quitin carboxyl-terminal hydrolase gene: (UCHL1), involved with protein degradation; the UCHL1 protein is highly expressed throughout the brain, to the extent that it makes up perhaps as much as 2% of total soluble brain protein. Replaceable neurons (such as those found in the dentate gyrus and the olfactory bulb, where neurogenesis occurs), and neurons that die in people with diseases such as Alzheimer's and Parkinson's have unusually low levels of UCHL1. Rising levels of UCHL1 may be associated with a reduced risk of neuronal death.