It is tempting to speculate that the need to segregate PD samples by genetic background may also extend to other PD-related genes (such as LRRK2, PRKN or PINK1), and it is possible that the true role of DNA methylation in PD will only be revealed once genetic and epigenetic analyses are considered in combination as a matter of routine. The gene discussed is LRRK2; the disease is Parkinson disease.