Drosophila LRRK (dLRRK) is the unique homolog of human LRRK2. Consistent with the notion that LRRK2 gain-of-function mutations cause PD, dLRRK null mutant flies show little or no defects in the viability of DA neurons [122], although some controversy exists [123]. This evidence concerns the gene LRRK2 and Parkinson disease.