<prompt> HHH syndrome is due to defect in:-Ornithine transcarbamoylaseOrnithine permeaseOrnithine decarboxylaseOrnithine  <response>: HHH syndrome is due to defect in Ornithine permease of mitochondrial membrane. Hyperornithinemia: As ornithine cant enter mitochondria, it accumulates in blood. Hyperammonemia: As ornithine is not available, urea cycle cant operate i.e. NH3 cant be detoxified. Homocitrullinuria: As ornithine is not available, ornithine homologue lysine reacts with Carbamoyl phosphate to produce homocitrulline. Difference between lysine and ornithine is just one CH2 group 