The mean disease duration was shorter for patients with any mutation in LRRK2 than for patients with idiopathic PD (10·9 years [SD 7·8 years] vs 15·1 years [SD 7·1 years], mean difference 4·2 years, 95% CI 3·2–5·2; p<0·0001). This evidence concerns the gene LRRK2 and Parkinson disease.