necessary amino acids except phenylalanine.
In the case of fatty acids (lipids), there are alterations to this metabolic route that cause an accumulation of some fatty acids in the cells. Dietary measures for these patients aim to restrict fat intake, not only on quantity but also in fat type (long, medium or short chain). At the same time, sufficient daily calorific intake must be ensured.
In conclusion, nutrition is the most useful tool for the therapeutic treatment of most CMDs. For now, while there is no specific treatment available, it is important that nutritional intervention is done specifically for each disorder, with the aim of achieving the best metabolic control possible.
Hospital Clínic of Barcelona has a Clinic Experts Unit (UEC) focused on rare hereditary metabolic diseases in Catalonia. In 2010, the adult metabolic disorders work group was formed, with professional, among those nutritionists, whose work is centred around understanding and treating CMDs.
Author: Cristina Montserrat, Dietitian-Nutritionist, Clínic Institute for Metabolic and Digestive Diseases
