Is opsoclonus-myoclonus-ataxia a genetic problem, if coming from breast cancer. my gran got it after breast cancer. i have autoimmune problems and was wondering, if it is a one off thing or genetic.

Not familial: I'm sorry about your grandmother and I am glad you are taking a proactive approach to your health. The syndrome you describe is usually due to anti-ri antibodies that attack a breast cancer and cross-react with some of the cells in the nervous system. If you do not have breast cancer, this is not a risk, and i've seen nothing to make me think that having other autoimmune disease puts you at risk.

Clarification: Most often associated with childhood hemangioblastoma, but can be seen with other conditions on a far less frequent basis. Likely not a clearcut autoimmune condition but more likely secondary to a paraneoplastic effect of a tumor, essentially a toxic response at a distance. Hard to say if truly genetic susceptibility and unlikely that you might be at risk.