Response to the letter "Reassessing the hypothesis of essential tremor as a prodromal feature of Parkinson's disease".

There is growing body of evidence that some patients with essential tremor (ET) have an increased risk for developing Parkinson's disease (PD) and, therefore, as noted in our paper, ET may be considered a prodromal feature of PD. Although a genetic causal link between ET and PD has not been established, future development of diagnostic and progression biomarkers may provide insight into the relationship between these common movement disorders.