GAD65 antibodies, chronic psychosis, and type 2 diabetes mellitus.

Glutamic acid decarboxylase is the rate-limiting enzyme in the production of gamma aminobutyric acid, an inhibitory neurotransmitter. Autoantibodies to the glutamic acid decarboxylase 65 isoform have been associated with chronic psychotic disorders and are found in neurons and pancreatic islets. Blood samples were collected from normal controls (n=16), individuals with chronic psychosis with type 2 diabetes mellitus (n=3), and patients with chronic psychosis without diabetes (n=8). No differences were found between any of the groups for frequency of positive glutamic acid decarboxylase 65Ab samples (98th percentile of a healthy control group) or in mean values of glutamic acid decarboxylase 65Ab. Sample size was likely too small to detect differences if they do exist.