Apolipoprotein E ε4 prevalence in Alzheimer's disease patients varies across global populations: a systematic literature review and meta-analysis.

Alzheimer's  patients from Asian and southern European/Mediterranean communities had significantly lower APOE4 carrier status estimates than those recruited in North America  or northern Europe;

This also appears to be the case for a number of polymorphic genes in schizophrenia and Alzheimer's disease See this page