Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) megalencephalic leukoencephalopathy with subcortical cysts ?
    ### Response:
    Megalencephalic leukoencephalopathy with subcortical cysts is a progressive condition that affects brain development and function. Individuals with this condition typically have an enlarged brain (megalencephaly) that is evident at birth or within the first year of life.
    