def getMissenseData(data):
    """
    Keeps only those rows that correspond to missense mutations and are not
    known SNPs.
    Arguments:
        data =  dataframe
    Returns:
        tp_data = dataframe
    """
    # Keep rows that have mutation type as "Substitution - Missense" and if it
    # is not known SNP
    tp_data = data[(data["Mutation Description"] == 'Substitution - Missense')]
    return tp_data