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PURPOSE To evaluate the safety and efficacy of N-acetylmannosamine (ManNAc) in GNE myopathy, a genetic muscle disease caused by deficiency of the rate-limiting enzyme in N-acetylneuraminic acid (Neu5Ac) biosynthesis. METHODS We conducted an open-label, phase 2, single-center (NIH, USA) study to evaluate oral ManNAc in 12 patients with GNE myopathy (ClinicalTrials.gov NCT02346461). Primary endpoints were safety and biochemical efficacy as determined by change in plasma Neu5Ac and sarcolemmal sialylation. Clinical efficacy was evaluated using secondary outcome measures as part of study extensions, and a disease progression model (GNE-DPM) was tested as an efficacy analysis method. RESULTS Most drug-related adverse events were gastrointestinal, and there were no serious adverse events. Increased plasma Neu5Ac (+2,159 nmol/L, p

Background GNE myopathy is a rare genetic muscle disease resulting from deficiency in an enzyme critical for the biosynthesis of N-acetylneuraminic acid (Neu5Ac, sialic acid). The uncharged Neu5Ac precursor, N-acetylmannosamine (ManNAc), is under development as an orphan drug for treating GNE myopathy. Methods A semi-mechanistic population pharmacokinetic model was developed to simultaneously characterize plasma ManNAc and its metabolite Neu5Ac following oral administration of ManNAc to subjects with GNE myopathy. Plasma ManNAc and Neu5Ac pharmacokinetic data were obtained from two clinical studies (ClinicalTrials.gov identifiers NCT01634750, NCT02346461) and were simultaneously modeled using NONMEM. Results ManNAc and Neu5Ac plasma concentrations were obtained from 34 subjects with GNE myopathy (16 male, 18 female, median age 39.5 years). The model parameter estimates included oral absorption rate (ka) = 0.256 h−1, relative bioavailability relationship with dose (F-Dose) slope = −0.405 (where F = 1 for 6-g dose), apparent clearance (CLM/F) = 631 L/h, volume of distribution (VM/F) = 506 L, Neu5Ac elimination rate constant (kout) = 0.283 h−1, initial ManNAc to Neu5Ac conversion (SLP0) = 0.000619 (ng/mL)−1 and at steady-state (SLPSS) = 0.00334 (ng/mL)−1, with a rate-constant of increase (kinc) = 0.0287 h−1. Goodness-of-fit plots demonstrated an acceptable and unbiased fit to the plasma ManNAc and Neu5Ac concentration data. Visual predictive checks demonstrated reasonable agreement between the 5th, 50th, and 95th percentiles of the observed and simulated data. Conclusions This population pharmacokinetic model can be used to evaluate ManNAc dosing regimens and to calculate Neu5Ac production and exposure following oral administration of ManNAc in subjects with GNE myopathy. Supplementary Information The online version contains supplementary material available at 10.1007/s40268-021-00343-6.

ObjectiveTo characterize muscle involvement and evaluate disease severity in patients with GNE myopathy using skeletal muscle MRI and proton magnetic resonance spectroscopy (1H-MRS).MethodsSkeletal muscle imaging of the lower extremities was performed in 31 patients with genetically confirmed GNE myopathy, including T1-weighted and short tau inversion recovery (STIR) images, T1 and T2 mapping, and 1H-MRS. Measures evaluated included longitudinal relaxation time (T1), transverse relaxation time (T2), and 1H-MRS fat fraction (FF). Thigh muscle volume was correlated with relevant measures of strength, function, and patient-reported outcomes.ResultsThe cohort was representative of a wide range of disease progression. Contractile thigh muscle volume ranged from 5.51% to 62.95% and correlated with thigh strength (r = 0.91), the 6-minute walk test (r = 0.82), the adult myopathy assessment tool (r = 0.83), the activities-specific balance confidence scale (r = 0.65), and the inclusion body myositis functional rating scale (r = 0.62). Four stages of muscle involvement were distinguished by qualitative (T1W and STIR images) and quantitative methods: stage I: unaffected muscle (T1 = 1,033 ± 74.2 ms, T2 = 40.0 ± 1.9 ms, FF = 7.4 ± 3.5%); stage II: STIR hyperintense muscle with minimal or no fat infiltration (T1 = 1,305 ± 147 ms, T2 = 50.2 ± 3.5 ms, FF = 27.6 ± 12.7%); stage III: fat infiltration and STIR hyperintensity (T1 = 1,209 ± 348 ms, T2 = 73.3 ± 12.6 ms, FF = 57.5 ± 10.6%); and stage IV: complete fat replacement (T1 = 318 ± 39.9 ms, T2 = 114 ± 21.2 ms, FF = 85.6 ± 4.2%). 1H-MRS showed a significant decrease in intramyocellular lipid and trimethylamines between stage I and II, suggesting altered muscle metabolism at early stages.ConclusionMRI biomarkers can monitor muscle involvement and determine disease severity noninvasively in patients with GNE myopathy.ClinicalTrials.gov IdentifierNCT01417533.

N-acetylneuraminic acid (Neu5Ac, sialic acid) is a negatively charged monosaccharide, and the predominant form of sialic acid in human cells (1). Sialic acid is typically found as the terminal monosaccharide on glycoconjugates, where it plays a role in various physiologic and pathologic interactions (1). Sialylated glycoconjugates are critical contributors to the polyanionic component of the glomerular glycocalyx, contributing to size and charge selectivity for plasma macromolecules (1,2). Podocyte foot process morphology is maintained by the anionic charged sialic acid residues on glycoconjugates in podocyte membranes (2). Free sialic acid is filtered but not reabsorbed by the human kidney, in a fashion similar to that for creatinine (3), but in contrast to the handling of other monosaccharides such as glucose, mannose, galactose, and fructose that are reabsorbed by tubular cells (4). Circulating sialic acid levels, both unbound and bound to glycoconjugates, have only been sporadically studied in different conditions, including some renal disorders (3,5−9); a possible causative link to reduced eGFRs has been seldom discussed or investigated. We designed this study to establish a correlation between eGFR and plasma free sialic acid across a range of subjects with glomerular disorders. This would not only emphasize this often-overlooked aspect of renal filtering of free sialic acid, but also inform our developmental program for glomerular diseases using the sialic acid precursor, N-acetylmannosamine (ManNAc) (10), which was expected to significantly increase plasma free sialic acid levels in subjects with reduced eGFR. Peripheral blood was obtained from eight subjects enrolled in National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) natural history study 94-DK-0127 (ClinicalTrials.gov identifier, NTC00001392), “Pathogenesis of FSGS,” and from eight subjects enrolled in NIDDK study 16-DK-0036 (ClinicalTrials.gov identifier, NCT02639260), “A Phase 1 Multiple Ascending Dose Study to Evaluate the Safety, Tolerability, and Pharmacokinetics of …

The biosynthesis of sialic acid (Neu5Ac) leads to the intracellular production of cytidine-5'-monophospho-N-acetylneuraminic acid (CMP-Neu5Ac), the active sialic acid donor to nascent glycans (glycoproteins and glycolipids) in the Golgi. UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase myopathy is a rare autosomal recessive muscular disease characterized by progressive muscle weakness and atrophy. To quantify the intracellular levels of CMP-Neu5Ac as well as N-acetylmannosamine (ManNAc) and Neu5Ac in human leukocytes, we developed and validated robust liquid chromatography-tandem mass spectrometry methods. A fit-for-purpose approach was implemented for method validation. Hydrophilic interaction chromatography was used to retain three hydrophilic analytes. The human leukocyte pellets were lysed and extracted in a methanol-water mixture and the leukocyte extract was used for LC-MS/MS analysis. The lower limits of quantitation for ManNAc, Neu5Ac and CMP-Neu5Ac were 25.0, 25.0 and 10.0 ng/ml, respectively. These validated methods were applied to a clinical study.

GNE myopathy, previously known as hereditary inclusion body myopathy (HIBM), or Nonaka myopathy, is a rare autosomal recessive muscle disease characterized by progressive skeletal muscle atrophy. It has an estimated prevalence of 1 to 9:1,000,000. GNE myopathy is caused by mutations in the GNE gene which encodes the rate-limiting enzyme of sialic acid biosynthesis. The pathophysiology of the disease is not entirely understood, but hyposialylation of muscle glycans is thought to play an essential role. The typical presentation is bilateral foot drop caused by weakness of the anterior tibialis muscles with onset in early adulthood. The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease. The diagnosis of GNE myopathy should be considered in young adults presenting with bilateral foot drop. Histopathologic findings on muscle biopsies include fiber size variation, atrophic fibers, lack of inflammation, and the characteristic “rimmed” vacuoles on modified Gomori trichome staining. The diagnosis is confirmed by the presence of pathogenic (mostly missense) mutations in both alleles of the GNE gene. Although there is no approved therapy for this disease, preclinical and clinical studies of several potential therapies are underway, including substrate replacement and gene therapy-based strategies. However, developing therapies for GNE myopathy is complicated by several factors, including the rare incidence of disease, limited preclinical models, lack of reliable biomarkers, and slow disease progression. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13311-018-0671-y) contains supplementary material, which is available to authorized users.

GNE myopathy is a rare, autosomal recessive, inborn error of sialic acid metabolism, caused by mutations in GNE, the gene encoding UDP-N-acetyl-glucosamine-2-epimerase/N-acetylmannosamine kinase. The disease manifests as an adult-onset myopathy characterized by progressive skeletal muscle weakness and atrophy. There is no medical therapy available for this debilitating disease. Hyposialylation of muscle glycoproteins likely contributes to the pathophysiology of this disease. N-acetyl-D-mannosamine (ManNAc), an uncharged monosaccharide and the first committed precursor in the sialic acid biosynthetic pathway, is a therapeutic candidate that prevents muscle weakness in the mouse model of GNE myopathy. We conducted a first-in-human, randomized, placebo-controlled, double-blind, single-ascending dose study to evaluate safety and pharmacokinetics of ManNAc in GNE myopathy subjects. Single doses of 3 and 6g of oral ManNAc were safe and well tolerated; 10g was associated with diarrhea likely due to unabsorbed ManNAc. Oral ManNAc was absorbed rapidly and exhibited a short half-life (~2.4h). Following administration of a single dose of ManNAc, there was a significant and sustained increase in plasma unconjugated free sialic acid (Neu5Ac) (Tmax of 8-11h). Neu5Ac levels remained above baseline 48h post-dose in subjects who received a dose of 6 or 10g. Given that Neu5Ac is known to have a short half-life, the prolonged elevation of Neu5Ac after a single dose of ManNAc suggests that intracellular biosynthesis of sialic acid was restored in subjects with GNE myopathy, including those homozygous for mutations in the kinase domain. Simulated plasma concentration-time profiles support a dosing regimen of 6g twice daily for future clinical trials.

Background GNE myopathy is a rare genetic disease characterized by progressive muscle atrophy and weakness. It is caused by biallelic mutations in the GNE gene that encodes for the bifunctional enzyme, uridine diphosphate (UDP)-N-acetylglucosamine (GlcNAc) 2-epimerase/N-acetylmannosamine (ManNAc) kinase. Typical characteristics of GNE myopathy include progressive myopathy, first involving anterior tibialis muscle and sparing the quadriceps, and rimmed vacuoles on muscle biopsy. Identifying biallelic mutations by sequencing of the GNE gene confirms the diagnosis of GNE myopathy. In a subset of patients, diagnostic confirmation is challenged by the identification of mutations in only one allele, suggesting mutations in deep intronic regions or regulatory regions. Methods We performed targeted sequencing and copy number variant (CNV) analysis of GNE in two siblings who clinically presented with GNE myopathy. Further molecular and biochemical studies were done to characterize the effect of a previously uncharacterized GNE mutation. Results We report two siblings of Indian descent with characteristic features of GNE myopathy, including progressive skeletal muscle weakness initially involving the anterior tibialis, and rimmed vacuoles on muscle biopsy, in which a heterozygous mutation, p.Val727Met, was identified in both affected siblings, but no other deleterious variants in either coding region or exon–intron boundaries of the gene. Subsequent insertion/deletion analysis identified a novel 11.3-kb deletion (Chr9 [GRCh37]: g.36257583_36268910del) encompassing the GNE promoter region, with breakpoints residing in Alu repeats. Gene expression analysis revealed reduced GNE mRNA and protein levels, confirming decreased expression of the deleted allele harboring the deletion. Conclusions We have identified GNE as one of the genes susceptible to Alu-mediated recombination. Our findings suggest that the deletion may encompass the promoter or another region necessary for GNE expression. In patients with typical manifestations of GNE myopathy and a single GNE variant identified, copy number variant (CNV) analysis may be useful in arriving at the diagnosis.

The aim of this analysis was to evaluate the psychometric properties of three patient reported outcome (PRO) measures characterizing physical function in GNE myopathy: the Human Activity Profile, the Inclusion Body Myositis Functional Rating Scale, and the Activities-specific Balance Confidence scale.This analysis used data from 35 GNE myopathy subjects participating in a natural history study. For construct validity, correlational and known-group analyses were between the PROs and physical assessments. Reliability of the PROs between baseline and 6 months was evaluated using the intra-class correlation coefficient model; internal consistency was tested with Cronbach's alpha.The hypothesized moderate positive correlations for construct validity were supported; the strongest correlation was between the human activity profile adjusted activity score and the adult myopathy assessment endurance subscale score (r = 0.81; p 0.0001). The PROs were able to discriminate between known high and low functioning groups for the adult myopathy assessment tool. Internal consistency of the PROs was high (α 0.8) and there was strong reliability (ICC0.62).The PROs are valid and reliable measures of physical function in GNE myopathy and should be incorporated in investigations to better understand the impact of progressive muscle weakness on physical function in this rare disease population. Implications for Rehabilitation GNE myopathy is a rare muscle disease that results in slow progressive muscle atrophy and weakness, ultimately leading to wheelchair use and dependence on a caregiver. There is limited knowledge on the impact of this disease on the health-related quality of life, specifically physical function, of this rare disease population. Three patient reported outcomes have been shown to be valid and reliable in GNE myopathy subjects and should be incorporated in future investigations to better understand how progressive muscle weakness impacts physical functions in this rare disease population. The patient reported outcome scores of GNE myopathy patients indicate a high risk for falls and impaired physical functioning, so it is important clinicians assess and provide interventions for these subjects to maintain their functional capacity.

Objective Creatine transporter deficiency (CTD) is an X-linked, neurometabolic disorder associated with intellectual disability that is characterized by brain creatine (Cr) deficiency and caused by mutations in SLC6A8, the Cr transporter 1 protein gene. CTD is identified by elevated urine creatine/creatinine (Cr/Crn) ratio or reduced Cr peak on brain magnetic resonance spectroscopy; the diagnosis is confirmed by decreased Cr uptake in cultured fibroblasts, and/or identification of a mutation in the SLC6A8 gene. Prevalence studies suggest this disorder may be underdiagnosed. We sought to identify cases from a well-characterized cohort of children diagnosed with neurodevelopmental disorders. Method Urine screening for CTD was performed on a cohort of 46 males with autism spectrum disorder (ASD) and 9 males with a history of non-ASD developmental delay (DD) classified with intellectual disability. Results We identified 1 patient with CTD in the cohort based on abnormal urine Cr/Crn, and confirmed the diagnosis by the identification of a novel frameshift mutation in the SLC6A8 gene. This patient presented without ASD but with intellectual disability, and was characterized by a nonspecific phenotype of early language delay and DD that persisted into moderate-to-severe intellectual disability, consistent with previous descriptions of CTD. Conclusion Identification of patients with CTD is possible by measuring urine Cr and Crn levels and the current case adds to the growing literature of neurocognitive deficits associated with the disorder that affect cognition, language and behavior in childhood.

Purpose To explore the ocular manifestations of cobalamin C ( cblC ) deficiency, an inborn error of intracellular vitamin B12 metabolism. Design Retrospective, observational case series. Participants Twenty-five cblC patients underwent clinical and ophthalmic examination at the National Institutes of Health between August 2004 and September 2012. Patient ages ranged from 2 to 27 years at last ophthalmic visit, and follow-up ranged from 0 to 83 months (median, 37 months; range, 13–83 months) over a total of 69 visits. Methods Best-corrected visual acuity, slit-lamp biomicroscopy, dilated fundus examination, wide-field photography, fundus autofluorescence imaging, sedated electroretinography, optical coherence tomography, genetics and metabolite assessment. Main Outcome Measures Visual acuity and presence and degree of retinal degeneration and optic nerve pallor. Results Nystagmus (64%), strabismus (52%), macular degeneration (72%), optic nerve pallor (68%), and vascular changes (64%) were present. c.271dupA (p.R91KfsX14) homozygous patients (n = 14) showed early and extensive macular degeneration. Electroretinography showed that scotopic and photopic responses were reduced and delayed, but were preserved remarkably in some patients despite severe degeneration. Optical coherence tomography images through the central macular lesion of a patient with severe retinal degeneration showed extreme thinning, some preservation of retinal lamination, and nearly complete loss of the outer nuclear layer. Despite hyperhomocysteinemia, no patients exhibited lens dislocation. Conclusions This longitudinal study reports ocular outcomes in the largest group of patients with cblC deficiency systematically examined at a single center over an extended period. Differences in progression and severity of macular degeneration, optic nerve pallor, and vascular attenuation between homozygous c.271dupA (p.R91KfsX14) patients and compound heterozygotes were noted. The pace and chronicity of ophthalmic manifestations lacked strict correlation to metabolic status as measured during visits. Prenatal or early treatment, or both, may have mitigated ocular disease, leading to better functional acuity, but patients still progressed to severe macular degeneration. The effects of prenatal or early treatment, or both, in siblings; the manifestation of severe disease in infancy; the presence of comorbid developmental abnormalities; and the possible laminar structural defect noted in many patients are findings showing that cblC deficiency displays a developmental as well as a degenerative ocular phenotype.

Introduction GNE myopathy is an adult-onset muscle disorder characterized by impaired sialylation of (muscle) glycans, detectable by lectin histochemistry. We describe a standardized method to quantify (lectin-) fluorescence in muscle sections, applicable for diagnosis and response to therapy for GNE myopathy. Methods Muscle sections were fluorescently labeled with the sialic acid-binding Sambucus nigra agglutinin (SNA) lectin and antibodies to sarcolemma residence protein caveolin-3 (CAV-3). Entire tissue sections were imaged in tiles and fluorescence was quantified. Results SNA fluorescence co-localizing with CAV-3 was ∼50% decreased in GNE myopathy biopsies compared with muscle-matched controls, confirming previous qualitative results. Discussion This quantitative fluorescence method can accurately determine sialylation status of GNE myopathy muscle biopsies. This method is adaptable for expression of other membrane-associated muscle proteins, and may be of benefit for disorders in which therapeutic changes in expression are subtle and difficult to assess by other methods. Muscle Nerve 58: 286-292, 2018.

One Sentence Summary: A Bayesian repeated measures model based on quantitative muscle strength data from a prospective Natural History Study was developed to determine disease progression and design clinical trials for GNE myopathy, a rare and slowly progressive muscle disease. GNE myopathy is a rare muscle disease characterized by slowly progressive weakness and atrophy of skeletal muscles. To address the significant challenges of defining the natural history and designing clinical trials for GNE myopathy, we developed a Bayesian latent variable repeated measures model to determine disease progression. The model is based on longitudinal quantitative muscle strength data collected as part of a prospective Natural History Study. The GNE Myopathy Progression Model provides an understanding of disease progression that would have otherwise required a natural history of unfeasible duration. "Disease age," the model-generated measure of disease progression, highly correlates with a variety of clinical, functional and patient-reported outcomes. With the incorporation of a treatment effect parameter to the GNE Disease Progression Model, we describe a novel GNE Myopathy Disease Modification Analysis that significantly increases power and reduces the number of subjects required to test the effectiveness of novel therapies when compared to more traditional analysis methods. The GNE Myopathy Disease Progression Model and Disease Modification Analysis can be applied to muscle diseases with prospectively collected muscle strength data, and a variety of rare and slowly progressive diseases.

24(S)-hydroxycholesterol [24(S)-HC] is a cholesterol metabolite that is formed almost exclusively in the brain. The concentrations of 24(S)-HC in cerebrospinal fluid (CSF) and/or plasma might be a sensitive marker of altered cholesterol metabolism in the CNS. A highly sensitive 2D-LC-MS/MS assay was developed for the quantification of 24(S)-HC in human plasma and CSF. In the development of an assay for 24(S)-HC in CSF, significant nonspecific binding of 24(S)-HC was observed and resolved with the addition of 2.5% 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) into CSF samples. The sample preparation consists of liquid-liquid extraction with methyl-tert-butyl ether and derivatization with nicotinic acid. Good linearity was observed in a range from 1 to 200 ng/ml and from 0.025 to 5 ng/ml, for plasma and CSF, respectively. Acceptable precision and accuracy were obtained for concentrations over the calibration curve ranges. Stability of 24(S)-HC was reported under a variety of storage conditions. This method has been successfully applied to support a National Institutes of Health-sponsored clinical trial of HP-β-CD in Niemann-Pick type C1 patients, in which 24(S)-HC is used as a pharmacodynamic biomarker.

GNE myopathy is a rare autosomal recessive muscle disease caused by mutations in GNE, the gene encoding the rate-limiting enzyme in sialic acid biosynthesis. GNE myopathy usually manifests in early adulthood with distal myopathy that progresses slowly and symmetrically, first involving distal muscles of the lower extremities, followed by proximal muscles with relative sparing of the quadriceps. Upper extremities are typically affected later in the disease. We report a patient with GNE myopathy who presented with asymmetric hand weakness. He had considerably decreased left grip strength, atrophy of the left anterior forearm and fibro-fatty tissue replacement of left forearm flexor muscles on T1-weighted magnetic resonance imaging. The patient was an endoscopist and thus the asymmetric hand involvement may be associated with left hand overuse in daily repetitive pinching and gripping movements, highlighting the possible impact of environmental factors on the progression of genetic muscle conditions.

Background GNE myopathy is a rare genetic disease characterized by progressive muscle atrophy and weakness. It is caused by biallelic mutations in the GNE gene that encodes for the bifunctional enzyme, uridine diphosphate (UDP)‐N‐acetylglucosamine (GlcNAc) 2‐epimerase/N‐acetylmannosamine (ManNAc) kinase. Typical characteristics of GNE myopathy include progressive myopathy, first involving anterior tibialis muscle and sparing the quadriceps, and rimmed vacuoles on muscle biopsy. Identifying biallelic mutations by sequencing of the GNE gene confirms the diagnosis of GNE myopathy. In a subset of patients, diagnostic confirmation is challenged by the identification of mutations in only one allele, suggesting mutations in deep intronic regions or regulatory regions. Methods We performed targeted sequencing and copy number variant (CNV) analysis of GNE in two siblings who clinically presented with GNE myopathy. Further molecular and biochemical studies were done to characterize the effect of a previously uncharacterized GNE mutation. Results We report two siblings of Indian descent with characteristic features of GNE myopathy, including progressive skeletal muscle weakness initially involving the anterior tibialis, and rimmed vacuoles on muscle biopsy, in which a heterozygous mutation, p.Val727Met, was identified in both affected siblings, but no other deleterious variants in either coding region or exon–intron boundaries of the gene. Subsequent insertion/deletion analysis identified a novel 11.3‐kb deletion (Chr9 [GRCh37]: g.36257583_36268910del) encompassing the GNE promoter region, with breakpoints residing in Alu repeats. Gene expression analysis revealed reduced GNE mRNA and protein levels, confirming decreased expression of the deleted allele harboring the deletion. Conclusions We have identified GNE as one of the genes susceptible to Alu‐mediated recombination. Our findings suggest that the deletion may encompass the promoter or another region necessary for GNE expression. In patients with typical manifestations of GNE myopathy and a single GNE variant identified, copy number variant (CNV) analysis may be useful in arriving at the diagnosis.

GNE myopathy is an autosomal recessive muscle disease caused by biallelic mutations in GNE, a gene encoding for a single protein with key enzymatic activities, UDP-N-acetylglucosamine 2-epimerase and N-acetylmannosamine kinase, in sialic acid biosynthetic pathway. The diagnosis should be considered primarily in patients presenting with distal weakness (foot drop) in early adulthood (other onset symptoms are possible too). The disease slowly progresses to involve other lower and upper extremities' muscles, with marked sparing of the quadriceps. Characteristic findings on biopsies of affected muscles include 'rimmed' (autophagic) vacuoles, aggregation of various proteins and fibre size variation. The diagnosis is confirmed by sequencing of the GNE gene. Note that we use a new mutation nomenclature based on the longest transcript (GenBank: NM_001128227), which encodes a 31-amino acid longer protein than the originally described one (GenBank: NM_005476), which has been used previously in most papers. Based upon the pathophysiology of the disease, recent clinical trials as well as early gene therapy trials have evaluated the use of sialic acid or N-acetylmannosamine (a precursor of sialic acid) in patients with GNE myopathy. Now that therapies are under investigation, it is critical that a timely and accurate diagnosis is made in patients with GNE myopathy.

GNE myopathy is an adult-onset progressive myopathy, resulting from mutations in GNE, the key enzyme of sialic acid synthesis. The pathomechanism of GNE myopathy likely involves aberrant sialylation, since administration of sialic acid itself, or its precursor, N-acetylmannosamine (ManNAc), rescued hyposialylation of GNE myopathy mice. Recently, clinical trials for GNE myopathy patients were initiated. A robust, noninvasive biomarker is highly desirable for diagnosis of GNE myopathy and for evaluating response to therapy. Since muscle biopsies of patients with GNE myopathy demonstrated hyposialylation of predominantly O-linked glycans, we analyzed the O-linked glycome of patients’ plasma proteins using mass spectrometry. Most patients showed increased plasma levels of the core 1 O-linked glycan, Thomsen-Friedenreich (T)-antigen and/or decreased amounts of its sialylated form, ST-antigen. In addition, compared to unaffected individuals, all analyzed patients had a consistently increased ratio of T-antigen to ST-antigen. Importantly, the T/ST ratios were in the normal range in a GNE myopathy patient treated with intravenous immunoglobulins as a source of sialic acid, indicating response to therapy. Natural history and clinical trial data will reveal whether T/ST ratios can be correlated to muscle function. These findings not only highlight plasma T/ST ratios as a robust blood-based biomarker for GNE myopathy, but may also help explain the pathology and course of the disease.

In 2010, the National Institutes of Health (NIH) established the Therapeutics for Rare and Neglected Diseases (TRND) program within the National Center for Advancing Translational Sciences (NCATS), which was created to stimulate drug discovery and development for rare and neglected tropical diseases through a collaborative model between the NIH, academic scientists, nonprofit organizations, and pharmaceutical and biotechnology companies. This paper describes one of the first TRND programs, the development of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) for the treatment of Niemann-Pick disease type C1 (NPC1). NPC is a neurodegenerative, autosomal recessive rare disease caused by a mutation in either the NPC1 (about 95% of cases) or the NPC2 gene (about 5% of cases). These mutations affect the intracellular trafficking of cholesterol and other lipids, which leads to a progressive accumulation of unesterified cholesterol and glycosphingolipids in the CNS and visceral organs. Affected individuals typically exhibit ataxia, swallowing problems, seizures, and progressive impairment of motor and intellectual function in early childhood, and usually die in adolescence. There is no disease modifying therapy currently approved for NPC1 in the US. A collaborative drug development program has been established between TRND, public and private partners that has completed the pre-clinical development of HP-β-CD through IND filing for the current Phase I clinical trial that is underway. Here we discuss how this collaborative effort helped to overcome scientific, clinical and financial challenges facing the development of new drug treatments for rare and neglected diseases, and how it will incentivize the commercialization of HP-β-CD for the benefit of the NPC patient community.

Contains fulltext : 172177.pdf (Publisher’s version ) (Closed access) PURPOSE: Cobalamin C (cblC) deficiency impairs the biosynthesis of 5'-deoxyadenosyl-adenosyl- and methyl-cobalamin, resulting in methylmalonic acidemia combined with hyperhomocysteinemia and hypomethioninemia. However, some patients with cblC deficiency are treated with medical foods, devoid of methionine and high in leucine content, that are formulated for patients with isolated propionate oxidative defects. We examined the effects of imbalanced branched-chain amino acid intake on growth outcomes in cblC-deficient patients. METHODS: Dietary intake was correlated with biochemical, anthropometric, and body composition measurements and other disease parameters in a cohort of 28 patients with early-onset cblC deficiency. RESULTS: Protein-restricted diets were followed by 21% of the patients, whereas 32% received medical foods. Patients on protein-restricted diets had lower height-for-age z-score (P = 0.034), whereas patients consuming medical foods had lower head circumference Z-scores (P = 0.037), plasma methionine concentrations (P = 0.001), and predicted methionine influx through the blood-brain barrier Z-score (-1.29 vs. -0.0617; P = 0.007). The combination of age at diagnosis, a history of seizures, and the leucine-to-valine dietary intake ratio best predicted head circumference Z-score based on multiple regression modeling (R(2) = 0.945). CONCLUSIONS: Patients with cblC deficiency treated with medical foods designed for isolated methylmalonic acidemia are at risk for iatrogenic methionine deficiency that could adversely affect brain growth and development.Genet Med 18 4, 396-404.

Combined methylmalonic acidemia and homocystinuria, cblC type, is an inborn error of intracellular cobalamin metabolism with a wide spectrum of clinical manifestations that is stated to be the most common inherited disorder of cobalamin metabolism. This metabolic disease is caused by mutations in the MMACHC gene and results in impaired intracellular synthesis of adenosylcobalamin and methylcobalamin, cofactors for the methylmalonyl-CoA mutase and methionine synthase enzymes. Elevated methylmalonic acid and homocysteine with decreased methionine production are the biochemical hallmarks of this disorder. Awareness of the diverse clinical presentations associated with cblC disease is necessary to provide a timely diagnosis, to guide management of affected individuals and to establish a framework for the future treatment of individuals detected through expanded newborn screening. This article reviews the biochemistry, clinical presentations, genotype-phenotype correlations, diagnosis and management of cblC disease.

The recessively inherited, adult onset, quadriceps sparing myopathy with a predilection for distal muscles has received multiple historic names. The disorder was described in 1981 in Japanese patients and termed Nonaka Distal Myopathy [1], later commonly referred to as Distal Myopathy with Rimmed Vacuoles (DMRV) (OMIM#605820). In 1984, the disorder was described as vacuolar myopathy sparing the quadriceps in Iranian-Jewish patients [2], later commonly referred to as Inclusion Body Myopathy 2 (IBM2) or Hereditary Inclusion Body Myopathy (HIBM) (OMIM#600737). Mapping of the causative gene to the same locus on chromosome 9 in different cohorts of patient [3, 4], and ultimately identification of mutations in the causative gene GNE in all cohorts [5, 6], confirmed that these myopathies are in fact the same condition. However, since identification of GNE as the common causative gene, the multiple historic names for the disorder continue to be used by research groups worldwide. This disease nomenclature becomes increasingly confusing for clinicians, patients and researchers. Therefore, an international consortium (of which the authors are also members) has recently proposed to rename the disorder “GNE myopathy”, substituting all previous disease definitions. We all are now using this new name and hope that it will become the only term worldwide. After initial discovery of GNE gene defects to be causative for GNE myopathy, eight different GNE mRNA splice variants were identified, encoding (at least theoretically) eight protein isoforms [7]. The human GNE gene (GenBank Gene ID: 10020, {"type":"entrez-nucleotide","attrs":{"text":"NC_000009","term_id":"568815589","term_text":"NC_000009"}}NC_000009; ENSEMBL ENSG00000159921) consists of 13 exons, but each of the individual GNE mRNA splice variants consists of fewer exons. However, for mutation annotation purposes, only two major transcripts are relevant, which together span all 13 exons (Figure 1) [7]. We provide NCBI GenBank accession numbers for the two major isoforms hGNE1 and hGNE2 in the text below, and provide their ENSEMBL IDs in Table 1. Figure 1 Human GNE mRNA transcripts and isoforms. Table 1 Most frequent GNE myopathy-associated GNE variants hGNE1 (GenBank {"type":"entrez-protein","attrs":{"text":"NP_005467","term_id":"4885285","term_text":"NP_005467"}}NP_005467) is the originally described GNE protein which covers 722 amino acids [5] and is, confusingly, encoded in GenBank by mRNA transcript variant 2 ({"type":"entrez-nucleotide","attrs":{"text":"NM_005476","term_id":"298566309","term_text":"NM_005476"}}NM_005476). The hGNE2 isoform ({"type":"entrez-protein","attrs":{"text":"NP_001121699","term_id":"190014632","term_text":"NP_001121699"}}NP_001121699) covers 753 amino acids and is encoded by the longest GNE mRNA transcript, variant 1 ({"type":"entrez-nucleotide","attrs":{"text":"NM_001128227","term_id":"298566310","term_text":"NM_001128227"}}NM_001128227). The discovery of the additional N-terminal sequence (and novel exon 1) [8] encoding hGNE2, is potentially confusing since most previous molecular and biochemical studies (including all mutation reports) refer to the hGNE1 isoform, while according to universally adapted gene/protein nomenclature rules the longest mRNA splice form ought to be used for annotating nucleotide/amino acid locations (http://www.hgvs.org/mutnomen/refseq.html). Hence, amino acid numbering of previously reported GNE studies (based on hGNE1 nomenclature), including patient mutation reports, should be supplemented with 31 amino acids to adhere to the current (hGNE2) nomenclature guidelines, and nucleotide numbering should be supplemented with 93 bases. For exon numbering, the numbering according to the entire 13 exon GNE gDNA gene ought to be used, which means that exon numbering of previously reported GNE studies (based on hGNE1 nomenclature) have to be supplemented with one exon. Adaptation to the hGNE2 nomenclature can initially be confusing; however, we strongly support adaptation of this ‘new’ nomenclature. Laboratories/researchers not familiar with the GNE myopathy field and disease/gene history will report patient mutations and research tools (antibodies, enzyme activities, siRNA, nextgen sequence databases, etc.) according to current universally adapted nomenclature rules. Moreover, although there are no variants reported yet in the additional 31 amino acids of hGNE2 (perhaps because this region has not been considered for mutation analysis in many patients), future variants in this region could not be accurately named using hGNE1 as a reference. To illustrate the new terminology, we list both hGNE2 (‘new’ nomenclature) and hGNE1 (previous nomenclature) classifications and up to date exon numbers of the most frequent GNE mutations associated with GNE myopathy in Table 1. However, since history will leave its tracks, we strongly suggest accompanying all future references to GNE with the appropriate GenBank accession numbers.

N-Acetylneuraminic acid (Neu5Ac or NANA) is the most predominant sialic acid in mammals. As a terminal component in many glycoproteins and glycolipids, sialic acid is believed to be an important biomarker related to various diseases. Its precursor, N-acetylmannosamine (ManNAc), is being investigated as a potential treatment for GNE myopathy. In this work, we developed two highly sensitive and selective liquid chromatography–tandem mass spectrometry (LC-MS/MS) methods for the quantitation of ManNAc and free Neu5Ac in human plasma. A fit-for-purpose approach was adopted during method validation and sample analysis. To measure the endogenous compounds and overcome the interference from plasma samples, a surrogate matrix that contained 5% bovine serum albumin (BSA) was used for the preparation of calibration standards and certain levels of quality control (QC) samples. QC samples at higher concentrations were prepared in the authentic matrix (human plasma) to best mimic incurred samples. For both methods, an Ostro 96-well phospholipid removal plate was used for sample extraction, which efficiently removed the phospholipids from the plasma samples prior to LC injection, eliminated matrix effect, and improved sensitivity. Chromatographic separation was achieved using hydrophilic interaction chromatography (HILIC) and gradient elution in order to retain the two polar compounds. The lower limit of quantitation (LLOQ) for ManNAc and Neu5Ac was 10.0 and 25.0 ng/mL, respectively. The overall accuracy of the two assays was no less than 91.7% based on three levels of QC samples. Inter- and intra-run precision (coefficient of variation [%CV]) across three analytical runs was less than 6.7% for ManNAc and less than 10.8% for Neu5Ac. These methods have been validated to support clinical studies.

Toll-like receptors (TLRs) mediate the cellular response to conserved molecular patterns shared by microorganisms. We report that TLR-2 on human NK cells is upregulated and stimulated by Leishmania major lipophosphoglycan (LPG), a phosphoglycan belonging to a family of unique Leishmania glycoconjugates. We found that purified L. major LPG upregulates both mRNA and the membrane expression of TLR-2 in NK cells. Additionally, IFN-gamma and TNF-alpha production and nuclear translocation of NF-kappaB was enhanced. The activation effect was more intense with LPG purified from infectious metacyclic parasites than from noninfectious procyclic Leishmania. Since the difference between the molecules derived from these two stages of the parasite growth cycle lies exclusively in the number of phosphosaccharide repeat domains and in the composition of glycan side chains that branch off these domains, we propose that TLR-2 possibly distinguishes between phosphorylated glycan repeats on LPG molecules. The effect of LPG on cytokine production and on membrane expression of TLR-2 could be blocked with F(ab')2 fragments of the mAb against LPG (WIC 79.3). Confocal microscopy demonstrated the co-localization of LPG and TLR-2 on the NK cell membrane. Binding of LPG to TLR-2 in NK cells was demonstrated by immunoprecipitations done with anti-TLR-2 and anti-LPG mAb followed by immunoblotting with anti-LPG and anti-TLR-2, respectively. Both antibodies recognized the immune complexes. These results suggest that NK cells are capable of recognition of, and activation by, Leishmania LPG through TLR-2, enabling them to participate autonomously in the innate immune system and thereby increasing the effective destruction of the parasite.

The use of adeno-associated virus (AAV) as a gene therapy vector has been approved recently for clinical use and has demonstrated efficacy in a growing number of clinical trials. However, the safety of AAV as a vector has been challenged by a single study that documented hepatocellular carcinoma (HCC) after AAV gene delivery in mice. Most studies have not noted genotoxicity following AAV-mediated gene delivery; therefore, the possibility that there is an association between AAV and HCC is controversial. Here, we performed a comprehensive study of HCC in a large number of mice following therapeutic AAV gene delivery. Using a sensitive high-throughput integration site-capture technique and global expressional analysis, we found that AAV integration into the RNA imprinted and accumulated in nucleus (Rian) locus, and the resulting overexpression of proximal microRNAs and retrotransposon-like 1 (Rtl1) were associated with HCC. In addition, we demonstrated that the AAV vector dose, enhancer/promoter selection, and the timing of gene delivery are all critical factors for determining HCC incidence after AAV gene delivery. Together, our results define aspects of AAV-mediated gene therapy that influence genotoxicity and suggest that these features should be considered for design of both safer AAV vectors and gene therapy studies.

The GNE gene encodes the rate-limiting, bifunctional enzyme of sialic acid biosynthesis, uridine diphosphate-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE). Biallelic GNE mutations underlie GNE myopathy, an adult-onset progressive myopathy. GNE myopathy-associated GNE mutations are predominantly missense, resulting in reduced, but not absent, GNE enzyme activities. The exact pathomechanism of GNE myopathy remains unknown, but likely involves aberrant (muscle) sialylation. Here, we summarize 154 reported and novel GNE variants associated with GNE myopathy, including 122 missense, 11 nonsense, 14 insertion/deletions, and seven intronic variants. All variants were deposited in the online GNE variation database (http://www.dmd.nl/nmdb2/home.php?select_db=GNE). We report the predicted effects on protein function of all variants well as the predicted effects on epimerase and/or kinase enzymatic activities of selected variants. By analyzing exome sequence databases, we identified three frequently occurring, unreported GNE missense variants/polymorphisms, important for future sequence interpretations. Based on allele frequencies, we estimate the world-wide prevalence of GNE myopathy to be ∼4-21/1,000,000. This previously unrecognized high prevalence confirms suspicions that many patients may escape diagnosis. Awareness among physicians for GNE myopathy is essential for the identification of new patients, which is required for better understanding of the disorder's pathomechanism and for the success of ongoing treatment trials.

Combined methylmalonic acidemia and homocystinuria, cblC type, is stated to be the most common inborn error of intracellular cobalamin metabolism. The disorder can display a wide spectrum of clinical manifestations, spanning the prenatal period through late adulthood. While increased homocysteine concentrations and impaired methyl group metabolism may contribute to disease-related complications, the characteristic macular and retinal degeneration seen in many affected patients appears to be unique to cblC disease. The early detection of cblC disease by newborn screening mandates a careful assessment of therapeutic approaches and provides a new opportunity to improve the outcome of affected patients. The following article reviews the current knowledge on the complications, pathophysiology, and outcome of cblC disease in an effort to better guide clinical practice and future therapeutic trials.

We used exome sequencing to identify the genetic basis of combined malonic and methylmalonic aciduria (CMAMMA). We sequenced the exome of an individual with CMAMMA and followed up with sequencing of eight additional affected individuals (cases). This included one individual who was identified and diagnosed by searching an exome database. We identify mutations in ACSF3, encoding a putative methylmalonyl-CoA and malonyl-CoA synthetase as a cause of CMAMMA. We also examined a canine model of CMAMMA, which showed pathogenic mutations in a predicted ACSF3 ortholog. ACSF3 mutant alleles occur with a minor allele frequency of 0.0058 in ∼1,000 control individuals, predicting a CMAMMA population incidence of ∼1:30,000. ACSF3 deficiency is the first human disorder identified as caused by mutations in a gene encoding a member of the acyl-CoA synthetase family, a diverse group of evolutionarily conserved proteins, and may emerge as one of the more common human metabolic disorders.

Propionic acidemia (PA) is an autosomal recessive disorder of metabolism caused by a deficiency of propionyl-coenzyme A carboxylase (PCC). Despite optimal dietary and cofactor therapy, PA patients still suffer from lethal metabolic instability and experience multisystemic complications. A murine model of PA (Pcca(-/-)) of animals that uniformly die within the first 48 hr of life was used to determine the efficacy of adeno-associated viral (AAV) gene transfer as a potential therapy for PA. An AAV serotype 8 (AAV8) vector was engineered to express the human PCCA cDNA and delivered to newborn mice via an intrahepatic injection. Greater than 64% of the Pcca(-/-) mice were rescued after AAV8-mediated gene transfer and survived until day of life 16 or beyond. Western analysis of liver extracts showed that PCC was completely absent from Pcca(-/-) mice but was restored to greater than wild-type levels after AAV gene therapy. The treated Pcca(-/-) mice also exhibited markedly reduced plasma levels of 2-methylcitrate compared with the untreated Pcca(-/-) mice, which indicates significant PCC enzymatic activity was provided by gene transfer. At the time of this report, the oldest treated Pcca(-/-) mice are over 6 months of age. In summary, AAV gene delivery of PCCA effectively rescues Pcca(-/-) mice from neonatal lethality and substantially ameliorates metabolic markers of the disease. These experiments demonstrate a gene transfer approach using AAV8 that might be used as a treatment for PA, a devastating and often lethal disorder desperately in need of new therapeutic options.

Methylmalonic acidemia is a severe metabolic disorder caused by a deficiency of the ubiquitously expressed mitochondrial enzyme, methylmalonyl-CoA mutase (MUT). Liver transplantation has been used to treat a small number of patients with variable success, and whether liver-directed gene therapy might be employed in such a pleiotropic metabolic disorder is uncertain. In this study, we examined the therapeutic effects of hepatocyte-directed delivery of the Mut gene to mice with a severe form of methylmalonic acidemia. We show that a single intrahepatic injection of recombinant adeno-associated virus serotype 8 expressing the Mut gene under the control of the liver-specific thyroxine-binding globulin (TBG) promoter is sufficient to rescue Mut(-/-) mice from neonatal lethality and provide long-term phenotypic correction. Treated Mut(-/-) mice lived beyond 1 year of age, had improved growth, lower plasma methylmalonic acid levels, and an increased capacity to oxidize [1-(13)C]propionate in vivo. The older treated mice showed increased Mut transcription, presumably mediated by upregulation of the TBG promoter during senescence. The results indicate that the stable transduction of a small number of hepatocytes with the Mut gene can be efficacious in the phenotypic correction of an inborn error of organic acid metabolism and support the rapid translation of liver-directed gene therapy vectors already optimized for human subjects to patients with methylmalonic acidemia.

Cobalamin C (cblC), a combined form of methylmalonic acidaemia and hyperhomocysteinaemia, is recognized as the most frequent inborn error of intracellular cobalamin metabolism. This condition can be detected by expanded newborn screening and can have an acute neonatal presentation that is life-threatening if not suspected and promptly treated. Intramuscular (IM) hydroxocobalamin (OHCbl) is the main treatment for patients with cblC, but formal dosing guidelines do not exist. A clinical improvement and a decrease of plasma methylmalonic acid (MMA) and total homocysteine (tHcy) levels, and an increase in methionine are typically observed after its initiation. It is well recognized that despite treatment, long-term complications such as developmental delay and progressive visual loss, may still develop. We describe the biochemical response of a 13-year-old boy with worsening metabolic parameters despite strict adherence to a conventional treatment regimen. We progressively increased the OHCbl dose from 1 to 20 mg IM per day and observed a dose-dependent response with an 80% reduction of plasma MMA (25 to 5.14 micromol/L; normal range0.27 micromol/L), a 55% reduction of tHcy (112 to 50 micromol/L; normal range: 0-13 micromol/L) and a greater than twofold increase in methionine (17 to 36 micromol/L; normal range: 7-47 micromol/L). This suggests that higher OHCbl doses might be required to achieve an optimal biochemical response in cblC patients, but it is unknown whether it may slow or eliminate other complications. Future clinical trials to determine the benefits of higher-dose OHCbl therapy in patients with cblC and other disorders of intracellular cobalamin metabolism should be planned.

Dendritic cells (DC) and macrophages (Mphi) are well known as important effectors of the innate immune system and their ability to produce IL-12 indicates that they possess the potential of directing acquired immunity toward a Th1-biased response. Interestingly, the intracellular parasite Leishmania has been shown to selectively suppress Mphi IL-12 production and are DC the principal source of this cytokine. The molecular details of this phenomenon remain enigmatic. In the present study we examined the effect of Leishmania mexicana lipophosphoglycan (LPG) on the production of IL-12, TNF-alpha, and IL-10 and nuclear translocation of NF-kappaB. The results show that LPG induced more IL-12 in human DC than in monocytes. This difference was due in part to nuclear translocation of NF-kappaB, since LPG induced more translocation in DC than in monocytes. These results suggest that Leishmania LPG impairs nuclear translocation of NF-kappaB in monocytes with the subsequent decrease in IL-12 production.

GNE myopathy is an adult-onset distal myopathy caused by mutations in the GNE gene, which codes for a bifunctional enzyme important in sialic acid biosynthesis. GNE myopathy is characterized by gradually progressive weakness and atrophy that preferentially involves distal extremities. Muscle degeneration occurs, with accumulation of inclusion bodies and rimmed vacuoles in muscle fibers. Although GNE myopathy is known to preferential affect skeletal muscles, there had been a few reports demonstrating involvement of the cardiac muscles. Through our Natural History Study (NCT01417533), we found that cardiac involvement in GNE myopathy patients may have a higher occurrence than expected. In this study we established a systematic evaluation of the cardiac involvement in GNE myopathy by analyzing the mouse model Gne-/-hGNED176VTg. Histopathology showed the presence of rimmed vacuoles and disorganization of cardiac myofibrils. Lectin staining array corroborated the hyposialylation of O-linked glycoproteins. Echocardiogram revealed decreased ejection fraction and fractional shortening, and increased left ventricle mass, indicating a decrease of cardiac function. These data were also confirmed by functional MRI on the mouse model. Our findings provide evidence that cardiac muscles are involved in GNE myopathy. We propose that hyposialylation of cardiac muscles can lead to impaired cardiac muscle contractility, and may be improved with sialylation-increasing therapies. It is important for clinicians to be aware of the possible occurrence of cardiac disease in GNE myopathy for careful examination of the cardiac function in patients and proper management.

To the editor, Intramuscular hydroxocobalamin (OHCbl) has been used empirically for the management of cblC patients for decades. Its beneficial effects are very clear in the newborn period, with patients achieving metabolic improvement shortly after its initiation. However, the optimal regimens for long-term management of cblC remain undefined and are complicated by the great heterogeneity of this condition. It is common practice to continue patients on the same 1-mg dose of OHCbl started in the newborn period throughout their lives. Furthermore, several of these patients are weaned from a daily dose to weekly or every other week as they grow older, mainly because of the concerns associated with daily intramuscular injections and the lack of evidence to do otherwise. It is also unclear whether disease-related complications, such as progressive visual loss, are intrinsic to the natural history of the disease or due to sub-optimal metabolic control and can be modified by therapy. OHCbl is a medication with few recognized adverse effects. Elevated blood pressure has been reported to occur in a dose-dependent fashion in patients given 5,000 and 10,000 mg of intravenous OHCbl. These doses are 200to 500-fold above the dose we have used (Uhl et al. 2006, 2008). Whether chronic doses of 25 mg hydroxocobalamin will have a similar effect remains to be determined. While we agree with Dr. Wiwanitkit in that the results presented in our case report may only represent a short-term outcome, we disagree with his contention that “there are some reports on the long term of using OHCbl and there is no finding that the dose adaptation brings a significant improvement on the outcome”. The opposite is suggested by the only report we are aware of that has attempted a dose escalation. Van Hove et al. (2002) demonstrated convincingly that increasing subcutaneous OHCbl from 1 to 5 mg daily was required to achieve clinical and metabolic control in two patients with cblC and thrombotic microangiopathy. On the other hand, the findings reported by Andersson et al. (1999) suggested cblC is a developmental disorder, not that OHcbl therapy was ineffective. These authors did not attempt dose adaptation studies. We welcome his comments as they highlight what we have emphasized in our report: a well-planned, long-term clinical trial of higher doses of OHCbl will be needed to determine whether it is possible to slow or ameliorate cblC disease-related complications.