Identification of Urine Organic Acids for the Detection of Inborn Errors of Metabolism Using Urease and Gas Chromatography-Mass Spectrometry (GC/MS).

A patient suspected of an inborn error of metabolism will commonly have urine organic acid analysis performed as part of their workup. The traditional urine organic acid method involves extraction of the acidic fraction from urine samples using an organic solvent, derivatization of extracted compounds, and identification using gas chromatography-mass spectrometry (GC/MS). Unfortunately, the extraction step results in the loss of many neutral and positively charged compounds which may be of interest to metabolic physicians and biochemical geneticists. By replacing the traditional extraction step with an enzymatic treatment of the sample with urease, an abundance of organic molecules is available for separation and quantification by GC/MS. The urease method is a useful adjunct to newborn screening follow-up, and it has the additional benefit of being able to identify many classes of biochemical compounds, such as amino acids, acylglycines, neurotransmitters, and carbohydrates. This method describes the urease treatment, derivatization, and the organic acids and other biochemical metabolites that can be identified.

Mutations in KAT6B, encoding a histone acetyltransferase, cause Genitopatellar syndrome.

Genitopatellar syndrome (GPS) is a skeletal dysplasia with cerebral and genital anomalies for which the molecular basis has not yet been determined. By exome sequencing, we found de novo heterozygous truncating mutations in KAT6B (lysine acetyltransferase 6B, formerly known as MYST4 and MORF) in three subjects; then by Sanger sequencing of KAT6B, we found similar mutations in three additional subjects. The mutant transcripts do not undergo nonsense-mediated decay in cells from subjects with GPS. In addition, human pathological analyses and mouse expression studies point to systemic roles of KAT6B in controlling organismal growth and development. Myst4 (the mouse orthologous gene) is expressed in mouse tissues corresponding to those affected by GPS. Phenotypic differences and similarities between GPS, the Say-Barber-Biesecker variant of Ohdo syndrome (caused by different mutations of KAT6B), and Rubinstein-Taybi syndrome (caused by mutations in other histone acetyltransferases) are discussed. Together, the data support an epigenetic dysregulation of the limb, brain, and genital developmental programs.

Maternal riboflavin deficiency, resulting in transient neonatal-onset glutaric aciduria Type 2, is caused by a microdeletion in the riboflavin transporter gene GPR172B.

Riboflavin, or vitamin B2, is a precursor to flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) molecules, required in biological oxidation-reduction reactions. We previously reported a case of a newborn female who had clinical and biochemical features of multiple acyl-CoA dehydrogenation deficiency (MADD), which was corrected by riboflavin supplementation. The mother was then found to be persistently riboflavin deficient, suggesting that a possible genetic defect in riboflavin transport in the mother was the cause of the transient MADD seen in the infant. Two recently-identified riboflavin transporters G protein-coupled receptor 172B (GPR172B or RFT1) and riboflavin transporter 2 (C20orf54 or RFT2) were screened for mutations. Two missense sequence variations, c.209A>G [p.Q70R] and c.886G>A [p.V296M] were found in GPR172B. In vitro functional studies of both missense variations showed that riboflavin transport was unaffected by these variations. Quantitative real-time PCR revealed a de novo deletion in GPR172B spanning exons 2 and 3 in one allele from the mother. We postulate that haploinsufficiency of this riboflavin transporter causes mild riboflavin deficiency, and when coupled with nutritional riboflavin deficiency in pregnancy, resulted in the transient riboflavin-responsive disease seen in her newborn infant. This is the first report of a genetic defect in riboflavin transport in humans.

Identification of urine organic acids for the detection of inborn errors of metabolism using urease and gas chromatography-mass spectrometry (GC-MS).

A patient suspected of an inborn error of metabolism will commonly have urine organic acid analysis performed as part of their workup. The traditional urine organic acid method involves extraction of the acidic fraction from urine samples using an organic solvent, derivatization of extracted compounds, and identification using gas chromatography-mass spectrometry (GC-MS). Unfortunately, the extraction step results in the loss of many neutral and positively charged compounds, which may be of interest to metabolic physicians and biochemical geneticists. By replacing the traditional extraction step with an enzymatic treatment of the sample with urease, an abundance of organic molecules are available for separation and quantitation by GC-MS. The urease method is a useful adjunct to newborn screening follow-up and it has the additional benefit of being able to identify many classes of biochemical compounds, such as amino acids, acylglycines, neurotransmitters, and carbohydrates. The method below describes the urease treatment, derivatization, and the organic acids, and other biochemical metabolites that can be identified.

National academy of clinical biochemistry laboratory medicine practice guidelines: follow-up testing for metabolic disease identified by expanded newborn screening using tandem mass spectrometry; executive summary.

BACKGROUND: Almost all newborns in the US are screened at birth for multiple inborn errors of metabolism using tandem mass spectrometry. Screening tests are designed to be sufficiently sensitive so that cases are not missed. The NACB recognized a need for standard guidelines for laboratory confirmation of a positive newborn screen such that all babies would benefit from equal and optimal follow-up by confirmatory testing. METHODS: A committee was formed to review available data pertaining to confirmatory testing. The committee evaluated previously published guidelines, published methodological and clinical studies, clinical case reports, and expert opinion to support optimal confirmatory testing. Grading was based on guidelines adopted from criteria derived from the US Preventive Services Task Force and on the strength of recommendations and the quality of the evidence. Three primary methods of analyte measurement were evaluated for confirmatory testing including measurement of amino acids, organic acids, and carnitine esters. The committee graded the evidence for diagnostic utility of each test for the screened conditions. RESULTS: Ample data and experience were available to make strong recommendations for the practice of analyzing amino acids, organic acids, and acylcarnitines. Likewise, strong recommendations were made for the follow-up test menu for many disorders, particularly those with highest prevalence. Fewer data exist to determine the impact of newborn screening on patient outcomes in all but a few disorders. The guidelines also provide an assessment of developing technology that will fuel a refinement of current practice and ultimate expansion of the diseases detectable by tandem mass spectrometry. CONCLUSIONS: Guidelines are provided for optimal follow-up testing for positive newborn screens using tandem mass spectrometry. The committee regards these tests as reliable and currently optimal for follow-up testing. .

Creating genetics-based infusion centers: a case study of two models.

In 1993, the first effective enzyme replacement therapy for a genetic disease, Ceredase (Genzyme Corporation, Cambridge, MA), was approved for use in patients with Gaucher disease. Over the next 13 years, enzyme replacement therapy became clinically available for the treatment of Fabry disease, mucopolysaccharidosis Type I, mucopolysaccharidosis Type II, mucopolysaccharidosis Type VI, and glycogen storage disease Type II. The development of enzyme replacement therapy to treat lysosomal storage diseases has resulted in an increasing number of genetic patients undergoing weekly or biweekly intravenous enzyme replacement therapy and an expanded role of the genetics team to include comprehensive care involving therapeutic intervention for lysosomal storage diseases. This article describes the development of two outpatient genetics-based infusion centers: the Northshore Genetics Infusion Clinic as part of the Children's Hospital of Wisconsin Lysosomal Diseases Treatment Center in conjunction with the Medical College of Wisconsin and the Emory Lysosomal Storage Disease Center for Genetic Infusions in the Emory University Department of Human Genetics.

Rescue from neonatal death in the murine model of hereditary tyrosinemia by glutathione monoethylester and vitamin C treatment.

Hereditary tyrosinemia type 1 (HT1) is a recessive disease caused by a deficiency of the enzyme fumarylacetoacetate hydrolase (FAH) that catalyzes the conversion of fumarylacetoacetate (FAA) into fumarate and acetoacetate. In mice models of HT1, FAH deficiency causes death within the first 24h after birth. Administration of 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3 cyclohexanedione (NTBC) prevents neonatal death in HT1 mice, ameliorates the HT1 phenotype but does not prevent development of hepatocellular carcinoma later on. FAA has been shown to deplete cells of glutathione by forming adducts. We tested whether a combination of a cell membrane permeable derivative of glutathione, glutathione monoethylester (GSH-MEE) and vitamin C could provide an alternative effective treatment for HT1. GSH-MEE (10 mmol/kg/j)/vitamin C (0.5 mmol/kg/j) treatment was given orally to pregnant/nursing female mice. While FAH-/- pups died in absence of treatment, all FAH-/- pups survived the critical first 24h of life when the mothers were on the GSH-MEE/vitamin C treatment and showed normal growth until postnatal day 10 (P10). However, after P10, pups showed failure to thrive, lethargy and died around P17. Thus, GSH-MEE/vitamin C supplementation could rescue the mice model of HT1 from neonatal death but it did not prevent the appearance of a HT1 phenotype in the second week after birth.

Survival after treatment with phenylacetate and benzoate for urea-cycle disorders.

BACKGROUND: The combination of intravenous sodium phenylacetate and sodium benzoate has been shown to lower plasma ammonium levels and improve survival in small cohorts of patients with historically lethal urea-cycle enzyme defects. METHODS: We report the results of a 25-year, open-label, uncontrolled study of sodium phenylacetate and sodium benzoate therapy (Ammonul, Ucyclyd Pharma) in 299 patients with urea-cycle disorders in whom there were 1181 episodes of acute hyperammonemia. RESULTS: Overall survival was 84% (250 of 299 patients). Ninety-six percent of the patients survived episodes of hyperammonemia (1132 of 1181 episodes). Patients over 30 days of age were more likely than neonates to survive an episode (98% vs. 73%, P<0.001). Patients 12 or more years of age (93 patients), who had 437 episodes, were more likely than all younger patients to survive (99%, P<0.001). Eighty-one percent of patients who were comatose at admission survived. Patients less than 30 days of age with a peak ammonium level above 1000 micromol per liter (1804 microg per deciliter) were least likely to survive a hyperammonemic episode (38%, P<0.001). Dialysis was also used in 56 neonates during 60% of episodes and in 80 patients 30 days of age or older during 7% of episodes. CONCLUSIONS: Prompt recognition of a urea-cycle disorder and treatment with both sodium phenylacetate and sodium benzoate, in conjunction with other therapies, such as intravenous arginine hydrochloride and the provision of adequate calories to prevent catabolism, effectively lower plasma ammonium levels and result in survival in the majority of patients. Hemodialysis may also be needed to control hyperammonemia, especially in neonates and older patients who do not have a response to intravenous sodium phenylacetate and sodium benzoate.

Newborn screening for medium-chain acyl-CoA dehydrogenase deficiency: a global perspective.

As judged by tandem mass spectrometry blood spot screening, the incidence of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is 1:14 600 (CI 95%: 1:13 500-1:15 900) in almost 8.2 million newborns worldwide and is 2- to-3 fold higher than that identified in the same populations after clinical presentation. In mass-screened newborn populations, the 985A>G (K329E) mutation accounts for 54-90% of disease alleles, with homozygotes representing about 47-80% of MCAD deficiency cases. Worldwide, octanoylcarnitine levels are an effective primary screen for MCAD deficiency in newborns. Newborns homozygous for the 985A < G mutation have higher octanoylcarnitine levels than do those compound heterozygous for 985A < G and those with other genotypes. Time of sampling after birth also significantly affects octanoylcarnitine levels in MCAD-deficient newborns. Tandem mass spectrometry newborn blood spot screening for MCAD deficiency is accurate and effective, reduces morbidity and mortality, and merits expansion to other populations worldwide.

Unmasked adult-onset urea cycle disorders in the critical care setting.

Most often, urea cycle disorders have been described as acute onset hyperammonemia in the newborn period; however, there is a growing awareness that urea cycle disorders can present at almost any age, frequently in the critical care setting. This article presents three cases of adult-onset hyperammonemia caused by inherited defects in nitrogen processing in the urea cycle, and reviews the diagnosis, management, and pathophysiology of adult-onset urea cycle disorders. Individuals who have milder molecular urea cycle defects can lead a relatively normal life until a severe environmental stress triggers a hyperammonemic crisis. Comorbid conditions such as physical trauma often delay the diagnosis of the urea cycle defect. Prompt recognition and treatment are essential in determining the outcome of these patients.

Considerations in the difficult-to-manage urea cycle disorder patient.

Today, patients with urea cycle disorder (UCD) may survive well beyond infancy. The goal of keeping them in consistent nitrogen balance can be undermined by changing metabolic needs throughout various stages of life, resulting in hyperammonemia in the short term, and poor growth and development in the long term. The specific UCD genotype can affect the risk of metabolic destabilization and management difficulties, as can variable protein tolerance secondary to changing growth demands, biochemical complications, and environmental influences. Preventing catabolic stress is as important as controlling dietary protein intake for avoiding metabolic decompensation. Optimal treatment, specifically pharmacologic therapy, possible branched chain amino acid (BCAA) supplementation, accurate laboratory monitoring, and psychosocial support, requires thorough understanding and careful application of each component.

Nutritional management of urea cycle disorders.

Nutritional management of patients who have urea cycle disorders is one of the most challenging tasks in clinical nutrition. The degree to which protein intake should be restricted in urea cycle disorders requires complex calculations which depend on many variables such as specific enzyme defect, age-related growth rate, current health status, level of physical activity, amount of free amino acids administered, energy intake, residual urea cycle function, family lifestyle, use of nitrogen-scavenging medications, and the patient's eating behaviors. This paper presents two case histories and a series of recommendations outlining the nutrition management of urea cycle disorders. It also identifies difficulties that arise in the course of treatment, and suggests practical solutions for overcoming them.

Genetic counseling issues in urea cycle disorders.

The goal of counseling families that have a urea cycle disorder (UCD) is to facilitate the process of scientific understanding, emotional acceptance, and decision-making in a nondirective way. A proper understanding of the genes involved, inheritance patterns, available testing, and complicating factors is critical to serving the families' needs. This article summarizes the needed information, in particular describing the complexities of prenatal testing and counseling issues for each UCD. Included case histories illustrate the genetic counseling process and the decision-making scenarios for two families.

Urea cycle disorders: clinical presentation outside the newborn period.

Although most commonly associated with infancy, the majority of individuals with urea cycle disorders (UCDs) present outside the neonatal period, frequently in childhood. Signs and symptoms are often vague, but recurrent; fulminant presentations associated with acute illness are also common. A disorder of urea cycle metabolism should be considered in children who have recurrent symptoms, especially neurologic abnormalities associated with periods of decompensation. Routine laboratory tests, including measurement of plasma ammonia concentrations, can indicate a potential UCD; however, specific metabolic testing and ultimately enzymatic or molecular confirmation are necessary to establish a diagnosis. Treatment with dietary protein restriction and medications may be challenging in children.

Ascorbate decreases Fabry cerebral hyperperfusion suggesting a reactive oxygen species abnormality: an arterial spin tagging study.

PURPOSE: To test the hypothesis that reactive oxygen species contribute to the cerebral hyperperfusion in Fabry disease. MATERIAL AND METHODS: We examined the effect of intravenous injection of ascorbate on cerebral blood flow (CBF) using magnetic resonance arterial spin tagging. Nineteen patients with Fabry disease and 15 control subjects were studied as part of a randomized double-blind placebo-controlled trial of enzyme replacement therapy (ERT). RESULTS: Vertebro-basilar hyperperfusion was observed in patients with Fabry disease. A decrease in systemic ascorbate levels relative to healthy controls was found in the patients. CBF decreased after ascorbate infusion in both control subjects and patients treated with ERT. The placebo group had a significantly delayed decrease in the CBF response after ascorbate infusion. Myeloperoxidase levels were elevated in Fabry patients, consistent with ongoing inflammatory processes in these patients. CONCLUSION: Increased CBF in Fabry disease may be related to increased production of reactive oxygen species, while low plasma ascorbate levels suggests a global redox imbalance. These abnormalities were improved by ERT. These observations have implications regarding oxidative processes contributing to accelerated atherosclerosis in Fabry disease.

The call from the newborn screening laboratory: frustration in the afternoon.

Newborn screening programs in the United States are evolving in concert with technologic advances in analytic chemistry and medicine. Many more disorders are being identified on dried filter paper blood spots without fundamentally altering the basic principles first put forward in the 1960s. Some disorders have been added without researchers knowing if there is a true benefit to early diagnosis and treatment; some disorders currently being detected will merit little or no follow-up in the future. The general principles underlying newborn screening are discussed, as are the individual disorders screened in most programs. The expanding and evolving impact of tandem mass spectrometry on newborn screening is also explored.

Genitopatellar syndrome: expanding the phenotype.

Genitopatellar syndrome is a recently described disorder with characteristic facies, genital anomalies, absent patella, flexion contractures, microcephaly, renal anomalies, and mental retardation. The presence of affected siblings in two of the original families suggests autosomal recessive inheritance. We report a new patient that exhibits all of these cardinal features and is also the second case to have additional, more severe findings including a congenital heart defect, anal anomalies, and features of an ectodermal dysplasia, thus expanding the phenotype to include these manifestations.

Evaluation of liver fatty acid oxidation in the leptin-deficient obese mouse.

We hypothesized that liver fatty acid oxidation (FAO) is compromised in the leptin-deficient obese (Lep(ob)/Lep(ob)) mouse model, and that this would be further challenged when these mice were fed a high-fat diet. Obese mice had a 3.8-fold increased body fat content and a 9-fold increased liver fat content as compared to control mice when both groups were fed a low-fat diet. The expression of liver FAO enzymes, carnitine palmitoyltransferase-1a, long-chain acyl-CoA dehydrogenase, medium-chain acyl-CoA dehydrogenase, and short-chain acyl-CoA dehydrogenase, was not affected in obese mice as compared to controls on either a low-fat or a high-fat diet. The expression of very-long-chain acyl-CoA dehydrogenase was elevated in obese mice on the control diet, as compared to control mice. For all measures evaluated, increasing the level of fat in the diet had a smaller effect than leptin deficiency. In summary, despite obese mice having an excess of fat available for mitochondrial beta-oxidation in liver, overall energy balance appeared to dictate that the net liver FAO remained at control levels.