Abnormal Storage Material Research Articles

Distinct Modes of Balancing Glomerular Cell Proteostasis in Mucolipidosis Type II and III Prevent Proteinuria.

The mechanisms balancing proteostasis in glomerular cells are unknown. Mucolipidosis (ML) II and III are rare lysosomal storage disorders associated with mutations of the Golgi-resident GlcNAc-1-phosphotransferase, which generates mannose 6-phosphate residues on lysosomal enzymes. Without this modification, lysosomal enzymes are missorted to the extracellular space, which results in lysosomal dysfunction of many cell types. Patients with MLII present with severe skeletal abnormalities, multisystemic symptoms, and early death; the clinical course in MLIII is less progressive. Despite dysfunction of a major degradative pathway, renal and glomerular involvement is rarely reported, suggesting organ-specific compensatory mechanisms. MLII mice were generated and compared with an established MLIII model to investigate the balance of protein synthesis and degradation, which reflects glomerular integrity. Proteinuria was assessed in patients. High-resolution confocal microscopy and functional assays identified proteins to deduce compensatory modes of balancing proteostasis. Patients with MLII but not MLIII exhibited microalbuminuria. MLII mice showed lysosomal enzyme missorting and several skeletal alterations, indicating that they are a useful model. In glomeruli, both MLII and MLIII mice exhibited reduced levels of lysosomal enzymes and enlarged lysosomes with abnormal storage material. Nevertheless, neither model had detectable morphologic or functional glomerular alterations. The models rebalance proteostasis in two ways: MLII mice downregulate protein translation and increase the integrated stress response, whereas MLIII mice upregulate the proteasome system in their glomeruli. Both MLII and MLIII downregulate the protein complex mTORC1 (mammalian target of rapamycin complex 1) signaling, which decreases protein synthesis. Severe lysosomal dysfunction leads to microalbuminuria in some patients with mucolipidosis. Mouse models indicate distinct compensatory pathways that balance proteostasis in MLII and MLIII.

Update on new muscle glycogenosis

The field of muscle glycogenoses has progressed in recent years by the identification of new disorders, and by reaching a better understanding of pathophysiology of the disorders and the physiology of glycogen metabolism. In this review, we describe the clinical and pathological features of the three most recently described muscle glycogenoses caused by recessive mutations in GYG1, RBCK1 and PGM1. The three involved enzymes play different roles in glycogen metabolism. Glycogenin-1 (GYG1) is involved in the initial steps of glycogen synthesis, whereas phosphoglucomutase catalyzes two metabolic pathways; the connection between galactose and glycogen on one side, and glucose metabolism on the other side. The metabolic consequences of mutations in the ubiquitin ligase gene RBCK1 are still poorly understood. GYG1 deficiency has been associated with cardiomyopathies with abnormal storage material in the heart, but most cases present with a polyglucosan body myopathy without cardiac involvement. The recent identification of new glycogenosis not only allows to improve the knowledge of glycogen metabolism, but also builds bridges with protein glycosylation and immune system.

Diagnosis and misdiagnosis of adult neuronal ceroid lipofuscinosis (Kufs disease).

To critically re-evaluate cases diagnosed as adult neuronal ceroid lipofuscinosis (ANCL) in order to aid clinicopathologic diagnosis as a route to further gene discovery. Through establishment of an international consortium we pooled 47 unsolved cases regarded by referring centers as ANCL. Clinical and neuropathologic experts within the Consortium established diagnostic criteria for ANCL based on the literature to assess each case. A panel of 3 neuropathologists independently reviewed source pathologic data. Cases were given a final clinicopathologic classification of definite ANCL, probable ANCL, possible ANCL, or not ANCL. Of the 47 cases, only 16 fulfilled the Consortium's criteria of ANCL (5 definite, 2 probable, 9 possible). Definitive alternate diagnoses were made in 10, including Huntington disease, early-onset Alzheimer disease, Niemann-Pick disease, neuroserpinopathy, prion disease, and neurodegeneration with brain iron accumulation. Six cases had features suggesting an alternate diagnosis, but no specific condition was identified; in 15, the data were inadequate for classification. Misinterpretation of normal lipofuscin as abnormal storage material was the commonest cause of misdiagnosis. Diagnosis of ANCL remains challenging; expert pathologic analysis and recent molecular genetic advances revealed misdiagnoses in >1/3 of cases. We now have a refined group of cases that will facilitate identification of new causative genes.

NCL diseases — clinical perspectives

The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage disorders and together are the most common degenerative brain diseases in childhood. They are a group of disorders linked by the characteristic accumulation of abnormal storage material in neurons and other cell types, and a degenerative disease course. All NCLs are characterized by a combination of dementia, epilepsy, and motor decline. For most childhood NCLs, a progressive visual failure is also a core feature. The characteristics of these symptoms can vary and the age at disease onset ranges from birth to young adulthood. Genetic heterogeneity, with fourteen identified NCL genes and wide phenotypic variability render diagnosis difficult. A new NCL classification system based on the affected gene and the age at disease onset allows a precise and practical delineation of an individual patient's NCL type. A diagnostic algorithm to identify each NCL form is presented here. Precise NCL diagnosis is essential not only for genetic counseling, but also for the optimal delivery of care and information sharing with the family and other caregivers. These aspects are challenging because there are also potential long term complications which are specific to NCL type. Therefore care supported by a specifically experienced team of clinicians is recommended. As the underlying pathophysiological mechanism is still unclear for all NCL forms, the development of curative therapies remains difficult. This article is part of a Special Issue entitled: The neuronal ceroid lipofuscinoses or Batten Disease.

Glycogenin-1 Deficiency and Inactivated Priming of Glycogen Synthesis

Glycogen, which serves as a major energy reserve in cells, is a large, branched polymer of glucose molecules. We describe a patient who had muscle weakness, associated with the depletion of glycogen in skeletal muscle, and cardiac arrhythmia, associated with the accumulation of abnormal storage material in the heart. The skeletal muscle showed a marked predominance of slow-twitch, oxidative muscle fibers and mitochondrial proliferation. Western blotting showed the presence of unglucosylated glycogenin-1 in the muscle and heart. Sequencing of the glycogenin-1 gene, GYG1, revealed a nonsense mutation in one allele and a missense mutation, Thr83Met, in the other. The missense mutation resulted in inactivation of the autoglucosylation of glycogenin-1 that is necessary for the priming of glycogen synthesis in muscle.

Neuronal ceroid lipofuscinosis caused by MFSD8 mutations: a common theme emerging

Neuronal ceroid lipofuscinoses (NCLs) are a group of lysosomal neurodegenerative disorders that have in common the characteristic accumulation of abnormal storage material. Old clinical classification based on age of onset is now being revisited with the quickly accumulating knowledge of the various genetic defects that underlie this group of genetically heterogeneous disorders. We report our linkage data on a family with late-infantile NCL and show that the disease in this family is due to a homozygous novel mutation in the most recently described NCL gene (MFSD8). We use clinical data from our patients and the few others that have previously been reported to delineate the phenotype associated with mutations in this gene. We conclude that the phenotype is fairly consistent, which is a helpful guide to clinicians as they decide on the most cost-effective molecular testing strategies for NCLs.

Palmitoyl-protein thioesterase 1 deficiency in Drosophila melanogaster causes accumulation of abnormal storage material and reduced life span.

Human neuronal ceroid lipofuscinoses (NCLs) are a group of genetic neurodegenerative diseases characterized by progressive death of neurons in the central nervous system (CNS) and accumulation of abnormal lysosomal storage material. Infantile NCL (INCL), the most severe form of NCL, is caused by mutations in the Ppt1 gene, which encodes the lysosomal enzyme palmitoyl-protein thioesterase 1 (Ppt1). We generated mutations in the Ppt1 ortholog of Drosophila melanogaster to characterize phenotypes caused by Ppt1 deficiency in flies. Ppt1-deficient flies accumulate abnormal autofluorescent storage material predominantly in the adult CNS and have a life span 30% shorter than wild type, phenotypes that generally recapitulate disease-associated phenotypes common to all forms of NCL. In contrast, some phenotypes of Ppt1-deficient flies differed from those observed in human INCL. Storage material in flies appeared as highly laminar spherical deposits in cells of the brain and as curvilinear profiles in cells of the thoracic ganglion. This contrasts with the granular deposits characteristic of human INCL. In addition, the reduced life span of Ppt1-deficient flies is not caused by progressive death of CNS neurons. No changes in brain morphology or increases in apoptotic cell death of CNS neurons were detected in Ppt1-deficient flies, even at advanced ages. Thus, Ppt1-deficient flies accumulate abnormal storage material and have a shortened life span without evidence of concomitant neurodegeneration.

Neurofibrillary tangles in Niemann—Pick disease type C

Post-mortem neuropathological examination of five cases of Niemann-Pick disease type C revealed neurofibrillary tangles in many parts of the brain. Tangles were a consistent finding in the hippocampus, hypothalamus, substantia innominata, midbrain pons and medulla. Other regions of the brain in which tangles were present included neocortex, basal ganglia, thalamus, cerebellar cortex in one case, and dentate nucleus in another. The tangles were argyrophilic, fluoresced under ultraviolet light when stained with thioflavin S, and reacted strongly with antibody to tau protein. Some of the tangles could be immunostained for ubiquitin. Electron microscopy, performed in one of the cases, showed the tangles to consist of paired helical filaments ultrastructurally identical to those of Alzheimer's disease. The distribution of the tangles in the central nervous system as a whole and also within many individual neurons corresponded fairly closely with that of the abnormal storage material. Both the tangles and the storage material extended into, and distended, the proximal parts of many dendrites and axons. No A4/beta protein, either in the form of plaques or in the walls of blood vessels, was detected in any of the cases. Our findings suggest that neurofibrillary tangles are a common feature of Niemann-Pick disease type C and that their formation may be a reaction to the abnormal storage material.

Type IV glyogenosis: Electron microscopic characterization of cytoplasmic accumulations

Type IV glycogenosis (amylopectinosis) is a heritable disease resulting from the deficient activity of the enzyme amylo-l,4--l ,6-transglucosidase. The clinical manifestations include hepatomegaly, portal fibrosis, and cirrhosis. In the strict sense of the term, this is not a true glycogenosis since the tissue concentration of glycogen has been reported as normal or even decreased, although the few light microscopic studies available have shown a definitive deposition of an abnormal storage material in a number of tissues but especially in the liver. While the histologic picture is inconclusive and may mimic other conditions, particularly alpha-l-antitrypsin deficiency, the electron microscopic pattern is quite unique and has been described elsewhere. The purpose of this study was to closely examine and characterize the storage material found in liver cells of a case of Type IV glycogenosis.

Neuropathologie Des Encéphalopathies Par Erreurs Innées Du Métabolisme Des Lipides, Des Glucides Et Des Acides Aminés

Summary Morphological features of the central nervous system, by light and electron microscopy, are reported in various encephalopathies by inborn enzymatic defect in lipid, glucidic and aminoacid metabolisms. The authors stress on the caracteristics of the abnormal storage material in Neurolipidoses, Ceroid-Lipofuscinoses, Glycogenosis type II and Lafora disease. On the other hand, they insist on the non specific lesions of the central nervous system in Aminoacidopathies by enzymatic defect.