Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Olivopontocerebellar atrophy ?
    ### Response:
    Olivopontocerebellar atrophy (OPCA) is a progressive condition characterized by the degeneration of nerve cells (neurons) in specific areas of the brain. It occurs in several neurodegenerative diseases, including multiple system atrophy (MSA) and inherited and non-inherited forms of ataxia.
    