Mutations could be introduced to mice by knockin, and the effects (clumping, levels of normal APP function) measured. Alternatively, this could be studied in isolated mouse cells by adding mutated cDNA's to them. These would then be expressed, allowing APP function and clumping to be measured. The first option would be better, with more generally applicable results.
Work Step by Step
First, consider how the mutations, which already exist, could be introduced to mice/their cells and expressed. Then recall what needs to be measured (APP function, clumping.)