Mast Cell Activation Disorder (MCAD), Chronic Illness, and its Role in Methylation. What do chronic illnesses such as Autism, Chronic Fatigue Syndrome (CFS. Program Per Pc Me Thy Pasa. Mast Cell Activation Syndrome (MCAS) is an idiopathic disorder of inappropriate mast cell activation and increased mediator release, despite a normal total number of. Mast cell activation syndrome (MCAS) is one type of mast cell activation disorder (MCAD), and is an immunological condition in which mast cells inappropriately and. Mast cell activation syndrome: A newly recognized disorder with systemic clinical manifestations Matthew J. Hamilton, MD, aJason L.