For some obscure reason, many neurologists (including leading MG experts) are very reluctant to consider CMS, in patients with seronegative MG.

There is a recent (relatively small) study that showed that 2/70 patients with seronegative myasthenia (one who had thymectomy and received immunsupressive treatment) had a mutation in the Rapsyn gene. And there are many other possible genetic abnormalities (in this study they only checked for a certain, relatively common mutation in Rapsyn and DOK7).

Even in seropositive patients it is possible that there is an underlying genetic abnormality. (there is one case report of two sisters with CMS and autoimmune MG).

It is possible to have genetic predisposition to an autoimmune disease, but when there is a cluster of family members it should at least raise the question of CMS. This is not an academic question because the management approach is very different.

alice