Background: Glutamic acid decarboxylase (GAD) is an enzyme present in central nervous system and in many other tissues including pancreas. It catalyses conversion of glutamate to gama-aminobutyric acid. Anti-GAD autoantibodies are present in 80% of patients at the time of diagnosis of type 1 Diabetes Mellitus. The link between presence of anti-GAD antibodies in Stiff-man syndrome has been known for years. However, recently, coexistence of cerebellar ataxia in patients with type 1 Diabetes Mellitus indicated a link between anti-GAD antibodies and cerebellar ataxia in adults. However, this is the first pediatric case with cerebellar ataxia and type 1 Diabetes Mellitus in children.Case Report: A 14 year-old boy who initially presented with cerebellar ataxia at age 11 years, was diagnosed with type 1 Diabetes Mellitus. The diagnostic work-up for cerebellar ataxia including metabolic studies, genetic study for Friedreich ataxia, and MRI of the brain were negative. He had a very high serum titer of anti-GAD antibodies at the time of and 2 years after the diagnosis of type 1 Diabetes Mellitus.Conclusions: Presence of anti-GAD antibodies in children may cause autoimmune cerebellar ataxia years before the onset of overt Type 1 Diabetes Mellitus. Therefore, in cases with cerebellar ataxia of unknown etiology in children, anti-GAD antibodies in serum or cerebrospinal fluid should be measured, not only to determine the etiology of ataxia but also to determine the future risk of other autoimmune endocrinopathies.

Keywords: Anti-Glutamic Acid Decarboxylase antibody, Autoimmunity, Cerebellar Ataxia, type 1 diabetes mellitus