Mušič et al. found DAO deficiency in 80% of 316 adult patients showing various symptoms associated with histamine intolerance (e.g., urticaria, pruritus, diarrhea, abdominal pain, vomiting, constipation, cough, rhinitis and headache), as well as significantly lower plasma DAO activity compared to the control group [83]. Here, DAO is linked to rhinitis.