The best example demonstrating the consequences of systemic folate deficiency is hereditary folate malabsorption due to gene defects of the proton-coupled folate transporter (PCFT), localized in the small intestine and at the choroid plexus, which leads to impaired intestinal folate absorption and transport across the choroid plexus to the brain [14]. The gene discussed is SLC46A1; the disease is folate deficiency.