SLC19A3 is a member of the reduced folate family of micronutrient transporter genes. It is a ubiquitously expressed transmembrane thiamine transporter that lacks folate transport activity yet mediates high affinity thiamine uptake propably via a proton anti-port mechanism. Mutations in this gene cause biotin-responsive basal ganglia disease (BBGD); a recessive disorder manifested in childhood that progresses to chronic encephalopathy, dystonia, quadriparesis, and death if untreated. Patients with BBGD have bilateral necrosis in the head of the caudate nucleus and in the putamen. Mutations in this gene also cause a Wernicke's-like encephalopathy.