Kao Y.H. et al. demonstrated that the expression of P-gp is upregulated in cerebral capillaries in the cerebral cortex and striatum of human patients with HD; in particular, P-gp expression in the cortex increased with the progression of the disease, and P-gp mRNA levels were higher in a later stage of the disease [45]. The gene discussed is PGP; the disease is Huntington disease.