Some consider essential tremor a risk factor for PD, but there is no consensus, and studies have reported controversial results.6Inspired by the Braak's theory, which suggested that alpha-synuclein could be deposited in the digestive tract and reach the central nervous system via retrograde transport through the vagus nerve, two studies have suggested that prior truncal vagotomy or appendectomy could be associated with a lower risk of developing PD.78 This evidence concerns the gene SNCA and Parkinson disease.