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.

Long-term safety and efficacy of glycerol phenylbutyrate for the management of urea cycle disorder patients.

INTRODUCTION: Glycerol phenylbutyrate (GPB) is currently approved for use in the US and Europe for patients of all ages with urea cycle disorders (UCD) who cannot be managed with protein restriction and/or amino acid supplementation alone. Currently available data on GPB is limited to 12 months exposure. Here, we present long-term experience with GPB. METHODS: This was an open-label, long-term safety study of GPB conducted in the US (17 sites) and Canada (1 site) monitoring the use of GPB in UCD patients who had previously completed 12 months of treatment in the previous safety extension studies. Ninety patients completed the previous studies with 88 of these continuing into the long-term evaluation. The duration of therapy was open ended until GPB was commercially available. The primary endpoint was the rate of adverse events (AEs). Secondary endpoints were venous ammonia levels, number and causes of hyperammonemic crises (HACs) and neuropsychological testing. RESULTS: A total of 45 pediatric patients between the ages of 1 to 17 years (median 7 years) and 43 adult patients between the ages of 19 and 61 years (median 30 years) were enrolled. The treatment emergent adverse events (TEAE) reported in ≥10% of adult or pediatric patients were consistent with the TEAEs reported in the previous safety extension studies with no increase in the overall incidence of TEAEs and no new TEAEs that indicated a new safety signal. Mean ammonia levels remained stable and below the adult upper limit of normal (<35 µmol/L) through 24 months of treatment in both the pediatric and adult population. Over time, glutamine levels decreased in the overall population. The mean annualized rate of HACs (0.29) established in the previously reported 12-month follow-up study was maintained with continued GPB exposure. CONCLUSION: Following the completion of 12-month follow-up studies with GPB treatment, UCD patients were followed for an additional median of 1.85 (range 0 to 5.86) years in the present study with continued maintenance of ammonia control, similar rates of adverse events, and no new adverse events identified.

Long-term velaglucerase alfa treatment in children with Gaucher disease type 1 naïve to enzyme replacement therapy or previously treated with imiglucerase.

BACKGROUND: Gaucher Disease type 1 (GD1) often manifests in childhood. Early treatment with enzyme replacement therapy (ERT) may prevent disease complications. We report the assessment of velaglucerase alfa ERT in pediatric GD1 patients who participated in a long-term extension study (HGT-GCB-044, ClinicalTrials.gov Identifier NCT00635427). METHODS: Safety and efficacy were evaluated in pediatric patients receiving velaglucerase alfa 30-60U/kg by intravenous infusion every other week. In addition to key hematological and visceral efficacy assessments, exploratory assessments conducted specifically in pediatric patients included evaluation of height, bone age, bone marrow burden, and Tanner stage of puberty. RESULTS: The study included 24 pediatric patients. Fifteen patients were naïve to ERT on entry into the preceding trials TKT032 (12-month trial) or HGT-GCB-039 (9-month trial): in the preceding trials, ten of these 15 patients received velaglucerase alfa and five patients received imiglucerase ERT. Nine patients in the study were previously treated with imiglucerase for >30months and were switched to velaglucerase alfa in the preceding trial TKT034 (12-month trial). Cumulative ERT exposure in the clinical studies ranged from 2.0 to 5.8years. Three serious adverse events, including a fatal convulsion, were reported; none were deemed related to velaglucerase alfa. One patient tested positive for anti-velaglucerase alfa antibodies. An efficacy assessment at 24months showed that velaglucerase alfa had positive effects on primary hematological and visceral parameters in treatment-naïve patients, which were maintained with longer-term treatment. Disease parameters were stable in patients switched from long-term imiglucerase ERT. Exploratory results may suggest benefits of early treatment to enable normal growth in pediatric patients. CONCLUSION: The safety profile and clinical response seen in pediatric patients are consistent with results reported in adults.

Self-reported treatment-associated symptoms among patients with urea cycle disorders participating in glycerol phenylbutyrate clinical trials.

BACKGROUND: Health care outcomes have been increasingly assessed through health-related quality of life (HRQoL) measures. While the introduction of nitrogen-scavenging medications has improved survival in patients with urea cycle disorders (UCDs), they are often associated with side effects that may affect patient compliance and outcomes. METHODS: Symptoms commonly associated with nitrogen-scavenging medications were evaluated in 100 adult and pediatric participants using a non-validated UCD-specific questionnaire. Patients or their caregivers responded to a pre-defined list of symptoms known to be associated with the use of these medications. Responses were collected at baseline (while patients were receiving sodium phenylbutyrate [NaPBA]) and during treatment with glycerol phenylbutyrate (GPB). RESULTS: After 3 months of GPB dosing, there were significant reductions in the proportion of patients with treatment-associated symptoms (69% vs. 46%; p<0.0001), the number of symptoms per patient (2.5 vs. 1.1; p<0.0001), and frequency of the more commonly reported individual symptoms such as body odor, abdominal pain, nausea, burning sensation in mouth, vomiting, and heartburn (p<0.05). The reduction in symptoms was observed in both pediatric and adult patients. The presence or absence of symptoms or change in severity did not correlate with plasma ammonia levels or NaPBA dose. CONCLUSIONS: The reduction in symptoms following 3 months of open-label GPB dosing was similar in pediatric and adult patients and may be related to chemical structure and intrinsic characteristics of the product rather than its effect on ammonia control.

Clinical management of patients with ASXL1 mutations and Bohring-Opitz syndrome, emphasizing the need for Wilms tumor surveillance.

Bohring-Opitz syndrome is a rare genetic condition characterized by distinctive facial features, variable microcephaly, hypertrichosis, nevus flammeus, severe myopia, unusual posture (flexion at the elbows with ulnar deviation, and flexion of the wrists and metacarpophalangeal joints), severe intellectual disability, and feeding issues. Nine patients with Bohring-Opitz syndrome have been identified as having a mutation in ASXL1. We report on eight previously unpublished patients with Bohring-Opitz syndrome caused by an apparent or confirmed de novo mutation in ASXL1. Of note, two patients developed bilateral Wilms tumors. Somatic mutations in ASXL1 are associated with myeloid malignancies, and these reports emphasize the need for Wilms tumor screening in patients with ASXL1 mutations. We discuss clinical management with a focus on their feeding issues, cyclic vomiting, respiratory infections, insomnia, and tumor predisposition. Many patients are noted to have distinctive personalities (interactive, happy, and curious) and rapid hair growth; features not previously reported.

Blood ammonia and glutamine as predictors of hyperammonemic crises in patients with urea cycle disorder.

PURPOSE: The aim of this study was to examine predictors of ammonia exposure and hyperammonemic crises in patients with urea cycle disorders. METHODS: The relationships between fasting ammonia, daily ammonia exposure, and hyperammonemic crises were analyzed in >100 patients with urea cycle disorders. RESULTS: Fasting ammonia correlated strongly with daily ammonia exposure (r = 0.764; P < 0.001). For patients with fasting ammonia concentrations <0.5 upper limit of normal (ULN), 0.5 to <1.0 ULN, and ≥1.0 ULN, the probability of a normal average daily ammonia value was 87, 60, and 39%, respectively, and 10.3, 14.1, and 37.0% of these patients, respectively, experienced ≥1 hyperammonemic crisis over 12 months. Time to first hyperammonemic crisis was shorter (P = 0.008) and relative risk (4.5×; P = 0.011) and rate (~5×, P = 0.006) of hyperammonemic crises were higher in patients with fasting ammonia ≥1.0 ULN vs. <0.5ULN; relative risk was even greater (20×; P = 0.009) in patients ≥6 years old. A 10- or 25-µmol/l increase in ammonia exposure increased the relative risk of a hyperammonemic crisis by 50 and >200% (P < 0.0001), respectively. The relationship between ammonia and hyperammonemic crisis risk seemed to be independent of treatment, age, urea cycle disorder subtype, dietary protein intake, or blood urea nitrogen. Fasting glutamine correlated weakly with daily ammonia exposure assessed as 24-hour area under the curve and was not a significant predictor of hyperammonemic crisis. CONCLUSION: Fasting ammonia correlates strongly and positively with daily ammonia exposure and with the risk and rate of hyperammonemic crises, suggesting that patients with urea cycle disorder may benefit from tight ammonia control.

Mutation Update for UBE3A variants in Angelman syndrome.

Angelman syndrome is a neurodevelopmental disorder caused by a deficiency of the imprinted and maternally expressed UBE3A gene. Although de novo genetic and epigenetic imprinting defects of UBE3A genomic locus account for majority of Angelman diagnoses, approximately 10% of individuals affected with Angelman syndrome are a result of UBE3A loss-of-function mutations occurring on the expressed maternal chromosome. The variants described in this manuscript represent the analysis of 2,515 patients referred for UBE3A gene sequencing at our institution, along with a comprehensive review of the UBE3A mutation literature. Of these, 267 (10.62%) patients had a report issued for detection of a UBE3A gene nucleotide variant, which in many cases involved family studies resulting in reclassification of variants of unknown clinical significance (VUS). Overall, 111 (4.41%) probands had a nucleotide change classified as pathogenic or strongly favored to be pathogenic, 29 (1.15%) had a VUS, and 126 (5.0%) had a nucleotide change classified as benign or strongly favored to be benign. All variants and their clinical interpretations are submitted to NCBI ClinVar, a freely accessible human variation and phenotype database.

Glycerol phenylbutyrate treatment in children with urea cycle disorders: pooled analysis of short and long-term ammonia control and outcomes.

OBJECTIVE: To evaluate glycerol phenylbutyrate (GPB) in the treatment of pediatric patients with urea cycle disorders (UCDs). STUDY DESIGN: UCD patients (n=26) ages 2months through 17years were treated with GPB and sodium phenylbutyrate (NaPBA) in two short-term, open-label crossover studies, which compared 24-hour ammonia exposure (AUC0-24) and glutamine levels during equivalent steady-state dosing of GPB and sodium phenylbutyrate (NaPBA). These 26 patients plus an additional 23 patients also received GPB in one of three 12-month, open label extension studies, which assessed long-term ammonia control, hyperammonemic (HA) crises, amino acid levels, and patient growth. RESULTS: Mean ammonia exposure on GPB was non-inferior to NaPBA in each of the individual crossover studies. In the pooled analyses, it was significantly lower on GPB vs. NaPBA (mean [SD] AUC0-24: 627 [302] vs. 872 [516] µmol/L; p=0.008) with significantly fewer abnormal values (15% on GPB vs. 35% on NaPBA; p=0.02). Mean ammonia levels remained within the normal range during 12months of GPB dosing and, when compared with the 12months preceding enrollment, a smaller percentage of patients (24.5% vs. 42.9%) experienced fewer (17 vs. 38) HA crises. Glutamine levels tended to be lower with GPB than with NaPBA during short-term dosing (mean [SD]: 660.8 [164.4] vs. 710.0 [158.7] µmol/L; p=0.114) and mean glutamine and branched chain amino acid levels, as well as other essential amino acids, remained within the normal range during 12months of GPB dosing. Mean height and weight Z-scores were within normal range at baseline and did not change significantly during 12months of GPB treatment. CONCLUSIONS: Dosing with GPB was associated with 24-hour ammonia exposure that was non-inferior to that during dosing with NaPBA in individual studies and significantly lower in the pooled analysis. Long-term GPB dosing was associated with normal levels of glutamine and essential amino acids, including branched chain amino acids, age-appropriate growth and fewer HA crises as compared with the 12month period preceding enrollment.

Changes in plasma and urine globotriaosylceramide levels do not predict Fabry disease progression over 1 year of agalsidase alfa.

PURPOSE: Globotriaosylceramide concentrations were assessed as potential predictors of change from baseline after 12 months by estimated glomerular filtration rate and left-ventricular mass index using pooled data from three randomized, placebo-controlled agalsidase alfa trials and open-label extensions of patients with Fabry disease. METHODS: Males (aged 18 years or older) with Fabry disease received agalsidase alfa (0.2 mg/kg every other week for 12 months). A backward-elimination approach evaluated potential predictors (baseline estimated glomerular filtration rate and left-ventricular mass index; age at first dose; baseline and change from baseline at 12 months of globotriaosylceramide (urine, plasma); urine protein excretion; and systolic and diastolic blood pressure). Subgroups included patients randomized to placebo or agalsidase alfa (double-blind phase), then to agalsidase alfa (open-label extensions; placebo→agalsidase alfa or agalsidase alfa→agalsidase alfa, respectively) and stage 2/3 chronic kidney disease patients. RESULTS: Baseline estimated glomerular filtration rate, age at first dose, baseline urine globotriaosylceramide excretion, and baseline and change from baseline urine protein excretion significantly predicted change from baseline estimated glomerular filtration rate in the analysis population (N = 73; all P<0.05), although not in all subgroups. Change from baseline urine and plasma globotriaosylceramide (baseline and change from baseline) concentrations did not predict change from baseline estimated glomerular filtration rate. No predictors of left-ventricular mass index were significant. CONCLUSION: Changes in globotriaosylceramide concentrations do not appear to be useful biomarkers for prediction of Fabry disease-related changes in estimated glomerular filtration rate or left-ventricular mass index.

Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin.

Short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD), also called 2-methylbutyryl CoA dehydrogenase deficiency (2-MBCDD), is a disorder of l-isoleucine metabolism of uncertain clinical significance. SBCADD is inadvertently detected on expanded newborn screening by elevated 2-methylbutyrylcarnitine (C5), which has the same mass to charge (m/s) on tandem mass spectrometry (MS/MS) as isovalerylcarnitine (C5), an analyte that is elevated in isovaleric acidemia (IVA), a disorder in leucine metabolism. SBCADD cases identified in the Hmong-American population have been found in association with the c.1165 A>G mutation in the ACADSB gene. The purposes of this study were to: (a) estimate the prevalence of SBCADD and carrier frequency of the c.1165 A>G mutation in the Hmong ethnic group; (b) determine whether the c.1165 A>G mutation is common to all Hmong newborns screening positive for SBCADD; and (c) evaluate C5 acylcarnitine cut-off values to detect and distinguish between SBCADD and IVA diagnoses. During the first 10years of expanded newborn screening using MS/MS in Wisconsin (2001-2011), 97 infants had elevated C5 values (≥0.44µmol/L), of whom five were Caucasian infants confirmed to have IVA. Of the remaining 92 confirmed SBCADD cases, 90 were of Hmong descent. Mutation analysis was completed on an anonymous, random sample of newborn screening cards (n=1139) from Hmong infants. Fifteen infants, including nine who had screened positive for SBCADD based on a C5 acylcarnitine concentration ≥0.44µmol/L, were homozygous for the c.1165 A>G mutation. This corresponds to a prevalence in this ethnic group of being homozygous for the mutation of 1.3% (95% confidence interval 0.8-2.2%) and of being heterozygous for the mutation of 21.8% (95% confidence interval 19.4-24.3%), which is consistent with the Hardy-Weinberg equilibrium. Detection of homozygous individuals who were not identified on newborn screening suggests that the C5 screening cut-off would need to be as low as 0.20µmol/L to detect all infants homozygous for the ACADSB c.1165 A>G mutation. However, lowering the screening cut-off to 0.20 would also result in five "false positive" (non-homozygous) screening results in the Hmong population for every c.1165 A>G homozygote detected. Increasing the cut-off to 0.60µmol/L and requiring elevated C5/C2 (acetylcarnitine) and C5/C3 (propionylcarnitine) ratios to flag a screen as abnormal would reduce the number of infants screening positive, but would still result in an estimated 5 infants with SBCADD per year who would require follow-up and additional biochemical testing to distinguish between SBCADD and IVA diagnoses. Further research is needed to determine the clinical outcomes of SBCADD detected on newborn screening and the c.1165 A>G mutation before knowing whether the optimal screening cut-off would minimize true positives or false negatives for SBCADD associated with this mutation.

Safety and efficacy of velaglucerase alfa in Gaucher disease type 1 patients previously treated with imiglucerase.

Velaglucerase alfa is a glucocerebrosidase produced by gene activation technology in a human fibroblast cell line (HT-1080), and it is indicated as an enzyme replacement therapy (ERT) for the treatment of Gaucher disease type 1 (GD1). This multicenter, open-label, 12-month study examined the safety and efficacy of velaglucerase alfa in patients with GD1 previously receiving imiglucerase. Eligible patients, ≥2 years old and clinically stable on imiglucerase therapy, were switched to velaglucerase alfa at a dose equal to their prior imiglucerase dose. Infusion durations were 1 hr every other week. Forty patients received velaglucerase alfa (18 male, 22 female; four previously splenectomized; age range 9-71 years). Velaglucerase alfa was generally well tolerated with most adverse events (AEs) of mild or moderate severity. The three most frequently reported AEs were headache (12 of 40 patients), arthralgia (9 of 40 patients), and nasopharyngitis (8 of 40 patients). No patients developed antibodies to velaglucerase alfa. There was one serious AE considered treatment-related: a grade 2 anaphylactoid reaction within 30 min of the first infusion. The patient withdrew; this was the only AE-related withdrawal. Hemoglobin concentrations, platelet counts, and spleen and liver volumes remained stable through 12 months. In conclusion, adult and pediatric patients with GD1, previously treated with imiglucerase, successfully transitioned to velaglucerase alfa, which was generally well tolerated and demonstrated efficacy over 12 months' treatment consistent with that observed in the velaglucerase alfa phase 3 clinical trial program.

Ammonia control and neurocognitive outcome among urea cycle disorder patients treated with glycerol phenylbutyrate.

UNLABELLED: Glycerol phenylbutyrate is under development for treatment of urea cycle disorders (UCDs), rare inherited metabolic disorders manifested by hyperammonemia and neurological impairment. We report the results of a pivotal Phase 3, randomized, double-blind, crossover trial comparing ammonia control, assessed as 24-hour area under the curve (NH3 -AUC0-24hr ), and pharmacokinetics during treatment with glycerol phenylbutyrate versus sodium phenylbutyrate (NaPBA) in adult UCD patients and the combined results of four studies involving short- and long-term glycerol phenylbutyrate treatment of UCD patients ages 6 and above. Glycerol phenylbutyrate was noninferior to NaPBA with respect to ammonia control in the pivotal study, with mean (standard deviation, SD) NH3 -AUC0-24hr of 866 (661) versus 977 (865) µmol·h/L for glycerol phenylbutyrate and NaPBA, respectively. Among 65 adult and pediatric patients completing three similarly designed short-term comparisons of glycerol phenylbutyrate versus NaPBA, NH3 -AUC0-24hr was directionally lower on glycerol phenylbutyrate in each study, similar among all subgroups, and significantly lower (P < 0.05) in the pooled analysis, as was plasma glutamine. The 24-hour ammonia profiles were consistent with the slow-release behavior of glycerol phenylbutyrate and better overnight ammonia control. During 12 months of open-label glycerol phenylbutyrate treatment, average ammonia was normal in adult and pediatric patients and executive function among pediatric patients, including behavioral regulation, goal setting, planning, and self-monitoring, was significantly improved. CONCLUSION: Glycerol phenylbutyrate exhibits favorable pharmacokinetics and ammonia control relative to NaPBA in UCD patients, and long-term glycerol phenylbutyrate treatment in pediatric UCD patients was associated with improved executive function (ClinicalTrials.gov NCT00551200, NCT00947544, NCT00992459, NCT00947297). (HEPATOLOGY 2012).

Pancreatic insufficiency in Toriello-Carey syndrome: report of a second patient.

Toriello-Carey syndrome is characterized by multiple congenital anomalies. Pancreatic insufficiency is suspected when patients present with poor weight gain, diarrhea, or maldigestion. The diagnosis is confirmed by low stool elastase and pancreatic stimulation testing. To our knowledge, only one patient with Toriello-Carey syndrome has been reported to have pancreatic insufficiency. We report on a second patient with Toriello-Carey syndrome and pancreatic insufficiency, and describe the management of pancreatic insufficiency in patients with this syndrome.

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.

Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease.

PURPOSE: Infantile Pompe disease resulting from a deficiency of lysosomal acid α-glucosidase (GAA) requires enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA). Cross-reactive immunologic material negative (CRIM-negative) Pompe patients develop high-titer antibody to the rhGAA and do poorly. We describe successful tolerance induction in CRIM-negative patients. METHODS: Two CRIM-negative patients with preexisting anti-GAA antibodies were treated therapeutically with rituximab, methotrexate, and gammaglobulins. Two additional CRIM-negative patients were treated prophylactically with a short course of rituximab and methotrexate, in parallel with initiating rhGAA. RESULTS: In both patients treated therapeutically, anti-rhGAA was eliminated after 3 and 19 months. All four patients are immune tolerant to rhGAA, off immune therapy, showing B-cell recovery while continuing to receive ERT at ages 36 and 56 months (therapeutic) and 18 and 35 months (prophylactic). All patients show clinical response to ERT, in stark contrast to the rapid deterioration of their nontolerized CRIM-negative counterparts. CONCLUSION: The combination of rituximab with methotrexate ± intravenous gammaglobulins (IVIG) is an option for tolerance induction of CRIM-negative Pompe to ERT when instituted in the naïve setting or following antibody development. It should be considered in other conditions in which antibody response to the therapeutic protein elicits robust antibody response that interferes with product efficacy.

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.

Novel ETF dehydrogenase mutations in a patient with mild glutaric aciduria type II and complex II-III deficiency in liver and muscle.

We describe a 22-year-old male who developed severe hypoglycemia and lethargy during an acute illness at 4 months of age and subsequently grew and developed normally. At age 4 years he developed recurrent vomiting with mild hyperammonemia and dehydration requiring frequent hospitalizations. Glutaric aciduria Type II was suspected based upon biochemical findings and managed with cornstarch, carnitine and riboflavin supplements. He did not experience metabolic crises between ages 4-12 years. He experienced recurrent vomiting, mild hyperammonemia, and generalized weakness associated with acute illnesses and growth spurts. At age 18 years, he developed exercise intolerance and proximal muscle weakness leading to the identification of multiple acyl-CoA dehydrogenase and complex II/III deficiencies in both skeletal muscle and liver. Subsequent molecular characterization of the ETFDH gene revealed novel heterozygous mutations, p.G274X:c.820 G > T (exon 7) and p.P534L: c.1601 C > T (exon 12), the latter within the iron sulfur-cluster and predicted to affect ubiquinone reductase activity of ETFDH and the docking of ETF to ETFDH. Our case supports the concept of a structural interaction between ETFDH and other enzyme partners, and suggests that the conformational change upon ETF binding to ETFDH may play a key role in linking ETFDH to II/III super-complex formation.

Phase 2 comparison of a novel ammonia scavenging agent with sodium phenylbutyrate in patients with urea cycle disorders: safety, pharmacokinetics and ammonia control.

UNLABELLED: Glycerol phenylbutyrate (glyceryl tri (4-phenylbutyrate)) (GPB) is being studied as an alternative to sodium phenylbutyrate (NaPBA) for the treatment of urea cycle disorders (UCDs). This phase 2 study explored the hypothesis that GPB offers similar safety and ammonia control as NaPBA, which is currently approved as adjunctive therapy in the chronic management of UCDs, and examined correlates of 24-h blood ammonia. METHODS: An open-label, fixed sequence switch-over study was conducted in adult UCD patients taking maintenance NaPBA. Blood ammonia and blood and urine metabolites were compared after 7 days (steady state) of TID dosing on either drug, both dosed to deliver the same amount of phenylbutyric acid (PBA). RESULTS: Ten subjects completed the study. Adverse events were comparable for the two drugs; 2 subjects experienced hyperammonemic events on NaPBA while none occurred on GPB. Ammonia values on GPB were approximately 30% lower than on NaPBA (time-normalized AUC=26.2 vs. 38.4 micromol/L; Cmax=56.3 vs. 79.1 micromol/L; not statistically significant), and GPB achieved non-inferiority to NaPBA with respect to ammonia (time-normalized AUC) by post hoc analysis. Systemic exposure (AUC(0-24)) to PBA on GPB was 27% lower than on NaPBA (540 vs. 739 microgh/mL), whereas exposure to phenylacetic acid (PAA) (575 vs. 596 microg h/mL) and phenylacetylglutamine (PAGN) (1098 vs. 1133 microg h/mL) were similar. Urinary PAGN excretion accounted for approximately 54% of PBA administered for both NaPBA and GPB; other metabolites accounted for <1%. Intact GPB was generally undetectable in blood and urine. Blood ammonia correlated strongly and inversely with urinary PAGN (r=-0.82; p<0.0001) but weakly or not at all with blood metabolite levels. CONCLUSIONS: Safety and ammonia control with GPB appear at least equal to NaPBA. Urinary PAGN, which is stoichiometrically related to nitrogen scavenging, may be a useful biomarker for both dose selection and adjustment for optimal control of venous ammonia.

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.