SD occurs mainly in lipid-rich areas of the skin (42), and several PD risk alleles either cause an abnormal accumulation of intracellular lipids (GBA, LRRK2, PINK1, SPG11) (103, 136, 139, 140) or increase lipase permeability of lipid droplets (SNCA) (141). The gene discussed is LRRK2; the disease is Parkinson disease.