Neurodegenerative diseases are a heterogeneous group of diseases with different clinical pictures and different medium , whose common feature is the dysfunction or loss of particularly vulnerable populations of nerve cells. The presence of a selective loss of nerve cells allows the use of a single therapeutic strategy is to replace losses of new cells , able to take the functions of lost cells. For 20 years now attempt to restore normal function via neural stem cell transplantation in neurodegenerative diseases , in particular Parkinson's disease and Huntington's .