Interaction of apolipoprotein E ε 4 with other genetic and non-genetic risk factors in late onset Alzheimer disease:: Problems pacing the investigator

The Apolipoprotein E4 allele (Apo-epsilon 4) is the major susceptibility gene for late onset Alzheimer Disease (AD) but epidemiological data suggest that the effect of this allele is modified in different individuals by genetic or environmental factors. Age and head injury are major non-genetic factors modifying the Apo-epsilon 4 risk. There is conflicting data as to whether alleles of other chaperon proteins (such as alpha-1-antichymotrypsin (ACT)) or Apo-epsilon 4 receptors (such as the VDRL receptor) modify the Apo-epsilon 4 risk for AD. We analyze problems posed by genetic association studies including those of multiple comparisons and selection of controls, the latter problem exacerbated by the wide variations in Apolipoprotein E allele frequencies observed in different groups and localities.