The aim of this review was to explore whether there was a demographic association with the presence of the Apolipoprotein E ε4 (APOEε4) allele in patients with early-onset Alzheimer disease (EOAD). 

Several studies have already shown the presence of the APOEε4 allele as a risk factor for developing EOAD. However, little information was available regarding the prevalence of APOEε4 alleles in EOAD patient according to their geographic data. 

This literature review was completed by three authors, including a scientific librarian. Eligible articles included patients diagnosed with EOAD and data on the presence or the absence of APOEε4 allele and the other mendelean mutations related to EOAD. 

Initially, 81 articles were sourced from PubMed and after screening, 18 articles were included. We obtained nine articles from Europe, two articles from North America, and seven articles from Asia which corresponds to 1434, 1221 and 946 patients respectively. The results showed that the prevalence of APOEε4 allele tended to vary in EOAD patients from Asia compared with European and North American. In fact, this review demonstrated that 55% of the European sample and 64% of the North American sample had the allele in question. Therefore, more than half of the sample had the allele in Europe and North America, while 37% of the Asian sample shows the APOEε4 allele, a notably lower occurrence. 

Given these results, it would be relevant to evaluate the genetics of the European and North American populations with EOAD to identify potential causes behind this tendency. Conversely, it would be interesting to evaluate the presence of other risk factors, both genetic and environmental, which could explain other risk factors predominant in the Asian early-onset Alzheimer disease population.