APOE and Parkinson disease: Earliest reports on the association of APOE e4 carrier status with age of PD onset were those by Zareparsi et al. (1997, 2002) and further supported by Pankratz et al. (2006) wherein subjects with APOE ε4 had a mean PD onset age of 59.7 years which was significantly lower in comparison to subjects homozygous for the more common ε4 allele with a mean onset age of 62.4 years.