AKT-0066

A 45-year-old man presents to his General Practitioner complaining of persistent urticaria, which he has experienced over the last six months. He obtains relief by taking antihistamine tablets. He takes no other medications and has restricted his diet to fresh food in an attempt to reduce the histamine exposure in his diet. He has not been in contact with any new chemicals or materials.
What is the most likely underlying cause of this patient’s presentation?