HHH syndrome is due to defect in -

Ans. is 'd' i.e., Ornithine transporter o Hyperornithinaemia, hvperammonaemia, homocitrullinuria (HHH) syndrome is an autosomal recessive disorder of ornithine transport caused by mutations in geneSLC 25A15 encoding the ornithine transorterprotein (ORNT1).o There is defective activity of the ornithine transporter across the mitochondrial membrane, which causes a functional deficiency of two mitochondrial enzymes:i) Ornithine transcarbomylase : Which catalyses the condensation of ornithine and carbamoylphosphate to citrulline.ii) Ornithine-8-aminotransferase (OAT): Which metabolizes the ornithine to D1 pyrroline-5-carboxylate and ultimately glutamate and proline.o Ornithine accumulates in the cytoplasm and its deficiency in mitochondria causes a secondary urea cycle disorder and hyperammonemia.o Carbamoylphosphate accumulates and undergoes alltemate metabolism to form :i) Homocitrulline - Excreted in urineii) Orotic acido Plasma citrullin level is normal.