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Biomedical subjects

V E Shih

Publications and source records attributed to V E Shih.

At least 37 records · Page 2Linked to original sources
PubMed1993

Molecular basis of cystathionine beta-synthase deficiency in pyridoxine responsive and nonresponsive homocystinuria.

Cystathionine beta-synthase (CBS) deficiency is an autosomal recessive disorder associated with multisystem clinical disease. We analyzed PCR amplified products from patients' RNA and genomic DNA. Direct sequencing of the entire coding region of the CBS gene revealed a G-919 to A transition in exon 8, resulting in replacement of Gly 307 by Ser (G307S) in the protein. The mutation was detected in one allele of patient L171 of French/Scottish ancestry and in both alleles of patient L198 of Irish ancestry. Amplifying and sequencing exon 8 from the genomic DNA showed that both parents of L198 were heterozygotes for G307S. The pathogenicity of the mutation was demonstrated in an expression experiment. The mutant protein was apparently stable in E.coli extracts and lacked catalytic activity. Sequencing of exon 8 revealed the G307S mutation in five additional families. All patients have pyridoxine nonresponsive homocystinuria. We have now observed this mutation in 9 of 52 apparently unrelated alleles of varied ethnic backgrounds. All 9 are from patients with Celtic (Irish/English/Scottish/French) ancestry in either one or both parents. The G307S mutation was detected in 50% (9 of 18) of the Celtic alleles in our series. The second mutation found in exon 8 is the I278T mutation, which was described previously in one allele of a pyridoxine responsive patient. This missense mutation was detected in one allele of a pyridoxine nonresponsive patient and in both alleles of a pyridoxine responsive patient. The latter suggests that I278T is probably associated with pyridoxine responsiveness.

Adult↗
PubMed1992

An antispasticity effect of threonine in multiple sclerosis.

To determine whether the naturally occurring amino acid threonine, a potential precursor for glycine biosynthesis in the spinal cord, has an effect on spasticity in multiple sclerosis, 26 ambulatory patients were entered into a randomized crossover trial. Threonine administered at a total daily dose of 7.5 g reduced signs of spasticity on clinical examination, although no symptomatic improvement could be detected by the examining physician or the patient. In contrast to the side effects of sedation and increased motor weakness associated with antispasticity drugs commonly used for the treatment of multiple sclerosis, no side effects or toxic effects of threonine were identified. Levels of threonine were elevated in serum and cerebrospinal fluid during treatment, but glycine levels did not change. Enhancement by threonine of glycinergic postsynaptic inhibition of the motor reflex arc in the spinal cord may represent a non-sedating, nontoxic approach to the management of spasticity in multiple sclerosis.

Adult↗
PubMed1992

A 15-bp deletion in exon 5 of the ornithine aminotransferase (OAT) locus associated with gyrate atrophy.

Gyrate atrophy of the choroid and retina (GA) is an autosomal recessive disorder in which a deficiency of the mitochondrial matrix enzyme ornithine aminotransferase (OAT) leads to progressive blindness. Previously, we and others have reported a number of missense mutations and splice defects in the OAT gene associated with GA. In the present case, through sequencing of the PCR amplified cDNA products, we have detected a novel 15-bp deletion within exon 5 of the OAT gene which retains the original reading frame. The deleted PCR product is the only one produced from the patient's mRNA, while mRNA from the patient's mother yields both deleted and normal length PCR products. The alternate, apparently nonexpressing OAT allele in this patient was inherited from the father, who displays only the normal length PCR product. The codon at the deletion joint remains unaltered, predicting the loss of the pentapeptide Tyr-Thr-Val-Lys-Gly without any other amino acid change. The breakpoints are adjacent to or within two copies of a 4-bp direct repeat, which may have implications for the mechanism of deletion.

Amino Acid Sequence↗
PubMed1992

Mapping of ornithine aminotransferase gene sequences to mouse chromosomes 7, X, and 3.

Ornithine aminotransferase (OAT), a mitochondrial matrix enzyme, is deficient in patients with gyrate atrophy of the choroid and retina. In human, the OAT structural gene maps to Chromosome (Chr) 10q26 and several OAT-related sequences, some of which are known to be processed pseudogenes, which map to Xp11.3-11.21. Here, we report chromosomal localization in the mouse of the OAT gene and related sequences. Genomic DNA blot analysis of a well-characterized panel of Chinese hamster x mouse somatic cell hybrids using a human OAT probe revealed two murine loci, one on mouse Chr 7 and the other on Chr X. In addition, segregation of restriction fragment length polymorphisms (RFLPs) detected by the OAT probe in recombinant inbred (RI) strains detected a third locus on Chr 3 and positioned the X locus near Cf-8 and Rsvp. Progeny of an intersubspecific backcross were used to map the Chr 7 locus between Tyr and Int-2, near Cyp2e-1.

Alleles↗
PubMed1992

Biochemical investigation of a Brazilian patient with a defect in mitochondrial acetoacetylcoenzyme-A thiolase.

A case report of 3-ketothiolase deficiency due to a defect of mitochondrial acetoacetyl-CoA thiolase protein in a Brazilian boy and its biochemical investigation is presented. The child had moderate generalized hypotonia, EEG alterations and crises of metabolic acidosis following infections. Hypotonia and EEG abnormalities disappeared with a low protein diet, and physical and mental development are normal. Urinary organic acid excretion was typical of 3-ketothiolase deficiency, showing consistently high levels of 2-methyl-3-hydroxybutyric acid and tiglylglycine. Activation of acetoacetyl-CoA thiolase activity by potassium (K) ion in cultured fibroblasts was not observed, demonstrating the lack of activity of mitochondrial acetoacetyl-CoA thiolase. In addition, the signal for the mitochondrial acetoacetyl-CoA thiolase protein was undetectable in the immunoblot analysis. In the pulse-chase experiments, the signal for mitochondrial acetoacetyl-CoA thiolase was detected after a 1-h pulse but not after a 24-h chase. These results indicate that the deficiency was caused by an unstable mitochondrial acetoacetyl-CoA thiolase protein.

Acetyl-CoA C-Acetyltransferase↗
PubMed1991

Dietary management reverses grooving and abnormal polarization of hair shafts in argininosuccinase deficiency.

We have observed that the fragile hair of two untreated patients with argininosuccinic aciduria showed abnormal alternating zones of bright and dark banding by polarizing microscopy. Scanning electron microscopy documented discontinuous grooves with a 50 to 100 microns periodicity. Results of amino acid analysis of the hair were essentially normal. After the patients were treated with a low-protein, arginine-supplemented diet, the hair assumed a normal appearance. Five patients already treated with diet showed no hair abnormalities. The pathogenesis of the hair changes in unknown, but our findings suggest that products generated in the disease can adversely affect metabolically active tissue such as hair.

Amino Acid Metabolism, Inborn Errors↗
PubMed1991

Detection of hereditary metabolic disorders involving amino acids and organic acids.

Inherited disorders in the metabolism of amino acids and organic acids may cause neurological dysfunction and acute metabolic crises. For many of these disorders, early diagnosis and early treatment can greatly improve the outcome. A general description of the clinical manifestations and a discussion of selected techniques and approaches for the laboratory diagnosis are reviewed.

Amino Acids↗
PubMed1991

Gyrate atrophy of the choroid and retina in a 5-year-old girl.

A 5-year-old Asian-Indian female presented with bilateral cobblestone-like peripheral lesions, a single area of chorioretinal atrophy, infero-nasal to the disc, in her right eye and a non-recordable single flash ERG. Serum ornithine level was assayed at 841 mumol/l, ten times normal levels, and a diagnosis of gyrate atrophy, due to ornithine aminotransferase deficiency was made. The patient was refractory to any form of therapy and her clinical lesions spread rapidly in both eyes, showing both centrifugal and centripetal spread in her right eye. A rapid deterioration in her psychophysical tests was also seen over the 28 months follow-up. The presence of cobblestone-like peripheral lesions in a child should alert the clinician to the possibility of gyrate atrophy, and the rapid spread of the chorioretinal lesions coupled with non-recordable single flash ERGs, in a young patient may suggest a much poorer prognosis.

Child, Preschool↗
PubMed1991

Molecular pathology of gyrate atrophy of the choroid and retina due to ornithine aminotransferase deficiency.

Gyrate atrophy (GA) is an autosomal recessive eye disease characterized by progressive loss of vision due to chorioretinal degeneration. It is associated with a deficiency of the mitochondrial enzyme ornithine aminotransferase (OATase) with consequent hyperornithinemia. Although the clinical phenotype is largely confined to the eye, OATase deficiency is a systemic disorder. A step toward delineation of the enzyme defect in GA at the molecular level has been made by cloning and characterizing the cDNA and structural gene for OATase. The structural gene for OATase maps to chromosome 10 (10q26) and OATase-related sequences map to the X chromosome (Xp11.2). A diverse number of mutations at the OATase locus in GA patients of varied ethnic origins have been defined employing polymerase chain reaction and other molecular biological techniques. The majority of these mutations are of the missense type although a splicing mutation in one patient has recently been identified. The functional consequences of some of these mutations have been tested and confirmed in a eukaryotic expression system. These mutations demonstrate the allelic heterogeneity, which extends to both pyridoxine responsive and non-responsive forms of GA, reflecting the clinical and biochemical heterogeneity observed in this disease. The molecular studies in addition to providing information on the structure/function of the enzyme will facilitate understanding of the retinal pathophysiology in this disorder.

Base Sequence↗
PubMed1990

Episodic hyperammonemia in adult siblings with hyperornithinemia, hyperammonemia, and homocitrullinuria syndrome.

A 39-year-old man and his 42-year-old sister, both vegetarians, had episodic confusion for many years, but their mental function was normal between those episodes. They were recently diagnosed with hyperornithinemia, hyperammonemia, and homocitrullinuria syndrome. Hyperammonemia was documented during an episode of confusion in the male sibling but not in his sister. Both had elevated plasma ornithine, glutamine, and alanine levels and persistently low plasma lysine levels. Homocitrulline was present in their urine, and orotic aciduria and orotidinuria developed in the male sibling following ingestion of allopurinol. Studies on their cultured skin fibroblasts showed deficient metabolism of ornithine, indicating a defect in ornithine transport across the mitochondrial membrane. During therapy with citrulline and phenylbutyrate sodium, plasma ornithine levels increased in both patients, while plasma levels of glutamine and alanine decreased to normal. Since therapy started, their clinical conditions have also improved, and no recurrent neurologic dysfunction has occurred during a follow-up period of 20 months.

Adult↗
PubMed1990

Brain glutamate metabolism during hypoxia and peripheral chemodenervation.

Glutamate stimulates resting ventilation by altering neural excitability centrally. Hypoxia increases central ventilatory drive through peripheral chemoreceptor stimulation and may also alter cerebral perfusion and glutamate metabolism locally. Therefore the effect of hypoxia and peripheral chemodenervation on cerebrospinal fluid (CSF) transfer rate of in vivo tracer amidated central nervous system glutamate was studied in intact and chemodenervated pentobarbital-anesthetized dogs during normoxia and after 1 h of hypoxia induced with 10 or 12% O2 in N2 breathing at constant expired ventilation and arterial CO2 tension. Chemodenervation was performed by bilateral sectioning of the carotid body nerves and cervical vagi. CSF transfer rates of radiotracer 13NH4+ and [13N]glutamine synthesized via the reaction, glutamate + NH4(+)----glutamine, in brain glia were measured during normoxia and after 1 h of hypoxia. At normoxia, maximal glial glutamine efflux rate jm = 103.3 +/- 11.2 (SE) mumol.l-1.min-1 in all animals. After 1 h of hypoxia in intact animals, jm = 78.4 +/- 10.0 mumol.l-1.min-1. In denervated animals, jm was decreased to 46.3 +/- 4.3 mumol.l-1.min-1. During hypoxia, mean cerebral cortical glutamate concentration was higher in denervated animals (9.98 +/- 1.43 mumol/g brain tissue) than in intact animals (7.63 +/- 1.82 mumol/g brain tissue) and corresponding medullary glutamate concentration tended to be higher in denervated animals. There were no differences between mean glutamine and gamma-aminobutyric acid concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1990

Splicing defect at the ornithine aminotransferase (OAT) locus in gyrate atrophy.

Gyrate atrophy (GA), a recessive eye disease involving progressive vision loss due to chorioretinal degeneration, is associated with the deficiency of the mitochondrial enzyme ornithine aminotransferase (OAT), with consequent hyperornithinemia. We and others have reported a number of missense mutations at the OAT locus which result in GA. Here we report a GA patient of Danish/Swedish ancestry in whom one OAT allele produces an mRNA that is missing a single 96-bp exon relative to the normal mRNA. Polymerase-chain-reaction amplification and sequencing revealed a 9-bp deletion covering the splice acceptor region of exon 5, resulting in the absence of exon 5 sequences from the mRNA with no disruption to the reading frame. This mutation, which was not present in 15 other independent GA patients, adds to the array of allelic heterogeneity observed in GA and represents the first example of a splicing mutation associated with this disorder.

Adult↗
PubMed1989

Defective lysosomal release of vitamin B12 (cb1F): a hereditary cobalamin metabolic disorder associated with sudden death.

Here we report on a girl who presented with failure to thrive, developmental delay, minor facial anomalies, stomatitis, skin rashes, macrocytosis, mild homocystinemia(uria), and methylmalonic acidemia(uria). Fibroblast studies showed abnormal intracellular cobalamin (vitamin B12) metabolism. Reduced incorporation of 14C from [14C] propionate and [14C] methyltetrahydrofolate into TCA-precipitable macromolecules reflected decreased synthesis of adenosylcobalamin and methylcobalamin respectively. The diagnosis of cb1F mutation was established by demonstrating the accumulation of unmetabolized free cyanocobalamin in fibroblasts and by lack of genetic complementation with fibroblasts from the only other known cb1F patient. The defect is in the lysosomal release of endocytosed cobalamin. Administration of hydroxocobalamin resulted in clinical and biochemical improvement but sudden death occurred at age 5 months. The absence of brain pathological changes suggests that early treatment may prevent the neurological complications in cobalamin cofactor deficiency.

Female↗
PubMed1989

Molybdenum cofactor biosynthesis in humans. Identification of two complementation groups of cofactor-deficient patients and preliminary characterization of a diffusible molybdopterin precursor.

Molybdenum cofactor deficiency is a devastating disease with affected patients displaying the symptoms of a combined deficiency of sulfite oxidase and xanthine dehydrogenase. Because of the extreme lability of the isolated, functional molybdenum cofactor, direct cofactor replacement therapy is not feasible, and a search for stable biosynthetic intermediates was undertaken. From studies of cocultured fibroblasts from affected individuals, two complementation groups were identified. Coculture of group A and group B cells, without heterokaryon formation, led to the appearance of active sulfite oxidase. Use of conditioned media indicated that a relatively stable, diffusible precursor produced by group B cells could be used to repair sulfite oxidase in group A recipient cells. Although the extremely low levels of precursor produced by group B cells preclude its direct characterization, studies with a heterologous, in vitro reconstitution system suggest that the precursor that accumulates in group B cells is the same as a molybdopterin precursor identified in the Neurospora crassa molybdopterin mutant nit-1, and that a converting enzyme is present in group A cells which catalyzes an activation reaction analogous to that of a converting enzyme identified in the Escherichia coli molybdopterin mutant ChlA1.

Cells, Cultured↗