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The eye
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Many late-onset macular dystrophies follow an autosomal dominant pattern, as well as the early-onset best macular degeneration (for which the BEST1 gene on chromosome 11q is the principal locus), while the juvenile Stargardt form is autosomal recessive. Stargardt disease shows locus heterogeneity; one form is associated with mutations in the ABCA4 ion transport gene on chromosome 1. Another rare but treatable recessive type is gyrate atrophy associated with a metabolic defect in ornithine aminotransferase. Cone dystrophies are a further heterogeneous group, associated with deterioration in colour vision.
-Glutamate(2-Oxoglutarate) Aminotransferases
Published in Elling Kvamme, Glutamine and Glutamate in Mammals, 1988
The most thoroughly studied ornithine aminotransferase (ORNAT) in mammalian tissues is a δ-ornithine aminotransferase (δ-ORNAT) (Equation 38). The product, L-glutamate semi-aldehyde spontaneously cyclizes (Equation 39).
Glutamate as a Neurotransmitter
Published in Elling Kvamme, Glutamine and Glutamate in Mammals, 1988
Richard P. Shank, M. H. Aprison
A recent study of considerable interest demonstrated that l-canaline, a potent inhibitor of ornithine aminotransferase, when injected into the septum caused a gradual decrease of 20 to 40% in the concentration of glutamate during a 2-hr period.101 This decrease was presumed to be due to the demonstrated inhibition of ornithine aminotransferase. However, this effect must be interpreted cautiously until possible effects of l-canaline on other biochemical systems involving glutamate are excluded.
A possible ocular biomarker for response to hyperornithinemia in gyrate atrophy: the effect of pyridoxine, lysine, and arginine-restricted diet in a patient with advanced disease
Published in Ophthalmic Genetics, 2023
Mariana Matioli da Palma, Cristy Ku, Austin D. Igelman, Amanda Burr, Liliya Shevchenko Sutherland, Celide Koerner, David Valle, Mark E. Pennesi, Paul Yang
While OAT is expressed in many tissues such as the brain, liver, intestine, skeletal muscle, kidney, and retina, the disease manifests only as a chorioretinal degeneration (6). Absent or reduced activity of ornithine aminotransferase, a nuclear encoded mitochondrial enzyme, leads to elevated concentrations of ornithine in all bodily fluids. This enzyme catalyzes the reversible conversion of ornithine (derived from arginine) to pyrroline-5 carboxylate and thence to glutamate or proline using an active form of vitamin B6 as a co-factor (7,8). It has been reported that vitamin B6 supplementation (pyridoxine) in patients with gyrate atrophy can reduce hyperornithinemia by improving the enzymatic function of mutant protein with reduced activity (1,9–11). Moreover, an arginine-restricted diet has been shown to reduce ornithine accumulation and slow the progression of chorioretinal degeneration (12–15). In a mouse model of gyrate atrophy, an arginine-restricted diet instituted at 1 month of age and designed to keep plasma ornithine at <200 µmol/L completely prevented retinal degeneration at 12 months of age (16).
High levels of blood glutamic acid and ornithine in children with intellectual disability
Published in International Journal of Developmental Disabilities, 2022
Muhammad Wasim, Haq Nawaz Khan, Hina Ayesha, Abdul Tawab, Fazal e Habib, Muhammad Rafique Asi, Mazhar Iqbal, Fazli Rabbi Awan
It has also been reported that the high level of plasma ornithine and ammonia have a role in ornithine aminotransferase (OAT) deficiency (Haberle et al.2012, Martinelli et al.2015). High level of ornithine and glutamine are also involved in the hyperornithinemia–hyperammonemia-homocitrullinuria (HHH) syndrome and Pyrroline-5-carboxylate synthase deficiency (Dogu et al.2015, Martinelli et al.2015, Silfverberg et al.2018, Perez-Arellano et al.2010). Urea Cycle Disorders have complex etiology, which are caused by different parameters, as high level of ornithine is not only the main cause of UCD, but also glutamine, citrulline and ammonia are involved (Brassier et al.2015, Haberle et al.2012). In the current study, the levels of ornithine and glutamic acid were 2-3 folds higher in the 40 intellectually disabled patients, so elevated levels might have a role to cause different UCD and autistic features in children. Alternatively, high level of glutamic acid might be due to the hemolysis or stored plasma for long period of time. However, their further biochemical and genetic analyses are required for the confirmation of suspected disorders.
Inherited hyperammonemias: a Contemporary view on pathogenesis and diagnosis
Published in Expert Opinion on Orphan Drugs, 2018
Evelina Maines, Giovanni Piccoli, Antonia Pascarella, Francesca Colucci, Alberto B. Burlina
Lysinuric protein intolerance (LPI, OMIM #222700) and ornithine aminotransferase deficiency (OAT, OMIM #258,870) have a tangential relationship with urea cycle disorders (UCDs), leading to a secondary low activity of the urea cycle pathway due to deficiencies of crucial intermediates [4,5].