A study showed a higher level of SDF-1 alpha in CSF of asymptomatic LRRK2 mutation carriers but statistically not significant.29 In PD patients, blood SDF-1 alpha was found to be significantly higher than control subjects.30,31 An upregulation of the CXCL12/CXCL4 signaling pathway has been shown to be involved in the loss of dopaminergic neurons in animal models.32 Whether increased SDF-1 alpha is mechanistically involved in LRRK2 mutations and increased PD risk requires more investigations. Here, CXCL12 is linked to Parkinson disease.