Sodium-dependent multivitamin transporter defects: a rare cause of recurrent vomiting and faltering growth

We describe the case of a previously fit child with recurrent vomiting, faltering growth, persistent diarrhoea and rashes who was diagnosed with a sodium-dependent multivitamin transporter (SMVT) defect. Whole exome sequencing revealed he was homozygous for a SLC5A6 missense variant. The SLC5A6 gene produces SMVTs, which are expressed in various tissues including the intestine, brain, liver, lung, kidney, cornea, retina and heart. It plays a major role in the uptake of biotin, pantothenate and lipoate in the digestive system and transporting B-group vitamins across the blood-brain barrier. This case was only the fourth described in literature. Management was with vitamin replacement therapy: biotin, dexpanthenol and α-lipoic acid. With treatment there was significant, sustained clinical improvement with resolution of recurrent vomiting, rashes and graduation to full enteral feeds. This case highlights how defects in multivitamin transporters can lead to multisystemic disease and subsequent targeted treatment leading to significant clinical improvement.