Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants.

PURPOSE: This study aimed to define the genotypic and phenotypic spectrum of reversible acute liver failure (ALF) of infancy resulting from biallelic pathogenic TRMU variants and determine the role of cysteine supplementation in its treatment. METHODS: Individuals with biallelic (likely) pathogenic variants in TRMU were studied within an international retrospective collection of de-identified patient data. RESULTS: In 62 individuals, including 30 previously unreported cases, we described 47 (likely) pathogenic TRMU variants, of which 17 were novel, and 1 intragenic deletion. Of these 62 individuals, 42 were alive at a median age of 6.8 (0.6-22) years after a median follow-up of 3.6 (0.1-22) years. The most frequent finding, occurring in all but 2 individuals, was liver involvement. ALF occurred only in the first year of life and was reported in 43 of 62 individuals; 11 of whom received liver transplantation. Loss-of-function TRMU variants were associated with poor survival. Supplementation with at least 1 cysteine source, typically N-acetylcysteine, improved survival significantly. Neurodevelopmental delay was observed in 11 individuals and persisted in 4 of the survivors, but we were unable to determine whether this was a primary or a secondary consequence of TRMU deficiency. CONCLUSION: In most patients, TRMU-associated ALF was a transient, reversible disease and cysteine supplementation improved survival.

Longitudinal Natural History of Pediatric Subjects Affected with Mucopolysaccharidosis IIIB.

OBJECTIVE: To characterize the longitudinal natural history of disease progression in pediatric subjects affected with mucopolysaccharidosis (MPS) IIIB. STUDY DESIGN: Sixty-five children with a confirmed diagnosis of MPS IIIB were enrolled into 1 of 2 natural history studies and followed for up to 4 years. Cognitive and adaptive behavior functions were analyzed in all subjects, and volumetric magnetic resonance imaging analysis of liver, spleen, and brain, as well as levels of heparan sulfate (HS) and heparan sulfate nonreducing ends (HS-NRE), were measured in a subset of subjects. RESULTS: The majority of subjects with MPS IIIB achieved an apex on both cognition and adaptive behavior age equivalent scales between age 3 and 6 years. Development quotients for both cognition and adaptive behavior follow a linear trajectory by which subjects reach a nadir with a score <25 for an age equivalent of 24 months by age 8 years on average and by 13.5 years at the latest. All tested subjects (n = 22) had HS and HS-NRE levels above the normal range in cerebrospinal fluid and plasma, along with signs of hepatomegaly. Subjects lost an average of 26 mL of brain volume (-2.7%) over 48 weeks, owing entirely to a loss of cortical gray matter (32 mL; -6.5%). CONCLUSIONS: MPS IIIB exists along a continuum based on cognitive decline and cortical gray matter atrophy. Although a few individuals with MPS IIIB have an attenuated phenotype, the majority follow predicted trajectories for both cognition and adaptive behavior. TRIAL REGISTRATION: ClinicalTrials.gov identifiers NCT02493998, NCT03227042, and NCT02754076.

Biallelic Variants in PYROXD2 Cause a Severe Infantile Metabolic Disorder Affecting Mitochondrial Function.

Pyridine Nucleotide-Disulfide Oxidoreductase Domain 2 (PYROXD2; previously called YueF) is a mitochondrial inner membrane/matrix-residing protein and is reported to regulate mitochondrial function. The clinical importance of PYROXD2 has been unclear, and little is known of the protein's precise biological function. In the present paper, we report biallelic variants in PYROXD2 identified by genome sequencing in a patient with suspected mitochondrial disease. The child presented with acute neurological deterioration, unresponsive episodes, and extreme metabolic acidosis, and received rapid genomic testing. He died shortly after. Magnetic resonance imaging (MRI) brain imaging showed changes resembling Leigh syndrome, one of the more common childhood mitochondrial neurological diseases. Functional studies in patient fibroblasts showed a heightened sensitivity to mitochondrial metabolic stress and increased mitochondrial superoxide levels. Quantitative proteomic analysis demonstrated decreased levels of subunits of the mitochondrial respiratory chain complex I, and both the small and large subunits of the mitochondrial ribosome, suggesting a mitoribosomal defect. Our findings support the critical role of PYROXD2 in human cells, and suggest that the biallelic PYROXD2 variants are associated with mitochondrial dysfunction, and can plausibly explain the child's clinical presentation.

Treatable lysosomal storage diseases in the advent of disease-specific therapy.

Lysosomal storage diseases (LSD) comprise a rare and heterogeneous group of nearly 50 heritable metabolic disorders caused by mutations in proteins critical for cellular lysosomal function. Defects in the activity of these proteins in multiple organs leads to progressive intra-lysosomal accumulation of specific substrates, resulting in disruption of cellular functions, extracellular inflammatory responses, tissue damage and organ dysfunction. The classification and clinical presentation of different LSD are dependent on the type of accumulated substrate. Some clinical signs and symptoms are common across multiple LSD, while others are more specific to a particular syndrome. Due to the rarity and wide clinical diversity of LSD, identification and diagnosis can be challenging, and in many cases diagnosis is delayed for months or years. Treatments, such as enzyme replacement therapy, haemopoietic stem cell transplantation and substrate reduction therapy, are now available for some of the LSD. For maximum effect, therapy must be initiated prior to the occurrence of irreversible tissue damage, highlighting the importance of prompt diagnosis. Herein, we discuss the clinical presentation, diagnosis and treatment of four of the treatable LSD: Gaucher disease, Fabry disease, Pompe disease, and two of the mucopolysaccharidoses (I and II). For each disease, we present illustrative case studies to help increase awareness of their clinical presentation and possible treatment outcomes.

Safety and Efficacy of Elosulfase Alfa in Australian Patients with Morquio a Syndrome: A Phase 3b Study

Abstract The safety and efficacy of elosulfase alfa were evaluated in a multicenter, open-label, phase 3b study in Australian Morquio A patients, consisting of a 49-week initial phase and an extension phase until elosulfase alfa was government funded. Thirteen patients (1-27 years) were enrolled. No new safety concerns were identified over 138 weeks. Most drug-related adverse events were mild or moderate in severity; none led to study discontinuation. After 49 weeks of treatment, median improvements from baseline were seen in the 6-minute walk test (+41.0 m), 3-minute stair climb test (+14.0 stairs/min), forced vital capacity (+16.4%), forced expiratory volume in 1 second (+14.1%), urine keratan sulfate (-7.1 µg/mg creatinine), and pain intensity. Growth, cardiac function, sleep, and quality of life results were mixed or stable. These results provide further evidence of the acceptable safety/tolerability profile of elosulfase alfa. The improvements in endurance, pulmonary function, and pain support findings from previous studies.

A Phase 3 Trial of Sebelipase Alfa in Lysosomal Acid Lipase Deficiency.

BACKGROUND: Lysosomal acid lipase is an essential lipid-metabolizing enzyme that breaks down endocytosed lipid particles and regulates lipid metabolism. We conducted a phase 3 trial of enzyme-replacement therapy in children and adults with lysosomal acid lipase deficiency, an underappreciated cause of cirrhosis and severe dyslipidemia. METHODS: In this multicenter, randomized, double-blind, placebo-controlled study involving 66 patients, we evaluated the safety and effectiveness of enzyme-replacement therapy with sebelipase alfa (administered intravenously at a dose of 1 mg per kilogram of body weight every other week); the placebo-controlled phase of the study was 20 weeks long and was followed by open-label treatment for all patients. The primary end point was normalization of the alanine aminotransferase level. Secondary end points included additional disease-related efficacy assessments, safety, and side-effect profile. RESULTS: Substantial disease burden at baseline included a very high level of low-density lipoprotein cholesterol (≥190 mg per deciliter) in 38 of 66 patients (58%) and cirrhosis in 10 of 32 patients (31%) who underwent biopsy. A total of 65 of the 66 patients who underwent randomization completed the double-blind portion of the trial and continued with open-label treatment. At 20 weeks, the alanine aminotransferase level was normal in 11 of 36 patients (31%) in the sebelipase alfa group and in 2 of 30 (7%) in the placebo group (P=0.03), with mean changes from baseline of -58 U per liter versus -7 U per liter (P<0.001). With respect to prespecified key secondary efficacy end points, we observed improvements in lipid levels and reduction in hepatic fat content (P<0.001 for all comparisons, except P=0.04 for triglycerides). The number of patients with adverse events was similar in the two groups; most events were mild and were considered by the investigator to be unrelated to treatment. CONCLUSIONS: Sebelipase alfa therapy resulted in a reduction in multiple disease-related hepatic and lipid abnormalities in children and adults with lysosomal acid lipase deficiency. (Funded by Synageva BioPharma and others; ARISE ClinicalTrials.gov number, NCT01757184.).

Metabolite studies in HIBCH and ECHS1 defects: Implications for screening.

3-Hydroxyisobutyryl-CoA hydrolase deficiency (HIBCHD) is a rare inborn error of the valine catabolic pathway associated with Leigh-like disease. We report a female patient who presented at the age of 5months with hypotonia, developmental delay and cerebral atrophy on MRI. Pyruvate dehydrogenase deficiency was initially suspected and decreased activity was shown in fibroblasts. Urine tandem mass spectrometry screening showed large increases in the cysteine conjugate of methacrylate previously described in HIBCHD. 3-hydroxyisobutyryl-CoA hydrolase activity in fibroblasts was below the limit of detection of the enzymatic assay and two novel HIBCH mutations were identified (c.[129dupA];[1033G>A]). Urine metabolite investigations also showed increases in 3-hydroxyisobutyryl carnitine, 2,3-dihydroxy-2-methylbutyrate and several metabolites indicating accumulation and subsequent metabolism of methacrylyl-CoA and acryloyl-CoA. The metabolites derived from acryloyl-CoA were also increased in patients with inborn errors of propionyl-CoA metabolism, indicating the involvement of a secondary propionyl-CoA pathway utilising 3-hydroxyisobutyryl-CoA hydrolase. With the exception of 3-hydroxyisobutyryl carnitine, the metabolite abnormalities were essentially the same as those observed in patients with ECHS1 mutations, a recently described disorder that also affects valine metabolism. Our findings demonstrate the benefits of urine tandem mass spectrometry screening for diagnosing HIBCH and ECHS1 defects and that propionate metabolism may play a role in their pathogenesis. These disorders should be considered during the differential diagnosis of Leigh like-diseases and hypotonia.

ECHS1 mutations in Leigh disease: a new inborn error of metabolism affecting valine metabolism.

Two siblings with fatal Leigh disease had increased excretion of S-(2-carboxypropyl)cysteine and several other metabolites that are features of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency, a rare defect in the valine catabolic pathway associated with Leigh-like disease. However, this diagnosis was excluded by HIBCH sequencing and normal enzyme activity. In contrast to HIBCH deficiency, the excretion of 3-hydroxyisobutyryl-carnitine was normal in the children, suggesting deficiency of short-chain enoyl-CoA hydratase (ECHS1 gene). This mitochondrial enzyme is active in several metabolic pathways involving fatty acids and amino acids, including valine, and is immediately upstream of HIBCH in the valine pathway. Both children were compound heterozygous for a c.473C > A (p.A158D) missense mutation and a c.414+3G>C splicing mutation in ECHS1. ECHS1 activity was markedly decreased in cultured fibroblasts from both siblings, ECHS1 protein was undetectable by immunoblot analysis and transfection of patient cells with wild-type ECHS1 rescued ECHS1 activity. The highly reactive metabolites methacrylyl-CoA and acryloyl-CoA accumulate in deficiencies of both ECHS1 and HIBCH and are probably responsible for the brain pathology in both disorders. Deficiency of ECHS1 or HIBCH should be considered in children with Leigh disease. Urine metabolite testing can detect and distinguish between these two disorders.

Fetal progenitor cell transplantation treats methylmalonic aciduria in a mouse model.

Methylmalonic aciduria is a rare disorder caused by an inborn error of organic acid metabolism. Current treatment options are limited and generally focus on disease management. We aimed to investigate the use of fetal progenitor cells to treat this disorder using a mouse model with an intermediate form of methylmalonic aciduria. Fetal liver cells were isolated from healthy fetuses at embryonic day 15-17 and intravenously transplanted into sub-lethally irradiated mice. Liver donor cell engraftment was determined by PCR. Disease correction was monitored by urine and blood methylmalonic acid concentration and weight change. Initial studies indicated that pre-transplantation sub-lethal irradiation followed by transplantation with 5 million cells were suitable. We found that a double dose of 5 million cells (1 week apart) provided a more effective treatment. Donor cell liver engraftment of up to 5% was measured. Disease correction, as defined by a decrease in blood methylmalonic acid concentration, was effected in methylmalonic acid mice transplanted with a double dose of cells and who showed donor cell liver engraftment. Mean plasma methylmalonic acid concentration decreased from 810 ± 156 (sham transplanted) to 338 ± 157 µmol/L (double dose of 5 million cells) while mean blood C3 carnitine concentration decreased from 20.5 ± 4 (sham transplanted) to 5.3 ± 1.9 µmol/L (double dose of 5 million cells). In conclusion, higher levels of engraftment may be required for greater disease correction; however these studies show promising results for cell transplantation biochemical correction of a metabolic disorder.

A retrospective audit of anesthetic techniques and complications in children with mucopolysaccharidoses.

OBJECTIVES AND AIMS: To document the incidence of difficult airway management and difficult intubation in the era of replacement therapy for Australian children with mucopolysaccharidosis (MPS). BACKGROUND: Medical treatment for MPS has developed significantly since 1980's with a large number of patients now being offered either bone marrow transplant or enzyme replacement. The impact of these therapies on the incidence of difficult airway management has not been adequately documented. Similarly, anesthesia techniques and airway devices have been developed, which are thought to have greatly increased the safety of managing these patients under anesthesia but their role in children with MPS has not been systematically described. METHODS: A retrospective chart review of 17 patients with MPS who had received anesthetics at the Royal Children's Hospital during the time frame January 1998-January 2011. The primary outcome was the incidence of difficult or failed intubation. Secondary outcomes were the relationship between the incidence of difficult intubation and treatment with enzyme replacement therapy (ERT) or bone marrow transplantation. RESULTS: Seventeen patients received 141 anesthetics for 214 procedures. Difficult face mask ventilation occurred in 20 anesthetics (14.2%). Difficult intubation occurred in 40 anesthetics (25%). Failed intubation occurred in two cases (1.6%).The incidence of difficult intubation was 12% in MPS I, 35% MPS II, 86.7% in MPS VI, and 0% in MPS III and IV. CONCLUSIONS: Hematopoietic stem cell transplantation prior to 2 years of age reduces the incidence of difficult mask ventilation and difficult intubation in children with MPS I. ERT was initiated late in the clinical course of MPS II and VI and induced improvements in upper airway patency but did not reduce the incidence of difficult airway management.

Alpers syndrome with mutations in POLG: clinical and investigative features.

Alpers syndrome is a rare autosomal recessive hepatocerebral degenerative disorder. Seventeen patients with Alpers syndrome or polymerase-γ gene mutations were identified. Case records of 12 patients with Alpers syndrome and polymerase-γ mutations in both alleles were reviewed. All patients manifested developmental delay or regression, refractory epilepsy, and biochemical liver dysfunction. Liver failure occurred in three patients previously treated with valproate. Other signs included ataxia, visual disturbance, motor paresis, and tremor. Myoclonic and focal motor seizures were common, often manifesting as status epilepticus. Electroencephalograms demonstrated absent/slow posterior dominant rhythms. Interictal discharges were common, usually involving the occipital lobes. Rhythmic high-amplitude delta with (poly)spikes was evident in four patients. Magnetic resonance imaging showed migratory, cortical, and subcortical T(2) hyperintensities in four children most often affected the parietal and occipital lobes. Developmental regression and refractory focal motor or myoclonic seizures are consistent clinical features of Alpers syndrome with polymerase-γ mutations. Liver dysfunction constitutes a late manifestation. Migratory T(2)/fluid attenuated inversion recovery signal abnormalities involving metabolically active occipital and sensorimotor cortical regions comprise characteristic imaging findings. Interictal and ictal electroencephalogram patterns are more variable than previously reported. Three common polymerase-γ mutations, in patients of European descent, can assist with rapid diagnosis, circumventing the need for liver biopsy.

A knock-out mouse model for methylmalonic aciduria resulting in neonatal lethality.

Methylmalonic aciduria is a human autosomal recessive disorder of organic acid metabolism resulting from a functional defect in the activity of the enzyme methylmalonyl-CoA mutase. Based upon the homology of the human mutase locus with the mouse locus, we have chosen to disrupt the mouse mutase locus within the critical CoA binding domain using gene-targeting techniques to create a mouse model of methylmalonic aciduria. The phenotype of homozygous knock-out mice (mut-/-) is one of early neonatal lethality. Mice appear phenotypically normal at birth and are indistinguishable from littermates. By 15 h of age, they develop reduced movement and suckle less. This is followed by the development of abnormal breathing, and all of the mice with a null phenotype die by 24 h of age. Urinary levels of methylmalonic and methylcitric acids are grossly increased. Measurement of acylcarnitines in blood shows elevation of propionylcarnitine with no change in the levels of acetylcarnitine and free carnitine. Incorporation of [14C]propionate in primary fibroblast cultures from mut-/- mice is reduced to approximately 6% of normal level, whereas there is no detectable synthesis of mut mRNA in the liver. This is the first mouse model that recapitulates the key phenotypic features of mut0 methylmalonic aciduria.

Cobalamin disorder Cbl-C presenting with late-onset thrombotic microangiopathy.

Two siblings, a boy age 12 and his sister age 4 years, presented with proteinuria and hematuria, hypertension, and chronic hemolytic anemia. At age 13 years, the boy developed an episode of severe hypertensive encephalopathy and transient renal failure. Both children are attending normal school, have no neurologic symptoms, and only minimal pigmentary retinal abnormalities. Renal biopsy showed a chronic thrombotic microangiopathic nephropathy. Both patients had hyperhomocysteinemia and mild methylmalonic aciduria. Fibroblasts showed decreased cobalamin uptake, reduced methyl- and adenosyl-cobalamin formation, and deficient incorporation of formate and propionate, compatible with the Cbl-C complementation group, but milder than that found in cells from most patients. Both patients and their father carry a balanced reciprocal translocation. Parenteral hydroxycobalamin treatment reduced the homocysteine levels, and methylmalonic acid disappeared. Increasing the dosage of hydroxycobalamin from 1 to 2.5, then 5 mg daily together with betaine, further reduced homocysteine levels (boy from 118 to 23 microM and girl from 59 to 14 microM). With this treatment, hemolysis has stopped, hematuria has disappeared, proteinuria has almost normalized, and creatinine clearance has been stable. Investigations for chronic thrombotic microangiopathy should include testing for this unusual but treatable disorder, regardless of age of presentation.