Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pervasive Developmental Disorders ?
    ### Response:
    The diagnostic category of pervasive developmental disorders (PDD) refers to a group of disorders characterized by delays in the development of socialization and communication skills. Parents may note symptoms as early as infancy, although the typical age of onset is before 3 years of age.
    