def is_mnp(var):
    """
    Check if the mutation is a multiple nucleotide polymorphism.
    """
    if len(str(var.ALT[0])) == len(str(var.REF)) and len(str(var.ALT[0])) > 1:
        return True
    elif len(str(var.ALT[0])) != len(str(var.REF)):
        return False