Neurotrophic factors, such as nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), and BDNF that regulate the growth, survival and differentiation of neurons and synapses in the CNS also play important parts in learning and memory and in a range of brain disorders have been also shown to be modulated by SCFAs (120–123). The gene discussed is GDNF; the disease is brain disorder.