abetapeptide length and apolipoprotein e genotype in alzheimers disease apolipoprotein e apoe epsilon4 allele a risk factor for the development of alzheimers disease ad is associated with increased amyloid deposition we examined cerebral cortex in 68 ad cases using antibodies to betaamyloid abeta peptides of different length abeta140 and abeta142 and found that the increased plaque frequency observed with epsilon4 genotypes may be largely attributed to an increase in abeta140positive plaques indeed both the number of abeta140positive plaques as well as the ratio of abeta140abeta142positive plaques increased with epsilon4 dosage in contrast the frequency of abeta142immunoreactive plaques was similar for epsilon3epsilon3 epsilon3epsilon4 and epsilon4epsilon4 genotypes apoe may influence abeta1 length by facilitating abeta140 deposition onto abeta142seeded plaques or by modulating the activity of a putative carboxypeptidase that forms abeta140 from abeta142 in situ