IDH1 and oligodendroglioma: For example, oligodendrogliomas are defined by co-deletion of chromosomal arms 1p and 19q (in addition to IDH mutation), but this represents a form of stable aneuploidy, mediated by an unbalanced translocation between chromosomes 1 and 19, with subsequent loss of the derivative chromosomal fragment der(1;19) (q10;p10) [82, 98, 171].