Huntingtin (HTT) is a cytoplasmic protein which is highly expressed in the brain, and whose anti-apoptotic role is critical for neuronal survival.
The wild-type (WT) protein has a functional structure, with a "normal" polyglutamine (polyQ) domain containing less than 36Q. The mutant HTT protein harbors an abnormally long polyQ tract (> 36Q), which causes the aggregation of the no longer functional protein. HTT aggregation leads to the selective neuronal cell death responsible for Huntington's Disease.