Malaria resistance, Cooley's anemia (thalassemia), and (hypothetically) in homozygotes, high risk of AD (both under- and over-expression of either HBB or HBD genes are associated with an increased risk of AD and more rapid cognitive decline (i.e., abnormal Hb abundance correlates with both AD and cognitive decline), whereas Aβ and Hb aggregate with each other near traumatic vascular injury in the brain); heterozygote protects from AD. The gene discussed is GSTM1; the disease is Alzheimer disease.