During the initial stages of brain development, most neurons that were originally part of the brain during a process called apoptosis-whereas because the connections they are a part of are faulty and therefore the neuron does not receive enough neurotrophins to stay alive. However, for some reason, the neurons in the central nervous system that go on to form the cerebellum retain many more neurons in its ganglial network, so much so that the adult brain contains half of its neurons in the cerebellum.
One theory behind this is that because the connections in the cerebellum are so vital to the early development life of any creature, these would naturally be the place where, in the early evolutionary development of all animals, the emphasis to control and to have life (in a sense, to be differentiated as an animal) would be paramount. The cerebellum, therefore, could be said to be the part of the central nervous system that has had the most time to evolutionarily mature. As such, it has, on an evolutionary scale, made stronger and more vital connections than any other part of the brain.
Because all segments of DNA in the human body are identical (unless you are a chimera) it seems only logical that the epigenetic expression of the neurons in the cerebellum are somehow activated so that, while the fetal brain is still developing, are retaining more of their usefullness to the struggling fetus than are the other parts of the brain through some strategy of enhanced connectivity, thereby being able to retain more neurons than the rest of the CNS.
My question, however, is this: what if some mutation caused the epigenetic expression of the genes in the cerebrum to retain as many connections and neurons as did the expression of the genes in the cerebellum? Would such an individual live, or would the unnatural expression of these genes cause them to die?