Is there a test to detect autoantibodies against metabotropic glutamate receptors?

Yes : This antibody is associated with neuropathological conditions such as subacute cerebellar ataxia and CNS paraneoplastic syndrome. Most research has been conducted in europe. Its not a commonly ordered test in clinical practice. A neurologist may help guide you.

You asked for it: Yes, there is. It's for research. Abs to the mGluR1 subunit of metabotropic Glu receptor 1 have been found in small groups of ataxia pts. They're also detected in nonimmunological neurological diseases eg stroke & trauma but these may be epiphenomena (due to spillage of cell contents outside the blood-brain barrier). If you're concerned, my advice is: Find something else to worry about.