ANTIBODIES TO I-125 GLUTAMIC-ACID DECARBOXYLASE IN PATIENTS WITH STIFF MAN SYNDROME

Antibodies to glutamic acid decarboxylase (GAD) are found in about 40% of patients with stiff man syndrome. A new assay involving immunoprec ipitation of I-125-glutamic acid decarboxylase was used to measure ant i-GAD antibodies in 18 patients with stiff man syndrome. Of the eight serum samples from patients with stiff man syndrome, that had previous ly been found positive by immunoprecipitation of S-35-GAD, seven were strongly positive with I-125-GAD and one gave an equivocal result. Oth er serum samples from patients with stiff man syndrome and from contro ls were negative except one from a patient who had a thymoma, acquired neuromyotonia, and myasthenia gravis. Nine of 35 serum samples referr ed for testing were positive; in two of these the serum titre was 20-5 0 times higher than that in the CSF. This assay should prove useful in the diagnosis, management, and investigation of stiff man syndrome.