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

Integration of metabolomics and transcriptomics data to aid biomarker discovery in type 2 diabetes

Type 2 diabetes (T2D), one of the most common diseases in the western world, is characterized by insulin resistance and impaired beta-cell function but currently it is difficult to determine the precise pathophysiology in individual T2D patients. Non-targeted metabolomics technologies have the potential for providing novel biomarkers of disease and drug efficacy, and are increasingly being incorporated into biomarker exploration studies. Contextualization of metabolomics results is enhanced by integration of study data from other platforms, such as transcriptomics, thus linking known metabolites and genes to relevant biochemical pathways. In the current study, urinary NMR-based metabolomic and liver, adipose, and muscle transcriptomic results from the db/db diabetic mouse model are described. To assist with cross-platform integration, integrative pathway analysis was used. Sixty-six metabolites were identified in urine that discriminate between the diabetic db/db and control db/+ mice. The combined analysis of metabolite and gene expression changes revealed 24 distinct pathways that were altered in the diabetic model. Several of these pathways are related to expected diabetes-related changes including changes in lipid metabolism, gluconeogenesis, mitochondrial dysfunction and oxidative stress, as well as protein and amino acid metabolism. Novel findings were also observed, particularly related to the metabolism of branched chain amino acids (BCAAs), nicotinamide metabolites, and pantothenic acid. In particular, the observed decrease in urinary BCAA catabolites provides direct corroboration of previous reports that have inferred that elevated BCAAs in diabetic patients are caused, in part, by reduced catabolism. In summary, the integration of metabolomics and transcriptomics data via integrative pathway mapping has facilitated the identification and contextualization of biomarkers that, presuming further analytical and biological validation, may be useful in future T2D clinical studies by identifying patient populations that share common disease pathophysiology and therefore may identify those patients that may respond better to a particular class of anti-diabetic drugs.

Lysine racemase: a novel non-antibiotic selectable marker for plant transformation

A non-antibiotic based selection system using L-lysine as selection agent and the lysine racemase (lyr) as selectable marker gene for plant transformation was established in this study. L-lysine was toxic to plants, and converted by Lyr into D-lysine which would subsequently be used by the transgenic plants as nitrogen source. Transgenic tobacco and Arabidopsis plants were successfully recovered on L-lysine medium at efficiencies of 23 and 2.4%, respectively. Phenotypic characterization of transgenic plants clearly revealed the expression of normal growth and developmental characteristics as that of wild-type plants, suggesting no pleiotropic effects associated with the lyr gene. The specific activity of Lyr in transgenic tobacco plants selected on L: -lysine ranged from 0.77 to 1.06 mU/mg protein, whereas no activity was virtually detectable in the wild-type plants. In addition, the composition of the free amino acids, except aspartic acid, was not affected by the expression of the lyr gene in the transgenic tobacco plants suggesting very limited interference with endogenous amino acid metabolism. Interestingly, our findings also suggested that the plant aspartate kinases may possess an ability to distinguish the enantiomers of lysine for feedback regulation. To our knowledge, this is the first report to demonstrate that the lysine racemase selectable marker system is novel, less controversial and inexpensive than the traditional selection systems.

Reassessment of phenylalanine tolerance in adults with phenylketonuria is needed as body mass changes

Lifelong treatment of phenylketonuria (PKU) includes a phenylalanine (phe) restricted diet that provides sufficient phe for growth and maintenance plus phe-free amino acid formula to meet requirements for protein, energy and micronutrients. Phe tolerance (mg phe/kg body weight/day) is the amount of phe those with PKU can consume and maintain acceptable blood phe levels; it requires individual assessment because of varying phenylalanine hydroxylase activity. The objective was to reassess phe tolerance in eight adults with PKU considering phe requirements, blood phe levels, genotype and phe tolerance at 5 years of age. Subjects had not received a personalized assessment of phe tolerance in several years, and five subjects were overweight, body mass index (BMI) 25-28. With the guidance of a metabolic dietitian, seven subjects increased phe tolerance (by 15-173%) without significantly increasing blood phe concentration. Increased phe tolerance was associated with both improved dietary compliance and inadequate phe intake at the onset of the protocol compared with current requirements. Improved dietary compliance reflected increased consumption of protein equivalents from amino acid formula and increased frequency of formula intake, from 2.2 to 3 times per day. Predictors of higher final phe tolerance following reassessment included being male and having a lower BMI (R(2)=0.588). This suggests that the rising trend of overweight and obesity may affect assessment of phe tolerance in adults. Therefore, interaction with the metabolic dietitian to reassess phe tolerance in relation to body mass is essential throughout adulthood to insure adequate intake of phe to support protein synthesis and prevent catabolism.

Evidence for the participation of the stimulated sympathetic nervous system in the regulation of carnitine blood levels of soccer players during a game

Catecholamines and carnitine blood levels are closely implicated with training. The aim of the study was to investigate the effect of sympathetic nervous system stimulation on carnitine and its fraction levels during training. Blood was obtained from 14 soccer players pregame, at intermission, and postgame. Catecholamines were measured with high-performance liquid chromatography methods; muscle enzymes creatine kinase and lactate dehydrogenase as well as lactate, pyruvate, and total antioxidant status with commercial kits; and carnitine and fraction levels with tandem mass spectrometry. Total antioxidant status (2.97 +/- 0.13 vs 0.96 +/- 0.10 mmol/L, P < .01) as well as free carnitine levels (20.47 +/- 4.0 vs 12.30 +/- 2.8 micromol/L, P < .001) were remarkably decreased especially postgame. Total acylcarnitines (5.20 +/- 1.8 vs 9.42 +/- 3.0 micromol/L, P < .001) and especially total very long-chain acylcarnitines (0.80 +/- 0.01 vs 1.85 +/- 0.03 micromol/L, P < .001) as well as catecholamine levels (adrenaline: 230 +/- 31 vs 890 +/- 110 pmol/L, P < .01; noradrenaline: 1.53 +/- 0.41 vs 3.7 +/- 0.6 nmol/L, P < .01) were significantly increased in players postgame. A statistically significant inverse correlation was found between adrenaline and free carnitine (r = -0.51, P < .01); and a positive correlation was found between adrenaline, total acylcarnitines (r = 0.58, P < .01), and total long-chain acylcarnitine (r = 0.49, P < .01). The significant positive correlation of adrenaline levels with total acylcarnitine and total long-chain acylcarnitine blood levels in athletes as well as the inverse correlation with free carnitine levels may indicate participation of the stimulated sympathetic nervous system in the regulation of some carnitine fraction levels during exercise.

Deuterated palmitate-driven acylcarnitine formation by whole-blood samples for a rapid diagnostic exploration of mitochondrial fatty acid oxidation disorders

BACKGROUND

The biochemical diagnosis of mitochondrial fatty acid oxidation defects (FAOD) currently rests on enzyme assays. A dynamic ex vivo exploration consisting of incubations of whole-blood samples with stable-labeled palmitate and determining leukocyte capacities to produce deuterated acylcarnitines was developed on healthy controls (n=52) and patients with very-long- (VLCADD) (n=2), medium- (MCADD) (n=6), or short- (SCADD) (n=1) chain acyl-CoA dehydrogenase deficiencies.

METHODS

Incubations were optimized with L-carnitine and [16-(2)H(3), 15-(2)H(2)]-palmitate at 37 degrees C for various time periods on MCADD and control whole-blood samples. Labeled acylcarnitines were quantified by electrospray-ionization tandem mass spectrometry after thawing, extraction and derivatization to their butyl esters and the method was applied to patients with defects mentioned above.

RESULTS

The production of acylcarnitines was linear until 6 h of incubation and optimal on 50 to 200 nmol deuterated substrate. A good discrimination between MCADD patient and control data was found, with median C8/C4 acylcarnitine production rate ratios of 81.0 (5th-95th percentile range: 16.6-209.9) and 0.21 (5th-95th percentile range: 0.06-0.79), respectively. The method also discriminated from controls the VLCADD and SCADD patients. Preliminary studies on a healthy control indicated that the storage at 4 degrees C does little or not alter capacities of whole-blood samples to generate labeled acylcarnitines over a period of 48 h.

CONCLUSION

The rapid management afforded by the method, its abilities to characterize patients and to work on whole-blood samples after a stay of 24-48 h at 4 degrees C make it promising for the diagnostic exploration of FAOD.

Improved nutritional management of phenylketonuria by using a diet containing glycomacropeptide compared with amino acids

BACKGROUND

Phenylketonuria (PKU) requires a lifelong low-phenylalanine diet that provides the majority of protein from a phenylalanine-free amino acid (AA) formula. Glycomacropeptide (GMP), an intact protein formed during cheese production, contains minimal phenylalanine.

OBJECTIVE

The objective was to investigate the effects of substituting GMP food products for the AA formula on acceptability, safety, plasma AA concentrations, and measures of protein utilization in subjects with PKU.

DESIGN

Eleven subjects participated in an inpatient metabolic study with two 4-d treatments: a current AA diet (AA diet) followed by a diet that replaced the AA formula with GMP (GMP diet) supplemented with limiting AAs. Plasma concentrations of AAs, blood chemistries, and insulin were measured and compared in AA (day 4) and GMP diets (day 8).

RESULTS

The GMP diet was preferred to the AA diet in 10 of 11 subjects with PKU, and there were no adverse reactions to GMP. There was no significant difference in phenylalanine concentration in postprandial plasma with the GMP diet compared with the AA diet. When comparing fasting with postprandial plasma, plasma phenalyalanine concentration increased significantly with the AA but not with the GMP diet. Blood urea nitrogen was significantly lower, which suggests decreased ureagenesis, and plasma insulin was higher with the GMP diet than with the AA diet.

CONCLUSIONS

GMP, when supplemented with limiting AAs, is a safe and highly acceptable alternative to synthetic AAs as the primary protein source in the nutritional management of PKU. As an intact protein source, GMP improves protein retention and phenylalanine utilization compared with AAs.

Challenges and developments in tandem mass spectrometry based clinical metabolomics

'Clinical metabolomics' aims at evaluating and predicting health and disease risk in an individual by investigating metabolic signatures in body fluids or tissues, which are influenced by genetics, epigenetics, environmental exposures, diet, and behaviour. Powerful analytical techniques like liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) offers a rapid, effective and economical way to analyze metabolic alterations of pre-defined target metabolites in biological samples. Novel hyphenated technical approaches like the combination of tandem mass spectrometry combined with linear ion trap (QTrap mass spectrometry) combines both identification and quantification of known and unknown metabolic targets. We describe new concepts and developments of mass spectrometry based multi-target metabolome profiling in the field of clinical diagnostics and research. Particularly, the experiences from newborn screening provided important insights about the diagnostic potential of metabolite profiling arrays and directs to the clinical aim of predictive, preventive and personalized medicine by metabolomics.

Inherited metabolic disorders and cerebral infarction

The association of genetic factors and cerebral infarction (CI) has long been established. A positive family history alone is a recognized risk factor for CI and vascular events in general. However, there are certain inherited conditions that further increase the risk of stroke. These conditions are generally metabolic and mitochondrial genetic defects that have variable modes of inheritance. This article reviews major inherited metabolic disorders that predispose an individual to CI. Ten main conditions will be discussed: Fabry's disease, cerebrotendinous xanthomatosis, tangier disease, familial hypercholesterolemia, homocystinuria, methylmalonic acidemia, glutaric aciduria type I, propionic acidemia, ornithine transcarbamylase deficiency and mitochondrial encephalopathy, lactic acidosis and stroke-like phenomenon.

Nutritional management of PKU with glycomacropeptide from cheese whey

Individuals with phenylketonuria (PKU) must follow a lifelong low-phenylalanine (Phe) diet to prevent neurological impairment. Compliance with the low-Phe diet is often poor owing to restriction in natural foods and the requirement for consumption of a Phe-free amino acid formula or medical food. Glycomacropeptide (GMP), a natural protein produced during cheese-making, is uniquely suited to a low-Phe diet because when isolated from cheese whey it contains minimal Phe (2.5-5 mg Phe/g protein). This paper reviews progress in evaluating the safety, acceptability and efficacy of GMP in the nutritional management of PKU. A variety of foods and beverages can be made with GMP to improve the taste, variety and convenience of the PKU diet. Sensory studies in individuals with PKU demonstrate that GMP foods are acceptable alternatives to amino acid medical foods. Studies in the PKU mouse model demonstrate that GMP supplemented with limiting indispensable amino acids provides a nutritionally adequate source of protein and improves the metabolic phenotype by reducing concentrations of Phe in plasma and brain. A case report in an adult with classical PKU who followed the GMP diet for 10 weeks at home indicates safety, acceptability of GMP food products, a 13-14% reduction in blood Phe levels (p<0.05) and improved distribution of dietary protein throughout the day compared with the amino acid diet. In summary, food products made with GMP that is supplemented with limiting indispensable amino acids provide a palatable alternative source of protein that may improve dietary compliance and metabolic control of PKU.

Glucose metabolism as a target of histone deacetylase inhibitors

The therapeutic efficacy of histone deacetylase inhibitors (HDACI) is generally attributed to their ability to alter gene expression secondary to their effects on the acetylation status of transcription factors and histones. However, because HDACIs exhibit similar transcriptional effects in most cells, the molecular basis for their therapeutic selectivity toward malignant cells is largely unknown. In this study, we report that HDACI, of distinct chemotypes, quantitatively inhibit glucose transporter 1 (GLUT1)-mediated glucose transport into multiple myeloma cells through both down-regulation of GLUT1 and inhibition of hexokinase 1 (HXK1) enzymatic activity. Unexpectedly, however, this inhibition of glucose utilization is accompanied by an increase in amino acid catabolism with no increase in fatty acid oxidation. Our findings suggest that an HDACI-induced change in carbon source preference could contribute to the therapeutic efficacy of these drugs by creating a pattern of fuel utilization that is incompatible with rapid tumor growth and survival. Furthermore, these results, which implicate glucose metabolism as a target of HDACI, suggest that caution should be exercised in attributing effects of this class of drug to primary alterations in gene transcription.

Incidence of 3-hydroxy-3-methylglutaryl-coenzyme A lyase (HL) deficiency in Brazil, South America

3-Hydroxy-3-methylglutaryl-CoA lyase (HL) deficiency (3-hydroxy-3-methylglutaric aciduria, 3-HMG) is a rare autosomal recessive inborn error of metabolism involving the final step of leucine degradation. HL is the key enzyme for the production of glucose-sparing ketone bodies for brain. Positive biochemical findings are metabolic acidosis, hyperammonaemia, and hypoketotic hypoglycaemia in the neonatal period or infancy. In the present study we report 15 Brazilian patients with HL deficiency and present their clinical and biochemical findings. Urine from all patients contained large amounts of 3-hydroxy-3-methylglutaric, 3-methylglutaconic, 3-hydroxyisovaleric and 3-methylglutaric acids, and 3-methylcrotonylglycine was also observed in 13 patients. The main features at clinical presentation were hypoglycaemia (12 patients), seizures (10 patients), metabolic acidosis (9 patients), vomiting (6 patients), and hepatomegaly (5 patients). All but two patients were of Portuguese ancestry. HL deficiency comprised 7.3% of total organic acidurias detected in our laboratory during a 13-year time span, indicating a high incidence of this disorder in Brazil. Limited molecular characterization (4/15 patients only) revealed two mutations common for individuals of Portuguese/Spanish (Iberian Peninsula) ancestry (E37X and V168fs(-2)). Our findings increase the number of HL-deficient patients and reinforce the characteristic phenotypic picture of the disease. Effective dietary interventions based on mild protein restriction and avoidance of fasting and possibly alternative C5 ketone body generating therapy for this disorder may provide further impetus and rationale for expanded newborn screening of HL deficiency.

Molecular analysis of Taiwanese patients with 3-hydroxy-3-methylglutaryl CoA lyase deficiency

BACKGROUND

3-Hydroxy-3-methylglutaryl CoA lyase deficiency (HL deficiency) is a rare autosomal recessive mitochondrial disease characterized by a deficiency in the enzyme 3-Hydroxy-3-methylglutaryl CoA lyase (HMGCL). Here, we report on novel mutations identified in the HMGCL gene in 2 Taiwanese patients with HL deficiency.

METHODS

Analysis of organic acids in urine was performed using gas chromatography-mass spectrometry to confirm HL deficiency in the two subjects. The mutations in their HMGCL genes then were determined by direct sequencing. In addition, the effect of a splice site mutation was determined using reverse transcription-polymerase chain reactions (RT-PCR).

RESULTS

A total of 3 novel mutations in the HMGCL gene were revealed by molecular analysis: one missense mutation (c.494G>T, p.Arg165Gln) and 2 splice site mutations (IVS3+1G>A, IVS6-1G>A). The results of RT-PCR revealed that an IVS3+1G>A mutation leads to skipping of exon3. We also calculated that the incidence of HL deficiency in Taiwan is <1 per 1,000,000 live births.

CONCLUSIONS

The results of this study suggest that unique HMGCL gene mutations exist in Taiwanese HL deficiency patients. Therefore, HMGCL gene profiling may be useful in genetic counseling for families affected by HL deficiency.

Application of metabolomic principles to disorders of nucleotide metabolism reveals new metabolic perturbations

A metabolomic analysis of plasma amino acids and acylcarnitines was applied to four disorders of nucleotide metabolism. Multivariate analysis gave score plots that show segregation of hypoxanthine phosphoribosyltransferase and adenine phosphoribosyltransferase deficient plasma from controls with equivocal results for adenosine deaminase and dihydropyrimidine dehydrogenase deficiencies. Loadings plots revealed the principal metabolites responsible for the discrimination between these classes. There were increases for HPRT in C4-, C6-, and C3-DC (malonyl)-carnitines, and decreased serine. For APRT there were increases in C4- to C10- and C3-DC to C6-DC-carnitines, urea, 1-methylhistidine, 3-methylhistidine, and decreased tryptophan. For ADA deficiency there were increases in C4- and C6-carnitines, taurine, and isoleucine.

Newborn screening for sickle cell disease using tandem mass spectrometry

BACKGROUND

Neonatal screening programs for sickle cell disease are now widespread in North American and European countries. Most programs apply isoelectric focusing or HPLC to detect hemoglobin variants. Because tandem mass spectrometry (MS/MS) is being used for screening of inherited metabolic disorders and allows protein identification, it was worth testing for hemoglobinopathy screening.

METHODS

We minimized sample preparation and analysis times by avoiding prior purification, derivatization, or separation. We developed a tryptic digestion methodology to screen for the main clinically important variants (Hb S, Hb C, and Hb E) and beta-thalassemia. To ensure proper discrimination between homozygote and heterozygote variants, we selected 4 transitions with good signal intensities for each specific peptide and calculated variant/Hb A ratios for each. Method validation included intra- and interseries variability, carryover, and limit of detection. We also performed a comparative study with isoelectric focusing results on 2082 specimens.

RESULTS

Intraassay imprecision values (CVs) varied between 2.5% and 30.7%. Interassay CVs were between 6.3% and 23.6%. Carryover was <0.03%, and the limit of detection was fixed at 1% of Hb S. According to the MS/MS settings (detection of Hb S, Hb C, Hb E, and beta-globin production defects), the comparative study did not yield any discrepant results between the 2 techniques.

CONCLUSIONS

MS/MS is a reliable method for hemoglobinopathy neonatal screening.

Homozygous carnitine palmitoyltransferase 1b (muscle isoform) deficiency is lethal in the mouse

Carnitine palmitoyltransferase-1 (CPT-1) catalyzes the rate-limiting step of mitochondrial beta-oxidation of long chain fatty acids (LCFA), the most abundant fatty acids in mammalian membranes and in energy metabolism. Human deficiency of the muscle isoform CPT-1b is poorly understood. In the current study, embryos with a homozygous knockout of Cpt-1b were lost before embryonic day 9.5-11.5. Also, while there were normal percentages of CPT-1b+/- pups born from both male and female CPT-1b+/- mice crossed with wild-type mates, the number of CPT-1b+/- pups from CPT-1b+/- breeding pairs was under-represented (63% of the expected number). Northern blot analysis demonstrated approximately 50% Cpt-1b mRNA expression in brown adipose tissue (BAT), heart and skeletal muscles in the CPT-1b+/- male mice. Consistent with tissue-specific expression of Cpt-1b mRNA in muscle but not liver, CPT-1+/- mice had approximately 60% CPT-1 activity in skeletal muscle and no change in total liver CPT-1 activity. CPT-1b+/- mice had normal fasting blood glucose concentration. Consistent with expression of CPT-1b in BAT and muscle, approximately 7% CPT-1b+/- mice (n=30) developed fatal hypothermia following a 3h cold challenge, while none of the CPT-1b+/+ mice (n=30) did. With a prolonged cold challenge (6h), significantly more CPT-1b+/- mice developed fatal hypothermia (52% CPT-1b+/- mice vs. 21% CPT-1b+/+ mice), with increased frequency in females of both genotypes (67% female vs. 38% male CPT-1b+/- mice, and 33% female vs. 8% male CPT-1b+/+ mice). Therefore, lethality of homozygous CPT-1b deficiency in the mice is consistent with paucity of human cases.

Blood phenylalanine monitoring for dietary compliance among patients with phenylketonuria: comparison of methods

PURPOSE

Blood phenylalanine monitoring is critical for the management of phenylketonuria. We compared three methods for measuring blood phenylalanine concentration: the amino acid analyzer, high-performance liquid chromatography with fluorometric detection, and tandem mass spectrometry.

METHODS

We studied 22 female patients with phenylketonuria, ages 12-48 years, who attended our Metabolic Camp. Blood was collected into heparinized tubes (for analysis by the amino acid analyzer) or filter paper (for analysis by high-performance liquid chromatography with fluorometric detection and tandem mass spectrometry).

RESULTS

Blood phenylalanine concentrations of plasma measured by the amino acid analyzer were significantly higher than those obtained from whole blood on filter paper by high-performance liquid chromatography (difference: 102 microM; 95% confidence interval: 23, 181) and tandem mass spectrometry (difference: 137 microM; 95% confidence interval: 58, 216). Phenylalanine concentrations from high-performance liquid chromatography and tandem mass spectrometry were not significantly different (P = 0.5).

CONCLUSIONS

When monitoring blood phenylalanine concentrations for dietary compliance, clinicians should be mindful of the method being used; analyses of whole blood on filter paper were consistently approximately 15% lower than analyses of plasma.

Determination of 3-hydroxyisovalerylcarnitine and other acylcarnitine levels using liquid chromatography-tandem mass spectrometry in serum and urine of a patient with multiple carboxylase deficiency

Due to its increased concentration in blood, 3-hydroxyisovalerylcarnitine (C5OH-I) is an important indicator for the diagnosis of organic acidemias in newborns. However, C5OH-I has not been used as a standard in tandem mass spectrometric (MS/MS) assays because its isolation is difficult. We developed a new synthesis of C5OH-I and investigated its behavior by MS/MS. A method using the multiple reaction monitoring (MRM) mode of MS/MS with HPLC was developed which provides high accuracy, precision and reproducibility. Acylcarnitine profiles in the serum and urine of a patient with multiple carboxylase deficiency (MCD) showed increased levels compared to a healthy patient.

Newborn screening in North America

Newborn screening in North America dates to the early work of Bob Guthrie in the USA. Screening programmes in both the USA and Canada began in the early 1960s, with documented programmes in both countries as early as 1962. Throughout the 1960s and 1970s, many of the screening tests that later became part of routine screening around the world were developed in US and Canadian laboratories, including tests for phenylketonuria, other inborn errors of metabolism, congenital hypothyroidism, congenital adrenal hyperplasia, and haemoglobinopathies. An automated punching machine developed in the USA facilitated screening expansion by significantly reducing sample preparation time and effort. US and Canadian programmes were leaders in applying computerized data management to newborn screening in the 1980s. In the 1990s, DNA and tandem mass spectrometry testing protocols were developed in the USA and applied to newborn screening. US programmes have continually expanded over time, while most Canadian programmes have not. With impetus from private laboratories and professional and consumer groups, many US programmes now screen for more than 50 conditions and there is increased expansion activity in Canada. NBS research in the USA is focused on improving system efficiency and translating other genetic testing to NBS, particularly where new technologies and treatment therapies exist. Although national newborn screening policies do not exist in either Canada or the USA, there are intense efforts to provide uniform access to screening nationwide in both countries. New partnerships between health professionals, consumers and politicians are benefiting the overall screening systems in both countries.

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.

Cost-effectiveness of neonatal screening for medium chain acyl-CoA dehydrogenase deficiency: the homogeneous population of The Netherlands

OBJECTIVE

To assess the cost-effectiveness of neonatal screening on medium chain acyl-CoA dehydrogenase (MCAD) deficiency in a homogeneous population.

STUDY DESIGN

For the scenario without neonatal screening, medical chart review and interviews were performed with physicians and families of 116 Dutch patients born between 1985 and July 2003 with clinically ascertained MCAD deficiency. For the scenario with neonatal screening, 66,205 unaffected and 11 affected newborns identified by prospective neonatal screening for MCAD deficiency in the northern part of the Netherlands were evaluated. The incremental cost-effectiveness ratio (ICER) used life years (LYs) as the outcome measure by combining both scenarios in a decision model with second-order Monte Carlo simulation.

RESULTS

For the scenarios with and without neonatal screening for MCAD deficiency, costs were $6.10 and $4.22 per newborn, respectively. The main cost categories were institutionalization (64%), admissions (17%), special education (8%), laboratory testing (4%), and (para)medical contact (4%). The resulting ICER was $1653 per LY gained. Sensitivity analysis generated an ICER between $14,839 and $4345 per LY gained.

CONCLUSIONS

Screening for MCAD deficiency in a well-defined population generates an ICER well within accepted boundaries for cost-effective interventions, even after sensitivity analysis.

Determination of ornithine in human plasma by hydrophilic interaction chromatography–tandem mass spectrometry

The amino acid ornithine (Orn) acts as a vital part in the physiologically fundamental urea cycle. As such, it is a main intermediate in the catabolic breakdown as well as in the synthesis of arginine and is involved in many other metabolic pathways with potential clinical implications. We here describe a LC-MS-MS method for the detection of Orn in human plasma which is fast, easy and precise. The sample preparation comprises only protein precipitation and the addition of the isotopic labeled I.S. The analytes are separated by hydrophilic interaction chromatography (HILIC) in less than 4min on a silica column with an isocratic mobile phase consisting of 0.1% trifluoroacetic acid in water and acetonitrile in the ratio of 25:75. Orn and its I.S. are detected and quantified by APCI tandem mass spectrometry. The calibration function is linear from 7.5 to 205 micromol/l and covers the range of concentrations found in patients undergoing different clinical interventions. The quantification results are independent with regard to the biological matrix analyzed. The intra-day and inter-day relative standard deviations are 1.1% and 3.5%, respectively. As an application of the described method in clinical investigations, we report arginine and ornithine plasma concentration results from an arginine supplementation study enrolling healthy volunteers and patients suffering from hypercholesterolemia. After oral dosing of 110 mg/kg arginine, ornithine plasma concentrations rose from 54 to 148 micromol/l after 2h and were back to baseline after 24h. However, arginine to ornithine ratios kept constant during the complete observation time.

Genetic mutation profile of isovaleric acidemia patients in Taiwan

Isovaleric acidemia (IVA), a rare recessive autosomal disorder, is caused by isovaleryl-CoA dehydrogenase (IVD) deficiency. IVA may present with symptoms during the acute stage of severe metabolic acidosis, ketosis, vomiting, and altered mental status. With the help of newborn screening (NBS) by tandem mass spectrometry (MS/MS), IVA can now be diagnosed presymptomatically. According to statistic data, the incidence of IVA in Taiwan was about 1/365,000. In this study, six IVA patients from five families were investigated and followed-up clinically. As for the timing, two patients were found before MS technique introduced to Taiwan, the others were identified after MS/MS applied to NBS. The blood level of C5-carnitine in our patients was 7.43-18.96 microM (with upper limit in our laboratory <0.51 microM) and all of their urines contained raised amounts of 3-hydroxyisovaleric acid and isovalerylglycine. Molecular analysis of their IVD gene revealed six mutation profiles, among which the 149G-->A (Arg21His) and 1174 C-->T (Arg363Cys) mutations have been reported previously, while the other four mutations, 386A-->G (His100Arg), 347C-->T (Ser87Phe), 1007G-->A (Cys307Tyr) and 1199A-->G (Tyr371Cys), were first reported. Specially, we found 1199A-->G (Tyr371Cys) mutated was a common recurring missense mutation in our population (4 in 10 mutant alleles).

High-throughput urine screening for Smith-Lemli-Opitz syndrome and cerebrotendinous xanthomatosis using negative electrospray tandem mass spectrometry

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) and cerebrotendinous xanthomatosis (CTX) are disorders affecting cholesterol metabolism. Currently, diagnosis relies on clinical recognition and specific and complex biochemical testing.

METHODS

A rapid, high-throughput urine test, suitable for mass screening for these two disorders, was developed using flow injection negative electrospray tandem mass spectrometry with multiple reaction monitoring. Cholestane-pentol glucuronide, a known marker for CTX, was measured and a steroid sulfate with a proposed keto-pregnadien-diol structure was identified and measured for SLOS. Measurement of the two markers was readily incorporated into an existing tandem mass spectrometry method for diagnosing inborn errors of amino and organic acid metabolism.

RESULTS

Levels in affected patients were well separated from 1738 controls, ranging from 6.7 to 100 times the 99.7th percentile of controls in SLOS patients (n=3) and 7.3 to 24 times the 99.7th percentile of controls in CTX patients (n=4).

CONCLUSIONS

The addition of testing for SLOS and CTX to a routine tandem mass spectrometry urine screening program simplifies the diagnosis of these two disorders and further extends the range of inborn errors of metabolism detected by this technique.

Strategy for the isolation, derivatization, chromatographic separation, and detection of carnitine and acylcarnitines

A strategy for detection of carnitine and acylcarnitines is introduced. This versatile system has four components: (1) isolation by protein precipitation/desalting and cation-exchange solid-phase extraction, (2) derivatization of carnitine and acylcarnitines with pentafluorophenacyl trifluoromethanesulfonate, (3) sequential ion-exchange/reversed-phase chromatography using a single non-end-capped C8 column, and (4) detection of carnitine and acylcarnitine pentafluorophenacyl esters using an ion trap mass spectrometer. Recovery of carnitine and acylcarnitines from the isolation procedure is 77-85%. Derivatization is rapid and complete with no evidence of acylcarnitine hydrolysis. Sequential ion-exchange/reversed-phase HPLC results in separation of reagent byproducts from derivatized carnitine and acylcarnitines, followed by reversed-phase separation of carnitine and acylcarnitine pentafluorophenacyl esters. Detection by MS/MS is highly selective, with carnitine pentafluorophenacyl ester yielding a strong product ion at m/z 311 and acylcarnitine pentafluorophenacyl ester fragmentation yielding two product ions: (1) loss of m/z 59 and (2) generation of an ion at m/z 293. To demonstrate this analytical strategy, phosphate buffered serum albumin was spiked with carnitine and 15 acylcarnitines and analyzed using the described protein precipitation/desalting and cation-exchange solid-phase extraction isolation, derivatization with pentafluorophenacyl trifluoromethanesulfonate, chromatography using the sequential ion-exchange/reversed-phase chromatography HPLC system, and detection by MS and MS/MS. Successful application of this strategy to the quantification of carnitine and acetylcarnitine in rat liver is shown.

Simultaneous quantification of acylcarnitine isomers containing dicarboxylic acylcarnitines in human serum and urine by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

Tandem mass spectrometry (MS/MS) has become a prominent method for screening newborns for diseases such as organic acidemia and fatty acid oxidation defects, although current methods cannot separate acylcarnitine isomers. Accurate determination of dicarboxylic acylcarnitines such as methylmalonylcarnitine and glutarylcarnitine has not been carried out, because obtaining standards of these acylcarnitines is difficult. We attempted the individual determinations of acylcarnitines with isomers and dicarboxylic acylcarnitines by applying high-performance liquid chromatography (HPLC). Chromatographic separation was performed by gradient elution using a mixture of 0.08% aqueous ion-pairing agent and acetonitrile as the mobile phase. Mass transitions of m/z 161.8-->84.8 for carnitine and m/z 164.8-->84.8 for deuterated carnitine were monitored in positive ion electrospray ionization mode. One carnitine and 16 acylcarnitines were quantified. The limit of quantitation (LOQ) was 0.1 micromol/L for methylmalonylcarnitine and 0.05 micromol/L for the other acylcarnitines. Intra-day and inter-day coefficients of variance (CVs) were <8.3% and <8.8%, respectively, for all acylcarnitines in serum, and both were <9.2% in urine. Mean recoveries were >90% for all acylcarnitines. Human samples were quantified by this method. After addition of deuterated acylcarnitines as internal standards, acylcarnitines in serum or urine were extracted using a solid-phase extraction cartridge. In healthy adult individuals, isobutyryl-, 2-methylbutyryl- and isovalerylcarnitine were detected in serum and urine. Dicarboxylic acylcarnitines were detected in urine. High concentrations of methylmalonylcarnitine and propionylcarnitine were found in both the serum and the urine of a patient with methylmalonic acidemia. The described HPLC/MS/MS method could separate most acylcarnitine isomers and quantify them, potentially allowing detailed diagnoses and follow-up treatment for those diseases.

Mutations underlying 3-hydroxy-3-methylglutaryl CoA lyase deficiency in the Saudi population

BACKGROUND

3-hydroxy-3-methylglutaric aciduria (3HMG, McKusick: 246450) is an autosomal recessive branched chain organic aciduria caused by deficiency of the enzyme 3-Hydroxy-3-Methylglutaryl CoA lyase (HL, HMGCL, EC 4.1.3.4). HL is encoded by HMGCL gene and many mutations have been reported. 3HMG is commonly observed in Saudi Arabia.

METHODS

We utilized Whole Genome Amplification (WGA), PCR and direct sequencing to identify mutations underlying 3HMG in the Saudi population. Two patients from two unrelated families and thirty-four 3HMG positive dried blood spots (DBS) were included.

RESULTS

We detected the common missense mutation R41Q in 89% of the tested alleles (64 alleles). 2 alleles carried the frame shift mutation F305fs (-2) and the last two alleles had a novel splice site donor IVS6+1G>A mutation which was confirmed by its absence in more than 100 chromosomes from the normal population. All mutations were present in a homozygous state, reflecting extensive consanguinity. The high frequency of R41Q is consistent with a founder effect. Together the three mutations described account for >94% of the pathogenic mutations underlying 3HMG in Saudi Arabia.

CONCLUSION

Our study provides the most extensive genotype analysis on 3HMG patients from Saudi Arabia. Our findings have direct implications on rapid molecular diagnosis, prenatal and pre-implantation diagnosis and population based prevention programs directed towards 3HMG.

Carnitine-esters from the mushroom Suillus laricinus

Carnitine-esters (1-8) including, a compound (R)-3-hydroxybutanoyl-(R)-carnitine (5), were isolated from the mushroom Suillus laricinus. Their structures were determined by spectroscopic analyses and by total synthesis. One of these, (R)-3-hydroxy-2-methylpropanoyl-(R)-carnitine (4), promoted hyaluronan-degradation by human skin fibroblasts.

ENU mutagenesis identifies mice with cardiac fibrosis and hepatic steatosis caused by a mutation in the mitochondrial trifunctional protein beta-subunit

Using the metabolomics-guided screening coupled to N-ethyl-N-nitrosourea-mediated mutagenesis, we identified mice that exhibited elevated levels of long-chain acylcarnitines. Whole genome homozygosity mapping with 262 SNP markers mapped the disease gene to chromosome 5 where candidate genes Hadha and Hadhb, encoding the mitochondria trifunctional protein (MTP) alpha- and beta-subunits, respectively, are located. Direct sequencing revealed a normal alpha-subunit, but detected a nucleotide T-to-A transversion in exon 14 (c.1210T>A) of beta-subunit (Hadhb) which resulted in a missense mutation of methionine to lysine (M404K). Western blot analysis showed a significant reduction of both the alpha- and beta-subunits, consistent with reduced enzyme activity in both the long-chain 3-hydroxyacyl-CoA dehydrogenase and the long-chain 3-ketoacyl-CoA thiolase activities. These mice had a decreased weight gain and cardiac arrhythmias which manifested from a prolonged PR interval to a complete atrio-ventricular dissociation, and died suddenly between 9 and 16 months of age. Histopathological studies showed multifocal cardiac fibrosis and hepatic steatosis. This mouse model will be useful to further investigate the mechanisms underlying arrhythmogenesis relating to lipotoxic cardiomyopathy and to investigate pathophysiology and treatment strategies for human MTP deficiency.

VLCAD deficiency: pitfalls in newborn screening and confirmation of diagnosis by mutation analysis

We diagnosed six newborn babies with very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) through newborn screening in three years in Victoria (prevalence rate: 1:31,500). We identified seven known and two new mutations in our patients (2/6 homozygotes; 4/6 compound heterozygotes). Blood samples taken at age 48-72 h were diagnostic whereas repeat samples at an older age were normal in 4/6 babies. Urine analysis was normal in 5/5. We conclude that the timing of blood sampling for newborn screening is important and that it is important to perform mutation analysis to avoid false-negative diagnoses of VLCADD in asymptomatic newborn babies. In view of the emerging genotype-phenotype correlation in this disorder, the information derived from mutational analysis can be helpful in designing the appropriate follow-up and therapeutic regime for these patients.

Determination of methylmalonic acid in urine by HPLC with intramolecular excimer-forming fluorescence derivatization

We developed and validated an HPLC method with intramolecular excimer-forming fluorescence derivatization to determine methylmalonic acid, a unique biochemical marker for methylmalonic aciduria. Methylmalonic acid in urine and an internal standard were derivatized with pyrenebutyric hydrazide and separated on a C8 column. The derivatives were detected by monitoring the fluorescence at 475 nm (excitation wavelength 345 nm). At a signal-to-noise ratio of 3, the detection limit was 0.33 pmol on the column and the calibration curve was linear up to 1 mmol[sol ]L in urine. In a retrospective study on a relatively large number of known methylmalonic aciduria cases (n = 48), the method enabled us to differentiate methylmalonic aciduria cases from healthy controls (n = 52), regardless of age of patients at sampling or years of specimen storage. No interference was observed from isomeric or other dicarboxylic acids, or other urine constituents. As described, the method can be used retrospectively or prospectively for the diagnosis of methylmalonic aciduria and can be easily adopted by laboratories with no access to gas chromatography-mass spectrometry.

Tandem Mass Neonatal Screening in Taiwan—Report from One Center

BACKGROUND/PURPOSE

Neonatal screening using tandem mass spectrometry (MS/MS) started in Taiwan in 2000. We evaluated the efficacy of this system by analyzing the frequency of diseases and the outcome of the patients identified.

METHODS

Between August 2001 and July 2004, 199, 922 neonates were screened for 10 amino acids and acylcarnitines using MS/MS in a single center.

RESULTS

In total, 29 cases of inborn errors of metabolism were detected. The overall prevalence was one per 6894 births. The most common inborn error found was 3-methylcrotonyl CoA carboxylase deficiency (10 cases, 34.5%), but none of the cases needed aggressive treatment. There were two cases of type I glutaric aciduria, two cases of maple syrup urine disease, and one case of type II citrullinemia, and early therapeutic intervention was effective for all of them.

CONCLUSION

We found that MS/MS neonatal screening was valuable in the early diagnosis of severe and treatable inborn errors of metabolism such as organic acidemias and urea cycle disorders. It also detected less severe disorders that required only observation.

Screening of newborns and high-risk group of children for inborn metabolic disorders using tandem mass spectrometry in South Korea: a three-year report

BACKGROUND

Mass screening using tandem mass spectrometry(MS/MS) was initiated to determine if the incidence of metabolic disorder is sufficiently high to meet the criteria for newborn screening, and whether or not early medical intervention might be beneficial to the patients.

METHODS

Newborns and children in a high-risk group were screened using MS/MS from April 2001 to March 2004. Blood spots of newborns were collected between 48 and 72 h after birth. The dried blood spots was extracted with 150 microl of methanol, and analyzed by MS/MS.

RESULTS

From April 2001 to March 2004, 79,179 newborns were screened for organic, amino and fatty acid metabolism disorders, which account for approximately 5.4% of annual births in South Korea. Twenty-eight newborns were diagnosed with one of the metabolic disorders and the collective estimated prevalence amounted to 1 in 2800 with a sensitivity of 97.67%, a specificity of 99.28%, a recall rate of 0.05%, and a positive predictive value of 6.38%. 6795 infants/children at high risk were screened and 20 were confirmed to have metabolic disorders.

CONCLUSION

The collective total prevalence of 1:2800 in newborns indicates an underestimation of the incidence of metabolic disorders prior to implementing MS/MS screening in South Korea.

Mass spectrometry in metabolome analysis

In the post-genomic era, increasing efforts have been made to describe the relationship between the genome and the phenotype in cells and organisms. It has become clear that even a complete understanding of the state of the genes, messages, and proteins in a living system does not reveal its phenotype. Therefore, researchers have started to study the metabolome (or the metabolic complement of functional genomics). Within this context, mass spectrometry (MS) has increasingly occupied a central position in the methodologies developed for determination of the metabolic state. This review is mainly focused on the status of MS in the metabolome field, trying to direct the reader to the main approaches for analysis of metabolites, reviewing basic methodologies in sample preparation, and the most recent MS techniques introduced. Apart from the description of the different methods, this review will try to state a general comparison between the several different techniques that involve MS and metabolite analysis, and will highlight their limitations and preferred applicability.

Medium-chain acyl-CoA dehydrogenase deficiency in gene-targeted mice

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common inherited disorder of mitochondrial fatty acid β-oxidation in humans. To better understand the pathogenesis of this disease, we developed a mouse model for MCAD deficiency (MCAD^−/−) by gene targeting in embryonic stem (ES) cells. The MCAD^−/− mice developed an organic aciduria and fatty liver, and showed profound cold intolerance at 4 °C with prior fasting. The sporadic cardiac lesions seen in MCAD^−/− mice have not been reported in human MCAD patients. There was significant neonatal mortality of MCAD^−/− pups demonstrating similarities to patterns of clinical episodes and mortality in MCAD-deficient patients. The MCAD-deficient mouse reproduced important aspects of human MCAD deficiency and is a valuable model for further analysis of the roles of fatty acid oxidation and pathogenesis of human diseases involving fatty acid oxidation.

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is one of the most common inherited disorders of metabolism. This defect in fatty acid oxidation can lead to severe and sometimes fatal disease, especially in young children because they are unable to tolerate a fasting episode. Metabolic complications include very low blood glucose concentrations and generation of toxic by-products. This disorder can result in sudden infant death. Using a process known as gene targeting in mouse embryonic stem cells, the authors have developed a mouse model with the same enzyme deficiency. This mouse model of MCAD deficiency develops many of the same disease characteristics found in affected children. The MCAD-deficient mouse model shows a high rate of newborn loss, intolerance to cold, and the characteristic biochemical changes in the blood, tissues, and urine that are very similar to those found in the human disease counterpart. The MCAD-deficient mouse model will allow researchers to better understand disease mechanisms so that new preventive measures or therapies can be developed.

Modelling of classification rules on metabolic patterns including machine learning and expert knowledge

Machine learning has a great potential to mine potential markers from high-dimensional metabolic data without any a priori knowledge. Exemplarily, we investigated metabolic patterns of three severe metabolic disorders, PAHD, MCADD, and 3-MCCD, on which we constructed classification models for disease screening and diagnosis using a decision tree paradigm and logistic regression analysis (LRA). For the LRA model-building process we assessed the relevance of established diagnostic flags, which have been developed from the biochemical knowledge of newborn metabolism, and compared the models' error rates with those of the decision tree classifier. Both approaches yielded comparable classification accuracy in terms of sensitivity (>95.2%), while the LRA models built on flags showed significantly enhanced specificity. The number of false positive cases did not exceed 0.001%.

Age-Related Variations in Acylcarnitine and Free Carnitine Concentrations Measured by Tandem Mass Spectrometry

Background: The acylcarnitine profiles obtained from dried blood spots on “Guthrie cards” have been widely used for the diagnosis and follow-up of children suspected of carrying an inherited error of metabolism, but little attention has been paid to potential age-related variations in the reference values. In this study, we evaluated the variations in free carnitine and acylcarnitine concentrations with age, as measured by tandem mass spectrometry.

Methods: Filter-paper blood spots were collected from 433 healthy individuals over a period of 17 months. Eight age groups were defined: cord blood, 3–6 days (control group), 15–55 days, 2–18 months, 19–59 months, 5–10 years, 11–17 years, and 18–54 years. Free carnitine and acylcarnitines were measured for each individual. Mean values were calculated for each age group and compared with those for the control group.

Results: Free carnitine was significantly higher in older children than in newborns (P &lt;0.05), but the concentrations of several acylcarnitines tended to be significantly lower in cord blood and in groups of older children than in the control group. Only minor sex-related differences were observed.

Conclusion: Although the risk of underdiagnosis of fatty acid oxidation disorders with the use of newborn values as reference can be considered as small, in some circumstances the use of age-related reference values may have a potential impact on the diagnosis and management of inherited errors of metabolism.

Quantitation of long-chain acylcarnitines by HPLC/fluorescence detection: application to plasma and tissue specimens from patients with carnitine palmitoyltransferase-II deficiency

BACKGROUND

Carnitine palmitoyltransferase-II deficiency (CPT-II deficiency) is a rare disorder of lipid metabolism, in which the accumulation of long-chain acylcarnitines is a diagnostic marker. HPLC with fluorescence detection is an attractive analysis method due to its favorable combination of sensitivity, specificity, ease of analysis and minimal capital equipment costs.

METHODS

Long-chain acylcarnitines were isolated from tissue homogenates (0.5-2 mg wet weight) or plasma (50 microl) using silica gel columns and derivatized with 2-(2,3-naphthalimino)ethyl trifluoromethanesulfonate. Quantitation was by HPLC and fluorescence detection with standard curves (0.0-5.0 nmol/ml) for myristoyl-, palmitoleoyl-, palmitoyl-, oleoyl- and stearoylcarnitine using heptadecanoylcarnitine as the internal standard.

RESULTS

Significantly greater amounts of long-chain acylcarnitines were quantified in patients with CPT-II deficiency when compared to controls; e.g. (nmol/ml in patient plasma, controls mean+/-standard deviation): myristoylcarnitine (0.3, not detectable), palmitoleoylcarnitine (0.5, 0.1+/-0.1), palmitoylcarnitine (0.9, 0.1+/-0.0), oleoylcarnitine (3.0, 0.2+/-0.1), stearoylcarnitine (0.4, not detectable).

CONCLUSIONS

This method can be used to quantitate long-chain acylcarnitines, illustrating their accumulation in CPT-II deficiency. The analysis was accomplished using inexpensive and widely available instrumentation and is appropriate for research investigators who require precise quantitation of long-chain acylcarnitines in complex biological samples.

Development of microwave-assisted derivatization followed by gas chromatography/mass spectrometry for fast determination of amino acids in neonatal blood samples

Analysis of amino acids in blood samples is an important tool for the diagnosis of neonatal amino acid metabolism disorders. In the work, a novel, rapid and sensitive method was developed for the determination of amino acids in neonatal blood samples, which was based on microwave-assisted silylation followed by gas chromatography/mass spectrometry (GC/MS). The amino acids were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) under microwave irradiation. The controlled reaction was carried out employing BSTFA under conventional heating at 120 degrees C for 30 min. Experimental results show that microwave irradiation can accelerate the derivatization reaction of amino acids with BSFTA, and much shorten analysis time. The method validations (linear range, detection limit, precision and recovery) were studied. Finally, the method was tested by determination of amino acids in neonatal blood by the measurement of their trimethylsilyl derivatives by GC/MS in electron impact (EI) mode. Two biomarkers of L-phenylalanine and L-tyrosine in phenylketonuria (PKU)-positive blood and control blood were quantitatively analyzed by the proposed method. The results demonstrated that microwave-assisted silylation followed by GC/MS is a rapid, simple and sensitive method for amino acid analysis and is also a potential tool for fast screening of neonatal aminoacidurias.

Infusionstherapie und Ernährung von Risikogruppen

Besondere Situationen erfordern ein besonderes Vorgehen. Während bisher das »Standardvorgehen« bezüglich der Ernährung von pädiatrischen Patienten dargestellt wurde, beschäftigt sich das vorliegende Kapitel mit »Sondersituationen« der pädiatrischen Infusionstherapie und Ernährung. Behandlungssituationen, die ein besonderes Vorgehen bei der Therapie oder spezielle Aufmerksamkeit bei der Anpassung der Ernährung erfordern, entstehen in der Regel durch 4 mögliche Situationen:

spezifische Physiologie von Patientengruppen (z. B. Früh- oder Neugeborene),

Auswirkungen von therapeutischen Maßnahmen (z. B. Operationen),

Pathophysiologie von Erkrankungen (z. B. angeborene Stoffwechselerkrankungen, Erkrankungen des onkologischen, rheumatischen oder atopischen Formenkreises, Anorexia nervosa, Bulimie oder Adipositas) oder

besondere körperliche Belastungen [z. B. (Leistungs-)Sport].

Bekannte Strategien werden systematisch und prägnant dargestellt und diskutiert.

Die Beschäftigung mit der Ernährung von »Risikogruppen« übt das Erkennen und den Umgang von potenziellen Gefahrensituationen bei der Verordnung von bilanzierter Ernährung. So sollte auch derjenige von dem Kapitel profitieren, der sich mit den behandelten Patientengruppen, Situationen, Erkrankungen üblicherweise nicht beschäftigen muss.

ENU mutagenesis identifies mice with mitochondrial branched-chain aminotransferase deficiency resembling human maple syrup urine disease

Tandem mass spectrometry was applied to detect derangements in the pathways of amino acid and fatty acid metabolism in N-ethyl-N-nitrosourea-treated (ENU-treated) mice. We identified mice with marked elevation of blood branched-chain amino acids (BCAAs), ketoaciduria, and clinical features resembling human maple syrup urine disease (MSUD), a severe genetic metabolic disorder caused by the deficiency of branched-chain alpha-keto acid dehydrogenase (BCKD) complex. However, the BCKD genes and enzyme activity were normal. Sequencing of branched-chain aminotransferase genes (Bcat) showed no mutation in the cytoplasmic isoform (Bcat-1) but revealed a homozygous splice site mutation in the mitochondrial isoform (Bcat-2). The mutation caused a deletion of exon 2, a marked decrease in Bcat-2 mRNA, and a deficiency in both BCAT-2 protein and its enzyme activity. Affected mice responded to a BCAA-restricted diet with amelioration of the clinical symptoms and normalization of the amino acid pattern. We conclude that BCAT-2 deficiency in the mouse can cause a disease that mimics human MSUD. These mice provide an important animal model for study of BCAA metabolism and its toxicity. Metabolomics-guided screening, coupled with ENU mutagenesis, is a powerful approach in uncovering novel enzyme deficiencies and recognizing important pathways of genetic metabolic disorders.

Pharmacokinetics of L-carnitine

L-Carnitine is a naturally occurring compound that facilitates the transport of fatty acids into mitochondria for beta-oxidation. Exogenous L-carnitine is used clinically for the treatment of carnitine deficiency disorders and a range of other conditions. In humans, the endogenous carnitine pool, which comprises free L-carnitine and a range of short-, medium- and long-chain esters, is maintained by absorption of L-carnitine from dietary sources, biosynthesis within the body and extensive renal tubular reabsorption from glomerular filtrate. In addition, carrier-mediated transport ensures high tissue-to-plasma concentration ratios in tissues that depend critically on fatty acid oxidation. The absorption of L-carnitine after oral administration occurs partly via carrier-mediated transport and partly by passive diffusion. After oral doses of 1-6g, the absolute bioavailability is 5-18%. In contrast, the bioavailability of dietary L-carnitine may be as high as 75%. Therefore, pharmacological or supplemental doses of L-carnitine are absorbed less efficiently than the relatively smaller amounts present within a normal diet.L-Carnitine and its short-chain esters do not bind to plasma proteins and, although blood cells contain L-carnitine, the rate of distribution between erythrocytes and plasma is extremely slow in whole blood. After intravenous administration, the initial distribution volume of L-carnitine is typically about 0.2-0.3 L/kg, which corresponds to extracellular fluid volume. There are at least three distinct pharmacokinetic compartments for L-carnitine, with the slowest equilibrating pool comprising skeletal and cardiac muscle.L-Carnitine is eliminated from the body mainly via urinary excretion. Under baseline conditions, the renal clearance of L-carnitine (1-3 mL/min) is substantially less than glomerular filtration rate (GFR), indicating extensive (98-99%) tubular reabsorption. The threshold concentration for tubular reabsorption (above which the fractional reabsorption begins to decline) is about 40-60 micromol/L, which is similar to the endogenous plasma L-carnitine level. Therefore, the renal clearance of L-carnitine increases after exogenous administration, approaching GFR after high intravenous doses. Patients with primary carnitine deficiency display alterations in the renal handling of L-carnitine and/or the transport of the compound into muscle tissue. Similarly, many forms of secondary carnitine deficiency, including some drug-induced disorders, arise from impaired renal tubular reabsorption. Patients with end-stage renal disease undergoing dialysis can develop a secondary carnitine deficiency due to the unrestricted loss of L-carnitine through the dialyser, and L-carnitine has been used for treatment of some patients during long-term haemodialysis. Recent studies have started to shed light on the pharmacokinetics of L-carnitine when used in haemodialysis patients.

Pseudo-glutarylcarnitinaemia in medium-chain acyl-CoA dehydrogenase deficiency detected by tandem mass spectrometry newborn screening

As well as characteristic increases in C(8) carnitine, dried blood spot samples from 11 newborns with medium-chain acyl-CoA dehydrogenase deficiency detected by tandem mass spectrometry screening using butyl esters showed apparent increases in glutarylcarnitine (m / z 388 signals). In four of the newborns in which it was measured, apparent increases in malonylcarnitine (m / z 360) were also detected. It was shown that the apparent increases were caused by interfering acylcarnitines, putatively identified as hydroxyoctanoylcarnitine and hydroxydecanoylcarnitine, respectively, using alternative derivatives for tandem mass spectrometry. Levels of the two abnormal carnitines correlated with C(8) carnitine levels and normalized with repeat testing in 10 cases. These results indicated that the abnormal carnitines were significantly elevated only during periods of increased fatty acid catabolism, as may occur in the immediate postnatal period.

Rapid determination of amino acids in neonatal blood samples based on derivatization with isobutyl chloroformate followed by solid-phase microextraction and gas chromatography/mass spectrometry

The purpose of this study was to develop a simple, rapid and sensitive analytical method for determination of amino acids in neonatal blood samples. The developed method involves the employment of derivatization and a solid-phase microextraction (SPME) technique together with gas chromatography/mass spectrometry (GC/MS). Amino acids in blood samples were derivatized by a mixture of isobutyl chloroformate, methanol and pyridine, and the N(O,S)-alkoxycarbonyl alkyl esters thus formed were headspace extracted by a SPME fiber. Finally, the extracted analytes on the fiber were desorbed and detected by GC/MS in electron impact (EI) mode. L-Valine, L-leucine, L-isoleucine, L-phenylanaline and L-tyrosine in blood samples were quantitatively analyzed by measurement of the corresponding N(O,S)-alkoxycarbonyl alkyl esters using an external standard method. SPME conditions were optimized, and the method was validated. The method was applied to diagnosis of neonatal phenylkenuria (PKU) and maple syrup urine disease (MSUD) by the analyses of five amino acids in blood samples. The results showed that the proposed method is a potentially powerful tool for simultaneous screening for neonatal PKU and MSUD.

Advances in analytical mass spectrometry to improve screening for inherited metabolic diseases

Gas chromatography/mass spectrometry became available more than 30 years ago and has subsequently profoundly contributed not only in the identification of a wide range of inborn errors but also as a key tool for clinical diagnostic screening of genetic metabolic disease. Due to extraordinary advances in liquid chromatography and mass spectrometry (MS) developed in the last decade, the utilisation of MS and the potential number of applications for the purpose of metabolic screening is currently undergoing considerable expansion.

CONCLUSIONS

This overview aims to describe only current new developments in clinically most relevant applications, in particular with focus on low molecular weight compounds.