Specific genotypes of HGSNAT (encoding heparan‐α‐glucosaminide N‐acetyltransferase) in which sequence variants generally cause mucopolysaccharidosis type IIIC (MPSIIIC) or Sanfilippo C syndrome (MIM 252930)—a severe childhood onset lysosomal storage disorder—have also been associated with isolated retinal disease in a few reported individuals. This evidence concerns the gene HGSNAT and lysosomal storage disease.