Trisomy of chromosome 21 genes other than APP does not increase APP abundance nor alter β-CTF/α-CTF ratio. (A, B and D) Full-length APP (FL-APP), APP β-CTF and APP α-CTF were measured in cortex (wild-type n = 17, trisomic n = 16, tgAPP n = 24, trisomic;tgAPP n = 19) and hippocampus (wild-type n = 11, trisomic n = 12, tgAPP n = 24, trisomic;tgAPP n = 17) at 3 months of age. (A) Full-length APP was higher in tgAPP and trisomic;tgAPP compared with wild-type or trisomic mice [cortex F(1,68) = 87.667, P < 0.001, hippocampus F(1,56) = 94.301, P < 0.001]. Trisomy did not alter full-length APP [trisomy–tgAPP interaction, cortex F(1,68) = 0.483, P = 0.489, hippocampus F(1,56) = 2.457, P = 0.123]. (B and C) In male mice, APP-CTF/full-length APP ratio was altered (cortex tgAPP n = 17, trisomic;tgAPP n = 11, hippocampus tgAPP n = 14, trisomic;tgAPP n = 8) β-CTF/full-length APP (t-test cortex P = 0.005, hippocampus P = 0.0217) and α-CTF/full-length APP (t-test cortex P = 0.005 hippocampus P < 0.001). (D) Trisomy did not alter the β-CTF/α-CTF ratio in the cortex [trisomy F(1,37) = 0.065, P = 0.799] or hippocampus [trisomy F(1,37) = 1.082, P = 0.305]. (B) Cropped western blot, four lanes of an eight-lane gel. Data are represented as mean ± SEM, *P < 0.05, **P < 0.01, ***P < 0.001. WT = wild-type.