To analyze whether LRRK1 can compensate for the loss of LRRK2 function, Giaime and colleagues [79] generated KO mice deficient in both Lrrk1 and Lrrk2 (Lrrk1/2 double KO (DKO)) and discovered that the Lrrk1/2 DKO mice show significant age-dependent neurodegeneration in areas relevant to PD. The gene discussed is LRRK2; the disease is Parkinson disease.