SLC52A2 and riboflavin transporter deficiency: Riboflavin transporter deficiency (RTD, OMIM 614707), formerly known as Brown‐Vialetto‐Van Laere (BVVL) or Fazio Londe syndrome (OMIM 211500) is an inborn error of metabolism caused by variants in SLC52A2 or SLC52A3, encoding the human riboflavin transporters RFVT2 and RFVT3, respectively.