Given that SNPs in CRHR1 have been previously reported to be associated with PD [5,32,36,37] and Alzheimer’s disease [38] and SNP–SNP interactions are identified in SNCA, GAK and MAPT, a well-known risk gene for PD, this suggests that these joint effects are true findings and nicely demonstrate the utility of our approach to identify joint genetic effects associated with complex diseases like PD. Here, GAK is linked to early-onset autosomal dominant Alzheimer disease.