Nephronophthisis can be also caused by mutations in genes encoding proteins other than nephrocystins, such as TTC21B, CEP164, ANKS6, CEP83 and DCD2. TTC21B encodes tetratricopeptide repeat-containing hedgehog modulator-1 (THM1), which is an axonemal protein required for intraflagellar transport. This evidence concerns the gene TTC21B and nephronophthisis.