Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Periodic fever, aphthous stomatitis, pharyngitis and adenitis ?
    ### Response:
    Periodic fever, aphthous stomatitis, pharyngitis, cervical adenitis (PFAPA) is a periodic disease, which is a heterogeneous group of disorders characterized by short episodes of illness that regularly recur for several years alternated with healthy periods.
    