CD4 and Salla disease: Beyond the strong association between PD and SD, and preliminary evidence of Malassezia's presence inside the CNS, three additional lines of evidence support a direct contribution of Malassezia in PD: [1] many PD risk alleles affect lipid metabolism (Malassezia are lipophilic), [2] Malassezia invasiveness and melanin production are both stimulated by L-DOPA (L-DOPA is naturally abundant in the substantia nigra), and [3] low CD4+ T cell counts observed in PD might contribute to the over proliferation of microbes such as Malassezia.