Intriguingly, other MBT proteins have been shown to act as tumour suppressors: lethal(3)malignant brain tumour [l(3)mbt)] mutants of Drosophila develop malignant transformations of the adult optic neuroblast and ganglion mother cells of the larval brain [9]; furthermore, the human MBT domain genes L3MBTL2, L3MBTL3 and SCML2 are mutated in rare cases of medulloblastoma [10]. The gene discussed is L3MBTL2; the disease is medulloblastoma.