Patients with idiopathic PD needed treatment earlier than patients with mutations in LRRK2: the mean time from the onset of PD to the start of dopamine-replacement treatment was 4·01 years (SD 2·50 years) for patients with mutations in LRRK2 and 3·03 years (2·90 years) for patients with idiopathic PD (difference 0·98 years, 95% CI 0·61–1·35 years; p<0·0001). The gene discussed is LRRK2; the disease is Parkinson disease.