Mutation of the CSMD1 gene, which encodes a protein that participates in complement activation and inflammation in the CNS, leads to familial Parkinson disease (PD) in the absence of other gene mutations, new research published in Neurology: Genetics suggests. Whole-exome sequencing was performed in two unrelated Spanish families with PD, in which the presence of other gene mutations known to cause PD had been ruled out. From this sequencing study, the investigators identified two possible PD-causing mutations in the CSMD1 gene, which were both located in complement control domains within the translated CSMD1 protein. As mutations in CSMD1 have already been implicated in schizophrenia and Alzheimer disease, the researchers suggest that the complement pathway could offer an important therapeutic target in PD and other neurodegenerative conditions.