The Arctic amyloid precursor protein (APP) Alzheimer mutation, is located inside the β-amyloid (Aβ) domain. Here, hybrid APP mutants containing both the Swedish and the Arctic APP mutations were investigated. ELISA measurements of cell media showed decreased levels of both Aβ40 and Aβ42. Similar results were obtained for the Dutch and Italian mutations, whereas the Flemish mutation displayed increased amounts of Aβ40 and Aβ42. Immunoprecipitation studies revealed increased Aβ40/p340 and Aβ42/p342 ratios for the Arctic mutation. These results were further verified by quantification revealing decreased levels of αAPPs accompanied by increased βAPPs levels in the media. Thus, the pathogenic effects of the Arctic mutation may not only be due to the changed properties of the peptide but also altered processing of Arctic APP.