Acyl-CoA oxidase (ACOX1) deficiency is a rare disorder of peroxisomal very-long chain fatty acid oxidation. No reports detailing attempted treatment, longitudinal imaging, or neuropathology exist. We describe the natural history of clinical symptoms and brain imaging in two siblings with ACOX1 deficiency, including the younger sibling's response to allogeneic unrelated donor hematopoietic stem cell transplantation (HSCT).
We conducted retrospective chart review to obtain clinical history, neuro-imaging, and neuropathology data. ACOX1 genotyping were performed to confirm the disease. In vitro fibroblast and neural stem cell fatty acid oxidation assays were also performed.
Both patients experienced a fatal neurodegenerative course, with late-stage cerebellar and cerebral gray matter atrophy. Serial brain magnetic resonance imaging in the younger sibling indicated demyelination began in the medulla and progressed rostrally to include the white matter of the cerebellum, pons, midbrain, and eventually subcortical white matter. The successfully engrafted younger sibling had less brain inflammation, cortical atrophy, and neuronal loss on neuroimaging and neuropathology compared to the untreated older sister. Fibroblasts and stem cells demonstrated deficient very long chain fatty acid oxidation.
Although HSCT did not halt the course of ACOX1 deficiency, it reduced the extent of white matter inflammation in the brain. Demyelination continued because of ongoing neuronal loss, which may be due to inability of transplant to prevent progression of gray matter disease, adverse effects of chronic corticosteroid use to control graft-versus-host disease, or intervention occurring beyond a critical point for therapeutic efficacy.
Multifactorial and polygenic inheritance is commonly recognized for many genetic conditions including physical anomalies, complex congenital malformation syndromes, and even common disorders such as adult-onset diabetes mellitus. It has only recently been suggested as a mechanism for inheritance in inborn errors of metabolism. This article reviews the phenomenon of multiple partial enzyme deficiencies leading to clinical relevant biochemical derangements (synergistic heterozygosity) and its implications for other more common disorders such as diabetes and obesity.
Niemann-Pick Disease, type C1 (NPC1) is an autosomal recessive lipid storage disorder in which a pathological cascade, including neuroinflammation occurs. While data demonstrating neuroinflammation is prevalent in mouse models, data from NPC1 patients is lacking. The current study focuses on identifying potential markers of neuroinflammation in NPC1 from both the Npc1 mouse model and NPC1 patients. We identified in the mouse model significant changes in expression of genes associated with inflammation and compared these results to the pattern of expression in human cortex and cerebellar tissue. From gene expression array analysis, complement 3 (C3) was increased in mouse and human post-mortem NPC1 brain tissues. We also characterized protein levels of inflammatory markers in cerebrospinal fluid (CSF) from NPC1 patients and controls. We found increased levels of interleukin 3, chemokine (C-X-C motif) ligand 5, interleukin 16 and chemokine ligand 3 (CCL3), and decreased levels of interleukin 4, 10, 13 and 12p40 in CSF from NPC1 patients. CSF markers were evaluated with respect to phenotypic severity. Miglustat treatment in NPC1 patients slightly decreased IL-3, IL-10 and IL-13 CSF levels; however, further studies are needed to establish a strong effect of miglustat on inflammation markers. The identification of inflammatory markers with altered levels in the cerebrospinal fluid of NPC1 patients may provide a means to follow secondary events in NPC1 disease during therapeutic trials.
Niemann-Pick Type C; NPC1; neuroinflammation; cerebrospinal fluid; neurodegeneration
Diet therapy for phenylketonuria (PKU) requires restricted phenylalanine (Phe) intake, with the majority of protein and other nutrients coming from synthetic medical food. The fatty acid docosahexaenoic acid (DHA) is important in brain development and function; however, there are reports of low blood DHA concentrations in people treated for PKU. Although the implications of this low blood DHA are unclear, subtle cognitive deficits have been reported in those treated early and continuously for PKU. For this study, we investigated the relationship between DHA status and cognitive performance in 41 females 12 years and older with PKU. Participants were attending the baseline visit of a research-based camp or a supplementation trial. We assessed the domains of verbal ability, processing speed, and executive function using standardized tests, and the proportions of DHA in plasma and red blood cell (RBC) total lipids using gas chromatography/mass spectrometry. Percent plasma and RBC total lipid DHA were significantly lower in the participants compared with laboratory controls (P < .001), and participants consumed no appreciable DHA according to diet records. Plasma and RBC DHA both negatively correlated with plasma Phe (P < .02), and performance on the verbal ability task positively correlated with RBC DHA controlling for plasma Phe (R=.32, P=.03). The relationship between DHA and domains related to verbal ability, such as learning and memory, should be confirmed in a controlled trial. Domains of processing speed and executive function may require a larger sample size to clarify any association with DHA.
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.
Classic galactosemia is a potentially lethal disorder that results from profound deficiency of galactose-1-phosphate uridylyltransferase (GALT), the second enzyme in the Leloir pathway of galactose metabolism. Although early diagnosis and rigorous dietary restriction of galactose prevent or resolve the potentially lethal acute symptoms, patients are at markedly increased risk of long term complications including significant cognitive, speech, and behavioral difficulties, among other problems. The mechanisms that underlie these long-term complications remain unclear, as do the factors that modify their severity. Here we explored the scholastic and behavioral outcomes experienced by a cohort of 54 school age children with classic galactosemia. Data collected included survey responses from parents and teachers, school records including standardized test scores, and GALT genotype data used to estimate predicted residual GALT activity based on a yeast expression system. As expected, many but not all of the children in our study demonstrated speech, scholastic, and behavioral difficulties. Perhaps most striking, we found that predicted cryptic residual GALT activity, often below the threshold of detection of clinical assays, appeared to modify scholastic outcome. These data raise the intriguing possibility that cryptic GALT activity might also influence the severity of other long-term complications in classic galactosemia.
Congenital disorders of glycosylation (CDG) comprise a group of inborn errors of metabolism with abnormal glycosylation of proteins and lipids. Patients with defective protein N-glycosylation are identified in routine metabolic screening via analysis of serum transferrin glycosylation. Defects in the assembly of the dolichol linked Glc3Man9GlcNAc2 glycan and its transfer to proteins lead to the (partial) absence of complete glycans on proteins. These defects are called CDG-I and are located in the endoplasmic reticulum (ER) or cytoplasm. Defects in the subsequent processing of protein bound glycans result in the presence of truncated glycans on proteins. These defects are called CDG-II and the enzymes involved are located mainly in the Golgi apparatus. In recent years, human defects have been identified in dolichol biosynthesis genes within the group of CDG-I patients. This has increased interest in dolichol metabolism, has resulted in specific recognizable clinical symptoms in CDG-I and has offered new mechanistic insights in dolichol biosynthesis. We here review its biosynthetic pathways, the clinical and biochemical phenotypes in dolichol-related CDG defects, up to the formation of dolichyl-P-mannose (Dol-P-Man), and discuss existing evidence of regulatory networks in dolichol metabolism to provide an outlook on therapeutic strategies.
Disorders of branched-chain amino/keto acid metabolism encompass diverse entities, including maple syrup urine disease (MSUD), the ‘classical’ organic acidurias isovaleric acidemia (IVA), propionic acidemia (PA), methylmalonic acidemia (MMA) and, among others, rarely described disorders such as 2-methylbutyryl-CoA dehydrogenase deficiency (MBDD) or isobutyryl-CoA dehydrogenase deficiency (IBDD). Our focus in this review is to highlight the biochemical basis underlying recent advances and ongoing challenges of long-term conservative therapy including precursor/protein restriction, replenishment of deficient substrates, and the use of antioxidants and anaplerotic agents which refill the Krebs cycle. Ongoing clinical assessments of affected individuals in conjunction with monitoring of disease-specific biochemical parameters remain essential. It is likely that mass spectrometry-based ‘metabolomics’ may be a helpful tool in the future for studying complete biochemical profiles and diverse metabolic phenotypes. Prospective studies are needed to test the effectiveness of adjunct therapies such as antioxidants, ornithine-alpha-ketoglutarate (OKG) or creatine in addition to specialized diets and to optimize current therapeutic strategies in affected individuals. With the individual lifetime risk and degree of severity being unknown in asymptomatic individuals with MBDD or IBDD, instructions regarding risks for metabolic stress and fasting avoidance along with clinical monitoring are reasonable interventions at the current time. Overall, it is apparent that carefully designed prospective clinical investigations and multicenter cohort-controlled trials are needed in order to leverage that knowledge into significant breakthroughs in treatment strategies and appropriate approaches.
Infantile neuronal ceroid lipofuscinosis (INCL) is a profoundly neurodegenerative disease of children caused by a deficiency in the lysosomal enzyme palmitoyl protein thioesterase-1 (PPT1). There is currently no effective therapy for this invariably fatal disease. To date, preclinical experiments using single treatments have resulted in incremental clinical improvements. Therefore, we determined the efficacy of CNS-directed AAV2/5-mediated gene therapy alone and in combination with the systemic delivery of the lysosomotropic PPT1 mimetic phosphocysteamine. Since CNS-directed gene therapy provides relatively high levels of PPT1 activity to specific regions of the brain, we hypothesized that phosphocysteamine would complement that activity in regions expressing sub therapeutic levels of the enzyme. Results indicate that CNS-directed gene therapy alone provided the greatest improvements in biochemical and histological measures as well as motor function and life span. Phosphocysteamine alone resulted in only minor improvements in motor function and no increase in lifespan. Interestingly, phosphocysteamine did not increase the biochemical and histological response when combined with AAV2/5-mediated gene therapy, but it did result in an additional improvement in motor function. These data suggest that a CNS-directed gene therapy approach provides significant clinical benefit, and the addition of the small molecule PPT1 mimetic can further increase that response.
Mutations in β-glucosidase (GBA1) are the most common genetic risk factor for Parkinson disease (PD). There is evidence to suggest that PD risk is greater (1) in GBA1 heterozygotes with non-N370S GBA1 mutations compared to N370S mutations and (2) in GD type 1 (GD1) patients compared to GBA1 heterozygotes. This study aimed to determine the comparative risk of parkin-sonism in individuals who are affected or carriers of Gaucher disease (GD) and to ascertain the influence of different GBA1 mutations on risk/clinical expression. We conducted a secondary analysis of cross-sectional data assessing the prevalence of parkinsonism in a population of GD1 patients and their heterozygote and non-carrier family members. Two logistic regression models, both employing a family-specific random effect, were used to assess (1) the association between GBA1 mutation (N370S or non-N370S) and parkinsonism among GBA1 heterozygotes and (2) the association between GBA1 genotype and parkinsonism. Parkinsonism was present in 8.6 % of GD1 (7/81), 8.7 % of GBA1 heterozygotes (18/207), and 2.2 % of non-carriers (1/45). For those greater than 60 years old, parkinsonism was present in 38.5 % (5/13) of GD1 (5/13), 15.3 % of GBA1 heterozygotes (13/85), and 7.1 % of non-carriers (1/14). Among GBA1 heterozygotes, non-N370S mutations were associated with a significantly increased risk of parkinsonism compared to N370S (OR=22.5; p=0.035; 95%CI: 1.24, 411). In this population, each additional GBA1 mutation was associated with a non-significant two-fold increased risk of parkinsonism. GBA1 heterozygotes with non-N370S mutations associated with Gaucher disease have an increased risk of parkinsonism compared to those with N370S mutations.
To assess the efficacy and safety of enzyme replacement therapy (ERT) with BMN 110 (elosulfase alfa) in patients with Morquio A syndrome (mucopolysaccharidosis IVA).
Patients with Morquio A aged ≥5 years (N = 176) were randomised (1:1:1) to receive elosulfase alfa 2.0 mg/kg/every other week (qow), elosulfase alfa 2.0 mg/kg/week (weekly) or placebo for 24 weeks in this phase 3, double-blind, randomised study. The primary efficacy measure was 6-min walk test (6MWT) distance. Secondary efficacy measures were 3-min stair climb test (3MSCT) followed by change in urine keratan sulfate (KS). Various exploratory measures included respiratory function tests. Patient safety was also evaluated.
At week 24, the estimated mean effect on the 6MWT versus placebo was 22.5 m (95 % CI 4.0, 40.9; P = 0.017) for weekly and 0.5 m (95 % CI −17.8, 18.9; P = 0.954) for qow. The estimated mean effect on 3MSCT was 1.1 stairs/min (95 % CI −2.1, 4.4; P = 0.494) for weekly and −0.5 stairs/min (95 % CI −3.7, 2.8; P = 0.778) for qow. Normalised urine KS was reduced at 24 weeks in both regimens. In the weekly dose group, 22.4 % of patients had adverse events leading to an infusion interruption/discontinuation requiring medical intervention (only 1.3 % of all infusions in this group) over 6 months. No adverse events led to permanent treatment discontinuation.
Elosulfase alfa improved endurance as measured by the 6MWT in the weekly but not qow dose group, did not improve endurance on the 3MSCT, reduced urine KS, and had an acceptable safety profile.
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Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease due to α-L-iduronidase (IDUA) deficiency that results in the accumulation of glycosaminoglycans (GAG). Systemic gene therapy to MPS I mice can reduce lysosomal storage in the brain, but few data are available regarding the effect upon behavioral function. Here, we investigated the effect of gene therapy with a long-terminal repeat (LTR)-intact retroviral vector or a self-inactivating (SIN) vector on behavioral function in MPS I mice. The LTR vector was injected intravenously to 6 week-old MPS I mice, while the SIN vector was given to neonatal or 6 week-old mice. Adult-LTR, Neonatal-SIN, and Adult-SIN-treated mice achieved serum IDUA activity that was 235±20 (84-fold normal), 127±10, and 71±7 units/ml, respectively. All groups had reduction in histochemical evidence of lysosomal storage in the brain, with the Adult-LTR group showing the best response, while Adult-LTR mice had reductions in lysosomal storage in the cristae of the vestibular system. Behavioral evaluation was performed at 8 months. Untreated MPS I mice had a markedly reduced ability to hold onto an inverted screen or climb down a pole. LTR vector-treated mice had marked improvements on both of these tests, while Neonatal-SIN mice had improvements in the pole test. We conclude that both vectors can reduce brain disease in MPS I mice, with the LTR vector achieving higher serum IDUA levels and better correction. Vestibular abnormalities may contribute to mobility problems in patients with MPS I, and gene therapy may reduce symptoms.
Transport of large neutral amino acids (LNAA) across the blood brain barrier (BBB) is facilitated by the L-type amino acid transporter, LAT1. Peripheral accumulation of one LNAA (e.g., phenylalanine (phe) in PKU) is predicted to increase uptake of the offending amino acid to the detriment of others, resulting in disruption of brain amino acid homeostasis. We hypothesized that selected non-physiological amino acids (NPAAs) such as DL-norleucine (NL), 2-aminonorbornane (NB; 2-aminobicyclo-(2,1,1)-heptane-2-carboxylic acid), 2-aminoisobutyrate (AIB), and N-methyl-aminoisobutyrate (MAIB), acting as competitive inhibitors of various brain amino acid transporters, could reduce brain phe in Pahenu2 mice, a relevant murine model of PKU. Oral feeding of 5% NL, 5% AIB, 0.5% NB and 3% MAIB reduced brain phe by 56% (p<0.01), −1% (p=NS), 27% (p<0.05) and 14% (p<0.01), respectively, compared to untreated subjects. Significant effects on other LNAAs (tyrosine, methionine, branched chain amino acids) were also observed, however, with MAIB displaying the mildest effects. Of interest, MAIB represents an inhibitor of the system A (alanine) transporter that primarily traffics small amino acids and not LNAAs. Our studies represent the first in vivo use of these NPAAs in Pahenu2 mice, and provide proof-of-principle for their further preclinical development, with the long-term objective of identifying NPAA combinations and concentrations that selectively restrict brain phe transport while minimally impacting other LNAAs and downstream intermediates.
Niemann Pick type C disease is an inherited autosomal recessive disorder characterised by the accumulation of unesterified cholesterol and sphingolipids within the endosomal/lysosomal compartments. It has been observed that the administration of hydroxypropyl-β-cyclodextrin (HPBCD) delays onset of clinical symptoms and reduces accumulation of cholesterol and gangliosides within neuronal cells. It was assumed that HPBCD exerts its action by readily entering the CNS and directly interacting with neurones and other brain cells to facilitate removal of stored cholesterol from the late endosomal/lysosomal compartment. Here, we present evidence that refutes this hypothesis. We use two well established techniques for accurately measuring brain uptake of solutes from blood and show that there is no significant crossing of HPBCD into the brain. The two techniques are brain in situ perfusion and intraperitoneal injection followed by multi-time-point regression analysis. Neither study demonstrates significant, time-dependent uptake of HPBCD in either adult or neonatal mice. However, the volume of distribution available to HPBCD (0.113±0.010ml/g) exceeds the accepted values for plasma and vascular volume of the brain. In fact, it is nearly three times larger than that for sucrose (0.039±0.006 ml/g). We propose that this indicates cell surface binding of HPBCD to the endothelium of the cerebral vasculature and may provide a mechanism for the mobilization and clearance of cholesterol from the CNS.
Niemann-Pick C Disease; Cyclodextrin; Blood-Brain Barrier
Targeting lysosomal enzymes to receptors involved in transport into and across cells holds promise to enhance peripheral and brain delivery of enzyme replacement therapies for lysosomal storage disorders. Receptors being explored include those associated with clathrin-mediated pathways, yet other pathways seem also viable. Well characterized examples are that of transferrin receptor (TfR) and intercellular adhesion molecule 1 (ICAM-1), involved in iron transport and leukocyte extravasation, respectively. TfR and ICAM-1 support ERT delivery via clathrin- vs. cell adhesion molecule-mediated mechanisms, displaying different valency and size restrictions. To comparatively assess this, we used antibodies vs. larger multivalent antibody-coated carriers and evaluated TfR vs. ICAM-1 binding and endocytosis in endothelial cells, as well as in vivo biodistribution and delivery of a model lysosomal enzyme required in peripheral organs and brain: acid sphingomyelinase (ASM), deficient in types A–B Niemann Pick disease. We found similar binding of antibodies to both receptors under control conditions, with enhanced binding to activated endothelium for ICAM-1, yet only anti-TfR induced endocytosis efficiently. Contrarily, antibody-coated carriers showed enhanced binding, engulfment, and endocytosis for ICAM-1. In mice, anti-TfR enhanced brain targeting over anti-ICAM, with an opposite outcome in the lungs, while carriers enhanced ICAM-1 targeting over TfR in both organs. Both targeted carriers enhanced ASM delivery to the brain and lungs vs. free ASM, with greater enhancement for anti-ICAM carriers. Therefore, targeting TfR or ICAM-1 improves lysosomal enzyme delivery. Yet, TfR targeting may be more efficient for smaller conjugates or fusion proteins, while ICAM-1 targeting seems superior for multivalent carrier formulations.
Transcription factor NF-E2-related factor-2 (Nrf2) is a key regulator of endogenous anti-oxidant systems shown to play a neuroprotective role in the adult by preserving blood–brain barrier function. The choroid plexus, site for the blood-CSF barrier, has been suggested to be particularly important in maintaining brain barrier function in development. We investigated the expression of Nrf2-and detoxification-system genes in choroid plexus following systemic LPS injections, unilateral cerebral hypoxia-ischemia (HI) as well as the combination of LPS and HI (LPS/HI). Plexuses were collected at different time points after LPS, HI and LPS/HI in 9-day old mice. mRNA levels of Nrf2 and many of its target genes were analyzed by quantitative PCR. Cell death was analyzed by caspase-3 immunostaining and TUNEL. LPS caused down-regulation of the Nrf2-system genes while HI increased expression at earlier time points. LPS exposure prior to HI prevented many of the HI-induced gene increases. None of the insults resulted in any apparent cell death to choroidal epithelium. These data imply that the function of the inducible anti-oxidant system in the choroid plexus is down-regulated by inflammation, even if choroid cells are not structurally damaged. Further, LPS prevented the endogenous antioxidant response following HI, suggesting the possibility that the choroid plexus may be at risk if LPS is united with an insult that increases oxidative stress such as hypoxia-ischemia.
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-CoAdehydrogenase 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.
Advanced therapies including stem cells are currently a major biotechnological development. Adult liver stem cells can differentiate into hepatocyte like cells and be infused in the recipient’s liver to bring a missing metabolic function. These cells can be produced in large quantities in vitro. Allogeneic stem cells are required to treat genetic diseases, and this approach allows to use one single source of tissue to treat different diseases and many recipients. Mesenchymal stem cells can in addition play an immunomodulatory and anti-inflammatory role and possibly prevent the accumulation of fibrous tissue in the liver. From a regulatory point of view, stem cells are considered as medicinal products, and must undergo a pharmaceutical development that goes beyond the research and proof-of-concept phases. Here, we review the track followed from the first hepatocyte transplantation in 2000 to the next generation product issued from stem cell technology, and the start of EMA approved clinical trials to evaluate the safety and potency of liver stem cells for the treatment of inborn errors of the liver metabolism.
No published clinical trial data are available to inform the use of enzyme replacement therapy (ERT) in patients with the severe (neuropathic) phenotype of mucopolysaccharidosis II (MPS II). Current guidelines recommend ERT administered intravenously be used on a trial basis in this population.
A retrospective chart review was conducted at five international centers for this case series of 22 patients with neuropathic MPS II who received intravenous idursulfase 0.5 mg/kg weekly for at least 2 consecutive years. We collected data about urinary glycosaminoglycan levels, adverse events, and the following somatic signs/symptoms: skeletal disease, joint range of motion, liver/spleen size, respiratory infections, cardiac disease, diarrhea, skin/hair texture, and hospitalizations.
The age at diagnosis was 2 months to 5 years, and the age at idursulfase initiation was between 18 months and 21 years. One of 22 patients experienced improvements in seven somatic signs/symptoms; 17/22 experienced improvements in five to six somatic signs/symptoms; and 4/22 experienced improvements in four somatic signs/symptoms. None experienced fewer than four improvements. No new safety concerns arose. Infusion-related reactions were experienced by 4/22 patients but were successfully managed using accepted strategies.
Long-term treatment with idursulfase was associated with improvements in somatic manifestations in this case series of patients with neuropathic MPS II. The family and medical team should maintain open lines of communication to make treatment decisions that take into consideration the benefits and limitations of ERT in this population.
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The online version of this article (doi:10.1007/s10545-014-9686-7) contains supplementary material, which is available to authorized users.
Mucopolysaccharidoses (MPS) are a group of lysosomal storage diseases caused by mutations in lysosomal enzymes involved in degradation of glycosaminoglycans (GAGs). Patients with MPS grow poorly and become physically disabled due to systemic bone disease. While many of the major skeletal effects in mouse models for MPS have been described, no detailed analysis that compares GAGs levels and characteristics of bone by micro-CT has been done.
The aims of this study were to assess severity of bone dysplasia among four MPS mouse models (MPS I, IIIA, IVA and VII), to determine the relationship between severity of bone dysplasia and serum keratan sulfate (KS) and heparan sulfate (HS) levels in those models, and to explore the mechanism of KS elevation in MPS I, IIIA, and VII mouse models.
Clinically, MPS VII mice had the most severe bone pathology; however, MPS I and IVA mice also showed skeletal pathology. MPS I and VII mice showed severe bone dysplasia, higher bone mineral density, narrowed spinal canal, and shorter sclerotic bones by micro-CT and radiographs. Serum KS and HS levels were elevated in MPS I, IIIA, and VII mice. Severity of skeletal disease displayed by micro-CT, radiographs and histopathology correlated with the level of KS elevation. We showed that elevated HS levels in MPS mouse models could inhibit N-acetylgalactosamine-6-sulfate sulfatase enzyme.
These studies suggest that KS could be released from chondrocytes affected by accumulation of other GAGs and that KS could be useful as a biomarker for severity of bone dysplasia in MPS disorders.
β-ureidopropionase (βUP) deficiency is an autosomal recessive disease characterized by N-carbamyl-β-amino aciduria. To date, only 16 genetically confirmed patients with βUP deficiency have been reported. Here, we report on the clinical, biochemical and molecular findings of 13 Japanese βUP deficient patients. In this group of patients, three novel missense mutations (p.G31S, p.E271K, and p.I286T) and a recently described mutation (p.R326Q) were identified. The p.R326Q mutation was detected in all 13 patients with eight patients being homozygous for this mutation. Screening for the p.R326Q mutation in 110 Japanese individuals showed an allele frequency of 0.9 %. Transient expression of mutant βUP enzymes in HEK293 cells showed that the p.E271K and p.R326Q mutations cause profound decreases in activity (≤ 1.3 %). Conversely, βUP enzymes containing the p.G31S and p.I286T mutations possess residual activities of 50 and 70 %, respectively, suggesting we cannot exclude the presence of additional mutations in the non-coding region of the UPB1 gene. Analysis of a human βUP homology model revealed that the effects of the mutations (p.G31S, p.E271K, and p.R326Q) on enzyme activity are most likely linked to improper oligomer assembly. Highly variable phenotypes ranging from neurological involvement (including convulsions and autism) to asymptomatic, were observed in diagnosed patients. High prevalence of p.R326Q in the normal Japanese population indicates that βUP deficiency is not as rare as generally considered and screening for βUP deficiency should be included in diagnosis of patients with unexplained neurological abnormalities.
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Vascular abnormalities and glycogen accumulation in vascular smooth muscle fibres have been described in Pompe disease. Using carotid-femoral pulse wave velocity (cfPWV), the gold standard methodology for determining aortic stiffness, we studied whether aortic stiffness is increased in patients with Pompe disease. Eighty-four adult Pompe patients and 179 age- and gender-matched volunteers participated in this cross-sectional case-controlled study. Intima media thickness and the distensibility of the right common carotid artery were measured using a Duplex scanner. Aortic augmentation index, central pulse pressure, aortic reflexion time and cfPWV were assessed using the SphygmoCor® system. CfPWV was higher in patients than in volunteers (8.8 versus 7.4 m/s, p < 0.001). This difference was still present after adjustment for age, gender, mean arterial blood pressure (MAP), heart rate and diabetes mellitus (p = 0.001), and was shown by subgroup analysis to apply to the 40-59 years age group (p = 0.004) and 60+ years age group (p = 0.01), but not to younger age groups (p = 0.99). Except for a shorter aortic reflexion time (p = 0.02), indirect indicators of arterial stiffness did not differ between patients and volunteers. Relative to volunteers (20 %), more Pompe patients had a history of hypertension (36 %, p = 0.005), and the MAP was higher than in volunteers (100 versus 92 mmHg, p < 0.001). This study shows that patients with non-classic Pompe disease have increased aortic stiffness and blood pressure. Whether this is due to glycogen accumulation requires further investigation. To reduce the potential risk of cardiovascular diseases, we recommend that blood pressure and other common cardiovascular risk factors are monitored regularly.
Barth syndrome (BTHS) is a rare X-linked disorder that is characterized by mitochondrial abnormalities, infantile or childhood onset of cardioskeletal myopathy, and high mortality rates. It is currently unknown if BTHS related mitochondrial dysfunction results in substrate metabolism abnormalities and thereby contributes to cardioskeletal myopathy in patients with BTHS.
Adolescents and young adults with BTHS (n=5, 20 ± 4 yrs) and age and activity matched healthy controls (n=5, 18 ± 4 yrs) underwent an hyperinsulinemic-euglycemic clamp procedure with stable isotopically labeled tracers for measurement of lipolysis, fatty acid oxidation, glucose disposal, and whole-body proteolysis rates; dual energy x-ray absorptiometry for measurement of body composition and 2-D and strain echocardiography for measurement of left ventricular function.
Participants with BTHS had lower fat-free mass (FFM) (BTHS: 31.4 ± 6.9 vs. Control: 46.7 ± 5.3 kg, p<0.005), lower systolic function (strain, BTHS: -15.2 ± 2.4 vs. Control: -19.0 ± 2.4 %, p<0.05), greater insulin-stimulated glucose disposal rate per kg FFM (BTHS: 96.5 ± 16.3 vs. Control: 67.4 ± 17.6 μmol/kgFFM/min, p<0.05), lower basal (BTHS: 4.6 ± 2.7 vs. Control: 11.9 ± 4.4 μmol/kgFM/min, p<0.05) and hyperinsulinemic (BTHS: 1.6 ± 0.4 vs. Control: 3.6 ± 1.6 μmol/kgFM/min, p<0.05) lipolytic rate per kg fat mass (FM), and a trend towards higher basal leucine rate of appearance per kg FFM (BTHS: 271.4 ± 69.3 vs. Control: 193.1 ± 28.7 μmol/kgFFM/hr, p=0.07) compared to controls. Higher basal leucine rate of appearance per kg FFM (i.e. whole-body proteolytic rate) tended to be associated with lower left ventricular systolic strain (r=-0.57, p=0.09).
Whole-body fatty acid, glucose and amino acid metabolism kinetics when expressed per unit of body composition are altered and appear to be related to cardioskeletal myopathy in humans with BTHS. Further studies examining myocardial substrate metabolism and whole-body substrate metabolism during increased energy demands (e.g. exercise) and their relationships to skeletal and cardiac function are recommended.