Prevalence and Clinical Picture of Diamine Oxidase Gene Variants in Children and Adolescents with Attention Deficit Hyperactivity Disorder: A Pilot Study

Background: Attention Deficit Hyperactivity Disorder (ADHD) is the most prevalent neurodevelopmental disorder worldwide. The diamine oxidase enzyme (DAO) is responsible for the histamine gastrointestinal degradation. Its deficient functioning may implicate an excess of histamine in the body. The excess of histamine (histamine intolerance, HIT) has been related with a growing number of diseases and pseudo-allergic symptomatology. However, data on the relationship between the DAO enzyme, HIT, and ADHD are lacking. The main objective of this pilot is to study the prevalence of the four most relevant SNP variants of the AOC1 gene affecting DAO enzyme functionality in a sample of patients diagnosed with ADHD attending child and adolescent mental health services. Methods: In a cohort of 303 participants, we measured the SNP variants of the AOC1 gene. Results: The prevalence of having at least one minor dysfunctional allele was 78.8%. No relationship between ADHD severity and DAO deficiency was found. However, some AOC1 gene variants associated with DAO deficiency were related to several meaningful medical comorbidities. Furthermore, we found a strong association between DAO activity and the intelligence quotient, particularly in working memory. Conclusions: Some SNP variants of the AOC1 gene associated with DAO deficiency are related to some medical comorbidities and cognitive dysfunction in ADHD children and adolescents. Studies including patients with other diagnoses and healthy controls and bigger samples are warranted to confirm our preliminary results.