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Concept: Inborn errors of metabolism

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BACKGROUND: Families of children living with a rare disease report significant health and social burden, however, few studies have systematically examined family needs by using validated tools to assess the scope and extent of this burden. Our aim was to develop a comprehensive survey to assess health, psychosocial and financial impacts on Australian families caring for a child with a rare disease. METHODS: We developed a self-administered survey for parents/carers incorporating pre-validated tools. The survey included questions about experiences of diagnosis, health services use and needs, needs for peer and financial supports. Forty-seven families attending the state-wide Genetic Metabolic Disorders Service at the Children’s Hospital at Westmead, Sydney were invited to participate. RESULTS: Of 46 families who received the survey, 30 (65%) completed it. Most (93%) found the survey acceptable and relevant (91%). Patients were 1–17 years old, 14 (47%) male, and 12 (40%) non-Caucasian. Eighteen (60%) had a lysosomal storage disease and 12(40%) had a mitochondrial disorder. Eleven (38%) saw 3–5 doctors and four (14%) saw 6–10 doctors before receiving the correct diagnosis; 43% felt diagnosis was delayed. Seven (33%) were dissatisfied with the way diagnosis was given, due to insensitive style of communication, inadequate information and psychological support. Psychosocial impact was moderate to high for 90% of families and the level of impact was not dependent on the level of health functioning of the child. Twenty-six (87%) wanted, but only 13(43%) received, information about peer-support groups. The 30 children accounted for 168 visits to general practitioners and 260 visits to specialist doctors; 21 (70%) children had at least one admission to hospital, including one who had 16 admissions in the previous 12 months. Most families (77%) received financial assistance but 52% believed this was insufficient. Families benefited from a specialised multi-disciplinary clinic but called for patient-held electronic medical records. CONCLUSIONS: Australian families caring for children with genetic metabolic disorders are adversely impacted by delays in diagnosis, lack of easy access to peer support groups and lack of psychological support. Further research is needed to estimate economic impact and to analyse health service delivery models for children with rare diseases in Australia.

Concepts: Health care, Medicine, Health, Epidemiology, Metabolism, Lysosomal storage disease, Physician, Inborn errors of metabolism

140

Human β-glucuronidase (GUS; EC 3.2.1.31) is a lysosomal enzyme that catalyzes the hydrolysis of β-d-glucuronic acid residues from the non-reducing termini of glycosaminoglycans. Impairment in GUS function leads to the metabolic disorder mucopolysaccharidosis type VII, also known as Sly syndrome. We produced GUS from a CHO cell line grown in suspension in a 15 L perfused bioreactor and developed a three step purification procedure that yields ∼99% pure enzyme with a recovery of more than 40%. The method can be completed in two days and has the potential to be integrated into a continuous manufacturing scheme.

Concepts: Protein, Cell, Metabolism, Enzyme, Lysosomal storage disease, Cell culture, Chinese hamster ovary cell, Inborn errors of metabolism

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Introduction: Glutaric aciduria type II (GAII) is a rare autosomal recessive disorder with variable clinical course. The disorder is caused by a defect in the mitochondrial electron transfer flavoprotein or the electron transfer flavoprotein dehydrogenase (ETFDH). Methods: We performed clinical characterization, brain and whole body MRI, muscle histopathology, and genetic analysis of the ETFDH gene in a young woman. Results: She presented with rhabdomyolysis and severe quadriparesis. We identified a novel homozygous missense mutation in ETFDH (c.1544G> T, p.Ser515Ile). Body fat MRI revealed a large amount of subcutaneous fat but no increase in visceral fat despite steatosis of liver and muscle. Diffusion tensor imaging (DTI) of cerebral MRI revealed reduced directionality of the white matter tracts. Histopathological findings showed lipid storage myopathy. Conclusion: In this study we highlighted diagnostic clues and body fat MRI in this rare metabolic disorder. © 2013 Wiley Periodicals, Inc.

Concepts: DNA, Mutation, Allele, Metabolism, Point mutation, Zygosity, Inborn errors of metabolism, Autosomal recessive disorders

27

We investigated the feasibility of using recombinant human acid-α glucosidase (rhGAA, Alglucosidase alfa), an FDA approved therapy for Pompe disease, as a treatment approach for glycogen storage disease type III (GSD III). An in vitro disease model was established by isolating primary myoblasts from skeletal muscle biopsies of patients with GSD IIIa. We demonstrated that rhGAA significantly reduced glycogen levels in the two GSD IIIa patients' muscle cells (by 17% and 48%, respectively) suggesting that rhGAA could be a novel therapy for GSD III. This conclusion needs to be confirmed in other in vivo models.

Concepts: Metabolism, Glucose, Therapy, Glycogen, In vitro, Glycogen storage disease, Inborn errors of metabolism, Glycogen storage disease type II

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Recent studies have implicated trimethylamine N-oxide (TMAO) in atherosclerosis, raising concern about L-carnitine, a common supplement for patients with inborn errors of metabolism (IEMs) and a TMAO precursor metabolized, in part, by intestinal microbes. Dietary meat restriction attenuates carnitine-to-TMAO conversion, suggesting that TMAO production may not occur in meat-restricted individuals taking supplemental L-carnitine, but this has not been tested. Here, we mine a metabolomic dataset to assess TMAO levels in patients with diverse IEMs, including organic acidemias. These data were correlated with clinical information and confirmed using a quantitative TMAO assay. Marked plasma TMAO elevations were detected in patients treated with supplemental L-carnitine, including those on a meat-free diet. On average, patients with an organic acidemia had ~45-fold elevated [TMAO], as compared to the reference population. This effect was mitigated by metronidazole therapy lasting 7 days each month. Collectively, our data show that TMAO production occurs at high levels in patients with IEMs receiving oral L-carnitine. Further studies are needed to determine the long-term safety and efficacy of chronic oral L-carnitine supplementation and whether suppression or circumvention of intestinal bacteria may improve L-carnitine therapy.

Concepts: Protein, Bacteria, Metabolism, Nutrition, Dietary supplement, Inborn error of metabolism, Inborn errors of metabolism, Propionic acidemia

6

Pompe disease, a rare lysosomal storage disease caused by deficiency of the lysosomal acid α-glucosidase (GAA), is characterized by glycogen accumulation, triggering severe secondary cellular damage and resulting in progressive motor handicap and premature death. Numerous disease-causing mutations in the gaa gene have been reported, but the structural effects of the pathological variants were unknown. Here we present the high-resolution crystal structures of recombinant human GAA (rhGAA), the standard care of Pompe disease. These structures portray the unbound form of rhGAA and complexes thereof with active site-directed inhibitors, providing insight into substrate recognition and the molecular framework for the rationalization of the deleterious effects of disease-causing mutations. Furthermore, we report the structure of rhGAA in complex with the allosteric pharmacological chaperone N-acetylcysteine, which reveals the stabilizing function of this chaperone at the structural level.

Concepts: Death, Structure, Lysosomal storage disease, Hierarchy, System, Glycogen storage disease, Inborn errors of metabolism, Acid alpha-glucosidase

2

Inherited metabolic diseases (IMD) are a large group of rare single-gene disorders that are typically diagnosed early in life. There are important evidence gaps related to the comparative effectiveness of therapies for IMD, which are in part due to challenges in conducting randomized controlled trials (RCTs) for rare diseases. Registry-based RCTs present a unique opportunity to address these challenges provided the registries implement standardized collection of outcomes that are important to patients and their caregivers and to clinical providers and healthcare systems. Currently there is no core outcome set (COS) for studies evaluating interventions for paediatric IMD. This protocol outlines a study that will establish COS for each of two relatively common IMD in children, phenylketonuria (PKU) and medium-chain acyl-CoA dehydrogenase (MCAD) deficiency.

Concepts: Medicine, Epidemiology, Clinical trial, Genetic disorder, Metabolism, Randomized controlled trial, Inborn errors of metabolism, Guthrie test

2

New insights into the pathophysiological mechanisms behind late-onset neurodegenerative diseases have come from unexpected sources in recent years. Specifically, the group of inherited metabolic disorders known as lysosomal storage diseases that most commonly affect infants has been found to have surprising similarities with adult neurodegenerative disorders. Most notable has been the identification of Gaucher’s disease as a comorbidity for Parkinson’s disease. Prompted by the recent identification of neuronal aggregates of α-synuclein in another lysosomal storage disease, Krabbe’s disease, we propose the idea that a similar connection exists between adult synucleinopathies and Krabbe’s. Similarities between the two diseases, including the pattern of α-synuclein aggregation in the brain of the twitcher mouse (the authentic murine model of Krabbe’s disease), changes to lipid membrane dynamics, and possible dysfunction in synaptic function and macroautophagy, underscore a link between Krabbe’s disease and late-onset synucleinopathies. Silent GALC mutations may even constitute a risk factor for the development of Parkinson’s in certain patients. More research is required to identify definitively any link and the validity of this hypothesis, but such a connection would prove invaluable for developing novel therapeutic targets for Parkinson’s based on our current understanding of Krabbe’s disease and for establishing new biomarkers for the identification of at-risk patients. © 2016 Wiley Periodicals, Inc.

Concepts: Metabolism, Lysosomal storage disease, Neurology, Neurodegenerative disorders, Parkinson's disease, Inborn errors of metabolism, Gaucher's disease, Lysosomal storage diseases

2

Late-onset Pompe disease (LOPD) is a rare treatable lysosomal storage disorder characterized by progressive lysosomal glycogen accumulation and muscle weakness, with often a limb-girdle pattern. Despite published guidelines, testing for LOPD is often overlooked or delayed in adults, owing to its low frequency compared to other muscle disorders with similar muscle patterns. Next-generation sequencing has the capability to test concurrently for several muscle disorders. This could potentially lead to increased diagnosis of LOPD, disorders with non-specific muscle weakness or atypical patients.

Concepts: Energy, Lysosomal storage disease, Neurology, Muscular system, Pattern, Glycogen storage disease, Inborn errors of metabolism, Lysosomal storage diseases

2

Inborn errors of metabolism (IEMs) are a large class of genetic disorders characterized by disruption of cellular biochemical functions. Although individual IEMs are rare, collectively they represent a large and diverse class of genetic conditions, with new disorders and disease mechanisms being described regularly. Advances in the understanding of the molecular and biochemical etiologies of many IEMs via modalities such as whole-exome sequencing and metabolomics have led to significant progress in detection and treatment in recent years. In this review, we examine the current state of newborn screening for IEMs, recent advances in therapy for IEMs (including glutaric aciduria type I, urea cycle disorders, mitochondrial disorders, and lysosomal storage disorders), and opportunities for further exploration and discovery.

Concepts: Genetic disorder, Metabolism, Mitochondrion, Genetic disorders, Inborn error of metabolism, Inborn errors of metabolism