SLC25A15 and Hyperornithinemia: Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH, MIM #238970) syndrome is a rare genetic disorder of the urea cycle (UC) caused by mutations in the SLC25A15 or ORNT1 gene (MIM*603861), which encodes for the mitochondrial ornithine carrier ORC1 [1].