For example, mutation, deletion or silencing of genes encoding tricarboxylic acid cycle (TCA cycle) proteins, including isocitrate dehydrogenases 1 and 2 (IDH1/2), are frequent in acute myeloid leukaemias and brain cancers (WHO grade 2 and 3 astrocytomas, oligodendrogliomas and secondary glioblastomas)2, 3. Here, IDH1 is linked to brain cancer.