Much progress has been made in delineating genome variation associated with susceptibility for developing PD,25, 37 but little is known about the genetic architecture controlling disease progression.11, 24, 38 In a surprising analogy to GD, GBA mutations enriched in neuropathic GD in homozygotes (leading to death at age 2 or severe neurological complications) were associated with aggressive cognitive decline in PD. The gene discussed is GBA1; the disease is Parkinson disease.