In the fifty years since its discovery, a substantial body of work has established that nerve growth factor plays a key role in promoting the survival of neurons during development; the recent demonstration that it can also promote cell death therefore comes as a surprise.
Davies, A. M. (1997). Neurotrophins: The yin and yang of nerve growth factor. Current Biology. Cell Press. https://doi.org/10.1016/s0960-9822(06)00016-9