Mutations of Rab GTPases and alterations in Rab-mediated membrane trafficking are also associated with the progression of neurodegenerative diseases, including Alzheimer's, Parkinson's, and Huntington's diseases, and enhanced expression of Rab GTPases may ameliorate neurodegenerative phenotypes (51, 52, 53, 54). This evidence concerns the gene RAB6A and juvenile Huntington disease.