The invention relates to a novel Glutamic Acid Decarboxylase (GAD). More specifically, novel DNA and protein sequences relating to GAD. Additionally, the invention discloses a novel composition and related methods for treating neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, epilepsy, and the like, using viral and non-viral delivery systems that deliver therapeutic agents to specific regions of the brain. More specifically, using an adeno-associated viral vector to deliver a nucleotide sequence encoding a novel glutamic acid decarboxylase (GAD) to specific regions of the brain that are over stimulated or disinhibited in various diseases, including neurodegenerative diseases.