Furthermore, a transgenic mouse model for AD (APP23 mice), in which the animals develop Aβ plaques and other pathological changes observable in the brains of AD patients [114, 115], was crossbred with aromatase-KO (Ar−/−) mice to test the influence of E2 on the formation of Aβ plaques. The gene discussed is CYP19A1; the disease is Alzheimer disease.