Today, April 25, is International DNA Day and the discovery of the structure that encodes our genes is celebrated. Watson and Crick published a model for this structure on April 25, 1953, although it would not have been possible without the previous contributions of Rosalind Franklin or Florence Bell, among many others. Since then, we have learned a lot about DNA and its function. What do we know about the genetics of allergies?
Is it the same genetics as hereditary?
First of all, it is essential to explain the difference between a genetic disease and a hereditary disease. A disease that is defined as genetic is one whose symptoms or pathologies are due to a mutation in some region of the DNA . This mutation can occur during early stages of development or it can be acquired over time, for example due to external environmental factors.
A hereditary disease is one that is inherited from one or both biological parents . If a genetic disease can be transferred to offspring because it affects gametes, then it is defined as hereditary. Symptoms of a hereditary disease can appear at birth or over the years.
Therefore, almost all hereditary diseases are genetic, but not all genetic diseases are hereditary. But is allergy a genetic disease?
Allergy is not a genetic disease
When the mechanism or pathology of a disease is studied, an attempt is made to find out what is the cause that triggers the symptoms or problems in the organism. However, most diseases have multiple factors that, together, cause a chain reaction that leads to symptoms .
Genetic diseases have the advantage of being able to identify the gene (or genes) that suffer from the mutation that drops the first piece and causes a domino effect in the organism. Sometimes, knowing the responsible gene does not mean that it can be cured, but treatments can be developed that address the consequences of the mutation.
Allergies have also been investigated from a genetic point of view, in search of the “allergy gene”. However, a century later, it has still not been found . It is true that mutations in molecules involved in the defense against pathogens, such as in the physical barriers of the skin, confer a predisposition to develop allergies.
However, this predisposition must be favored by environmental factors that tip the balance towards tolerance or allergy. All the evidence indicates that allergies appear when the set of genetic and environmental factors shape the immune system in one direction.
Despite this, pediatricians began to notice that children of allergic parents were more likely to have allergies . Furthermore, this observation was more pronounced if both parents had the same type of allergy. If allergies are not genetic, how can they be inherited?
Inheritance of a genetic predisposition
Since allergies have a genetic factor, if that factor is transferred through the eggs or sperm, an allergic predisposition can be inherited. If several predisposing factors are added, children can develop the disease . Several studies have confirmed that the offspring of parents suffering from allergies (food, asthma, allergic rhinitis or eczema) have a higher risk of developing these allergies.
These types of studies are very useful since measures can be taken during infancy or the first years of development during which the immune system is malleable . Certain recurring events in childhood, such as viral infections, an environment that is too hygienic, or contact with dogs, can prevent or cause allergies.
Information is power
As in many other aspects of science, the more information we get about a process, the more likely we are to understand it and be able to solve it. In this case, evaluating the risk of developing allergies according to the diseases suffered by the biological parents allows specialists to take the necessary measures.
In recent years, several studies have been carried out with children who have a high risk of suffering from peanut allergy, where they have tried to implement measures to prevent this allergy. Although it may be counterintuitive, exposing these infants to peanuts may have a favorable effect on developing tolerance to eating peanuts.
In other types of parental allergies, breastfeeding may be more advisable than the use of formulas , or prebiotic or probiotic supplements during pregnancy . In order to assess the level of impact of all these measures, it is necessary to identify which genetic factors are important in the development of allergies.
Although it is accepted that there is a clear hereditary predisposition factor to develop allergies, there are other environmental factors that can reverse its influence . As it is a multifactorial disease, studies are still necessary to find the answers to so many unknowns.
References:
Ferreira et al. 2017. Shared genetic origin of asthma, hay fever and eczema elucidates allergic disease biology. Nature Genetics. doi: 10.1038/ng.3985
Koplin et al. 2013. The Impact of Family History of Allergy on Risk of Food Allergy: A Population-Based Study of Infants. Int J Environ Res Public Helath. doi: 10.3390/ijerph10115364Portelli et al. 2015. Genetic risk factors for the development of allergic disease identified by genome-wide association. Clin Exp Allergy. doi: 10.1111/cea.12327.Westman et al. 2013. The link between parental allergy and offspring allergic and nonallergic rhinitis. Allergy. doi: 10.1111/all.12267
