We sought to examine the hypothesis that mutations in GBA and LRRK2 would have asymmetrical loss of radioligand, reflecting initially focal neurodegeneration due to interactions with additional endogenous or exogenous pathogenic factors, whilst PD with bi-allelic PINK1 or Parkin mutations would manifest more symmetrical radioligand loss since mutations in these genes alone is sufficient to induce neurodegeneration. Here, GBA1 is linked to Parkinson disease.