The ethnic heterogeneity within the subject sample is an important potential limitation. Although we did not detect differences in hippocampus morphology between ethnic groups and effects of the VEGFA genotypes were similar in the groups, it is still possible that population stratification influenced our findings, and replication in larger, more homogeneous samples will be important. Additionally, in order to have comparable group sizes, we grouped minor allele heterozygotes and homozygotes; this is consistent with a dominant model but would also have reasonable power if the alleles were codominant (the most likely case where the markers studied are in LD with an ungenotyped functional variant). If the correct mode of effect is recessive, then there is the potential for Type II error in analyses for SNP-1 and SNP-4. These results should be considered preliminary, especially owing to the modest sample size, and replication studies are warranted.
