Dear Glenn,
The current literature on anti-GAD and Stiff-Person Syndrome and/or cerebellar ataxia doesn't discuss GAD67 any more. It is agreed that the antigen recognised is a different epitope on GAD65 to that recognised by diabetics without SPS (Solimena M and Carmilli PD TINS, 14(10) 452, 1991).
The majority of patients with SPS or cerebellar ataxia produce a "cobble-stone" immunofluorescence pattern in the granular layer on monkey cerebellum (see attached PDF). We screened around 20 diabetics with high levels of anti-GAD (RSR ELISA) with no evidence of neurological disease and none demonstrated the "cobble-stone" pattern. This suggests that the SPS sera recognize a fixation-dependent epitope on GAD65.
The presence of anti-amphiphysin IIF (and anti-amphiphysin blot positive) in patients with anti-GAD increases the likelihood of a tumour.
Regards
Bob Wilson
