Glyoxylate Aminotransferase Activity Research Articles

Insights into the pathogenesis of primary hyperoxaluria type I from the structural dynamics of alanine:glyoxylate aminotransferase variants.

Primary hyperoxaluria type I (PH1) is caused by deficient alanine:glyoxylate aminotransferase (AGT) activity. PH1-causing mutations in AGT lead to protein mistargeting and aggregation. Here, we use hydrogen-deuterium exchange (HDX) to characterize the wild-type (WT), the LM (a polymorphism frequent in PH1 patients) and the LM G170R (the most common mutation in PH1) variants of AGT. We provide the first experimental analysis of AGT structural dynamics, showing that stability is heterogeneous in the native state and providing a blueprint for frustrated regions with potentially functional relevance. The LM and LM G170R variants only show local destabilization. Enzymatic transamination of the pyridoxal 5-phosphate cofactor bound to AGT hardly affects stability. Our study, thus, supports that AGT misfolding is not caused by dramatic effects on structural dynamics.

Chronic effects of microcystin-LR at environmental relevant concentrations on photosynthesis of Typha angustifolia Linn.

Understanding the growth and development of aquatic plants in eutrophic water is of great significance for the selection of potential candidate plant for use in the phytoremediation of eutrophic aquatic ecosystems. The present study aimed to investigate the chronic effects of microcystin-LR (MC-LR) on photosynthesis in the leaves of Typha angustifolia Linn. Photosynthetic activity was stimulated in the leaves following exposure to 4.6 μg L-1 MC-LR for six weeks based on the enhancement of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activity and net photosynthetic rate (PN). However, PN decreased significantly after exposure to 49.1 or 98.3 μg L-1 MC-LR, via non-stomatal limitation by reducing the chlorophyll a and b contents and Rubisco activity. In addition, glycolate oxidase (GO) and serine:glyoxylate aminotransferase (SGAT) activities decreased significantly, indicating that the photorespiration pathway was affected adversely. The intercellular carbon dioxide (Ci) concentration decreased significantly following exposure to 98.3 μg L-1 MC-LR, accompanied with decreases in PN and stomatal conductivity (gs), indicating that stomatal limitation on the photosynthesis system in T. angustifolia L. was observed after exposure to 98.3 μg L-1 MC-LR. Under long-term exposure to MC-LR (49.1-98.3 μg L-1), oxidation stress was severe in the aquatic plant, and non-stomatal limitation or stomatal limitation effects on the photosynthesis system were obvious, resulting in decreases in photosynthesis rates.

The Arabidopsis thaliana gene annotated by the locus tag At3g08860 encodes alanine aminotransferase.

The aminotransferase gene family in the model plant Arabidopsis thaliana consists of 44 genes, eight of which are suggested to be alanine aminotransferases. One of the putative alanine aminotransferases genes, At3g08860, was attributed the function of alanine:glyoxylate aminotransferase/β‐alanine:pyruvate aminotransferase based on the analysis of gene expression networks and homology to other β‐alanine aminotransferases in plants. It was earlier demonstrated that At3g08860 is specifically upregulated in response to osmotic stress, but not other stresses (β‐alanine is an osmoprotectant in plants). Furthermore, it was shown that the expression of At3g08860 is highly coordinated with the genes of the uracil degradation pathway leading to the non‐proteinogenic amino acid β‐alanine. These evidence were suggestive of the involvement of At3g08860 in β‐alanine metabolism. However, direct experimental evidence for the function of At3g08860 was lacking, and therefore, the goal of this study was to elucidate the function of the uncharacterized aminotransferase annotated by the locus tag At3g08860. The cDNA of At3g08860 was demonstrated to functionally complement two E. coli mutants auxotrophic for the amino acids, L‐alanine (proteinogenic) and β‐alanine (non‐proteinogenic). Enzyme activity using purified recombinant At3g08860 further demonstrated that the enzyme is endowed with L‐alanine:glyoxylate aminotransferase activity.

High serine:glyoxylate aminotransferase activity lowers leaf daytime serine levels, inducing the phosphoserine pathway in Arabidopsis.

Serine:glyoxylate aminotransferase (SGAT) converts glyoxylate and serine to glycine and hydroxypyruvate during photorespiration. Besides this, SGAT operates with several other substrates including asparagine. The impact of this enzymatic promiscuity on plant metabolism, particularly photorespiration and serine biosynthesis, is poorly understood. We found that elevated SGAT activity causes surprisingly clear changes in metabolism and interferes with photosynthetic CO2 uptake and biomass accumulation of Arabidopsis. The faster serine turnover during photorespiration progressively lowers day-time leaf serine contents and in turn induces the phosphoserine pathway. Transcriptional upregulation of this additional route of serine biosynthesis occurs already during the day but particularly at night, efficiently counteracting night-time serine depletion. Additionally, higher SGAT activity results in an increased use of asparagine as the external donor of amino groups to the photorespiratory pathway but does not alter leaf asparagine content at night. These results suggest leaf SGAT activity needs to be dynamically adjusted to ensure (i) variable flux through the photorespiratory pathway at a minimal consumption of asparagine and (ii) adequate serine levels for other cellular metabolism.

Caenorhabditis elegans AGXT-1 is a mitochondrial and temperature-adapted ortholog of peroxisomal human AGT1: New insights into between-species divergence in glyoxylate metabolism

In humans, glyoxylate is an intermediary product of metabolism, whose concentration is finely balanced. Mutations in peroxisomal alanine:glyoxylate aminotransferase (hAGT1) cause primary hyperoxaluria type 1 (PH1), which results in glyoxylate accumulation that is converted to toxic oxalate. In contrast, glyoxylate is used by the nematode Caenorhabditis elegans through a glyoxylate cycle to by-pass the decarboxylation steps of the tricarboxylic acid cycle and thus contributing to energy production and gluconeogenesis from stored lipids. To investigate the differences in glyoxylate metabolism between humans and C. elegans and to determine whether the nematode might be a suitable model for PH1, we have characterized here the predicted nematode ortholog of hAGT1 (AGXT-1) and compared its molecular properties with those of the human enzyme. Both enzymes form active PLP-dependent dimers with high specificity towards alanine and glyoxylate, and display similar three-dimensional structures. Interestingly, AGXT-1 shows 5-fold higher activity towards the alanine/glyoxylate pair than hAGT1. Thermal and chemical stability of AGXT-1 is lower than that of hAGT1, suggesting temperature-adaptation of the nematode enzyme linked to the lower optimal growth temperature of C. elegans. Remarkably, in vivo experiments demonstrate the mitochondrial localization of AGXT-1 in contrast to the peroxisomal compartmentalization of hAGT1. Our results support the view that the different glyoxylate metabolism in the nematode is associated with the divergent molecular properties and subcellular localization of the alanine:glyoxylate aminotransferase activity.

ROS production is associated with glycolate metabolism in Chlamydomonas reinhardtii (Chlorophyceae) under salt stress

:The photorespiration metabolism in unicellular algae is different from that in higher plants because of the absence of peroxisomes, and conversion of glycolate to glyoxylate is catalyzed by glycolate dehydrogenase without the production of reactive oxygen species (ROS). It has been reported that the glycolate–quinone oxidoreductase system (GQOS) also plays a role in the formation of glyoxylate from glycolate that is coupled to photosynthetic electron transport. In this study, we showed that production of ROS was associated with the oxidation of glycolate in chloroplasts of Chlamydomonas reinhardtii cells and that both ROS accumulation and photorespiration were promoted by NaCl stress. Salicylhydroxamic acid (SHAM) and methoxylamine (MOA) are inhibitors that block effectively the GQOS oxidation of glycolate and glycine decarboxylase complex, respectively. Our data showed that in the dark, whether or not the cells were treated with inhibitor, no remarkable difference was found in ROS levels under the same NaCl stress. In the light, however, the ROS level in the cells treated with SHAM or MOA was significantly lower than that in nontreated cells, with SHAM being more effective. The increase in serine:glyoxylate aminotransferase (SGAT) activity and glycine/serine (Gly/Ser) ratio were 8.3% and 30.8% under 50 mM, and reached 34.4% and 1.5-fold under 100 mM NaCl stress.

Two Hydroxypyruvate Reductases Encoded by OsHPR1 and OsHPR2 are Involved in Photorespiratory Metabolism in Rice

Mutations in the photorespiration pathway display a lethal phenotype in atmospheric air, which can be fully recovered by elevated CO2 . An exception is that mutants of peroxisomal hydroxypyruvate reductase (HPR1) do not have this phenotype, indicating the presence of cytosolic bypass in the photorespiration pathway. In this study, we constructed overexpression of the OsHPR1 gene and RNA interference plants of OsHPR1 and OsHPR2 genes in rice (Oryza sativa L. cv. Zhonghua 11). Results from reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and enzyme assays showed that HPR1 activity changed significantly in corresponding transgenic lines without any effect on HPR2 activity, which is the same for HPR2. However, metabolite analysis and the serine glyoxylate aminotransferase (SGAT) activity assay showed that the metabolite flux of photorespiration was disturbed in RNAi lines of both HPR genes. Furthermore, HPR1 and HPR2 proteins were located to the peroxisome and cytosol, respectively, by transient expression experiment. Double mutant hpr1 × hpr2 was generated by crossing individual mutant of hpr1 and hpr2. The phenotypes of all transgenic lines were determined in ambient air and CO2 -elevated air. The phenotype typical of photorespiration mutants was observed only where activity of both HPR1 and HPR2 were downregulated in the same line. These findings demonstrate that two hydroxypyruvate reductases encoded by OsHPR1 and OsHPR2 are involved in photorespiratory metabolism in rice.

Abstract 19245: Heart of Stone: A Mysterious Case of Diastolic Dysfunction

A 27 year old Somali female initially presented with renal failure and a creatinine of 10mg/dl. A kidney biopsy showed crystalline nephropathy and she was initiated on hemodialysis. A year later while she was pregnant she had multiple heart failure admissions. Echocardiograms (echo) showed normal ejection fraction (EF). A month after delivery she was admitted again with heart failure. Vital signs were stable with elevated JVP and a pansystolic murmur at the apex. Chest x ray showed pulmonary edema. Echo showed moderately concentric left ventricular hypertrophy (LVH) with an EF of 40% and severe mitral regurgitation (MR). Doppler echo showed restrictive filling pattern. Pulmonary artery pressure (PA) was 99 mm of Hg + right atrial pressure (RA) with dilated vena cava. Repeat echocardiogram post ultrafiltration of just 1 liter of volume reduced PA pressures from 99 mm+RA to about 35 mm Hg+ RA with a simultaneous reduction in MR, demonstrating marked preload dependency of left sided filing pressures. Her myocardium demonstrated an echodense speckled reflection and infiltrative cardiomyopathy was suspected. EKG showed LVH making amyloidosis unlikely diagnosis. Right ventricular endomyocardial biopsy showed extensive deposition of calcium oxalate crystals in myocardium. Further tests showed increased serum oxalate level: 140 μmoles/L (ref. upto 27), increased urinary oxalic acid excretion:171 μgm (ref. < 57) and increased urine glycolate: 101 μg/mg Cr (ref. < 79) . Liver biopsy showed very low AGT (Alanine glyoxylate aminotransferase) activity of 3.0 μmol/h/mg protein (Ref. 19.1-47.9) along with negative AGT immunoreactivity . These results confirmed diagnosis of primary hyperoxaluria type 1 (PH1) . She was started on intense hemodialysis regimen and underwent a deceased donor combined liver-kidney transplantation (CLKT). Repeat echo 6 months later shows normal EF, normal PA pressures, regression of infiltrative process with improvement in diastolic function. This is a rare case of PH1 with cardiac involvement leading to progressive infiltrative restrictive cardiomyopathy and recurrent heart failure. Early recognition of the disease is important because CLKT may achieve long-term survival and regression of cardiomyopathy.

Apical Sparing of Longitudinal Strain, Left Ventricular Rotational Abnormalities, and Short-Axis Dysfunctionin Primary Hyperoxaluria Type 1

A 24-year-old woman with end-stage renal failure because of primary hyperoxaluria type 1 was evaluated in our hospital for systemic calcium oxalate deposition in the course of long-term (5 years) hemodialysis therapy. Diagnosis of primary hyperoxaluria type 1, a hereditary cause of calcium oxalate kidney stones or progressive nephrocalcinosis that frequently results in end-stage renal failure,1 was made by liver biopsy (reduced alanine:glyoxylate aminotransferase activity, 3.0 µmol/h per milligram protein; normal, 19.1–47.9) and by genetic testing (homozygosity for the c.302 T>C, AGXT mutation). Her plasma oxalate level on regular hemodialysis (3× per week over 4 hours) was increased (86 µmol/L predialysis; normal, <10 µmol/L). Transthoracic echocardiography revealed increased wall thickness of the left ventricle (LV; Figure 1). The LV was mildly dilated and showed a decreased systolic function. Flow across the mitral valve demonstrated a restrictive filling pattern. Moreover, the myocardium had a characteristic echo-dense granular sparkling appearance (Movie in the online-only Data Supplement).2 Both atria were enlarged. Moderate tricuspid regurgitation was present. A right ventricle systolic pressure of 62 …

Purification of three aminotransferases from Hydrogenobacter thermophilus TK-6 - novel types of alanine or glycine aminotransferase

Aminotransferases catalyse synthetic and degradative reactions of amino acids, and serve as a key linkage between central carbon and nitrogen metabolism in most organisms. In this study, three aminotransferases (AT1, AT2 and AT3) were purified and characterized from Hydrogenobacter thermophilus, a hydrogen-oxidizing chemolithoautotrophic bacterium, which has been reported to possess unique features in its carbon and nitrogen anabolism. AT1, AT2 and AT3 exhibited glutamate:oxaloacetate aminotransferase, glutamate:pyruvate aminotransferase and alanine:glyoxylate aminotransferase activities, respectively. In addition, both AT1 and AT2 catalysed a glutamate:glyoxylate aminotransferase reaction. Interestingly, phylogenetic analysis showed that AT2 belongs to aminotransferase family IV, whereas known glutamate:pyruvate aminotransferases and glutamate:glyoxylate aminotransferases are members of family Igamma. In contrast, AT3 was classified into family I, distant from eukaryotic alanine:glyoxylate aminotransferases which belong to family IV. Although Thermococcus litoralis alanine:glyoxylate aminotransferase is the sole known example of family I alanine:glyoxylate aminotransferases, it is indicated that this alanine:glyoxylate aminotransferase and AT3 are derived from distinct lineages within family I, because neither high sequence similarity nor putative substrate-binding residues are shared by these two enzymes. To our knowledge, this study is the first report of the primary structure of bacterial glutamate:glyoxylate aminotransferase and alanine:glyoxylate aminotransferase, and demonstrates the presence of novel types of aminotransferase phylogenetically distinct from known eukaryotic and archaeal isozymes.

Assay of alanine:glyoxylate aminotransferase in human liver by its serine: glyoxylate aminotransferase activity

We have examined assay methods and conditions for human liver alanine:glyoxylate aminotransferase (AGT). This enzyme shows not only the AGT activity but also serine:pyruvate and serine: glyoxylate aminotransferase (SPT and SGT) activities. In the assay of AGT activity using crude enzyme preparations, there is the complication that glutamate:glyoxylate aminotransferase (GGT) also contributes to AGT activity, but at present no other enzyme is known to catalyze transamination between L-serine and glyoxylate or pyruvate. Therefore, an assay for AGT using its SGT activity was investigated in which hydroxypyruvate formed from L-serine in the enzymic reaction with glyoxylate was determined by lactate dehydrogenase (LDH) in the presence of tris(hydroxym ethyl)aminomethane (Tris) at pH 8.4. A possible obstacle to this assay is that pyruvate formed from L-serine by serine dehydratase (SDH) interferes with SGT assay as an additional substrate of LDH and AGT. However, the SDH activity in human liver is very low, and by performing the SGT reaction in the presence and absence of glyoxylate the SGT activity was represented as the glyoxylate-dependent hydroxypyruvate formation from L-serine. There was a combined good correlation between the AGT, SGT and SPT activities, and the activity ratio, AGT : SGT : SPT was about 1.0 : 0.17 : 0.13.

Selected Exonic Sequencing of the AGXT Gene Provides a Genetic Diagnosis in 50% of Patients with Primary Hyperoxaluria Type 1

Definitive diagnosis of primary hyperoxaluria type 1 (PH1) requires analysis of alanine:glyoxylate aminotransferase (AGT) activity in the liver. We have previously shown that targeted screening for the 3 most common mutations in the AGXT gene (c.33_34insC, c.508G>A, and c.731T>C) can provide a molecular diagnosis in 34.5% of PH1 patients, eliminating the need for a liver biopsy. Having reviewed the distribution of all AGXT mutations, we have evaluated a diagnostic strategy that uses selected exon sequencing for the molecular diagnosis of PH1. We sequenced exons 1, 4, and 7 for 300 biopsy-confirmed PH1 patients and expressed the identified missense mutations in vitro. Our identification of at least 1 mutation in 224 patients (75%) and 2 mutations in 149 patients increased the diagnostic sensitivity to 50%. We detected 29 kinds of sequence changes, 15 of which were novel. Four of these mutations were in exon 1 (c.2_3delinsAT, c.30_32delCC, c.122G>A, c.126delG), 7 were in exon 4 (c.447_454delGCTGCTGT, c.449T>C, c.473C>T, c.481G>A, c.481G>T, c.497T>C, c.424-2A>G), and 4 were in exon 7 (c.725insT, c.737G>A, c.757T>C, c.776 + 1G>A). The missense changes were associated with severely decreased AGT catalytic activity and negative immunoreactivity when expressed in vitro. Missense mutation c.26C>A, previously described as a pathological mutation, had activity similar to that of the wild-type enzyme. Selective exon sequencing can allow a definitive diagnosis in 50% of PH1 patients. The test offers a rapid turnaround time (15 days) with minimal risk to the patient. Demonstration of the expression of missense changes is essential to demonstrate pathogenicity.

Presentation and role of transplantation in adult patients with type 1 primary hyperoxaluria and the I244T AGXT mutation: Single-center experience

Primary hyperoxaluria type 1 (PH1) is a rare genetic disorder characterized by allelic and clinical heterogeneity. We aim to describe the presentation and full single-center experience of the management of PH1 patients bearing the mutation described in our community (I244T mutation+polymorphism P11L). Since 1983, 12 patients with recurrent renal lithiasis have been diagnosed with PH1 and renal failure in the Canary Islands, Spain. Diagnostic confirmation was based on the presence of oxalosis in undecalcified bone or kidney allograft biopsy, reduced alanine:glyoxylate aminotransferase activity in liver biopsy, and blood DNA analysis. Patients underwent different treatment modalities depending on individual clinical circumstances and therapeutic possibilities at the time of diagnosis: hemodialysis, isolated kidney, simultaneous liver-kidney, or pre-emptive liver transplantation. In all cases, the presentation of advanced renal disease was relatively late (>13 years) and no cases were reported during lactancy or childhood. The eight patients treated with hemodialysis or isolated kidney transplantation showed unfavorable evolution leading to death over a variable period of time. In contrast, the four patients undergoing liver transplantation (three liver+kidney and one pre-emptive liver alone) showed favorable long-term allograft and patient survival (up to 12 years follow-up). In conclusion, in this PH1 population, all bearing the I244T mutation, the development of end-stage renal disease was distinctive during late adolescence or adulthood. Our long-term results support pre-emptive liver transplantation at early stages of renal failure, and kidney-liver transplantation for those with advanced renal disease.

Stones, bones, and heredity

AbstractGenetic disorders of mineral metabolism cause urolithiasis, renal disease, and osteodystrophy. Most are rare, such that the full spectrum of clinical expression is difficult to appreciate. Diagnosis is further complicated by overlap of clinical features. Dent's disease and primary hyperoxaluria, inherited causes of calcium urolithiasis, are both associated with nephrocalcinosis and urolithiasis in early childhood and renal failure that can occur at any age but is seen more often in adulthood. Bone disease is an inconsistent feature of each. Dent's disease is caused by mutations of the CLCN‐5 gene with impaired kidney‐specific CLC‐5 chloride channel expression in the proximal tubule, thick ascending limb of Henle, and the collecting ducts. Resulting hypercalciuria and proximal tubule dysfunction, including phosphate wasting, are primarily responsible for the clinical manifestations. Low‐molecular‐weight proteinuria is characteristic. Definitive diagnosis is made by DNA mutation analysis. Primary hyperoxaluria, type I, is due to mutations of the AGXT gene leading to deficient hepatic alanine–glyoxylate aminotransferase activity. Marked overproduction of oxalate by hepatic cells results in the hyperoxaluria responsible for clinical features. Definitive diagnosis is by liver biopsy with measurement of enzyme activity, with DNA mutation analysis used increasingly as mutations and their frequency are defined.ConclusionThese disorders of calcium urolithiasis illustrate the value of molecular medicine for diagnosis and the promise it provides for innovative and more effective future treatments.

Effect of vitamin B6 deficiency on glyoxylate metabolism in rats with or without glyoxylate overload

We examined the effect of vitamin B6 deficiency on glyoxylate metabolism and hepatic alanine: glyoxylate aminotransferase (AGT) activity in rats with normal or high glyoxylate intake. Male rats were divided into four groups: a control group, a vitamin B6-free diet group, a glyoxylate water group, and a vitamin B6-free diet + glyoxylate water group. Each group was given special diet (control or vitamin B6-deficient diet) and drinking water (plain or 0.5% glyoxylate water) for 4 weeks, after which biochemical parameters and hepatic AGT mRNA level were measured. Compared with control rats, the urinary oxalate/creatinine ratio was higher in each of the other 3 groups. The urinary glycolate/creatinine ratio was also higher in the vitamin B6-free diet group and the vitamin B6-free diet + glyoxylate water group than the control group, while the urinary glycine/creatinine and citrate/creatinine ratio was lower in both groups. The hepatic AGT mRNA level was reduced in the vitamin B6-free diet group, but was increased in the glyoxylate water group than the control group. These results suggest that vitamin B6 is necessary for glyoxylate metabolism as a coenzyme of AGT. Especially in the presence of a high glyoxylate intake, vitamin B6 deficiency leads to severe hyperoxaluria and hypocituria.

Crystal structure and confirmation of the alanine:glyoxylate aminotransferase activity of the YFL030w yeast protein

We have determined the three-dimensional crystal structure of the protein encoded by the open reading frame YFL030w from Saccharomyces cerevisiae to a resolution of 2.6 Å using single wavelength anomalous diffraction. YFL030w is a 385 amino-acid protein with sequence similarity to the aminotransferase family. The structure of the protein reveals a homodimer adopting the fold-type I of pyridoxal 5′-phosphate (PLP)-dependent aminotransferases. The PLP co-factor is covalently bound to the active site in the crystal structure. The protein shows close structural resemblance with the human alanine:glyoxylate aminotransferase (EC 2.6.1.44), an enzyme involved in the hereditary kidney stone disease primary hyperoxaluria type 1. In this paper we show that YFL030w codes for an alanine:glyoxylate aminotransferase, highly specific for its amino donor and acceptor substrates.

Implications of Genotype and Enzyme Phenotype in Pyridoxine Response of Patients with Type I Primary Hyperoxaluria

Background: Marked hyperoxaluria due to liver-specific deficiency of alanine:glyoxylate aminotransferase activity (AGT) characterizes type I primary hyperoxaluria (PHI). Approximately half of PHI patients experience improvement in the degree of hyperoxaluria following pyridoxine (VB6) treatment. Recently, we showed an association between VB6 response and the commonest PHI mutation G170R, with patients possessing one or two copies showing 50% reduction or complete to near complete normalization of oxaluria, respectively. Two patients showed responses varying from this pattern. To further clarify the molecular basis of VB6 response in PHI, we performed additional genotyping. Methods: 23 PHI patients diagnosed via hepatic enzyme analysis, hyperoxaluria and hyperglycolic aciduria or homozygosity for a known mutation, availability of pre- and post-VB6 24-hour urine oxalate and GFR >40 ml/min/1.73 m² were included. Data was retrieved retrospectively, oxalate measured by oxalate oxidase, and genotyping performed by PCR-based methods. Results: VB6 response was associated with the G170R and F152I mutations. Eight new sequence changes were detected. Conclusions: In PHI, two mutations resulting in AGT mistargeting are associated with VB6 response. Whether this favorable effect is specific to the peroxisomal-to-mitochondrial mistargeting caused by these changes or due to another mechanism remains to be determined.

Evaluation of mutation screening as a first line test for the diagnosis of the primary hyperoxalurias

A definitive diagnosis of primary hyperoxaluria type 1 (PH1) and primary hyperoxaluria type 2 (PH2) requires the measurement of alanine:glyoxylate aminotransferase (AGT) and glyoxylate reductase (GR) activities, respectively, in a liver biopsy. We have evaluated a molecular genetic approach for the diagnosis of these autosomal-recessive diseases. Polymerase chain reaction (PCR) was used to detect three common mutations in the AGXT gene (c.33_34insC, c.508G>A, and c.731T>C) and one, c.103delG, in the GRHPR gene in DNA samples from 365 unrelated individuals referred for diagnosis of PH1 and/or PH2 by liver enzyme analysis. One or more of these mutations was found in 183 (68.8%) biopsy proven cases of PH1 and PH2 with a test negative predictive value of 62% and 2%, respectively. 102 (34.1%) patients were homozygous or compound heterozygous, making a molecular diagnosis possible. Age of onset and presenting features were similar in patients homozygous for any of the four mutations. Of the AGXT homozygotes, only the c.508G>A mutant was associated with significant AGT catalytic activity and in two of these activity was in the low normal range, possibly reflecting variation in mitochondrial content of the biopsy as this particular mutation is associated with mitochondrial mistargeting. Limited mutation analysis can provide a useful first line test for PH1 and PH2 in patients in whom primary hyperoxaluria is suspected and in whom secondary causes have been excluded. Those patients in whom a single mutation, or no mutation, is found can then be selectively targeted for liver biopsy.

Glycogénoses, hyperoxaluries, aminoacidopathies et hyperlipidémies

Glycogen storage diseases (GSDs) are inherited disorders that affect glycogen metabolism. The glycogen found in these disorders is abnormal in quantity, quality or both. Liver and muscle have abundant quantities of glycogen and are the most commonly and seriously affected tissues. Because carbohydrate metabolism in the liver is responsible for plasma glucose homeostasis, GSDs that affect mainly the liver usually present as a hepatomegaly and a hypoglycaemia. In contrast, the role of glycogen in muscle is to provide substrates for the generation of ATP for muscle contraction. The predominant clinical features of muscular GSD are muscle cramps, exercise intolerance, susceptibility to fatigue, and progressive weakness. Hyperoxaluria or primary oxalosis is an autosomal recessive disease divided into two forms : type 1, caused by the absence of glyoxylate aminotransferase activity, and type 2 caused by a defect in D-glycerate dehydrogenase/gloxylate reductase. The overproduction of oxalate that is related to these enzyme defect is accompanied by its accumulation in various tissues. Damage to the kidneys, presenting as calcium oxalate nephrolithiasis and nephrocalcinosis, induces progressive renal failure and uraemia treatable by hemodialysis and renal transplantation. Phenylalanine hydroxylase (PAH) deficiency results in an intolerance to dietary intakes of the essential aminoacid phenylalanine and produces a spectrum of disorders including phenylketonuria and non PKU hyperphenylalaninemia. Tyrosinemia encompasses several entities, of which tyrosinemia type 1 (or hepatorenal tyrosinemia) results in the pathological manifestations involving mainly the liver, kidney and peripheral nerves. Classical homocystinuria is an inherited metabolic disorder that arises from defects in either the re-methylation or transsulphuration pathways of homocystein metabolism and leads to skeletal abnormalities, mental retardation and a high risk of vascular disease. Cystinosis is a rare autosomal recessive disorder characterized by the widespread of deposition of cystine crystals in body tissues, particularly in the kidney that results in renal insufficiency treatable by renal transplantation and cysteamine. Familial hypercholesterolemia is characterized by elevated serum cholesterol, tendon xanthomas, xanthelasmas, arcus corneae and premature atherosclerosis. Rheumatological manifestations include acute episodes of polyarthritis and tendinitis. Patients who are homozygous for familial hypercholesterolemia have cardiovascular and rheumatological manifestations more frequently and at earlier age than patients who are heterozygous. Potential myopathy and hepatotoxicity have long been acknowledged as uncommon adverse effects with statins.

Hepatic Alanine-glyoxylate Aminotransferase Activity and Oxalate Metabolism in Vitamin B6 Deficient Rats

Hepatic Alanine-glyoxylate Aminotransferase Activity and Oxalate Metabolism in Vitamin B6 Deficient Rats