The lysosomal storage disorders mucolipidosis type II, type III alpha/beta, and type III gamma: Update on GNPTAB and GNPTG mutations.

Mutations in the GNPTAB and GNPTG genes cause mucolipidosis (ML) type II, type III alpha/beta, and type III gamma, which are autosomal recessively inherited lysosomal storage disorders. GNPTAB and GNPTG encode the α/ß-precursor and the γ-subunit of N-acetylglucosamine (GlcNAc)-1-phosphotransferase, respectively, the key enzyme for the generation of mannose 6-phosphate targeting signals on lysosomal enzymes. Defective GlcNAc-1-phosphotransferase results in missorting of lysosomal enzymes and accumulation of non-degradable macromolecules in lysosomes, strongly impairing cellular function. MLII-affected patients have coarse facial features, cessation of statural growth and neuromotor development, severe skeletal abnormalities, organomegaly, and cardiorespiratory insufficiency leading to death in early childhood. MLIII alpha/beta and MLIII gamma are attenuated forms of the disease. Since the identification of the GNPTAB and GNPTG genes, 564 individuals affected by MLII or MLIII have been described in the literature. In this report, we provide an overview on 258 and 50 mutations in GNPTAB and GNPTG, respectively, including 58 novel GNPTAB and seven novel GNPTG variants. Comprehensive functional studies of GNPTAB missense mutations did not only gain insights into the composition and function of the GlcNAc-1-phosphotransferase, but also helped to define genotype-phenotype correlations to predict the clinical outcome in patients.

Loss of CLN7 results in depletion of soluble lysosomal proteins and impaired mTOR reactivation.

Defects in the MFSD8 gene encoding the lysosomal membrane protein CLN7 lead to CLN7 disease, a neurodegenerative lysosomal storage disorder belonging to the group of neuronal ceroid lipofuscinoses. Here, we have performed a SILAC-based quantitative analysis of the lysosomal proteome using Cln7-deficient mouse embryonic fibroblasts (MEFs) from a Cln7 knockout (ko) mouse model. From 3335 different proteins identified, we detected 56 soluble lysosomal proteins and 29 highly abundant lysosomal membrane proteins. Quantification revealed that the amounts of 12 different soluble lysosomal proteins were significantly reduced in Cln7 ko MEFs compared with wild-type controls. One of the most significantly depleted lysosomal proteins was Cln5 protein that underlies another distinct neuronal ceroid lipofuscinosis disorder. Expression analyses showed that the mRNA expression, biosynthesis, intracellular sorting and proteolytic processing of Cln5 were not affected, whereas the depletion of mature Cln5 protein was due to increased proteolytic degradation by cysteine proteases in Cln7 ko lysosomes. Considering the similar phenotypes of CLN5 and CLN7 patients, our data suggest that depletion of CLN5 may play an important part in the pathogenesis of CLN7 disease. In addition, we found a defect in the ability of Cln7 ko MEFs to adapt to starvation conditions as shown by impaired mammalian target of rapamycin complex 1 reactivation, reduced autolysosome tubulation and increased perinuclear accumulation of autolysosomes compared with controls. In summary, depletion of multiple soluble lysosomal proteins suggest a critical role of CLN7 for lysosomal function, which may contribute to the pathogenesis and progression of CLN7 disease.

[Novel therapies in neurometabolic diseases: the importance of early intervention]. / Terapias novedosas en enfermedades neurometabolicas: importancia de una intervencion precoz.

INTRODUCTION: Individually, neurometabolic diseases are ultra rare, but for some of them there is an effective treatment. DEVELOPMENT: Several recent therapeutic advances are reviewed. Today, the possibilities of treatment for lysosomal diseases have improved. In recent years the use of enzyme replacement therapy has become more widely extended to treat mucopolysaccharidosis type IVA (Morquio A), mucopolysaccharidosis type VII (Sly syndrome), lysosomal acid lipase deficiency and alpha-mannosidosis. It has been proven that very early treatment of mucopolysaccharidoses can change their natural course. Intrathecal enzyme replacement therapy is being tried in some mucopolysaccharidoses with cognitive involvement, in an attempt to halt neurodegeneration. Very positive results have been obtained with genetically modified autotransplants in late-onset infantile metachromatic leukodystrophy and research is being conducted on other pathologies (mucopolysaccharidosis type III, X-linked adrenoleukodystrophy). Novel outcomes are also being achieved in the treatment of some encephalopathies that are sensitive to vitamins or cofactors: triple therapy in pyridoxine dependency, treatment with thiamine for some subacute encephalopathies with involvement of the basal ganglia, treatment with folinic acid for children with cerebral folate deficiency, or treatment with cyclic pyranopterin monophosphate in molybdenum cofactor deficiency type A. CONCLUSIONS: As neuropaediatricians we must update our knowledge, especially in the case of treatable neurometabolic pathologies, since early treatment can change their prognosis significantly.

TITLE: Terapias novedosas en enfermedades neurometabolicas: importancia de una intervencion precoz.Introduccion. Las enfermedades neurometabolicas son individualmente ultrarraras, pero algunas de ellas tienen un tratamiento eficaz. Desarrollo. Se revisan algunas novedades terapeuticas. Las enfermedades lisosomales tienen actualmente mejores posibilidades de tratamiento. En los ultimos años se ha extendido el uso de la terapia enzimatica sustitutiva a la mucopolisacaridosis tipo IVA (Morquio A), a la mucopolisacaridosis tipo VII (enfermedad de Sly), al deficit de lipasa acida lisosomal y a la alfa-manosidosis. Se ha constatado que un tratamiento muy precoz de las mucopolisacaridosis puede cambiar su historia natural. Se esta probando la terapia enzimatica sustitutiva intratecal en algunas mucopolisacaridosis con afectacion cognitiva, en el intento de frenar la neurodegeneracion. Se han obtenido resultados muy positivos con autotrasplante modificado geneticamente en leucodistrofia metacromatica infantil tardia y se esta trabajando en otras patologias (mucopolisacaridosis tipo III, adrenoleucodistrofia ligada a X). Tambien hay novedades en la terapia de algunas encefalopatias sensibles a vitaminas o cofactores: la triple terapia en la dependencia de piridoxina, el tratamiento con tiamina de algunas encefalopatias subagudas con afectacion de ganglios basales, el tratamiento con acido folinico de niños con deficiencia de folato cerebral, o el tratamiento con monofosfato de piranopterina ciclico en los defectos de cofactor de molibdeno de tipo A. Conclusiones. Los neuropediatras debemos actualizar nuestro conocimiento especialmente en aquellas patologias neurometabolicas tratables, dado que una terapia precoz puede cambiar de forma significativa su pronostico.

Congenital disorders of autophagy: an emerging novel class of inborn errors of neuro-metabolism.

Single gene disorders of the autophagy pathway are an emerging, novel and diverse group of multisystem diseases in children. Clinically, these disorders prominently affect the central nervous system at various stages of development, leading to brain malformations, developmental delay, intellectual disability, epilepsy, movement disorders, and neurodegeneration, among others. Frequent early and severe involvement of the central nervous system puts the paediatric neurologist, neurogeneticist, and neurometabolic specialist at the forefront of recognizing and treating these rare conditions. On a molecular level, mutations in key autophagy genes map to different stages of this highly conserved pathway and thus lead to impairment in isolation membrane (or phagophore) and autophagosome formation, maturation, or autophagosome-lysosome fusion. Here we discuss 'congenital disorders of autophagy' as an emerging subclass of inborn errors of metabolism by using the examples of six recently identified monogenic diseases: EPG5-related Vici syndrome, beta-propeller protein-associated neurodegeneration due to mutations in WDR45, SNX14-associated autosomal-recessive cerebellar ataxia and intellectual disability syndrome, and three forms of hereditary spastic paraplegia, SPG11, SPG15 and SPG49 caused by SPG11, ZFYVE26 and TECPR2 mutations, respectively. We also highlight associations between defective autophagy and other inborn errors of metabolism such as lysosomal storage diseases and neurodevelopmental diseases associated with the mTOR pathway, which may be included in the wider spectrum of autophagy-related diseases from a pathobiological point of view. By exploring these emerging themes in disease pathogenesis and underlying pathophysiological mechanisms, we discuss how congenital disorders of autophagy inform our understanding of the importance of this fascinating cellular pathway for central nervous system biology and disease. Finally, we review the concept of modulating autophagy as a therapeutic target and argue that congenital disorders of autophagy provide a unique genetic perspective on the possibilities and challenges of pathway-specific drug development.

Diminished MTORC1-Dependent JNK Activation Underlies the Neurodevelopmental Defects Associated with Lysosomal Dysfunction.

Here, we evaluate the mechanisms underlying the neurodevelopmental deficits in Drosophila and mouse models of lysosomal storage diseases (LSDs). We find that lysosomes promote the growth of neuromuscular junctions (NMJs) via Rag GTPases and mechanistic target of rapamycin complex 1 (MTORC1). However, rather than employing S6K/4E-BP1, MTORC1 stimulates NMJ growth via JNK, a determinant of axonal growth in Drosophila and mammals. This role of lysosomal function in regulating JNK phosphorylation is conserved in mammals. Despite requiring the amino-acid-responsive kinase MTORC1, NMJ development is insensitive to dietary protein. We attribute this paradox to anaplastic lymphoma kinase (ALK), which restricts neuronal amino acid uptake, and the administration of an ALK inhibitor couples NMJ development to dietary protein. Our findings provide an explanation for the neurodevelopmental deficits in LSDs and suggest an actionable target for treatment.

Gaucher disease: a lysosomal neurodegenerative disorder.

Gaucher disease is a multisystemic disorder that affects men and woman in equal numbers and occurs in all ethnic groups at any age with racial variations and an estimated worldwide incidence of 1/75,000. It is caused by a genetic deficient activity of the lysosomal enzyme glucocerebrosidase due to mutations in the ß-glucocerebrosidase gene, and resulting in lack of glucocerebroside degradation. The subsequent accumulation of glucocerebroside in lysosomes of tissue macrophages primarily in the liver, bone marrow and spleen, causes damage in haematological, skeletal and nervous systems. The clinical manifestations show a high degree of variability with symptoms that varies according to organs involved. In many cases, these disorders do not correlate with mutations in the ß-glucocerebrosidase gene. Although several mutations have been identified as responsible for the deficient activity of glucocerebrosidase, mechanisms by which this enzymatic defect leads to Gaucher disease remain poorly understood. Recent reports indicate the implication of complex mechanisms, including enzyme deficiency, substrate accumulation, unfolded protein response, and macrophage activation. Further elucidating these mechanisms will advance understanding of Gaucher disease and related disorders.

A diagnostic approach for cerebral palsy in the genomic era.

An ongoing challenge in children presenting with motor delay/impairment early in life is to identify neurogenetic disorders with a clinical phenotype, which can be misdiagnosed as cerebral palsy (CP). To help distinguish patients in these two groups, conventional magnetic resonance imaging of the brain has been of great benefit in "unmasking" many of these genetic etiologies and has provided important clues to differential diagnosis in others. Recent advances in molecular genetics such as chromosomal microarray and next-generation sequencing have further revolutionized the understanding of etiology by more precisely classifying these disorders with a molecular cause. In this paper, we present a review of neurogenetic disorders masquerading as cerebral palsy evaluated at one institution. We have included representative case examples children presenting with dyskinetic, spastic, and ataxic phenotypes, with the intent to highlight the time-honored approach of using clinical tools of history and examination to focus the subsequent etiologic search with advanced neuroimaging modalities and molecular genetic tools. A precise diagnosis of these masqueraders and their differentiation from CP is important in terms of therapy, prognosis, and family counseling. In summary, this review serves as a continued call to remain vigilant for current and other to-be-discovered neurogenetic masqueraders of cerebral palsy, thereby optimizing care for patients and their families.

Proteostasis: bad news and good news from the endoplasmic reticulum.

The endoplasmic reticulum (ER) is an intracellular compartment dedicated to the synthesis and maturation of secretory and membrane proteins, totalling about 30% of the total eukaryotic cells proteome. The capacity to produce correctly folded polypeptides and to transport them to their correct intra- or extracellular destinations relies on proteostasis networks that regulate and balance the activity of protein folding, quality control, transport and degradation machineries. Nutrient and environmental changes, pathogen infection aging and, more relevant for the topics discussed in this review, mutations that impair attainment of the correct 3D structure of nascent polypeptide chains may compromise the activity of the proteostasis networks with devastating consequences on cells, organs and organisms' homeostasis. Here we present a review of mechanisms regulating folding and quality control of proteins expressed in the ER, and we describe the protein degradation and the ER stress pathways activated by the expression of misfolded proteins in the ER lumen. Finally, we highlight select examples of proteopathies (also known as conformational disorders or protein misfolding diseases) caused by protein misfolding in the ER and/or affecting cellular proteostasis and therapeutic interventions that might alleviate or cure the disease symptoms.

Factors and processes modulating phenotypes in neuronopathic lysosomal storage diseases.

Lysosomal storage diseases are inherited metabolic disorders caused by genetic defects causing deficiency of various lysosomal proteins, and resultant accumulation of non-degraded compounds. They are multisystemic diseases, and in most of them (>70%) severe brain dysfunctions are evident. However, expression of various phenotypes in particular diseases is extremely variable, from non-neuronopathic to severely neurodegenerative in the deficiency of the same enzyme. Although all lysosomal storage diseases are monogenic, clear genotype-phenotype correlations occur only in some cases. In this article, we present an overview on various factors and processes, both general and specific for certain disorders, that can significantly modulate expression of phenotypes in these diseases. On the basis of recent reports describing studies on both animal models and clinical data, we propose a hypothesis that efficiency of production of compounds that cannot be degraded due to enzyme deficiency might be especially important in modulation of phenotypes of patients suffering from lysosomal storage diseases.

Lysosomal diseases: biochemical pathways and investigations.

This chapter summarizes our current knowledge of lysosomes and lysosomal proteins referring to recent reviews, general schemes for degradation of substrates, and various causes of lysosomal storage diseases (LSDs). It then discusses the main principles for laboratory diagnosis. Initial screening by study of accumulated substrates in urine is helpful for mucopolysaccharidoses and oligosaccharidoses. A majority of LSDs result from the deficient activity of one acid hydrolase (in some diseases, several). Establishment of the diagnosis in this group of disorders is based on the measurement of the particular enzymic activity. Pseudodeficiencies are a possible source of error. For defects in lysosomal membrane transporters such as cystinosin or sialin, study of substrate accumulation in readily available cells/fluids is still the method of choice. Demonstration of a metabolic block in living cells is rarely used today, except for Niemann-Pick C disease. For primary diagnosis of patients, molecular genetic testing is necessary when no functional tests exist (e.g., many ceroid lipofuscinoses, Danon disease) and it is the preferred strategy when functional tests are too elaborate. Genotyping patients already diagnosed by biochemical methods is, however, essential for genetic counseling in the family; it may also be useful for optimal management.

[Inborn errors of metabolism in adult neurology]. / Les maladies métaboliques héréditaires en neurologie adulte.

Inborn errors of metabolism (IEM) are caused by mutations in genes coding for enzymes and other proteins involved in cell metabolism. Many IEM can be treated effectively. Although IEM have usually been considered pediatric diseases, they can present at any age, mostly with neurological and psychiatric symptoms, and therefore constitute an integral subspeciality of neurology. However, although they are increasingly being recognized, IEM remain rare, and the care for patients should be optimized in specialized reference centers. Since the number of different diseases is very large, the diagnostic approach needs to be rigorous, starting at the clinics and calling upon the additional help of neuroradiology, biochemistry and molecular biology. In practice, it is important for the neurologist to recognize: (1) when to start suspecting an IEM; and (2) how to correlate a given clinical presentation with one of the five major groups of diseases affecting the nervous system. These five groups may be classified as: (a) energy metabolism disorders such as respiratory chain disorders, pyruvate dehydrogenase deficiency, GLUT1 deficiency, fatty-acid ß-oxidation defects, and disorders involving key cofactors such as electron transfer flavoprotein, thiamine, biotin, riboflavin, vitamin E and coenzyme Q10; (b) intoxication syndromes such as porphyrias, urea-cycle defects, homocystinurias, organic acidurias and amino acidopathies; (c) lipid-storage disorders such as lysosomal storage disorders (Krabbe disease, metachromatic leukodystrophy, Niemann - Pick disease type C, Fabry disease and Gaucher's disease), peroxisomal disorders (adrenomyeloneuropathy, Refsum disease, disorders of pristanic acid metabolism, peroxisome biogenesis disorders), Tangier disease and cerebrotendinous xanthomatosis; (d) metal-storage diseases such as iron, copper and manganese metabolic disorders; and (e) neurotransmitter metabolism defects, including defects of serotonin, dopamine and glycine metabolism.

Astrocyte dysfunction triggers neurodegeneration in a lysosomal storage disorder.

The role of astrocytes in neurodegenerative processes is increasingly appreciated. Here we investigated the contribution of astrocytes to neurodegeneration in multiple sulfatase deficiency (MSD), a severe lysosomal storage disorder caused by mutations in the sulfatase modifying factor 1 (SUMF1) gene. Using Cre/Lox mouse models, we found that astrocyte-specific deletion of Sumf1 in vivo induced severe lysosomal storage and autophagy dysfunction with consequential cytoplasmic accumulation of autophagic substrates. Lysosomal storage in astrocytes was sufficient to induce degeneration of cortical neurons in vivo. Furthermore, in an ex vivo coculture assay, we observed that Sumf1(-/-) astrocytes failed to support the survival and function of wild-type cortical neurons, suggesting a non-cell autonomous mechanism for neurodegeneration. Compared with the astrocyte-specific deletion of Sumf1, the concomitant removal of Sumf1 in both neurons and glia in vivo induced a widespread neuronal loss and robust neuroinflammation. Finally, behavioral analysis of mice with astrocyte-specific deletion of Sumf1 compared with mice with Sumf1 deletion in both astrocytes and neurons allowed us to link a subset of neurological manifestations of MSD to astrocyte dysfunction. This study indicates that astrocytes are integral components of the neuropathology in MSD and that modulation of astrocyte function may impact disease course.

Oxidative stress induces overgrowth of the Drosophila neuromuscular junction.

Synaptic terminals are known to expand and contract throughout an animal's life. The physiological constraints and demands that regulate appropriate synaptic growth and connectivity are currently poorly understood. In previous work, we identified a Drosophila model of lysosomal storage disease (LSD), spinster (spin), with larval neuromuscular synapse overgrowth. Here we identify a reactive oxygen species (ROS) burden in spin that may be attributable to previously identified lipofuscin deposition and lysosomal dysfunction, a cellular hallmark of LSD. Reducing ROS in spin mutants rescues synaptic overgrowth and electrophysiological deficits. Synapse overgrowth was also observed in mutants defective for protection from ROS and animals subjected to excessive ROS. ROS are known to stimulate JNK and fos signaling. Furthermore, JNK and fos in turn are known potent activators of synapse growth and function. Inhibiting JNK and fos activity in spin rescues synapse overgrowth and electrophysiological deficits. Similarly, inhibiting JNK, fos, and jun activity in animals with excessive oxidative stress rescues the overgrowth phenotype. These data suggest that ROS, via activation of the JNK signaling pathway, are a major regulator of synapse overgrowth. In LSD, increased autophagy contributes to lysosomal storage and, presumably, elevated levels of oxidative stress. In support of this suggestion, we report here that impaired autophagy function reverses synaptic overgrowth in spin. Our data describe a previously unexplored link between oxidative stress and synapse overgrowth via the JNK signaling pathway.

Cell microencapsulation: a potential tool for the treatment of neuronopathic lysosomal storage diseases.

Lysosomal storage disorders (LSD) are monogenic diseases caused by the deficiency of different lysosomal enzymes that degrade complex substrates such as glycosaminoglycans, sphingolipids, and others. As a consequence there is multisystemic storage of these substrates. Most treatments for these disorders are based in the fact that most of these enzymes are soluble and can be internalized by adjacent cells via mannose-6-phosphate receptor. In that sense, these disorders are good candidates to be treated by somatic gene therapy based on cell microencapsulation. Here, we review the existing data about this approach focused on the LSD treatments, the advantages and limitations faced by these studies.

[Peripheral neuropathies associated with hereditary cerebellar ataxias]. / Neuropathies périphériques associées aux ataxies cérébelleuses héréditaires.

Inherited cerebellar ataxias constitute a complicated and heterogeneous group of neurodegenerative disorders affecting the cerebellum and/or spinocerebellar tract, spinal cord and peripheral nerves. A peripheral neuropathy is frequently seen in inherited cerebellar ataxias although it rarely reveals the disease. Moreover, the peripheral neuropathy is helpful for the diagnostic procedure and contributes to the functional prognosis of the disease. Thus, electroneuromyography is essential in the algorithm for the diagnosis of inherited cerebellar ataxias, as well as brain MRI (looking especially for cerebellar atrophy) and the assessment of several biomarkers (alpha-foetoprotein, vitamin E, albumin, LDL cholesterol, lactic acid, phytanic acid).

Clinical aspects of neuropathic lysosomal storage disorders.

The purpose of this review is to describe neurological phenotypes associated with lysosomal storage diseases (LSDs), focusing on features arising from primary neuronal involvement. Clinical presentation, progression and genetic data, are discussed in detail in Part 2, the electronic material. Main features are summarized in Part 1. Insights gained from several observational studies are discussed. Prospective studies of the natural history of most neuronopathic LSDs have been hampered by the rarity of these conditions and the short survival of affected patients. Increasingly, longitudinal observations relating to neurological manifestations are being reported. Better clinical studies are necessary, including repeated measurements of disease progression to facilitate the development of sensitive scoring systems and appropriate counseling of affected individuals and their families. Ideally, clinical studies should involve a large cohort. As treatment becomes available, knowledge of disease expression and factors that influence the phenotype may enable critical assessment of therapeutic outcomes. It is hoped that increased familiarity with the clinical expression of individual LSDs will allow early diagnosis, so families at risk are given options to consider during future pregnancies. Early diagnosis also permits the introduction of timely intervention, to favoring improved outcome in cases that are potentially treatable.

The trigeminal retrograde transfer pathway in the treatment of neurodegeneration.

The trigeminal sensory system was evaluated for the retrograde transfer of gene therapy vectors into the CNS. The feline immunodeficiency viral vector, FIV(HEXB), encoding for the human HEXB gene, was injected intra-articularly in the temporomandibular joint of 12 week-old HexB(-/-) mice displaying clinical and histopathological signs of Sandhoff disease. This treatment regiment reduced GM(2) storage and ameliorated neuroinflammation in the brain of HexB(-/-) mice, as well as attenuated behavioral deficits. In conclusion, retrograde transfer along trigeminal sensory nerves may prove to be a valuable route of gene therapy administration for the treatment of lysosomal storage disorders and other neurodegenerative diseases.

A double TRPtych: six views of transient receptor potential channels in disease and health.

At the 2008 Annual Meeting of the Society for Neuroscience, a Mini-Symposium entitled "Contributions to TRP Channels to Neurological Disease" included talks from six heads of newly established laboratories, each with a unique research focus, model system, and set of experimental tools. Some of the questions addressed in these talks include the following. What is the role of transient receptor potential (TRP) channels in pain perception? How do normally functioning TRP channels contribute to cell death pathways? What are the characteristics of TRPpathies, disease states that result from overactive or underactive TRP channels? How are TRP channels regulated by signal transduction cascades? This review summarizes recent results from those laboratories and provides six perspectives on the subject of TRP channels and disease.