Mutations in critical transporter and enzyme genes disrupt these steps and underlie a spectrum of neurological disorders collectively termed “riboflavin-responsive neurometabolic diseases.” A representative example is riboflavin transporter deficiency (RTD), caused by loss-of-function mutations in SLC52A2 and SLC52A3, which encode the riboflavin transporters RFVT2 and RFVT3, respectively. The gene discussed is SLC52A3; the disease is renal tubular dysgenesis of genetic origin.