Disclosed is a pharmaceutical composition for the treatment and/or prevention of a disease involving abnormal accumulation of amyloid β protein comprising ILEI, or a vector into which a polynucleotide encoding ILEI is inserted a method for screening a compound for the treatment and/or prevention of a disease involving abnormal accumulation of amyloid β protein and a method for treating and/or preventing a disease involving abnormal accumulation of amyloid β protein.
