HHH syndrome is due to defect in:-
Ornithine transcarbamoylase
Ornithine permease
Ornithine decarboxylase
Ornithine
HHH syndrome is due to defect in Ornithine permease of mitochondrial membrane. Hyperornithinemia: As ornithine can't enter mitochondria, it accumulates in blood. Hyperammonemia: As ornithine is not available, urea cycle can't operate i.e. NH3 can't 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)
Urea cycle