DAO deficiency and Attention Deficit Hyperactivity Disorder (ADHD)

For some years now, an excess of histamine not mediated by IgE has been related to neurodevelopmental disorders such as Attention Deficit Hyperactivity Disorder (ADHD) and neurodegenerative diseases including Alzheimer’s. Both scientifically and empirically there is evidence of this link, increasingly with respect to ADHD. 

Attention deficit hyperactivity disorder, known as ADHD, is a disorder that is more prevalent in children and is characterized by moderate to severe distractibility, short attention spans, motor restlessness, emotional instability, and impulsive behaviors. It is a behavioral syndrome with neurobiological bases and it has a strong genetic component. It has been determined that it affects between 5-10% of the child and adolescent population and is about 3 times more frequent in males.

The main symptoms of ADHD are, on the one hand, difficulty sustaining concentration (attention deficit), as well as hyperactivity (motor restlessness) and impulsive behavior (lack of cognitive control). It should be noted that these can appear separately or in combination. Furthermore, it has been shown to have a chronic character, since in most cases, the symptoms persist in the years after adolescence. In this sense, due to the high prevalence of this disorder and the relationship that is being observed with the Diamine Oxidase (DAO) deficiency, this connection is being studied by researchers.

Histamine is known to be an important mediator of many biological processes: gastric acid secretion, inflammation, neuromodulation and regulation of immune function. This amine is produced by the body itself and it can also enter externally through the intake of certain foods and fermented beverages. However, when free histamine concentrations in the blood are high, they trigger a series of unwanted side effects.

The main route of inactivation of histamine ingested with food is through DAO enzyme, in order to prevent this amine from reaching the bloodstream. Following this line, the Child and Adolescent Psychiatrist Dr. Hilario Blasco-Fontecilla, together with his team of researchers, Ping Wang, Chao Li, Adriana Duelo and Teresa Perucho, are carrying out a study on the prevalence and clinical profile of Diamino Oxidase (DAO) deficiency in patients with Attention Deficit Hyperactivity Disorder. Currently, there are some preliminary results of the study presented last month at the National Congress of the Spanish Association of Child and Adolescent Psychiatry in Madrid, and it is observed that, of 89 patients, 77% have a reduction of the activity of the DAO enzyme and that 15.9% presented a severe reduction. Consequently, histamine cannot be metabolized properly and travels to the bloodstream. In this way, it was detailed that the prevalence of DAO deficiency is very high in children and adolescents with ADHD and that the severity of DAO reduction is related to various allergic, respiratory and gastrointestinal symptoms, among others.

It should be noted that the problem is accentuated by the fact that some drugs indicated for the treatment of ADHD are inhibitors of DAO activity. Initially, the drugs that are administered, they manage to alleviate the symptoms; however, in the long term, its dose must be increased due to the dependence they create. In this way, a vicious circle is entered in which more medication is administered and, consequently, the blood histamine levels increase.

In conclusion, these data are of great interest to be able to continue researching in this field and to be able to confirm what we have been seeing for years. An improvement in symptoms (more concentration and calm) thanks to following a low-histamine diet supplemented with the enzyme DAO in patients with ADHD. In this way, a better comprehensive approach could be carried out in these patients, in order to improve their quality of life.

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