Riboflavin transporter deficiency (RTD), previously known as Brown-Vialetto–Van Laere syndrome, is a childhood-onset neurodegenerative disorder characterized by sensory and motor neuron degeneration causing ataxia, muscle weakness, optic atrophy, and respiratory failure. Mutations in SLC52A2 and SLC52A3, solute carrier family members that encode riboflavin (RF) transporters RFVT2 and RFVT3, are known to cause RTD types 2 and 3, respectively.1 RF transport activity analysis showed that SLC52A2 missense mutations caused a complete or moderate reduction in RF uptake and reduced RFVT2 protein expression in vitro,1 suggesting a loss-of-function disease mechanism.