Diagnosis of inborn errors of metabolism from blood spots by acylcarnitines and amino acids profiling using automated electrospray tandem mass spectrometry

Acylcarnitine profiling from blood or plasma samples by electrospray tandem mass spectrometry (ESI-MS/MS) has been recognized recently as a useful tool in the biochemical diagnosis of propionic acidemia, methylmalonic acidemia together with short-chain and medium-chain acyl-CoA dehydrogenase deficiencies. In the current study, we have investigated the diagnostic capabilities of ESI-MS/MS in other types of organic acidemias and amino acid catabolism disorders. Using multiple scanning functions, we examined the potential for the simultaneous profiling of both acylcarnitines and amino acids, in each of the samples. Our method was found to be specific and accurate; allowing quantification of acylcarnitines and amino acids well below, and significantly above, published normal levels. Complete automation of sample introduction has been achieved, allowing the analysis of up to 200 samples in one injection sequence, at a rate of one sample every 3 min, with excellent separation between successive injections. In our hands, this method permits screening for 20 organic acid and amino acid disorders, using a single sample injection. In our laboratory, more than 2000 blood samples have been analyzed, and 52 new cases were diagnosed by this method. We also confirmed the diagnosis of another 75 previously known cases.

Detection and characterization of the eae gene of Shiga-like toxin-producing Escherichia coli using polymerase chain reaction

In this study, the polymerase chain reaction (PCR) was used in the detection of the attaching and effacing (eae) gene of Shiga-like toxin-producing Escherichia coli (SLT-EC). Oligonucleotide primers, complementary to the 5' portion of the eae gene of the enteropathogenic E. coli E2348/69 (O127:H6) and of SLT-EC CL8 and EDL933 (O157:H7), generated PCR products of the predicted sizes with DNA from the majority of human clinical SLT-EC strains tested from O serogroups 5, 26, 103, 111, 121, 128, 145, and 157; all SLT-EC strains of O serogroups 5, 26, and 111 from cattle; and a minority of porcine SLT-EC strains (one strain each from O serogroups 107 and 130 and one rough strain). Five HaeIII digestion profiles were obtained for PCR products generated by amplification of a 2.3-kb DNA fragment from the 5' end of eae. The HaeIII profiles for SLT-EC O serogroups, such as 26, 103, and 157, differed from each other but were consistent among strains within these O serogroups. Oligonucleotide primer pairs complementary to the 3' end of either the O127:H6 E. coli or the O157:H7 eae nucleotide sequence only amplified DNA from E. coli strains from a few of the SLT-EC O serogroups examined. One primer pair with homology to the 3' nucleotide sequence of eae from E. coli O157:H7 appeared to be relatively specific for this O serogroup by PCR. No PCR products were obtained in amplification experiments with the eae primers using DNA from human SLT-EC of O serogroups 38 (1 0f 1) and 91 (3 or 3), 15 of 15 SLT-EC strains from edema disease, or 29 of 29 non-SLT-EC strains from pigs and calves with diarrhea.

Probing the basis of antibody reactivity with a panel of constrained peptide libraries displayed by filamentous phage

The structural requirements for peptide binding to an antibody may be elucidated by probing it with a variety of peptides having different constraints. To this end, we have constructed and screened a panel of peptide libraries displayed by filamentous bacteriophage. The peptides in most of the libraries have the potential for constraint by fixed Cys residues, which have been placed at different sites within a randomized amino acid sequence of varying length. When taken together, the binding data obtained from screening the panel with a given antibody allow one to determine the types of constraints that promote binding, as well as the residues that are critical for binding. We describe the construction of 11, pVIII-displayed, peptide libraries, whose sizes range from 150 million to 10 billion clones. The libraries were screened with a number of polyclonal and monoclonal antibodies against peptides, proteins and carbohydrates. Cross-reactivity with peptides was always found for antibodies produced against peptides, linear epitopes on folded proteins and, surprisingly, carbohydrates, whereas antibodies against discontinuous epitopes on proteins were found less frequently. The implications of these results are discussed in terms of the structural basis for cross-reactivity with peptides.

Clinical applications of tandem mass spectrometry: ten years of diagnosis and screening for inherited metabolic diseases

This paper reviews the clinical applications of tandem mass spectrometry (MS-MS) in diagnosis and screening for inherited metabolic diseases in the last 10 years. The broad-spectrum of diseases covered, specificity, ease of sample preparation, and high throughput provided by the MS-MS technology has led to the development of multi-disorder newborn screening programs in many countries for amino acid disorders, organic acidemias, and fatty acid oxidation defects. Issues related to sample acquisition, sample preparation, quantification of metabolites, and validation are discussed. Our current experience with the technique in screening is presented. The application of MS-MS in selective screening has revolutionized the field and made a major impact on the detection of certain disease classes such as the fatty acid oxidation defects. New specific and rapid MS-MS and LC-MS-MS methods for highly polar small molecules are supplementing or replacing some of the classical GC-MS methods for a multitude of metabolites and disorders. New exciting applications are appearing in fields of prenatal, postnatal, and even postmortem diagnosis. Examples for pitfalls in the technique are also presented.

Exploring the basis of peptide-carbohydrate crossreactivity: evidence for discrimination by peptides between closely related anti-carbohydrate antibodies

To investigate the molecular basis of antigenic mimicry by peptides, we studied a panel of closely related mAbs directed against the cell-wall polysaccharide of group A Streptococcus. These antibodies have restricted V-gene usage, indicating a shared mechanism of binding to a single epitope. Epitope mapping studies using synthetic fragments of the cell-wall polysaccharide supported this conclusion. All of the mAbs isolated crossreactive peptides from a panel of phage-displayed libraries, and competition studies indicated that many of the peptides bind at or near the carbohydrate binding site. Surprisingly, the peptides isolated by each mAb fell into distinct consensus-sequence groups that discriminated between the mAbs, and in general, the peptides bound only to the mAbs used for their isolation. Similar results were obtained with polyclonal antibodies directed against synthetic oligosaccharide fragments of the streptococcal cell-wall polysaccharide. Thus, the peptides appear to be specific for their isolating antibodies and are not recognized by the same mechanism as their carbohydrate counterparts.

Biotransformation of methyl isocyanate in the rat. Evidence for glutathione conjugation as a major pathway of metabolism and implications for isocyanate-mediated toxicities

S-(N-Methylcarbamoyl)-N-acetylcysteine (AMCC), a chemically labile mercapturic acid conjugate, was identified by liquid chromatography-mass spectrometry (LC-MS) in the urine of rats dosed intraperitoneally with methyl isocyanate (MIC; 45.2 mumol). The corresponding cysteine conjugate, however, was not detected in urine. Following methylation, urine extracts were analyzed by thermospray LC-MS and the AMCC methyl ester was quantified by means of a stable isotope dilution assay procedure which utilized S-(N-methylcarbamoyl)-N-[2H3]-acetylcysteine [( 2H3]AMCC) as internal standard. The results showed that the fraction of the injected dose of MIC which appeared in 24-h urine collections as AMCC was 24.8 +/- 1.9% (mean +/- SD, N = 4). Thus, conjugation of MIC with glutathione (GSH), followed by metabolism of the resulting adduct to AMCC, appears to represent a quantitatively important pathway of biotransformation of MIC in the rat. However, in view of the known carbamoylating properties and in vitro cytotoxicity of S-linked conjugates of MIC, it seems unlikely that the GSH pathway of metabolism fulfills a conventional detoxification role in the case of MIC. In contrast, it is proposed that carbamate thioester conjugates of MIC, which can revert spontaneously to free MIC under physiological conditions, may actually contribute to the multisystem adverse effects of this highly toxic isocyanate in vivo.

Inborn errors of metabolism diagnosed in sudden death cases by acylcarnitine analysis of postmortem bile

Fatty acid oxidation (FAO) disorders represent a frequently misdiagnosed group of inborn errors of metabolism. Some patients die at the first episode of fasting intolerance and, if appropriate investigations are not undertaken, often meet the criteria of sudden infant death syndrome (SIDS). To expand existing protocols for the postmortem diagnosis of FAO and other metabolic disorders, we tested the hypothesis that analysis for acylcarnitine in bile, a specimen readily available at autopsy, may be utilized for diagnostic purposes. Using electrospray/tandem mass spectrometry, we analyzed for acylcarnitine postmortem bile specimens from two infants with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, one infant with glutaryl-CoA dehydrogenase deficiency, and 17 uninformative SIDS cases as controls. The affected cases, and none of the controls, showed marked accumulation of C10-C18 acylcarnitines or glutarylcarnitine (acyl/free carnitine ratio: 5.2, 2.7, and 1.9, respectively; controls 0.2 +/- 0.1). In one patient, all other diagnostic methods were uninformative, suggesting that bile acylcarnitine profiling could lead to identification of previously overlooked cases.

Cytochrome P-450 isozyme selectivity in the oxidation of acetaminophen

Highly purified isozymes of cytochrome P-450 catalyzed the formation of 3-glutathion-S-ylacetaminophen (GS-APAP) and 3-hydroxyacetaminophen (3-OH-APAP) from acetaminophen (APAP). A major isozyme from untreated male rats (P-450UT-A) catalyzed the formation of ca. 2.0 nmol/nmol of P-450/10 min of 3-OH-APAP and approximately 7.2 nmol of GS-APAP/nmol of P-450/10 min. Antibodies specific for cytochrome P-450UT-A caused a decrease in the amounts of both metabolites produced in microsomal incubations. In contrast to these results, two other constitutive P-450 isozymes from rat liver, cytochrome P-450UT-F and the female specific isozyme P-450UT-I, produced less of both oxidative metabolites. Moreover, they produced significantly more of the catechol metabolite than the glutathione conjugate. These results are in accord with the observation that male rats are more susceptible to acetaminophen hepatotoxicity than female rats. Isozymes induced by phenobarbital also produced more of the catechol than the glutathione conjugate. Conversely, the major isozyme induced by beta-naphthoflavone, cytochrome P-450 beta NF-B, produced a significantly greater amount of GS-APAP than 3-OH-APAP. When comparison was made to a major phenobarbital inducible form (cytochrome P-450PB-B) a definite isozyme specificity for the formation of the two metabolites was seen. The catechol was formed at rates of 2.21 and 0.53 nmol/nmol of P-450/10 min by cytochromes P-450PB-B and P-450 beta NF-B, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Newborn screening: experiences in the Middle East and North Africa

This review presents the current experiences with newborn screening in the Middle East and North Africa region. The population in the region is about 400 million, with high birth rate and an estimated 10 million newborns per year. The majority of the population is of the Islamic faith and mostly Arab. The population is characterized by a high consanguinity (25-70%) and a high percentage of first-cousin marriages. Haemoglobin disorders, inherited metabolic disorders, neurogenetic disorders and birth defects are relatively common among the population. There is a rather slow progress in developing and implementing preventive genetic programmes owing to legal, cultural, political and financial issues. Although research spending is rather soft in the region, there are numerous pilot studies that highlighted the high incidence of genetic defects and the need for newborn screening programmes. Currently, there are only four countries that are executing national newborn screening but they vary from one disease to 23 and coverage is not complete. The region needs to take big steps towards developing national strategies for prevention and should learn from experiences of regional and international screening programmes.

Application of electrospray tandem mass spectrometry to neonatal screening

For the past 30 years, neonatal screening programs have been performed largely by using the bacterial inhibition assays developed by Dr Robert Guthrie. These programs focused on a small number of diseases such as phenylketonuria and maple syrup urine disease and involved one test for each disease. During the same period many new diseases were discovered, such as organic acidemias and fatty acid oxidation defects, and they presented a diagnostic challenge to biochemical laboratories. Different mass spectrometric approaches have been the main tools for the diagnosis; however, each has its own limitation. Recently, electrospray tandem mass spectrometry (MS/MS) has provided an alternative automated high throughput, specific, and broad-spectrum approach to screening for a relatively large number of disorders, including those covered by bacterial inhibition assays tests. By using specific scan functions, a large number of amino acids and acylcarnitines in blood spots are quantified in 2 minutes analytical time. A new scan function is described here for quantification and screening for argininosuccinic acid in blood spots, which is a key metabolite in the diagnosis of argininosuccinase deficiency. We describe the results of a 3-year tandem MS/MS-based neonatal study that was performed in our newborn population. We screened 27,624 blood spots and identified 20 cases yielding a frequency of 1:1,381. No false-negative cases were identified, but several false-positive cases were eliminated by repeat analysis by MS/MS of blood or by other means. We also used MS/MS analysis of urine or blood either for confirmation of initial positive results or for follow-up of treatment, such as in glutaric acidemia, citrullinemia, argininosuccinase deficiency, and biopterin-dependent phenylketonuria.

The T/G 13915 variant upstream of the lactase gene (LCT) is the founder allele of lactase persistence in an urban Saudi population

BACKGROUND

The prevalence of lactase persistence is high in Saudi Arabia.

OBJECTIVE

To identify a DNA variant for the lactase persistence/non-persistence trait in adult Arabs in Saudi Arabia.

METHODS

We sequenced DNA from 432 anonymous neonatal blood donors from five different regions of Saudi Arabia to cover the 400 bp region surrounding the previously identified lactase persistence/non-persistence variant C/T-13910 residing in intron 13 of the MCM6 gene.

RESULTS

Two anonymous blood donors carried the C/T-13910 genotype. One variant, T/G -13915, residing 5 bp upstream of the C/T-13910 variant, was present in 332 of 432 (76.9%) of the neonatal samples, compatible with previous prevalence figures of lactase persistence in urban Saudi populations. Determination of disaccharidase activities in 25 intestinal biopsy samples showed a highly significant correlation between lactase activity and the T/G-13915 genotypes (p<0.001; Fisher exact test) as well as between the L:S ratio and the aforementioned genotypes (p<0.001; Fisher exact test).

CONCLUSION

The T/G-13915 variant is the founder mutation of lactase persistence in an urban Saudi population. The results obtained here have implications for genetic testing of adult-type hypolactasia and to analysis of human evolution, the origin of cattle domestication and migrations of the populations in the Arabian peninsula.

In vitro effects of acetaminophen metabolites and analogs on the respiration of mouse liver mitochondria

Acetaminophen, an analgesic and antipyretic, is toxic in overdose to liver and kidney. The effects on mitochondrial respiration of acetaminophen, its less toxic analog, 3-hydroxyacetanilide, and metabolites which arise from these compounds have been investigated. The parent compounds inhibited NADH-linked respiration reversibly, whereas the metabolites inhibit all mitochondrial respiration, apparently in the Complex III region of the respiratory chain. The quinone derivatives, 4-acetamido-o-benzoquinone and 2-acetamido-p-benzoquinone, are the best inhibitors, with the onset of inhibition dependent on active respiration, suggesting interaction of these compounds with oxidized components of the electron transport chain.

Molecular phylogeny of the live-bearing fish genus Poecilia (Cyprinodontiformes: Poeciliidae)

Members of the genus Poecilia exhibit extensive morphological, behavioral, and life history variation within and between species. This natural variation, coupled with short generation times and the ease with which members of this genus can be cultured in the lab, have made several species model systems for studying the effects of sexual and natural selection on the evolution of natural populations. Given that there is no clear understanding of the phylogenetic relationships within the genus, these studies have not been put into a historical context, and between-species comparisons have been limited. We sequenced the complete NADH Dehydrogenase Subunit 2 (ND2) mitochondrial gene (1047 bp) in representatives of the major divisions of the genus in order to examine these relationships. The subgeneric groups of Rosen and Bailey (1963) are, for the most part, supported, with some adjustment within the subgenera Poecilia and Pamphorichthys. The morphological distinctness of the groups within Poecilia suggest that the original generic designations be reinstated, but this awaits a more thorough analysis. Two implications from the phylogeny are particularly relevant to sexual selection studies: within the North and Central American mollies, the three species of sailfin mollies form a monophyletic group, and within the subgenus Lebistes, the sister taxon to the guppy, P. reticulata, is most likely the group of species previously designated as Micropoecilia.

Carbamoylation of peptides and proteins in vitro by S-(N-methylcarbamoyl)glutathione and S-(N-methylcarbamoyl)cysteine, two electrophilic S-linked conjugates of methyl isocyanate

The reactivity toward peptides and proteins of S-(N-methylcarbamoyl)glutathione (SMG), the glutathione conjugate of methyl isocyanate, and the corresponding cysteine adduct, S-(N-methylcarbamoyl)cysteine (SMC), was investigated with the aid of in vitro model systems. Incubation of SMC or a trideuteriomethyl analogue of SMC with either the reduced or oxidized forms of oxytocin afforded similar mixtures of mono-, bis- and tris-N-methylcarbamoylated peptides. Structure elucidation of the mono and bis adducts by fast atom bombardment tandem mass spectrometry indicated that carbamoylation of oxytocin occurred preferentially at Cys-6 and that Cys-1 and/or Tyr-2 were secondary sites of modification. Upon incubation of S-[N-([14C]methyl)carbamoyl]glutathione (14C-SMG) with native bovine serum albumin (BSA), radioactivity became bound covalently to the protein in a time- and concentration-dependent fashion. "Blocking" of the lone Cys-34 thiol group of BSA in the form of a disulfide prior to exposure of the protein to 14C-SMG failed to decrease significantly the extent or time course of this covalent binding. It is concluded that carbamate thioester conjugates of MIC are reactive, carbamoylating entities which can donate the elements of MIC to nucleophilic functionalities on peptides and proteins. Free thiols appear to be preferred sites for such carbamoylation processes, a phenomenon that may have important toxicological consequences in the pathology of tissue lesions induced by MIC and related isocyanates.

S-(N-methylcarbamoyl)glutathione: a reactive S-linked metabolite of methyl isocyanate

S-(N-methylcarbamoyl)glutathione, a chemically-reactive glutathione conjugate, has been isolated from the bile of rats administered methyl isocyanate and characterized, as its N-benzyloxycarbonyl dimethylester derivative, by tandem mass spectrometry. The ability of this glutathione adduct to donate an N-methylcarbamoyl moiety to the free -SH group of cysteine was evaluated in vitro with the aid of a highly specific thermospray LC/MS assay procedure. The glutathione adduct reacted readily with cysteine in buffered aqueous media (pH 7.4, 37 degrees C) and after 2 hr, 42.5% of the substrate existed in the form of S-(N-methylcarbamoyl)cysteine. The reverse reaction, i.e. between the cysteine adduct and free glutathione, also took place readily under these conditions. It is concluded that conjugation of methyl isocyanate with glutathione in vivo affords a reactive S-linked product which displays the potential to carbamoylate nucleophilic amino acids. The various systemic toxicities associated with exposure of animals or humans to methyl isocyanate could therefore be due to release of the isocyanate from its glutathione conjugate, which thus may serve as a vehicle for the transport of methyl isocyanate in vivo.

Unusual presentations of propionic acidemia

The files of 25 patients with propionic acidemia (PA), followed by the Inborn Errors of Metabolism Service (IEMS) at King Faisal Specialist Hospital and Research Centre (KFSH & RC) from 1990 to 1993, were studied retrospectively. In 14 patients PA presented acutely with acidosis, hyperammonemia and thrombocytopenia, while in 11 patients the presentation of the disease was unusual. In the latter group, two neonates with PA initially appeared as a primarily hyperammonemic metabolic disease. In two other neonates the vomiting was so severe that they were diagnosed as intestinal obstruction in referral hospitals. The presentation in three infants was primarily as an immune disorder. In four infants, PA appeared as an acute or chronic encephalopathy, i.e. as a silent organic acidemia, with few other findings of the disease. The clinical picture of PA includes facial and nipple dysmorphia, severe hypotonia and vomiting. Severe thrombocytopenia is the hallmark of the metabolic crisis. In one patient it was noticed late and caused intracranial hemorrhage, while in three others intracranial bleeding caused death. The prognosis in PA remained grave despite rigorous treatment. Only seven of the 25 PA patients remained to have a normal life-style, while eight patients expired. The diagnosis is readily achieved by urine gas chromatography/mass spectrometry (GC/MS), by tandem mass spectrometry (MS/MS), or by enzyme analysis of fibroblasts. While there may be both examiner- and patient-related reasons for the variations in the presentation of PA, one other reason may be the heterogeneity of the molecular defect in propionyl-CoA carboxylase.

3-Ketothiolase deficiency: a review and four new patients with neurologic symptoms

3-Ketothiolase deficiency (3KTD) manifests with intermittent acidosis and is due to deficiency of mitochondrial 2-methylacetoacetate thiolase. Only 22 patients have been previously reported. Although its variable clinical presentation is recognized, the associated neurological findings have not been detailed. We report four new patients all with significant neurological symptoms. Three patients were examined with MRI of the brain which showed increased T2 intensity within the posterior lateral part of the putamen bilaterally. In two the MRI was otherwise normal; in one delayed myelination was also seen. These MRI putaminal findings may be typical enough to suggest the diagnosis of 3KTD. Two of the three had abnormal EEGs; one had an abnormal VEP. 3KTD can thus occur as an organic acidemia associated with encephalopathy.

Glutaric aciduria type II: observations in seven patients with neonatal- and late-onset disease

The clinical, biochemical, and neuroradiologic findings and clinical follow-up of seven patients with glutaric aciduria type II are reported. Three phenotypes of the disease are encountered: neonatal-onset form with congenital anomalies (two patients) or without congenital anomalies (three patients) and late-onset form (two patients). The neonatal-onset form presents as an overwhelming illness, with severe hypoglycemia and metabolic acidosis leading to rapid death. Frequently it is associated with perinatal energy deprivation, a neonate with low birth weight and prematurity. The late-onset form presents with intermittent episodes of vomiting, hypoglycemia, and acidosis especially after meals rich in fat and/or proteins. All parents are consanguineous and have a first- or second-degree relationship. Initially, in the two phenotypes with neonatal onset and during crisis in the late-onset phenotype, routine laboratory evaluation showed severe metabolic acidosis, with an increased anion gap, hypoglycemia without ketonuria, and disturbed liver function tests. In the majority of patients with neonatal-onset forms, the kidneys, liver, and at times the spleen are enlarged with an increased echogenic pattern; however, no hepatic or renal cysts are detected. Cardiomegaly is observed in most patients. The diagnosis can be easily and rapidly reached through tandem mass spectrometry study of the blood and can further be confirmed by gas chromatography/mass spectrometry analysis of the urine organic acids. In this report, the magnetic resonance imaging/computed tomography brain studies showed brain atrophy, white matter disease, and in one patient, fluid-filled cavities in the periventricular area and putamina. Fluorine-18-labeled 2-fluoro-2-deoxyglucose positron emission tomographic (FDG PET) brain studies in two patients with late-onset disease showed slightly decreased activity in the cerebral cortex in one and in the caudate nuclei in the other. Brain FDG PET scan and magnetic resonance spectroscopy were normal in one patient with neonatal-onset disease. All patients were treated with a diet low in fat and protein, oral riboflavin, and carnitine. The results were promising for the late-onset disease. Intravenous carnitine gave rewarding results in one patient with neonatal-onset disease.

Ethylmalonic aciduria: an organic acidemia with CNS involvement and vasculopathy

Five infants from 3 families, one Egyptian, two Yemeni, are described with a progressive encephalopathy, four of whom have been studied in detail. All patients showed vascular lesions of the skin, characterized by waxing and waning petechiae and ecchymoses. Acrocyanosis was present in three patients. All patients showed retinal lesions characterized by tortuous veins. Protracted diarrhea was not a consistent finding, although they had metabolic crisis in association with diarrhea. They did not show failure to thrive. The neurologic symptoms were indicative of a progressive pyramidal tract disease. Three patients died following sudden emergence of severe basal ganglia, putaminal and head of caudate lesions. In one patient the CT changes in brain were suggestive of infarction. The patients who died manifested pulmonary congestion, or wet lung, and respiratory difficulties during the terminal stage of the disease. In all patients before and during the terminal event, mild-to-moderate hematuria, and in two RBC in CSF, was observed. In one patient there was mild hemoperitoneum at the terminal event. The urine organic acids indicated increased excretion of ethylmalonic, methylsuccinic, glutaric, and adipic acids. The patients invariably showed lactic acidosis, but no ketosis, during and in between the acidotic attacks of the disease. The acylcarnitine profile in blood of two patients showed a pronounced increase in C4 and C5 carnitine esters. In three patients, biopsies from petechiae indicated absence of an immune event, showing only fresh hemorrhage. An immunologic study in one patient was normal for the suppressor:cytotoxic lymphocyte ratio and concentration of interleukin-2 receptor during and in between hemorrhagic attacks. The cytochrome c oxidase activity in fibroblasts was normal. The rate of oxidation of glucose, leucine, isoleucine, valine, propionate and butyrate by fibroblasts was normal. The disease is not responsive to treatment with riboflavin, ascorbic acid, vitamin E, glycine, or carnitine. One patient remained stable on prolonged large doses of methylprednisolone. The biochemical defect leading to ethylmalonic aciduria in this disease remains unknown.

Chiral liquid chromatography tandem mass spectrometry in the determination of the configuration of 2-hydroxyglutaric acid in urine

D-2-Hydroxyglutaric aciduria and L-2-hydroxyglutaric aciduria are two distinct inherited metabolic diseases. The accurate diagnosis of the exact disorder relies on the determination of the configuration of the enantiomers, either D-2-hydroxyglutaric acid or L-2-hydroxyglutaric acid excreted in excess in urine of patients. The enantiomeric chiral separation of 2-hydroxyglutaric acid was achieved using a ristocetin A glycopeptide antibiotic silica gel bonded column. The chiral column was interfaced with a tandem mass spectrometer for the purpose of specifically detecting the eluting 2-hydroxyglutaric acid. Tandem mass spectrometry was employed using an electrospray ion source in the negative ion mode. Three parent-to-daughter transitions under collision-induced dissociation conditions were used to detect only 2-hydroxyglutaric acid. The two forms of the compound were satisfactorily separated with almost baseline resolution at 4.95 and 5.5 min. Three known patients with 2-hydroxyglutaric aciduria were identified to have L-2-hydroxyglutaric aciduria. The method is simple, selective, rapid, and free from interference.

Experience of King Faisal Specialist Hospital and Research Center with Saudi organic acid disorders

The Inborn Errors of Metabolism and Neurology Services of the King Faisal Specialist Hospital and Research Centre (KFSH&RC) and Armed Forces Hospital have received more than 1,500 patients suspected of having an organic acid disorder (OAD) during a period of four years. Of these, 307 patients suspected of having an organic acid disorder (OAD) during a period of four years. Of these, 307 patients, approximately 20%, had a clearly identifiable disorder. Identified OAD's constituted one-quarter of all patients diagnosed as having various types of inborn errors of metabolism during this period, in these clinical services. Prolonged follow-up was available in the majority of cases, allowing detailed clinical, neuroradiologic and neurophysiologic descriptions. Fifty patients (16%) had rare disorders by standards in the West. Approximately 25% were 'neurologic organic acidurias.' This is a new term we are introducing for OAD's manifesting primarily with neurologic signs, but without appreciable acidosis, hypoglycemia or hyperammonemia. In this special issue, we present the KFSH&RC experience with the rare disorders as individual articles. We estimate the frequency of OAD's in Saudi Arabia as 1/740 births. The increased frequency of OAD's in Saudi Arabia is probably due to increased consanguinity, since most OAD's occurred in excess in certain tribes; and due to increased surveillance and testing by our group. Saudi Arabia provides a unique opportunity for research in this area of pediatrics.

Extended right hemicolectomy and left hemicolectomy for colorectal cancers between the distal transverse and proximal descending colon

INTRODUCTION

We report our experience with extended right hemicolectomy (ERH) and left hemicolectomy (LH) for the treatment of cancers located between the distal transverse and the proximal descending colon, and compare postoperative morbidity, mortality, pathological results and survival for the two techniques.

METHODS

A retrospective review was performed of a single institution series over ten years. Patients who underwent different operations, had benign disease or received palliative resections were excluded. Data collected were patient demographics, type and duration of surgery, tumour site, postoperative complications and histology results.

RESULTS

Ninety-eight patients were analysed (64 ERHs, 34 LHs). ERH was conducted using an open approach in 93.8% of cases compared with 73.5% for LH. The anastomotic leak rate was similar for both groups (ERH: 6.3%, LH: 5.9%). This was also the case for other postoperative complications, mortality (ERH: 1.6%, LH: 2.9%) and overall survival (ERH: 50.4 months, LH: 51.8 months). All but one patient in the ERH cohort had clear surgical margins. Nodal evaluation for staging was adequate in 78.1% of ERH cases and 58.8% of LH cases.

CONCLUSIONS

In our experience, both ERH and LH are adequate for tumours located between the distal transverse and the proximal descending colon.

The use of mass spectrometry in the study of chemically-reactive drug metabolites. Application of MS/MS and LC/MS to the analysis of glutathione- and related S-linked conjugates of N-methylformamide

The S-(N-methylcarbamoyl) derivatives of glutathione, cysteine and N-acetylcysteine, the S-linked conjugates derived from a reactive metabolite of N-methylformamide (NMF), were studied in mice dosed with an equimolar mixture of NMF and deuterium-labelled NMF. Following preparation of N-benzyloxycarbonyl derivatives in aqueous media, the title conjugates were isolated, purified as their methyl esters and subjected to analysis by fast atom bombardment mass spectrometry (FAB/MS), fast atom bombardment tandem mass spectrometry (FAB/MS/MS) or thermospray liquid chromatography/mass spectrometry (TSP LC/MS). Characteristic isotope clusters in the FAB or TSP mass spectra facilitated recognition of drug metabolites, while constant neutral loss (89 u) and daughter ion scanning tandem mass spectrometry (MS/MS) experiments provided unique structural information on the conjugates of interest. It is concluded that the combined use of stable isotopes, aqueous-phase derivatization and contemporary mass spectrometric techniques represents a powerful approach for the analysis of glutathione adducts and related S-linked conjugates of chemically-reactive drug metabolites.

Characterization of glutathione conjugates of reactive metabolites of 3'-hydroxyacetanilide, a nonhepatotoxic positional isomer of acetaminophen

3'-Hydroxyacetanilide (AMAP) is a nonhepatotoxic regioisomer of acetaminophen (APAP) that nonetheless does form reactive metabolites which bind to hepatic proteins. Because differences in the nature of reactive metabolites formed from AMAP and APAP may explain differences in their propensity to cause hepatotoxicity, characterization of the reactive metabolites of AMAP was undertaken. The naturally occurring sulfhydryl-containing tripeptide glutathione (GSH) was used to trap the reactive metabolites. Four mono-GSH conjugates and one di-GSH conjugate of oxidative AMAP metabolites were characterized by 1H NMR and soft ionization (LSIMS or FAB) mass spectral techniques, as well as by comparison of liquid chromatographic and spectral characteristics with synthetic standards. Two isomeric mono-GSH conjugates of 2-acetamidohydroquinone (2-AcHQ) are formed as well as a bis-GSH conjugate. A mono-GSH conjugate of 3',4'-dihydroxyacetanilide (3-OH-APAP) also was formed. Thus, these GSH conjugates most likely arise by reaction of GSH with 2-acetamido-p-benzoquinone (2-APBQ) and 4-acetamido-o-benzoquinone (4-AOBQ), respectively, as oxidation products of the known AMAP metabolites 2-AcHQ and 3-OH-APAP. Finally, a GSH conjugate of 3'-methoxy-4'-hydroxy-acetanilide (3-OMe-APAP) was detected in bile of mice administered AMAP. This conjugate probably arises by oxidation of 3-OMe-APAP, another known metabolite of AMAP. The presumed oxidation product, N-acetyl-3-methoxy-p-benzoquinone imine (MAPQI), was synthesized and found to react with GSH to give the same GSH conjugate as that detected in bile and in incubations of 3-OMe-APAP with mouse liver microsomes plus GSH.(ABSTRACT TRUNCATED AT 250 WORDS)