Although familial essential tremor is associated with a gene defect, can it be triggered or worsened nonetheless by a chronic virus, and if so, in what percent of cases?

This malady can exist entirely on its own but, as with other viral caused maladies, there will be a worsening if a viral infection gets going and compounds production of symptoms. That might well confound an accurate diagnosis by making someone with the gene defect have symptoms that more resemble another form of tremor.