Although there is no direct published evidence demonstrate that complex of the abnormal MCTs expression in the hippocampus and other parts of limbic system may induce the present spatial memory deficits, it is reported that increased MCT2 but reduced MCT4 levels were found in posterior cingulate (one part of the limbic system) of young adult APOE4 carriers, those who have a huge genetic risk for late-onset AD (Perkins et al., 2016). The gene discussed is APOE; the disease is Alzheimer disease.