Niemann-Pick disease: a frequent missense mutation in the acid sphingomyelinase gene of Ashkenazi Jewish type A and B patients

Alterations in Proteostasis Mechanisms in Niemann-Pick Type C Disease

Niemann-Pick Type C (NPC) represents an autosomal recessive disorder with an incidence rate of 1 in 150,000 live births, classified within lysosomal storage diseases (LSDs). The abnormal accumulation of unesterified cholesterol characterizes the pathophysiology of NPC. This phenomenon is not unique to NPC, as analogous accumulations have also been observed in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. Interestingly, disturbances in the folding of the mutant protein NPC1 I1061T are accompanied by the aggregation of proteins such as hyperphosphorylated tau, α-synuclein, TDP-43, and β-amyloid peptide. These accumulations suggest potential disruptions in proteostasis, a regulatory process encompassing four principal mechanisms: synthesis, folding, maintenance of folding, and protein degradation. The dysregulation of these processes leads to excessive accumulation of abnormal proteins that impair cell function and trigger cytotoxicity. This comprehensive review delineates reported alterations across proteostasis mechanisms in NPC, encompassing changes in processes from synthesis to degradation. Additionally, it discusses therapeutic interventions targeting pharmacological facets of proteostasis in NPC. Noteworthy among these interventions is valproic acid, a histone deacetylase inhibitor (HDACi) that modulates acetylation during NPC1 synthesis. In addition, various therapeutic options addressing protein folding modulation, such as abiraterone acetate, DHBP, calnexin, and arimoclomol, are examined. Additionally, treatments impeding NPC1 degradation, exemplified by bortezomib and MG132, are explored as potential strategies. This review consolidates current knowledge on proteostasis dysregulation in NPC and underscores the therapeutic landscape targeting diverse facets of this intricate process.

The Genetic Basis, Lung Involvement, and Therapeutic Options in Niemann-Pick Disease: A Comprehensive Review

Niemann-Pick Disease (NPD) is a rare autosomal recessive disease belonging to lysosomal storage disorders. Three types of NPD have been described: NPD type A, B, and C. NPD type A and B are caused by mutations in the gene SMPD1 coding for sphingomyelin phosphodiesterase 1, with a consequent lack of acid sphingomyelinase activity. These diseases have been thus classified as acid sphingomyelinase deficiencies (ASMDs). NPD type C is a neurologic disorder due to mutations in the genes NPC1 or NPC2, causing a defect of cholesterol trafficking and esterification. Although all three types of NPD can manifest with pulmonary involvement, lung disease occurs more frequently in NPD type B, typically with interstitial lung disease, recurrent pulmonary infections, and respiratory failure. In this sense, bronchoscopy with broncho-alveolar lavage or biopsy together with high-resolution computed tomography are fundamental diagnostic tools. Although several efforts have been made to find an effective therapy for NPD, to date, only limited therapeutic options are available. Enzyme replacement therapy with Olipudase α is the first and only approved disease-modifying therapy for patients with ASMD. A lung transplant and hematopoietic stem cell transplantation are also described for ASMD in the literature. The only approved disease-modifying therapy in NPD type C is miglustat, a substrate-reduction treatment. The aim of this review was to delineate a state of the art on the genetic basis and lung involvement in NPD, focusing on clinical manifestations, radiologic and histopathologic characteristics of the disease, and available therapeutic options, with a gaze on future therapeutic strategies.

Evaluation of the Genetic Background of Patients with Niemann-Pick Disease

Background

Congenital liver disease refers to a group of heterogeneous diseases from a clinical genetic point of view. The most crucial features are hepatosplenomegaly and elevated liver enzymes. This study aims to identify genetic variants causing the disease in three Iranian families with congenital liver disease using molecular techniques.

Methods

Patients were referred to Next Generation Genetic Polyclinic (NGGC) in Mashhad after confirmed congenital liver disease diagnosis by gastroenterologists. Following informed consent signed by participants, DNA was extracted from blood samples. Whole exome sequencing (WES) was performed for three probands. After the analysis of raw data, candidate variants were confirmed in the patients and their parents.

Results

We have found the possible disease-causing variant as the c.1718G>C variant (p. Trp573Ser) in the SMPD1 gene in the F-1 patient and c.1718G>C (p. Trp573Ser) in the SMPD1 gene in the F-3 patient. Moreover, we have found the c.3175C>T variant (p. Arg1059Ter) in the NPC1 gene in the F-2 patient.

Conclusions

In this study, disease-causing variants were identified in three probands suspected of Niemann-Pick disease. Such results show the relatively high power of molecular techniques to assist clinicians with disease management, therapeutic strategies, and preventive options such as preimplantation genetic diagnosis and prenatal diagnosis.

Consensus clinical management guidelines for acid sphingomyelinase deficiency (Niemann-Pick disease types A, B and A/B)

BACKGROUND

Acid Sphingomyelinase Deficiency (ASMD) is a rare autosomal recessive disorder caused by mutations in the SMPD1 gene. This rarity contributes to misdiagnosis, delayed diagnosis and barriers to good care. There are no published national or international consensus guidelines for the diagnosis and management of patients with ASMD. For these reasons, we have developed clinical guidelines that defines standard of care for ASMD patients.

METHODS

The information contained in these guidelines was obtained through a systematic literature review and the experiences of the authors in their care of patients with ASMD. We adopted the Appraisal of Guidelines for Research and Evaluation (AGREE II) system as method of choice for the guideline development process.

RESULTS

The clinical spectrum of ASMD, although a continuum, varies substantially with subtypes ranging from a fatal infantile neurovisceral disorder to an adult-onset chronic visceral disease. We produced 39 conclusive statements and scored them according to level of evidence, strengths of recommendations and expert opinions. In addition, these guidelines have identified knowledge gaps that must be filled by future research.

CONCLUSION

These guidelines can inform care providers, care funders, patients and their carers about best clinical practice and leads to a step change in the quality of care for patients with ASMD with or without enzyme replacement therapy (ERT).

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

SUCCESSFUL PREGNANCY OUTCOME IN PATIENT WITH NIEMANN-PICK DISEASE TYPE B AND REVIEW OF THE LITERATURE

Niemann-Pick disease (NPD), is a rare autosomal recessive lysosomal storage disorder. Niemann-Pick A and B are caused by homozygous or compound heterozygous mutations in the sphingomyelin phosphodiesterase-1 (SMPD1) gene on chromosome 11p15. Type B is panethnic, although its frequency is increased in Turkish, Arabic and North African populations. Clinical features vary significantly among patients. It is a rare condition and information about its management an outcome during pregnancy and labor is limited. Both maternal mortality and morbidity due to severe postpartum hemorrhage has been reported. We represent a case of successful pregnancy outcome in patient with NPD type B. Type of mutations in SMPD 1 gene and severity of disease before pregnancy can predict the prognosis of pregnancy.

Analysis of the HEXA, HEXB, ARSA, and SMPD1 Genes in 68 Iranian Patients

Lysosomal storage diseases (LSDs) are known as genetic disorders with an overall prevalence of 1 per 7700 live births. Sphingolipidosis, which is a subgroup of LSDs, is resulted from mutations in the coding genes of specific enzymes of sphingolipid hydrolases. The current study aimed to provide additional knowledge on the genotype of sphingolipidoses disease among Iranian patients affected by the disease. In this research, we studied 68 unrelated Iranian patients diagnosed with one kind of sphingolipidoses from 2014 to 2019. Thereafter, genomic DNA was isolated from their peripheral blood leukocytes samples in EDTA in terms of the manufacturer's protocol. All the coding exons and exon-intron boundaries of the related genes were sequenced and then analyzed using the NCBI database. Finally, they were reviewed using some databases such as the Human Gene Mutation Database (HGMD) and ClinVar ( https://www.ncbi.nlm.nih.gov/clinva ). By studying 22 MLD patients, 18 different variations of the ARSA gene were found, one of which was new including, named as c.472 T > G p. (Cys158Gly). Out of 15 Sandhoff disease (SD) patients, 11 different variations of the HEXB gene were found. Correspondingly, the c.1083-2delA was not reported earlier. By investigating 21 Iranian patients with Tay-Sachs disease (TSD), one new variant was found as c.622delG. The study of 10 Niemann-Pick disease A/B (NPDA/B (patients has led to the identification of 9 different SMPD1 gene variations, among which 3 variations were novel mutations. The results of the present study can be expanded to the genotypic spectrum of Iranian patients with MLD, SD, TSD, and NPD diseases and also used to innovate more effective methods for the detection of genetic carriers as well as diagnosing and counseling of Iranian patients affected with these disorders.

Acid Sphingomyelinase, a Lysosomal and Secretory Phospholipase C, Is Key for Cellular Phospholipid Catabolism

Here, we present the main features of human acid sphingomyelinase (ASM), its biosynthesis, processing and intracellular trafficking, its structure, its broad substrate specificity, and the proposed mode of action at the surface of the phospholipid substrate carrying intraendolysosomal luminal vesicles. In addition, we discuss the complex regulation of its phospholipid cleaving activity by membrane lipids and lipid-binding proteins. The majority of the literature implies that ASM hydrolyses solely sphingomyelin to generate ceramide and ignores its ability to degrade further substrates. Indeed, more than twenty different phospholipids are cleaved by ASM in vitro, including some minor but functionally important phospholipids such as the growth factor ceramide-1-phosphate and the unique lysosomal lysolipid bis(monoacylglycero)phosphate. The inherited ASM deficiency, Niemann-Pick disease type A and B, impairs mainly, but not only, cellular sphingomyelin catabolism, causing a progressive sphingomyelin accumulation, which furthermore triggers a secondary accumulation of lipids (cholesterol, glucosylceramide, GM2) by inhibiting their turnover in late endosomes and lysosomes. However, ASM appears to be involved in a variety of major cellular functions with a regulatory significance for an increasing number of metabolic disorders. The biochemical characteristics of ASM, their potential effect on cellular lipid turnover, as well as a potential impact on physiological processes will be discussed.

Functional characterization of novel variants in SMPD1 in Indian patients with acid sphingomyelinase deficiency

Pathogenic variations in SMPD1 lead to acid sphingomyelinase deficiency (ASMD), that is, Niemann-Pick disease (NPD) type A and B (NPA, NPB), which is a recessive lysosomal storage disease. The knowledge of variant spectrum in Indian patients is crucial for early and accurate NPD diagnosis and genetic counseling of families. In this study, we recruited 40 unrelated pediatric patients manifesting symptoms of ASMD and subnormal ASM enzyme activity. Variations in SMPD1 were studied using Sanger sequencing for all exons, followed by interpretation of variants based on American College of Medical Genetics and Genomics & Association for Molecular Pathology (ACMG/AMP) criteria. We identified 18 previously unreported variants and 21 known variants, including missense, nonsense, deletions, duplications, and splice site variations with disease-causing potential. Eight missense variants were functionally characterized using in silico molecular dynamic simulation and in vitro transient transfection in HEK293T cells, followed by ASM enzyme assay, immunoblot, and immunofluorescence studies. All the variants showed reduced ASM activity in transfected cells confirming their disease-causing potential. The study provides data for efficient prenatal diagnosis and genetic counseling of families with NPD type A and B.

In Silico Analysis of the Molecular-Level Impact of SMPD1 Variants on Niemann-Pick Disease Severity

Sphingomyelin phosphodiesterase (SMPD1) is a key enzyme in the sphingolipid metabolism. Genetic SMPD1 variants have been related to the Niemann-Pick lysosomal storage disorder, which has different degrees of phenotypic severity ranging from severe symptomatology involving the central nervous system (type A) to milder ones (type B). They have also been linked to neurodegenerative disorders such as Parkinson and Alzheimer. In this paper, we leveraged structural, evolutionary and stability information on SMPD1 to predict and analyze the impact of variants at the molecular level. We developed the SMPD1-ZooM algorithm, which is able to predict with good accuracy whether variants cause Niemann-Pick disease and its phenotypic severity; the predictor is freely available for download. We performed a large-scale analysis of all possible SMPD1 variants, which led us to identify protein regions that are either robust or fragile with respect to amino acid variations, and show the importance of aromatic-involving interactions in SMPD1 function and stability. Our study also revealed a good correlation between SMPD1-ZooM scores and in vitro loss of SMPD1 activity. The understanding of the molecular effects of SMPD1 variants is of crucial importance to improve genetic screening of SMPD1-related disorders and to develop personalized treatments that restore SMPD1 functionality.

Genetic perspective on the synergistic connection between vesicular transport, lysosomal and mitochondrial pathways associated with Parkinson's disease pathogenesis

Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) are symptomatically characterized by parkinsonism, with the latter presenting additionally a distinctive range of atypical features. Although the majority of patients with PD and APS appear to be sporadic, genetic causes of several rare monogenic disease variants were identified. The knowledge acquired from these genetic factors indicated that defects in vesicular transport pathways, endo-lysosomal dysfunction, impaired autophagy-lysosomal protein and organelle degradation pathways, α-synuclein aggregation and mitochondrial dysfunction play key roles in PD pathogenesis. Moreover, membrane dynamics are increasingly recognized as a key player in the disease pathogenesis due lipid homeostasis alterations, associated with lysosomal dysfunction, caused by mutations in several PD and APS genes. The importance of lysosomal dysfunction and lipid homeostasis is strengthened by both genetic discoveries and clinical epidemiology of the association between parkinsonism and lysosomal storage disorders (LSDs), caused by the disruption of lysosomal biogenesis or function. A synergistic coordination between vesicular trafficking, lysosomal and mitochondria defects exist whereby mutations in PD and APS genes encoding proteins primarily involved one PD pathway are frequently associated with defects in other PD pathways as a secondary effect. Moreover, accumulating clinical and genetic observations suggest more complex inheritance patters of familial PD exist, including oligogenic and polygenic inheritance of genes in the same or interconnected PD pathways, further strengthening their synergistic connection.Here, we provide a comprehensive overview of PD and APS genes with functions in vesicular transport, lysosomal and mitochondrial pathways, and highlight functional and genetic evidence of the synergistic connection between these PD associated pathways.

Mechanism of Secondary Ganglioside and Lipid Accumulation in Lysosomal Disease

Gangliosidoses are caused by monogenic defects of a specific hydrolase or an ancillary sphingolipid activator protein essential for a specific step in the catabolism of gangliosides. Such defects in lysosomal function cause a primary accumulation of multiple undegradable gangliosides and glycosphingolipids. In reality, however, predominantly small gangliosides also accumulate in many lysosomal diseases as secondary storage material without any known defect in their catabolic pathway. In recent reconstitution experiments, we identified primary storage materials like sphingomyelin, cholesterol, lysosphingolipids, and chondroitin sulfate as strong inhibitors of sphingolipid activator proteins (like GM2 activator protein, saposin A and B), essential for the catabolism of many gangliosides and glycosphingolipids, as well as inhibitors of specific catabolic steps in lysosomal ganglioside catabolism and cholesterol turnover. In particular, they trigger a secondary accumulation of ganglioside GM2, glucosylceramide and cholesterol in Niemann–Pick disease type A and B, and of GM2 and glucosylceramide in Niemann–Pick disease type C. Chondroitin sulfate effectively inhibits GM2 catabolism in mucopolysaccharidoses like Hurler, Hunter, Sanfilippo, and Sly syndrome and causes a secondary neuronal ganglioside GM2 accumulation, triggering neurodegeneration. Secondary ganglioside and lipid accumulation is furthermore known in many more lysosomal storage diseases, so far without known molecular basis.

Generation of an induced pluripotent stem cell line (TRNDi004-I) from a Niemann-Pick disease type B patient carrying a heterozygous mutation of p.L43_A44delLA in the SMPD1 gene

Niemann-Pick disease type B (NPB) is a rare autosomal recessive lysosomal storage disease caused by mutations in the SMPD1 gene, which encodes for acid sphingomyelinase. A human induced pluripotent stem cell (iPSC) line was generated from dermal fibroblasts of a 1-year old male patient with NPB that has a heterozygous mutation of a p.L43_A44delLA of SMPD1 using non-integrating Sendai virus technique. This iPSC line offers a useful resource to study the disease pathophysiology and as a cell-based model for drug development to treat NPB.

Deep sequencing of SMPD1 gene revealed a heterozygous frameshift mutation (p.Ser192Alafs) in a Palestinian infant with Niemann-Pick disease type A: a case report

Background

Niemann–Pick disease is caused by reduced level of the lysosomal enzyme acid sphingomyelinase. Children can survive between 2 and 12 years based on the disease type. Two main types are well known: type A and B. Niemann–Pick disease type A is characterized by severe central nervous system deterioration and hepatosplenomegaly while type B is a progressive hypersplenism accompanied with gradual deterioration of pulmonary function.

Case presentation

We describe an 11-month-old Palestinian baby boy with hepatosplenomegaly, hypotonia, delayed motor development, laryngomalacia, bilateral cherry-red spots, and failure to thrive. Metabolic screening, blood count, differential tests, immunology screen, infectious disease screen, urine, biochemical tests as well as molecular diagnosis were performed. The molecular diagnosis was done by amplifying the whole sphingomyelin phosphodiesterase 1 (SMPD1) gene, followed by deep sequencing. The obtained sequences were aligned, de novo assembled and compared to human reference gene (GenBank GeneID: NG_011780.1, Ensembl version ENSG00000166311 and protein identified as UniProtKB – P17405).

Two known mutations were identified in our patient: the pathogenic frameshift mutation NM_000543.4(SMPD1):c.573delT (p.Ser192Alafs) and the benign polymorphism NM_000543.4(SMPD1):c.107T>C (p.Val36Ala). The enzyme study showed a very low level of enzymatic activity of acidic sphingomyelinase (0.1 nmol/ml per hour). Correlations between clinical findings, laboratory data, and sequence analysis are presented.

Conclusions

In conclusion, this is the first report about a heterozygote frameshift p.Ser192AlafsX65 in a Palestinian patient with Niemann–Pick disease type A, emphasizing the importance of deep sequencing in genetic diagnosis of this rare inherited disease.

Quantitation of plasmatic lysosphingomyelin and lysosphingomyelin-509 for differential screening of Niemann-Pick A/B and C diseases

Acid sphingomyelinase deficiency (ASMd, Niemann-Pick disease A/B) and Niemann-Pick type C disease (NPC) share core clinical symptoms. Initial diagnostic discrimination of these two rare lysosomal storage diseases is thus difficult. As sphingomyelin accumulates in ASMd as well as NPC, lysosphingomyelin (sphingosylphosphorylcholine) and its m/z 509 analog were suggested as biomarkers for both diseases. Herein we present results of simultaneous LC-ESI-MS/MS measurements of lysosphingomyelin and lysosphingomyelin 509 in plasma and dried blood spots (DBS) collected from ASMd and NPC patients and suggest that the plasma but not DBS levels of the two analytes allow differential biochemical screening of ASMd and NPC.

The structure and catalytic mechanism of human sphingomyelin phosphodiesterase like 3a--an acid sphingomyelinase homologue with a novel nucleotide hydrolase activity

Human sphingomyelinase phosphodiesterase like 3a (SMPDL3a) is a secreted enzyme that shares a conserved catalytic domain with human acid sphingomyelinase (aSMase), the enzyme carrying mutations causative of Niemann-Pick disease. We have solved the structure of SMPDL3a revealing a calcineurin-like fold. A dimetal site, glycosylation pattern and a disulfide bond network are likely to be conserved also in human aSMase. We show that the binuclear site of SMPDL3a is occupied by two Zn(2+) ions and that excess Zn(2+) leads to inhibition of enzyme activity through binding to additional sites. As an extension of recent biochemical work we uncovered that SMPDL3a catalyses the hydrolysis of several modified nucleotides that include cytidine 5'-diphosphocholine, cytidine diphosphate ethanolamine and ADP-ribose, but not the aSMase substrate, sphingomyelin. We subsequently determined the structure of SMPDL3a in complex with the product 5'-cytidine monophosphate (CMP), a structure that is consistent with several distinct coordination modes of the substrate/product in the active site during the reaction cycle. Based on the structure of CMP complexes, we propose a phosphoryl transfer mechanism for SMPDL3a. Finally, a homology model of human aSMase was constructed to allow for the mapping of selected Niemann-Pick disease mutations on a three-dimensional framework to guide further characterization of their effects on aSMase function.

DATABASE

Structural data are available in the PDB database under the accession numbers 5EBB and 5EBE.

Regulation of sphingomyelin metabolism

Sphingolipids (SFs) represent a large class of lipids playing diverse functions in a vast number of physiological and pathological processes. Sphingomyelin (SM) is the most abundant SF in the cell, with ubiquitous distribution within mammalian tissues, and particularly high levels in the Central Nervous System (CNS). SM is an essential element of plasma membrane (PM) and its levels are crucial for the cell function. SM content in a cell is strictly regulated by the enzymes of SM metabolic pathways, which activities create a balance between SM synthesis and degradation. The de novo synthesis via SM synthases (SMSs) in the last step of the multi-stage process is the most important pathway of SM formation in a cell. The SM hydrolysis by sphingomyelinases (SMases) increases the concentration of ceramide (Cer), a bioactive molecule, which is involved in cellular proliferation, growth and apoptosis. By controlling the levels of SM and Cer, SMSs and SMases maintain cellular homeostasis. Enzymes of SM cycle exhibit unique properties and diverse tissue distribution. Disturbances in their activities were observed in many CNS pathologies. This review characterizes the physiological roles of SM and enzymes controlling SM levels as well as their involvement in selected pathologies of the Central Nervous System, such as ischemia/hypoxia, Alzheimer disease (AD), Parkinson disease (PD), depression, schizophrenia and Niemann Pick disease (NPD).

SMPD1 Mutation Update: Database and Comprehensive Analysis of Published and Novel Variants

Niemann-Pick Types A and B (NPA/B) diseases are autosomal recessive lysosomal storage disorders caused by the deficient activity of acid sphingomyelinase (ASM) because of the mutations in the SMPD1 gene. Here, we provide a comprehensive updated review of already reported and newly identified SMPD1 variants. Among them, 185 have been found in NPA/B patients. Disease-causing variants are equally distributed along the SMPD1 gene; most of them are missense (65.4%) or frameshift (19%) mutations. The most frequently reported mutation worldwide is the p.R610del, clearly associated with an attenuated NP disease type B phenotype. The available information about the impact of 52 SMPD1 variants on ASM mRNA and/or enzymatic activity has been collected and whenever possible, phenotype/genotype correlations were established. In addition, we created a locus-specific database easily accessible at http://www.inpdr.org/genes that catalogs the 417 SMPD1 variants reported to date and provides data on their in silico predicted effects on ASM protein function or mRNA splicing. The information reviewed in this article, providing new insights into the genotype/phenotype correlation, is extremely valuable to facilitate diagnosis and genetic counseling of families affected by NPA/B.

Systematic Genetic Analysis of the SMPD1 Gene in Chinese Patients with Parkinson's Disease

To examine the association between the sphingomyelin phosphodiesterase 1, acid lysosomal (SMPD1) gene, and Parkinson's disease (PD) in Han Chinese from Central South part of Mainland China, we performed systematic genetic analysis in 502 Chinese Han patients with PD and 637 gender-, age-, and ethnicity-matched normal controls from Central South part of the Mainland China. We identified 11 single nucleotide variants and Leu-Ala (Val) repeat variants in the SMPD1 gene in our large cohort. Two novel missense variants, c.638A > C (p.H213P) and c.1673T > C (p.L558P), and a rare known missense variant, c.1805G > A (p.R602H, rs370129081), were identified in three sporadic PD cases. None of these three variants were observed in controls. Additionally, case-control analysis showed association between Leu-Ala (Val) repeat variants in SMPD1 and Chinese Han patients with PD (P = 0.015, χ (2) = 8.451). Our data provide supportive evidence that some genetic variants in SMPD1 increase the risk of PD in the Chinese Han population.

Cell biology. Metabolic control of cell death

Beyond their contribution to basic metabolism, the major cellular organelles, in particular mitochondria, can determine whether cells respond to stress in an adaptive or suicidal manner. Thus, mitochondria can continuously adapt their shape to changing bioenergetic demands as they are subjected to quality control by autophagy, or they can undergo a lethal permeabilization process that initiates apoptosis. Along similar lines, multiple proteins involved in metabolic circuitries, including oxidative phosphorylation and transport of metabolites across membranes, may participate in the regulated or catastrophic dismantling of organelles. Many factors that were initially characterized as cell death regulators are now known to physically or functionally interact with metabolic enzymes. Thus, several metabolic cues regulate the propensity of cells to activate self-destructive programs, in part by acting on nutrient sensors. This suggests the existence of "metabolic checkpoints" that dictate cell fate in response to metabolic fluctuations. Here, we discuss recent insights into the intersection between metabolism and cell death regulation that have major implications for the comprehension and manipulation of unwarranted cell loss.

Identification of a distinct mutation spectrum in the SMPD1 gene of Chinese patients with acid sphingomyelinase-deficient Niemann-Pick disease

Background

Clinical observations and molecular analysis of the SMPD1 gene in Chinese patients with acid sphingomyelinase deficiency Niemann-Pick disease (NPD) are scarce.

Methods

A cohort of 27 Chinese patients diagnosed with acid sphingomyelinase deficiency, within the past five years, were collected and investigated for genotype, phenotype, and their correlations.

Results

The majority of our patients (25/27) were under 18 years of age. From the cohort group, eight (30%) fulfilled characters of type A. Four other patients experienced neurologic involvement after two years of age, these were classified as intermediate type. The remaining fifteen presented without clear neurologic involvement and were regarded as type B. One patient, from the type B group, presented with the unusual symptom of a secondary amenorrhea. Three patients, one from the type B group and two from the intermediate group, presented with pronounced proteinuria, in the late stages of the disease, indicating possible kidney involvement in NPD. Twenty-four SMPD1 gene mutations had been identified; eighteen of these are novel ones. These included four exonic small deletions/duplications (c.4delC, c.147_150del4, c.842-849dup8, c.1307-1312dup6), one termination mutation (p.Glu248X), and thirteen exonic point mutations (p.Gly336Ser, p.Trp342Cys, p.Leu382Phe, p.Pro429Leu, p.Pro430Ser, p.Trp437Arg, p.Thr451Pro, p.His461Pro, p.Ala484Val, p.Ser486Arg, p.Tyr500His, p.Pro533Leu, p.Val559Leu). Notably, eight mutations had more than one occurrence with c.4delC and p.Glu248X accounting for ~30% of all alleles. Correlation analysis of genotype and phenotype indicated eight mutations, c.842-849dup8, p.Glu248X, p.Arg230Cys, p.Trp437Arg, p.His461Pro, p.Ala484Val p.Ser486Arg, and p.Pro533Leu,to be severe mutations. Five mutations, c.4delC, p.Leu382Phe, p.Pro429Leu, p.Pro430Ser and p.Val559Leu were projected to be mild mutations. Interestingly, three intermediate individuals carried combinations of a mild mutation, c.4delC, on one allele and a severe mutation on the other allele.

Conclusions

The Chinese population may have a comparably high incidence of sphingomyelinase-deficient Niemann-Pick disease type A. This study has identified some novel genotype and phenotype correlations in this rare and devastating disorder.

Molecular diagnosis of genodermatoses

The progress of molecular genetics helps clinicians to prove or exclude a suspected diagnosis for a vast and yet increasing number of genodermatoses. This leads to precise genetic counselling, prenatal diagnosis and preimplantation genetic haplotyping for many inherited skin conditions. It is also helpful in such occasions as phenocopy, late onset and incomplete penetrance, uniparental disomy, mitochondrial inheritance and pigmentary mosaicism. Molecular methods of two genodermatoses are explained in detail, i.e. genodermatoses with skin fragility and neurofibromatosis type 1.

Developmentally regulated sphingolipid degradation in Leishmania major

Leishmania parasites alternate between extracellular promastigotes in sandflies and intracellular amastigotes in mammals. These protozoans acquire sphingolipids (SLs) through de novo synthesis (to produce inositol phosphorylceramide) and salvage (to obtain sphingomyelin from the host). A single ISCL (Inositol phosphoSphingolipid phospholipase C-Like) enzyme is responsible for the degradation of both inositol phosphorylceramide (the IPC hydrolase or IPCase activity) and sphingomyelin (the SMase activity). Recent studies of a L. major ISCL-null mutant (iscl⁻) indicate that SL degradation is required for promastigote survival in stationary phase, especially under acidic pH. ISCL is also essential for L. major proliferation in mammals. To further understand the role of ISCL in Leishmania growth and virulence, we introduced a sole IPCase or a sole SMase into the iscl⁻ mutant. Results showed that restoration of IPCase only complemented the acid resistance defect in iscl⁻ promastigotes and improved their survival in macrophages, but failed to recover virulence in mice. In contrast, a sole SMase fully restored parasite infectivity in mice but was unable to reverse the promastigote defects in iscl⁻. These findings suggest that SL degradation in Leishmania possesses separate roles in different stages: while the IPCase activity is important for promastigote survival and acid tolerance, the SMase activity is required for amastigote proliferation in mammals. Consistent with these findings, ISCL was preferentially expressed in stationary phase promastigotes and amastigotes. Together, our results indicate that SL degradation by Leishmania is critical for parasites to establish and sustain infection in the mammalian host.

My journey into the world of sphingolipids and sphingolipidoses

Analysis of lipid storage in postmortem brains of patients with amaurotic idiocy led to the recognition of five lysosomal ganglioside storage diseases and identification of their inherited metabolic blocks. Purification of lysosomal acid sphingomyelinase and ceramidase and analysis of their gene structures were the prerequisites for the clarification of Niemann-Pick and Farber disease. For lipid catabolism, intraendosomal vesicles are formed during the endocytotic pathway. They are subjected to lipid sorting processes and were identified as luminal platforms for cellular lipid and membrane degradation. Lipid binding glycoproteins solubilize lipids from these cholesterol poor membranes and present them to water-soluble hydrolases for digestion. Biosynthesis and intracellular trafficking of lysosomal hydrolases (hexosaminidases, acid sphingomyelinase and ceramidase) and lipid binding and transfer proteins (GM2 activator, saposins) were analyzed to identify the molecular and metabolic basis of several sphingolipidoses. Studies on the biosynthesis of glycosphingolipids yielded the scheme of Combinatorial Ganglioside Biosynthesis involving promiscuous glycosyltransferases. Their defects in mutagenized mice impair brain development and function.

Clear cell chondrosarcoma in association with niemann-pick disease

Purpose: The purpose of this case report is to bring to light this unusual combination of two rare diseases, namely Neimann-Pick disease Type B and clear cell chondrosarcoma occurring in the same patient. This has not previously been reported in the world literature.

Subject: Niemann-Pick disease (NPD) is a rare autosomal recessive inborn error of metabolism. Type B NPD is even rarer. It is a lysosomal storage disorder affecting children and adolescents often causing death in early childhood, although in milder form patients may survive up to adulthood, like our patient. Clear cell chondrosarcoma is a very rare type of chondrosarcoma affecting the epiphyseo-metaphyseal region of long bones. We present a patient suffering from a milder form of Neimann Pick disease who developed a clear cell chondrosarcoma. We investigated to find if there was likely to be any relationship between these two events.

Results: NPD type B is caused by a three-base deletion in chromosome 11. Chondrosarcoma and multiple exostoses occur due to loss of tumour suppressor gene EXT 2 from centromeric region on chromosome 11, though it is difficult to establish the link between the two, as the two together have not yet been reported in the literature. NPD may present diagnostic difficulties when it occurs with chondrosarcoma.

Discussion: We conclude that the two diseases have not been reported together in the world literature and there is some evidence to show that chromosome 11 is central to both diseases. More research is needed to see if one leads to the other.

Characterization of common SMPD1 mutations causing types A and B Niemann-Pick disease and generation of mutation-specific mouse models

Herein we describe detailed characterization of four common mutations (L302P, H421Y, R496L and DeltaR608) within the acid sphingomyelinase (ASM) gene causing types A and B Niemann-Pick disease (NPD). In vitro and in situ enzyme assays revealed marked deficiencies of ASM activity in NPD cell lines homoallelic for each mutation, although Western blotting and fluorescent microscopy showed that the mutant ASM polypeptides were expressed at normal levels and trafficked to lysosomes. Co-immunoprecipitation of the polypeptides with the ER chaperone, BiP, confirmed these findings, as did in vitro expression of the mutant cDNAs in reticulocyte lysates. We further developed a computer assisted, three-dimensional model of human ASM based on homologies to known proteins, and used this model to map each NPD mutation in relation to putative substrate binding, hydrolysis and zinc-binding domains. Lastly, we generated transgenic mice expressing the R496L and DeltaR608 mutations on the complete ASM knock-out background (ASMKO), and established breeding colonies for the future evaluation of enzyme enhancement therapies. Analysis of these mice demonstrated that the mutant ASM transgenes were expressed at high levels in the brain, and in the case of the DeltaR608 mutation, produced residual ASM activity that was significantly above the ASMKO background.

Carrier Testing for Autosomal- Recessive Disorders

The aim of carrier testing is to identify carrier couples at risk of having offspring with a serious genetic (autosomal recessive) disorder. Carrier couples are offered genetic consultation where their reproductive options, including prenatal diagnosis, are explained. The Ashkenazi Jewish population is at increased risk for several recessively inherited disorders (Tay-Sachs disease, Cystic fibrosis, Canavan disease, Gaucher disease, Familial Dysautonomia, Niemann-Pick disease, Fanconi anemia, and Bloom syndrome). Unlike Tay-Sachs disease, there is no simple biochemical or enzymatic test to detect carriers for these other disorders. However, with the rapid identification of disease-causing genes in recent years, DNA-based assays are increasingly available for carrier detection. Approximately 5% of the world's population carries a mutation affecting the globin chains of the hemoglobin molecule. Among the most common of these disorders are the thalassemias. The global birth rate of affected infants is at least 2 per 1000 (in unscreened populations), with the greatest incidence in Southeast Asian, Indian, Mediterranean, and Middle Eastern ethnic groups. Carriers are detected by evaluation of red cell indices and morphology, followed by more sophisticated hematological testing and molecular analyses. The following issues need to be considered in the development of a carrier screening program: (1) test selection based on disease severity and test accuracy; (2) funding for testing and genetic counselling; (3) definition of the target population to be screened; (4) development of a public and professional education program; (5) informed consent for screening; and (6) awareness of community needs.

The pathogenesis and treatment of acid sphingomyelinase-deficient Niemann-Pick disease

Patients with types A and B Niemann-Pick disease (NPD) have an inherited deficiency of acid sphingomyelinase (ASM) activity. The clinical spectrum of this disorder ranges from the infantile, neurological form that results in death by 3 years of age (type A NPD) to the non-neurological form (type B NPD) that is compatible with survival into adulthood. Intermediate cases also have been reported, and the disease is best thought of as a single entity with a spectrum of phenotypes. ASM deficiency is panethnic, but appears to be more frequent in individuals of Middle Eastern and North African descent. Current estimates of the disease incidence range from approximately 0.5 to 1 per 100,000 births. However, these approximations likely under estimate the true frequency of the disorder since they are based solely on cases referred to biochemical testing laboratories for enzymatic confirmation. The gene encoding ASM (SMPD1) has been studied extensively; it resides within an imprinted region on chromosome 11, and is preferentially expressed from the maternal chromosome. Over 100 SMPD1 mutations causing ASM-deficient NPD have been described, and some useful genotype-phenotype correlations have been made. Based on these findings, DNA-based carrier screening has been implemented in the Ashkenazi Jewish community. ASM 'knockout' mouse models also have been constructed and used to investigate disease pathogenesis and treatment. Based on these studies in the mouse model, an enzyme replacement therapy clinical trial has recently begun in adult patients with non-neurological ASM-deficient NPD.

Cell biology of membrane trafficking in human disease

Understanding the molecular and cellular mechanisms underlying membrane traffic pathways is crucial to the treatment and cure of human disease. Various human diseases caused by changes in cellular homeostasis arise through a single gene mutation(s) resulting in compromised membrane trafficking. Many pathogenic agents such as viruses, bacteria, or parasites have evolved mechanisms to subvert the host cell response to infection, or have hijacked cellular mechanisms to proliferate and ensure pathogen survival. Understanding the consequence of genetic mutations or pathogenic infection on membrane traffic has also enabled greater understanding of the interactions between organisms and the surrounding environment. This review focuses on human genetic defects and molecular mechanisms that underlie eukaryote exocytosis and endocytosis and current and future prospects for alleviation of a variety of human diseases.

Real-time quantitative polymerase chain reaction: a potential tool for genetic analysis in neuropathology

Since its introduction in the early- to mid-1980s, the polymerase chain reaction (PCR) has been modified and optimized for an increasing number of applications. Early on, the focus was on the amplification of a specific nucleic acid template into quantities amenable to identification and experimental manipulation. While this remains an important application, recent technology has allowed the use of PCR to accurately quantitate the amount of a specific nucleic acid template present in a complex sample. Rather than simply analyzing the final product amount following the course of sequential cycles of amplification, quantitative PCR allows one to measure the accumulation of PCR product during the course of the reaction ("real-time PCR"). Under the appropriate conditions the number of PCR cycles required for the accumulation of a specific amount of product (during the exponential phase of the reaction) is a reflection of the relative amount of nucleic acid template present in the sample under analysis. Real-time quantitative PCR allows one to analyze a relatively large number of samples in a short period of time, potentially allowing multiple markers to be applied on a sample within a time frame consistent with clinical settings. In this overview, we will highlight the uses of real-time quantitative PCR as a potential diagnostic tool in neuropathology, focusing on the analysis of CNS tumors.

Ocular manifestations of Niemann–Pick disease type B

PURPOSE

To investigate the ocular manifestations in Niemann-Pick disease type B (NPD-B).

DESIGN

Observational case series.

PARTICIPANTS

Forty-five patients (23 male and 22 female) with NPD-B from 37 unrelated families.

METHODS

Serial clinical evaluations were carried out over a 2- to 14-year period, including a complete physical examination, neurologic assessment, and ophthalmologic examination. Genotyping of the specific mutations in the acid sphingomyelinase (ASM) gene was performed when possible for genotype-phenotype correlations.

MAIN OUTCOME MEASURES

Fundus photographs to evaluate the retina, ASM genotype, and neurologic examination findings.

RESULTS

Ophthalmoscopic examination revealed retinal stigmata in 15 of 45 patients, 3 with macular halos and 12 with cherry red maculae. Neurologic examinations did not reveal any evidence of neurodegeneration, and there was no consistent relationship between retinal findings and genotype.

CONCLUSIONS

The presence of macular halos and/or cherry red maculae is not an absolute predictor of neurodegeneration, but should prompt a thorough evaluation to determine the underlying etiology and the precise diagnosis.

Lipid abnormalities in children with types A and B Niemann Pick disease

OBJECTIVE

To characterize the lipid profiles in patients with types A and B Niemann Pick disease (NPD) and determine if lipid abnormalities are associated with evidence of early cardiovascular disease or correlate with genotype.

STUDY DESIGN

The study was a cross-sectional analysis of 10 patients with NPD type A and 30 patients with NPD type B that was carried out in the General Clinical Research Center. For each patient, fasting lipid profile and glucose, T4, height or length, weight, resting blood pressure, and acid sphingomyelinase deficiency genotype were measured. In type B patients, electrocardiograhic-gated helical computed tomography of the heart also was obtained.

RESULTS

Lipid abnormalities included low (<35 mg/dL) high-density lipoprotein cholesterol in 100% of patients and hypertriglyceridemia and increased low-density lipoprotein cholesterol in 62% (25/40) and 67% (27/40) of patients, respectively. Coronary artery calcium scores were positive (>1.0) in 10 of 18 type B patients studied. There was no correlation of the Delta R608 genotype with a milder phenotype for the lipid abnormalities, as has been observed for a number of other NPD manifestations.

CONCLUSIONS

Lipid abnormalities are part of the phenotype in types A and B NPD and may be associated with early atherosclerotic heart disease.

Growth restriction in children with type B Niemann-Pick disease

OBJECTIVES

To compare growth of children with type B Niemann-Pick disease (NPD) with disease variables including genotype, organomegaly, bone age, and serum insulin-like growth factor-1 (IGF-1).

STUDY DESIGN

A cross-sectional analysis of growth was performed in 23 children and adolescents with enzymatically and genotypically confirmed NPD. Liver and spleen volumes were measured by quantitative computed tomography and skeletal age by a wrist radiograph.

RESULTS

The mean Z scores for height and weight were -1.24 (29th percentile) and -0.75 (34th percentile). The mean liver and spleen volumes were 2.06 and 13.46 times normal for weight, respectively. Skeletal age was delayed by an average of 2.5 years, and serum IGF-1 level was at or below the 2nd percentile in 8 of 12 patients. Short stature and low weight were significantly correlated with large organ volumes, delayed bone age, and low IGF-1 levels. In contrast to patients with other mutations, individuals homozygous for the DeltaR608 mutation had normal height and weight, markedly less hepatosplenomegaly and bone age delay, and normal IGF-1 levels.

CONCLUSIONS

Abnormal linear growth and delayed skeletal maturation are common in children and adolescents with type B NPD; however, homozygosity for DeltaR608 is associated with normal growth.

Seven novel acid sphingomyelinase gene mutations in Niemann-Pick type A and B patients

We have analyzed acid sphingomyelinase (SMPD1; E.C. 3.1.4.12) gene mutations in four Niemann-Pick disease (NPD) type A and B patients of Turkish ancestry and in three patients of Dutch origin. Among four NPD type A patients we found two homozygotes for the g.1421C > T (H319Y) and g.3714T > C (Y537H) mutations and two compound heterozygotes, one for the g.3337T > C (F463S) and g.3373C > T (P475L) mutations and the other for the g.84delC (G29fsX74) and g.1208A > C (S248R) mutations. One of the type B patients was homozygous for the g.2629C>T (P371S) mutation. The last two type B patients were homozygotes for the common g.3927_3929delCGC (R608del) mutation. The G29fsX74, S248R, H319Y, P371S, F463S, P475L and Y537H SMPD1 mutations are all novel and were verified by PCR/RFLP and/or ARMS. All of the identified mutations are likely to be rare or private, with the exception of R608del which is prevalent among NPD type B patients from the North-African Maghreb region. Geographical and/or social isolation of the affected families are likely contributing factors for the high number of homozygotes in our group.

The demographics and distribution of type B Niemann-Pick disease: novel mutations lead to new genotype/phenotype correlations

We have collected demographic and/or mutation information on a worldwide sample of 394 patients with type B Niemann-Pick disease (NPD). The disorder is panethnic, with the highest incidence occurring in individuals of Turkish, Arabic, and North African descent. Only five of the 394 patients were Ashkenazi Jewish, revealing that, unlike the type A form of NPD, type B NPD does not occur frequently within this population. Mutation analysis of the acid sphingomyelinase (ASM) gene (designated "SMPD1") was performed on 228 patients (324 unique alleles), and several novel, "common" mutations were found. Among these were the L137P, fsP189, and L549P mutations, which accounted for approximately 75% of the alleles in Turkish patients, the H421Y and K576N mutations, which accounted for approximately 85% of the alleles in Saudi Arabian patients, the S379P, R441X, R474W, and F480L mutations, which accounted for approximately 55% of the alleles in Portuguese/Brazilian patients, and the A196P mutation, which accounted for approximately 42% of the alleles in Scottish/English patients. The previously reported DeltaR608 mutation occurred on approximately 12% of the alleles studied. Overall, a total of 45 novel mutations were found, and several new genotype/phenotype correlations were identified. In particular, the L137P, A196P, and R474W mutations were consistent with a less severe form of type B NPD, whereas the H421Y and K576N mutations led to an early-onset, more severe form that was specific to Saudi Arabia. These data provide the first extensive demographic assessment of this disorder and describe several new mutations that can be used to predict phenotypic outcome and to gain new insights into the structure and function of ASM.

Niemann-Pick disease type C: two cases and an update

We describe two patients with juvenile-onset Niemann-Pick disease type C (NPC) to illustrate the variable neurologic features of this condition. One presented with hypersplenism at age 10 and was misdiagnosed with Gaucher disease. He developed complex partial seizures in his teens but remained otherwise neurologically asymptomatic until his mid 30s. At age 45, he had mild dementia and dysarthria, vertical supranuclear ophthalmoplegia, axonal sensorimotor polyneuropathy, and cerebellar ataxia. The second patient presented with rapidly progressive dystonia at age 8, and mild hepatosplenomegaly, vertical supranuclear ophthalmoplegia, severe behavioral disorder, and dementia by age 14. The diagnosis of NPC was based on deficient cholesterol esterification and excessive lysosomal filipin staining in cultured skin fibroblasts. Current notions about diagnosis and pathogenesis of NPC are reviewed.

Activation of sphingosine kinase by tumor necrosis factor-alpha inhibits apoptosis in human endothelial cells

Human umbilical vein endothelial cells (HUVEC), like most normal cells, are resistant to tumor necrosis factor-alpha (TNF)-induced apoptosis in spite of TNF activating sphingomyelinase and generating ceramide, a known inducer of apoptosis. Here we report that TNF activates another key enzyme, sphingosine kinase (SphK), in the sphingomyelin metabolic pathway resulting in production of sphingosine-1-phosphate (S1P) and that S1P is a potent antagonist of TNF-mediated apoptosis. The TNF-induced SphK activation is independent of sphingomyelinase and ceramidase activities, suggesting that TNF affects this enzyme directly other than through a mass effect on sphingomyelin degradation. In contrast to normal HUVEC, in a spontaneously transformed endothelial cell line (C11) TNF stimulation failed to activate SphK and induced apoptosis as characterized by morphological and biochemical criteria. Addition of exogenous S1P or increasing endogenous S1P by phorbol ester markedly protected C11 cell line from TNF-induced apoptosis. Conversely, N, N-dimethylsphingosine, an inhibitor of SphK, profoundly sensitized normal HUVEC to killing by TNF. Thus, we demonstrate that the activation of SphK by TNF is an important signaling for protection from the apoptotic effect of TNF in endothelial cells.

Niemann-Pick disease: mutation update, genotype/phenotype correlations, and prospects for genetic testing

Niemann-Pick Disease (NPD) is an autosomal recessive lysosomal storage disorder caused by a deficiency of acid sphingomyelinase (ASM). NPD occurs in two forms, neuronopathic Type A and nonneuronopathic Type B. The incidence of Type A NPD is highest among Ashkenazi Jews. Type B NPD is more common in non-Jews but has been reported in Ashkenazi Jews. Different mutations in ASM are presumed to be responsible for the different NPD phenotypes. Three mutations are predicted to account for > 95% of all Type A NPD chromosomes among Ashkenazi Jews (L302P, R496L, fsP330). Based on limited screens for these mutations among Ashkenazi Jews, a carrier frequency for Type A NPD of 1:90 is reported for this population. Less is known about mutations responsible for Type B NPD, although one mutation (delta R608) has been identified in both Ashkenazi Jews and non-Jews. Screening of the Ashkenazi Jewish population to detect > 95% of NPD carriers can be accomplished with a four-mutation panel that includes L302P, R496L, fsP330, and delta R608, the three predominant Type A mutations and one recurrent Type B mutation.

Purification and characterization of a membrane bound neutral pH optimum magnesium-dependent and phosphatidylserine-stimulated sphingomyelinase from rat brain

Sphingomyelin hydrolysis and ceramide generation catalyzed by sphingomyelinases (SMase) are key components of the signaling pathways in cytokine- and stress-induced cellular responses. In this study, we report the partial purification and characterization of the membrane bound, neutral pH optimal, and magnesium-dependent SMase (N-SMase) from rat brain. Proteins from Triton X-100 extract of brain membrane were purified sequentially with DEAE-Sephacel, heparin-Sepharose, ceramic hydroxyapatite, Mono Q, phenyl-Superose, and Superose 12 column chromatography. After eight purification steps, the specific activity of the enzyme increased by 3030-fold over the brain homogenate. The enzyme hydrolyzed sphingomyelin but not phosphatidylcholine and its activity was dependent upon magnesium with an optimal pH of 7.5 and a native pI of 5.2. Delipidation of the enzyme through chromatographic purification or by extraction with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid followed by gel filtration revealed that the enzyme became increasingly dependent on phosphatidylserine (PS). Up to 20-fold stimulation was observed with PS whereas other lipids examined were either ineffective or only mildly stimulatory. The Km of the enzyme for substrate sphingomyelin (3.4 mol %) was not affected by PS. The highly purified enzyme was inhibited by glutathione with a >95% inhibition observed with 3 mM glutathione and with a Hill number calculated at approximately 8. The significance of these results to the regulation of N-SMase is discussed.

The cellular trafficking and zinc dependence of secretory and lysosomal sphingomyelinase, two products of the acid sphingomyelinase gene

The acid sphingomyelinase (ASM) gene, which has been implicated in ceramide-mediated cell signaling and atherogenesis, gives rise to both lysosomal SMase (L-SMase), which is reportedly cation-independent, and secretory SMase (S-SMase), which is fully or partially dependent on Zn2+ for enzymatic activity. Herein we present evidence for a model to explain how a single mRNA gives rise to two forms of SMase with different cellular trafficking and apparent differences in Zn2+ dependence. First, we show that both S-SMase and L-SMase, which contain several highly conserved zinc-binding motifs, are directly activated by zinc. In addition, SMase assayed from a lysosome-rich fraction of Chinese hamster ovary cells was found to be partially zinc-dependent, suggesting that intact lysosomes from these cells contain subsaturating levels of Zn2+. Analysis of Asn-linked oligosaccharides and of N-terminal amino acid sequence indicated that S-SMase arises by trafficking through the Golgi secretory pathway, not by cellular release of L-SMase during trafficking to lysosomes or after delivery to lysosomes. Most importantly, when Zn2+-dependent S-SMase was incubated with SMase-negative cells, the enzyme was internalized, trafficked to lysosomes, and became zinc-independent. We conclude that L-SMase is exposed to cellular Zn2+ during trafficking to lysosomes, in lysosomes, and/or during cell homogenization. In contrast, the pathway targeting S-SMase to secretion appears to be relatively sequestered from cellular pools of Zn2+; thus S-SMase requires exogeneous Zn2+ for full activity. This model provides important information for understanding the enzymology and regulation of L- and S-SMase and for exploring possible roles of ASM gene products in cell signaling and atherogenesis.

Glycogen storage disease type 1a in Israel: biochemical, clinical, and mutational studies

Glycogen storage disease type 1a (von Gierke disease, GSD 1a) is caused by the deficiency of microsomal glucose-6-phosphatase (G6Pase) activity which catalyzes the final common step of glycogenolysis and gluconeogenesis. The recent cloning of the G6Pase cDNA and characterization of the human G6Pase gene enabled the characterization of the mutations causing GSD 1a. This, in turn, allows the introduction of a noninvasive DNA-based diagnosis that provides reliable carrier testing and prenatal diagnosis. In this study, we report the biochemical and clinical characteristics as well as mutational analyses of 12 Israeli GSD 1a patients of different families, who represent most GSD 1a patients in Israel. The mutations, G6Pase activity, and glycogen content of 7 of these patients were reported previously. The biochemical data and clinical findings of all patients were similar and compatible with those described in other reports. All 9 Jewish patients, as well as one Muslim Arab patient, presented the R83C mutation. Two Muslim Arab patients had the V166G mutation which was not found in other patients' populations. The V166G mutation, which was introduced into the G6Pase cDNA by site-directed mutagenesis following transient expression in COS-1 cells, was shown to cause complete inactivation of the G6Pase. The characterization of all GSD 1a mutations in the Israeli population lends itself to carrier testing in these families as well as to prenatal diagnosis, which was carried out in 2 families. Since all Ashkenzai Jewish patients harbor the same mutation, our study suggests that DNA-based diagnosis may be used as an initial diagnostic step in Ashkenazi Jews suspected of having GSD 1a, thereby avoiding liver biopsy.

Zn2+-stimulated sphingomyelinase is secreted by many cell types and is a product of the acid sphingomyelinase gene

Mammalian sphingomyelinases have been implicated in many important physiological and pathophysiological processes. Although several mammalian sphingomyelinases have been identified and studied, one of these, an acidic Zn2+-stimulated sphingomyelinase (Zn-SMase) originally found in fetal bovine serum, has received little attention since its first and only report 7 years ago. We now show that Zn-SMase activity is secreted by human and murine macrophages, human skin fibroblasts, microglial cells, and several other cells in culture and is markedly up-regulated during differentiation of human monocytes to macrophages. Remarkably, peritoneal macrophages from mice in which the acid SMase gene had been disrupted by homologous recombination secreted no Zn-SMase activity, indicating that this enzyme and the intracellular lysosomal SMase, which is Zn-independent, arise from the same gene. Furthermore, skin fibroblasts from patients with types A and B Niemann-Pick disease, which are known to lack lysosomal SMase activity, also lack Zn-SMase activity in their conditioned media. Chinese hamster ovary cells stably transfected with a cDNA encoding lysosomal SMase massively overexpress both cellular lysosomal SMase and secreted Zn-SMase activities. Thus, Zn-SMase arises independently of alternative splicing, suggesting a post-translational process. In summary, a wide variety of cell types secrete Zn-SMase activity, which arises from the same gene as lysosomal SMase. This secreted enzyme may play roles in physiological and pathophysiological processes involving extracellular sphingomyelin hydrolysis.

Acid sphingomyelinase-deficient human lymphoblasts and mice are defective in radiation-induced apoptosis

Stress is believed to activate sphingomyelinase to generate ceramide, which serves as a second messenger in initiating the apoptotic response. Conclusive evidence for this paradigm, however, is lacking. In the present study, we used a genetic approach to address this issue directly. We show that lymphoblasts from Niemann-Pick patients, which have an inherited deficiency of acid sphingomyelinase activity, fail to respond to ionizing radiation with ceramide generation and apoptosis. These abnormalities are reversible up on restoration of acid sphingomyelinase activity by retroviral transfer of human acid sphingomyelinase cDNA. Acid sphingomyelinase knockout mice also expressed defects in radiation-induced ceramide generation and apoptosis in vivo. Comparison with p53 knockout mice revealed that acid sphingomyelinase-mediated apoptosis and p53-mediated apoptosis are likely distinct and independent. These genetic models provide definitive evidence for the involvement of acid sphingomyelinase in one form of stress-induced apoptosis.

Mucopolysaccharidosis type I: identification of common mutations that cause Hurler and Scheie syndromes in Japanese populations

alpha-L-Iduronidase (IDUA) deficiency (mucopolysaccharidosis type I; MPS-I) is an inborn error of lysosomal degradation of glycosaminoglycans that results in storage of undegraded glycosaminoglycans in lysosomes. Previous studies in Caucasian populations showed that (1) homozygosity or compound heterozygosity for the W402X and Q70X mutations are the common causes of MPS-I with a severe form (Hurler syndrome), and (2) the presence of R89Q may lead to a milder phenotype. We studied mutations in the IDUA gene from 19 MPS-I patients, including two pairs of siblings, with various clinical phenotypes (Hurler, 6 cases; Hurler/Scheie, 7 cases; Scheie, 6 cases). We report the presence of two common mutations that account for 42% of the 38 alleles in these patients. One is a novel 5-bp insertion between the thymidine at nt 704 and a cytosine at nt 705 (704ins5), which is seen only in the Japanese population. The other is a missense mutation, R89Q, which is also seen in Caucasians, although uncommonly. In the 19 Japanese MPS-I patients, the 704ins5 mutation accounted for 7 of 38 alleles (18%), while the R89Q accounted for 9 of 38 (24%). No Japanese patient was found to carry the W402X or Q70X alleles, the two most common MPS-I mutations in Caucasians. Homozygosity for the 704ins5 mutation is associated with a severe phenotype, and for the R89Q mutation with a mild phenotype. Compound heterozygosity for these two mutations produced an intermediate phenotype. Haplotype analysis using polymorphisms linked to the IDUA locus demonstrated that each mutation occurs on a different specific haplotype, suggesting that individuals with each of these common mutations derive from common founders. These data continue to document the molecular heterogeneity and racial differences in mutations in MPS-I.