https://www.ncbi.nlm.nih.gov/pubmed/27065452#

This is a retrospective study of patients with and without certain antibodies, including GAD65, and their disease course, and likelihood of dx of SPS.

They looked back across several years to determine the role of antibodies such as GAD65 and a few others, in the prognosis, and severity of SPS symptoms.

Positive GAD65 predicts for a worse outcome with respect to SPS symptoms.

(Of course, we know that there are exceptions to this. We all know from either a friendís course, or readings on FB SPS pages, that there are people with SPS whose GAD65 levels are normal.)