Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Subacute Sclerosing Panencephalitis ?
    ### Response:
    Subacute sclerosing panencephalitis (SSPE) is a progressive neurological disorder of children and young adults that affects the central nervous system (CNS). It is a slow, but persistent, viral infection caused by defective measles virus. SSPE has been reported from all parts of the world, but it is considered a rare disease in developed countries, with fewer than 10 cases per year reported in the United States.
    