When the cohorts containing only PD cases and controls were analyzed jointly (WUSTL and PPMI – N = 700 cases and 189 controls), the APOE locus was GWAS significant (effect = − 0.50, p = 9.25 × 10−19) but not the HLA region (effect = 0.22, p = 3.58 × 10−04). This evidence concerns the gene APOE and Parkinson disease.