ABCG2 and Parkinson disease: Furthermore, the BBB and ABC transporter dysfunction exacerbates numerous diseases and pathologies including stroke, Alzheimer disease, Parkinson disease, diabetes, acute liver failure, etc. Loss of BBB integrity (i.e., leak or dysfunction of ABC transporters) exposes the brain to potentially harmful concentrations of substances in the peripheral circulation (e.g., ions, amino acids, neurotransmitters, proteins, and other macromolecules) that may disrupt brain homeostasis and adversely affect neuronal signaling (Abbott et al., 2010).