Tumors that develop in TSC are known to develop through a two hit mechanism, in which there is uniform germ-line or mosaic inactivating mutation in TSC1 or TSC2, and second hit inactivating mutation in the other allele of the same gene to lead to loss of function of either TSC1 or TSC2 in the cells comprising the tumor [2–8]. This evidence concerns the gene TSC2 and tuberous sclerosis.