<prompt> HHH syndrome is due to defect in ?Tryptophan metabolismHistidine transpoerBranched chain AA metabolismOrnithine transpoer  <response>: Ans. is d i.e., Ornithine transpoer Hyperornithinaemia, hyperammonaemia, homocitrullinuria HHH syndrome is an autosomal recessive disorder of ornithine transpo caused by mutations in gene SLC 25A15 encoding the ornithine transoer protein ORNT1.There is defective activity of the ornithine transpoer across the mitochondrial membrane, which causes a functional deficiency of two mitochondrial enzymes:Ornithine transcarbomylase : Which catalyses the condensation of ornithine and carbamoylphosphate to citrulline.Ornithine-8-aminotransferase OAT : Which metabolizes the ornithine to .-pyrroline-5-carboxylate and ultimately glutamate and proline.Ornithine accumulates in the cytoplasm and its deficiency in mitochondria causes a secondary urea cycle disorder and hyperammonemia.Carbamoylphosphate accumulates and undergoes allternate metabolism to form :Homocitrulline - Excreted in urineOrotic acidPlasma 