A small study involving 50 children and teens living in Mexico City (aged 13.4 ± 4.8 years) has found that those with the 'Alzheimer's gene' APOEε4 (22 of the 50) were more vulnerable to the effects of air pollution on cognition. Those with the gene variant had a reduced NAA/Cr ratio in the right frontal white matter (as those with Alzheimer's do), poorer attention and short-term memory, and below-average scores in Verbal and Full Scale IQ (>10 points), compared to those with the 'normal' ε3 variant. They also had problems with odor detection, also typical of those developing Alzheimer's.
The study is small and lacks a proper control group, but while other studies have found some signs of early brain differences in those carrying the ε4 variant, they have not been nearly as marked as this. The finding certainly warrants concern and further study.
Calderón-Garcidueñas, L. et al. 2015. Decreases in Short Term Memory, IQ, and Altered Brain Metabolic Ratios in Urban Apolipoprotein ε4 Children Exposed to Air Pollution. Journal of Alzheimer's Disease, 45(3)