Gaucher disease as a paradigm of current issues regarding single gene mutations of humans

CRISPR Correction of the GBA Mutation in Human-Induced Pluripotent Stem Cells Restores Normal Function to Gaucher Macrophages and Increases Their Susceptibility to Mycobacterium tuberculosis

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the β-glucocerebrosidase (GCase) GBA gene, which result in macrophage dysfunction. CRISPR (clustered regularly interspaced short palindromic repeats) editing of the homozygous L444P (1448T→C) GBA mutation in type 2 GD (GBA-/-) human-induced pluripotent stem cells (hiPSCs) yielded both heterozygous (GBA+/-) and homozygous (GBA+/+) isogenic lines. Macrophages derived from GBA-/-, GBA+/- and GBA+/+ hiPSCs showed that GBA mutation correction restores normal macrophage functions: GCase activity, motility, and phagocytosis. Furthermore, infection of GBA-/-, GBA+/- and GBA+/+ macrophages with the Mycobacterium tuberculosis H37Rv strain showed that impaired mobility and phagocytic activity were correlated with reduced levels of bacterial engulfment and replication suggesting that GD may be protective against tuberculosis.

Genetics of enzymatic dysfunctions in metabolic disorders and cancer

Inherited metabolic disorders arise from mutations in genes involved in the biogenesis, assembly, or activity of metabolic enzymes, leading to enzymatic deficiency and severe metabolic impairments. Metabolic enzymes are essential for the normal functioning of cells and are involved in the production of amino acids, fatty acids and nucleotides, which are essential for cell growth, division and survival. When the activity of metabolic enzymes is disrupted due to mutations or changes in expression levels, it can result in various metabolic disorders that have also been linked to cancer development. However, there remains much to learn regarding the relationship between the dysregulation of metabolic enzymes and metabolic adaptations in cancer cells. In this review, we explore how dysregulated metabolism due to the alteration or change of metabolic enzymes in cancer cells plays a crucial role in tumor development, progression, metastasis and drug resistance. In addition, these changes in metabolism provide cancer cells with a number of advantages, including increased proliferation, resistance to apoptosis and the ability to evade the immune system. The tumor microenvironment, genetic context, and different signaling pathways further influence this interplay between cancer and metabolism. This review aims to explore how the dysregulation of metabolic enzymes in specific pathways, including the urea cycle, glycogen storage, lysosome storage, fatty acid oxidation, and mitochondrial respiration, contributes to the development of metabolic disorders and cancer. Additionally, the review seeks to shed light on why these enzymes represent crucial potential therapeutic targets and biomarkers in various cancer types.

Neurogenetic motor disorders

Advances in the field of neurogenetics have practical applications in rapid diagnosis on blood and body fluids to extract DNA, obviating the need for invasive investigations. The ability to obtain a presymptomatic diagnosis through genetic screening and biomarkers can be a guide to life-saving disease-modifying therapy or enzyme replacement therapy to compensate for the deficient disease-causing enzyme. The benefits of a comprehensive neurogenetic evaluation extend to family members in whom identification of the causal gene defect ensures carrier detection and at-risk counseling for future generations. This chapter explores the many facets of the neurogenetic evaluation in adult and pediatric motor disorders as a primer for later chapters in this volume and a roadmap for the future applications of genetics in neurology.

Metabolizing profile of the cytochrome pathway CYP2D6, CYP3A4 and the ABCB 1 transporter in Spanish patients affected by Gaucher disease

Several therapeutic options are available for type 1 Gaucher disease (GD1), including enzymatic replacement therapy (ERT) and substrate reduction therapy (SRT). Eliglustat is a selective inhibitor of glucosylceramide synthase that is extensively metabolized by CYP2D6 and, to a lesser extent by CYP3A4; it is also an inhibitor of the P-gp transporter. The aim of this study is to evaluate the metabolizer profile of these cytochrome isoforms in 61 GD1 patients, and to analyze interferences with concomitant therapies. Patients were selected from the Spanish Gaucher Disease Registry considering clinical data, GBA genotype, severity score index, comorbidities, concomitant drugs, type and response to therapy and adverse effects. The polymorphisms of CYP2D6, CYP3A4 and three ABCB1 transporter variants were analyzed by Polymerase Chain Reaction (PCR). The most frequent metabolizer profile was extensive or intermediate for CYP2D6, extensive for CYP3A4*1B and CYP3A4*22 and normal activity for ABCB1. Correlations between metabolizer profile and other variables were analyzed by multiple regression study. Twenty-eight patients received ERT, 17 eliglustat and seven miglustat. Forty-two patients (68.8%) had associated diseases and 54.5% were taking daily concomitant medication. Nine patients under eliglustat therapy received concomitant drugs that interact with the CYPs and/or ABCB1, five of these did not reach therapeutic goals and three presented mild or moderate adverse effects (headache and gastrointestinal disorders). Detailed analysis in four patients with TTT haplotype, corresponding to lack of activity of the transporter, was performed. In order to apply personalized medicine and avoid interferences and adverse effects, the individual CYP metabolizer profile and transporter must be considered when choosing the concomitant medication and/or making dose adjustments.

Gaucher Disease Type I: A Case Report

Gaucher disease (GD) is a multi-systemic disease with a low population frequency. It is a lysosomal storage disorder (LSD) that causes accumulation of glucocerebroside in the so called Gaucher cells predominantly in areas like the spleen, liver and bone marrow. Type I GD (GDI) is the most common form and usually does not involve the brain and the spinal cord. The symptoms can range from mild to severe and may appear anytime from childhood to adulthood. Diagnostics can often be challenging and imposes looking at person’s medical history, symptoms, physical exam, and laboratory test results. We present a difficult to diagnose case of a 34-year-old woman admitted to the Clinic of Hematology, “Sv. I. Rilski” hospital with splenomegaly, normal laboratory findings and non-enlarged liver. She didn’t show focal neurological symptoms. A series of tests were assigned including genetic targeted analysis. The case is an example of a rare genetic disease with mild clinical symptoms. Diagnosis of Gaucher disease, type I was confirmed by measurement of a GBA enzyme activity and identification of mutations in the GBA gene inherited in an autosomal recessive manner. Thanks to the efforts of the clinical team, the assignment of adequate clinical and laboratory tests and their correct interpretation, the patient was subjected to enzyme replacement therapy (ERT). Although the diagnosis was settled relatively late (at 34 years of age), the correct therapy slowed down the invalidation and improved the quality of life of the patient.

Clinical phenotype features and genetic etiologies of 38 children with progressive myoclonic epilepsy

Background

Progressive myoclonic epilepsy (PME) is a group of neurodegenerative diseases with genetic heterogeneity and phenotypic similarities, and many cases remain unknown of the genetic causes. This study is aim to summarize the clinical features and study the genetic causes of PME patients.

Methods

Sanger sequencing of the target gene, Next Generation Sequencing (NGS) panels of epilepsy, trio-based Whole Exome Sequencing (WES) and detection of cytosine-adenine-guanine (CAG) repeat number were used to investigate the genetic causes of PME patients.

Results

Thirty-eight children with PME whose seizure onset age ranged from 3 months to 12 years were collected from February 2012 to November 2019 in three hospitals in Beijing, China. The seizure types included myoclonic seizures (n = 38), focal seizures (n = 19), generalized tonic-clonie seizure (GTCS) (n = 13), absence seizures (n = 4), atonic seizures (n = 3), epileptic spasms (n = 2) and tonic seizures (n = 1). Twenty-seven cases were sporadic and 11 had family members affected. Established PME-related genes were identified in 30 out of 38 (78.9%) patients who had either recessively inherited or de novo heterozygous mutations. Among these 30 cases, there were 12 cases (31.6%) of neuronal ceroid lipofuscinoses (the causing gene contains TPP1, PPT1, CLN5, CLN6 and MFSD8), two cases of sialidosis (the causing gene is NEU1), two cases of neuronopathic Gaucher disease (the causing gene is GBA), one case of spinal muscular atrophy-progressive myoclonic epilepsy (the causing gene is ASAH1), four cases of KCNC1 mutation-related PME, four cases of KCTD7 mutation-related PME, two cases of TBC1D24 mutation-related PME, one case of GOSR2 related PME, and two of dentatorubral-pallidoluysian atrophy (the causing gene is ATN1). In total, 13 PME genes were identified in our cohort. The etiology was not clear in eight patients.

Conclusion

PME is a group of clinically and genetically heterogeneous diseases. Genetic diagnosis was clear in 78.9% of PME patients. Various of genetic testing methods could increase the rate of genetic diagnosis. Neuronal ceroid lipofuscinoses (NCL) is the most common etiology of PME in children. Nearly one third PME children were diagnosed with NCL. GOSR2 related PME was in our cohort in Asia for the first time.

Ethical issues in managing Lysosomal storage disorders in children in low and middle income countries

The lysosomal storage diseases are a group of rare, inherited metabolic diseases affecting about 1 in 7000 to 8000 people. In recent years, the introduction of enzyme replacement therapy, substrate reduction therapy and small molecule therapy, has changed the natural course of this otherwise progressive group of disorders leading to severe morbidity and early mortality. These treatment options, however, are extremely expensive and are needed for life thus presenting an economical as well as ethical challenge to the affected families and the health care system of a country. This paper presents a case for the prevention of the lysosomal storage disorders as a model for other inherited metabolic disorders in the form of antenatal testing and cascade screeningfor couples and families at risk of having affected off-springs and compares it to the cost incurred on the enzyme replacement therapy in the backdrop of the health care prioritiesof Pakistan, a low middle income country. Similar economic and ethical challenges are faced by most low and middle income countries. The literature search was done using Pubmed and Clinical trials databases using key words: “Lysosomal storage disorders”, “natural course”, “ethics”, “cascade screening”, “Thalassemia” and “cascade screening”. A total of 225 articles in English language were scanned from 1980-2016, 80 articles describing the natural course of LSD with and without ERT, ethical issues related to the treatment of LSD and strategies employed for the prevention of genetic disorders were prioritized.

Gaucher disease and comorbidities: B-cell malignancy and parkinsonism

Data emerging from the International Collaborative Gaucher Group (ICGG) Gaucher Registry together with other contemporary clinical surveys have revealed a close association between Gaucher disease and non-Hodgkin's B-cell lymphoma and myeloma and Gaucher disease and Parkinson's disease. Several possible explanations for increased B-cell proliferation and neoplasia in Gaucher disease have been proposed, including the possible influence of sphingosine (derived from the extra lysosomal metabolism of glucosylceramide), gene modifiers, splenectomy and immune system deregulation induced by cytokines, chemokines, and hydrolases released from Gaucher cells. Parkinson's disease is frequently seen in the otherwise-healthy relatives of Gaucher disease patients leading to the finding that GBA mutations represent a genetic risk factor for Parkinson's disease. The mechanism of the association between GBA mutations and Parkinson's disease has yet to be elucidated but the pathogenesis appears distinct from that of Gaucher disease. Several pathogenic pathways have been proposed including lysosomal and/or mitochondrial dysfunction. The effect of Gaucher disease specific therapies on the incidence of cancer or Parkinson's disease are not clear and will likely be evaluated in future ICGG Gaucher Registry studies.

Gaucher disease and malignancy: a model for cancer pathogenesis in an inborn error of metabolism

Clinical observations spanning almost half a century have demonstrated a consistent association of type 1 Gaucher disease (GD1) and cancers. However, the cellular and molecular bases of the association are not understood. Gaucher disease (GD) is a lysosomal storage disorder due to an inherited deficiency of acid β-glucosidase that underlies the accumulation of glucosylceramide in lysosomes of mononuclear phagocytes and immune dysregulation. The overall cancer risk is markedly increased in GD, and the determinants of malignancy in a subset of patients with GD1 are not known. The association of GD and cancer is most striking for hematological malignancies, with the risk for multiple myeloma estimated at almost 37-fold compared to the general population; some studies have also suggested increased cancer risk for non-hematological malignancies. There is no association of overall severity of GD to risk of cancer, although there is an increased prevalence of splenectomy among patients exhibiting the GD/cancer phenotype. Moreover, there appears to be an increased incidence of multiple consecutive cancers in individual patients. Several factors could contribute to cancer development in GD, including polarization of macrophages to the alternatively activated phenotype, chronic inflammation, chronic B-cell stimulation, splenectomy, hyperferritinemia, lysosomal dysfunction, and endoplasmic reticulum stress. Recent studies have highlighted T-cell dysfunction and modifier genes contributing to an increased cancer risk in GD. Macrophage-targeted enzyme replacement therapy (ERT) reverses systemic features of GD1; while cancer risk appears to be reduced in the era of ERT, it is not known whether this is a direct effect of therapy. Delineation of the mechanisms underlying the increased cancer risk in GD will provide additional novel insights into the role of lipids and macrophages in cancer pathogenesis and, moreover, have the potential to reveal novel therapeutic targets.

Generation of a Chinese hamster ovary cell line producing recombinant human glucocerebrosidase

Impaired activity of the lysosomal enzyme glucocerebrosidase (GCR) results in the inherited metabolic disorder known as Gaucher disease. Current treatment consists of enzyme replacement therapy by administration of exogenous GCR. Although effective, it is exceptionally expensive, and patients worldwide have a limited access to this medicine. In Brazil, the public healthcare system provides the drug free of charge for all Gaucher's patients, which reaches the order of $ 84 million per year. However, the production of GCR by public institutions in Brazil would reduce significantly the therapy costs. Here, we describe a robust protocol for the generation of a cell line producing recombinant human GCR. The protein was expressed in CHO-DXB11 (dhfr⁻) cells after stable transfection and gene amplification with methotrexate. As expected, glycosylated GCR was detected by immunoblotting assay both as cell-associated (~64 and 59 kDa) and secreted (63–69 kDa) form. Analysis of subclones allowed the selection of stable CHO cells producing a secreted functional enzyme, with a calculated productivity of 5.14 pg/cell/day for the highest producer. Although being laborious, traditional methods of screening high-producing recombinant cells may represent a valuable alternative to generate expensive biopharmaceuticals in countries with limited resources.

Synthesis of N-substituted ε-hexonolactams as pharmacological chaperones for the treatment of N370S mutant Gaucher disease

A series of N-substituted ε-hexonolactams have been designed and prepared by a concise route with a tandem ring-expansion reaction as the key step. Some of the N-substituted ε-hexonolactams show better enhancements to N370S mutant β-glucocerebrosidase activity than NB-DNJ and NN-DNJ. Both the experimental results and computational studies highlight the importance of the carbonyl group for stabilizing protein folds in the mutant enzyme. The structure-activity relationships are also discussed. These novel N-alkylated iminosugars are promising pharmacological chaperones for the treatment of N370S mutant Gaucher disease.

Decreased glucocerebrosidase activity in Gaucher disease parallels quantitative enzyme loss due to abnormal interaction with TCP1 and c-Cbl

Gaucher disease (GD), the most common lysosomal storage disorder of humans, is caused by mutations in the gene coding for the enzyme glucocerebrosidase (GCase). Clinical manifestations vary among patients with the three types of GD, and phenotypic heterogeneity occurs even among patients with identical mutations. To gain insight into why phenotypic heterogeneity occurs in GD, we investigated mechanisms underlying the net loss of GCase catalytic activity in cultured skin fibroblasts derived from patients with the three types of GD. The findings indicate that the loss of catalytic activity of GCase correlates with its quantitative reduction, rather than a decrease in functional capacity of mutant enzyme. Use of a proteasome inhibitor, lactacystin, resulted in increased expression of GCase, suggesting a mechanism of protein degradation in GD. Furthermore, reduced binding of GCase to TCP1 ring complex (TRiC), a regulator of correct protein folding, may result in defective maturation of nascent GCase in GD cells. Additionally, increased interaction between GCase and c-Cbl, an E3 ubiquitin ligase, may be involved in the degradation and loss of GCase in GD. The findings suggest that specific molecular mediators involved in GCase maturation and degradation could be responsible for phenotypic variation among patients with the same genotypes and that these mediators could be therapeutically targeted to increase GCase activity in patients with GD.

Glucocerebroside: an evolutionary advantage for patients with Gaucher disease and a new immunomodulatory agent

Gaucher disease (GD) is caused by the reduced activity of a lysosomal enzyme, glucocerebrosidase, leading to the accumulation of glucocerebroside (GC). The relatively high prevalence of this disease within an ethnic group is believed to reflect a selective advantage. Treatment with enzyme replacement therapy (ERT) is safe and effective in ameliorating the primary symptoms of the disease, yet there have been reports that some patients on ERT have developed type 2 diabetes or metabolic syndrome, malignancies and central nervous system disorders. A series of animal studies suggest that these complications may be related to the reduction of GC levels by the enzyme administered. GC has been shown to have an immunomodulatory effect through the promotion of dendritic cells, natural killer T cells, and regulatory T cells. The break down of GC to ceramide can underline part of these findings. Clinical trials suggested a beneficial effect of GC in type 2 diabetes or nonalcoholic steatohepatitis. This review of the data from animal models and humans proposes that the increased level of GC may provide an evolutionary advantage for patients with GD. Indirectly, these data support treating symptomatic patients with mild/moderate GD with low-dose ERT and re-evaluating the use of ERT in asymptomatic patients.

Consequences of diagnostic delays in type 1 Gaucher disease: the need for greater awareness among hematologists-oncologists and an opportunity for early diagnosis and intervention

Gaucher disease (GD) is a progressive macrophage lipidosis capable of causing disabling and life-threatening complications. Anecdotal experiences suggest that GD may go undiagnosed for many years, leading to severe complications that are preventable or reversible by enzyme replacement therapy (ERT) with imiglucerase. We conducted surveys of patients and Hematology-Oncology specialists to assess the frequency of diagnostic delays. Additionally, we report a series of patients who suffered diagnostic delays and as a result developed disabilities including potentially life-threatening manifestations of GD. Of 136 patients surveyed, the average time from first appearance of GD symptoms to final diagnosis was 48.7 +/- 123.6 months. More than two-thirds were evaluated and managed by a hematologist-oncologist (Hem-Onc). A global survey of 406 Hem-Oncs found that only 20% considered GD in the differential diagnosis for all of its classic symptoms (cytopenia, hepatosplenomegaly, bone pain); the diagnosis considered most likely included leukemia, lymphoma, and multiple myeloma. To illustrate actual consequences of diagnostic delays, we describe 14 patients with GD who suffered from symptoms for up to 10 years before correct diagnosis. Diagnostic delays led to complications that are preventable or reversible with ERT (i.e., avascular necrosis, severe bleeding, chronic bone pain, life-threatening sepsis, pathologic fractures, growth failure, liver pathology). Patients homozygous for N370S mutation in this series were vulnerable to diagnostic delays. In conclusion, prolonged diagnostic delays occur in GD and may result in severe disease manifestations. Our findings suggest that physician education will increase the likelihood of prompt detection of GD and improve its management with ERT with imiglucerase when indicated.

Ashkenazi Jews and breast cancer: the consequences of linking ethnic identity to genetic disease

We explored the advantages and disadvantages of using ethnic categories in genetic research. With the discovery that certain breast cancer gene mutations appeared to be more prevalent in Ashkenazi Jews, breast cancer researchers moved their focus from high-risk families to ethnicity. The concept of Ashkenazi Jews as genetically unique, a legacy of Tay-Sachs disease research and a particular reading of history, shaped this new approach even as methodological imprecision and new genetic and historical research challenged it. Our findings cast doubt on the accuracy and desirability of linking ethnic groups to genetic disease. Such linkages exaggerate genetic differences among ethnic groups and lead to unequal access to testing and therapy.

Lysosomal storage diseases: natural history and ethical and economic aspects

Potential treatment for lysosomal diseases now includes enzyme replacement therapy, substrate reduction therapy, and chaperone therapy. The first two of these have been implemented commercially, and the spectrum of diseases that are now treatable has expanded from Gaucher disease to include several other disorders. Treatment of these diseases is extremely costly. We explore some of the reasons for the high cost and discuss how, by proper selection of patients and appropriate dosing, the economic burden on society of treating these disease may be ameliorated, at least in part. However, the cost of treating rare diseases is a growing problem that society needs to address.

Secretion of human glucocerebrosidase from stable transformed insect cells using native signal sequences

The lysosomal hydrolase, glucocerebrosidase (GBA), catalyses the penultimate step in the breakdown of membrane glycosphingolipids. An inherited deficiency of this enzyme activity leads to the onset of Gaucher disease, the most common lysosomal storage disorder. Affected individuals range from adults with hepatosplenomegaly, haematological complications, and bone pain (type 1 disease) to children and neonates with severe neuronopathy leading to neurological degradation and premature death (type 2 and type 3 disease). Enzyme replacement therapy has become the standard of treatment for type I Gaucher disease but remains an expensive option, in part because of the cost of recombinant enzyme production using mammalian cell culture. Using a nonlytic integrative plasmid expression system, we have successfully produced active human GBA in stable transformed Sf9 (Spodoptera frugiperda) cells. Both the 39 and 19 amino acid native GBA signal sequences were capable of endoplasmic reticulum targeting, which led to secretion of the recombinant protein, although approximately 30% more enzyme was produced using the longer signal sequence. The secreted product was purified to apparent electrophoretic homogeneity using hydrophobic interaction chromatography and found to be produced in a fully glycosylated and a hypoglycosylated form, both of which cross-reacted with a human GBA-specific monoclonal antibody. The pH optimum (at pH 5.5) for activity of the recombinant enzyme was as expected for human GBA using the artificial substrate 4-methyl-umbelliferyl-β-D-glycopyranoside. With initial nonoptimized expression levels estimated at 10–15 mg/L using small-scale batch cultures, stable transformed insect cells could provide a viable alternative system for the heterologous production of human GBA when grown under optimized perfusion culture conditions.Key words: Gaucher disease, glucocerebrosidase, protein expression, enzyme purification, Sf9 cells.

Storage solutions: treating lysosomal disorders of the brain

Many neurodegenerative diseases are characterized by the accumulation of undegradable molecules in cells or at extracellular sites in the brain. One such family of diseases is the lysosomal storage disorders, which result from defects in various aspects of lysosomal function. Until recently, there was little prospect of treating storage diseases involving the CNS. However, recent progress has been made in understanding these conditions and in translating the findings into experimental therapies. We review the developments in this field and discuss the similarities in pathological features between these diseases and some more common neurodegenerative disorders.

Phenotypic Heterogeneity in Patients with Gaucher Disease and the N370S/V394L Genotype

Correlation between genotype and phenotype in Gaucher disease is limited. It is known that the most common mutation N370S is protective of neurological involvement, but for the V394L mutation, described as the fifth most common among Ashkenazi Jews, little data are available. This study reports all known patients from a large referral clinic and from the international registry with Gaucher disease who are documented to have the N370S/V394L genotype. Of 476 patients in the Gaucher Clinic, 7 patients (2.0%) had the N370S/V394L genotype; of 2,836 patients in the registry, there were 14 patients (0.8%) with this genotype. There was an overlap of 3 patients, making a total of 18 patients, reflecting the rarity of this genotype among the studied cohorts. Most of these patients had mild disease; only 8 patients required specific enzyme therapy, none was splenectomized. Only 3 patients had skeletal involvement, but other baseline parameters were very diverse. Although genotype-phenotype correlation in this case may be difficult, because the V394L mutation when seen in a compound heterozygote with a null allele results in neuronopathic disease, one cannot conclude that this mutation is protective of neuronopathic disease and hence this is important for counseling of at-risk populations.

Comparative and genetic analysis of the porcine glucocerebrosidase (GBA) gene

The genomic sequence of the porcine (Sus scrofa) glucocerebrosidase (GBA) gene (approximately 5.7 kb), encoding glucocerebrosidase (glucosylceramidase; acid beta-glucosidase; EC 3.2.1.45), was determined and compared with human (Homo sapiens) GBA and GBAP (pseudogene). The porcine gene harbours 11 exons and 10 introns, and the genomic organization is identical with human GBA. The exon sequences, coding for signal peptide and mature protein, show 81% and 90% sequence identity, respectively, with the corresponding human GBA sequences. Short interspersed elements, SINEs (PREs), are present in introns 2, 4 and 7. There is no evidence of a pseudogene in pig. The deduced protein sequence of GBA consists of 39 amino acids of signal peptide (long form) and 497 amino acids of the mature protein; the latter shows 90% sequence identity with the human protein. Four polymorphisms were observed within the porcine gene: insertion/deletion of one of the two SINEs (PREs) in intron 2 (locus PREA); deletion of a 37- to 39-bp stretch in intron 4 (one direct repeat and 5' end of PRE); deletion of a 47-bp stretch in the middle part of PRE in intron 4 (locus PREB); and single-base transition (C-T) in intron 6 (locus HaeIII-RFLP). GBA was assigned to chromosome 4q21 by FISH and was localized to the same region by linkage analysis and RH mapping, i.e., to the chromosome 4 segment where quantitative trait loci for growth and some carcass traits are located.

Pediatric non-neuronopathic Gaucher disease: presentation, diagnosis and assessment. Consensus statements

Gaucher disease is caused by defective activity of glucocerebrosidase. The resulting accumulation of glucocerebroside in the lysosomes of visceral macrophages in various tissue and organ compartments leads to multiple manifestations, including hepatosplenomegaly, anemia, thrombocytopenia, growth retardation and skeletal disease. The most prevalent form of Gaucher disease is the non-neuronopathic (type 1) variant, which lacks primary involvement of the central nervous system. Traditionally, this has been referred to as the 'adult type'; however, 66% of individuals with symptomatic non-neuronopathic Gaucher disease manifest in childhood. Onset in childhood is usually predictive of a severe, rapidly progressive phenotype and children with non-neuronopathic Gaucher disease are at high risk for morbid complications. Enzyme therapy with recombinant human glucocerebrosidase in childhood can restore health in reversible manifestations and prevent the development of irreversible symptoms. A heightened focus on pediatric Gaucher disease is therefore needed. Although some correlation has been found between genotype and phenotype, mutation analysis is of limited value in disease prognosis. Management of pediatric Gaucher disease should be underpinned by a thorough assessment of the phenotype at baseline with regular monitoring thereafter. Excluding neuronopathic disease is recommended as the first step. Subsequently, baseline evaluation should focus on staging of different storage tissues, particularly the bone the involvement of which results in the greatest long-term morbidity. These organ assessments are recommended because bone disease severity may not correlate with disease severity in other organs and vice versa. In addition, different organs may respond differently to therapy. Initial assessment of each organ system can enable setting of realistic and individualized goals.

CONCLUSION

A thorough approach to baseline assessment will improve the understanding of childhood Gaucher disease, optimizing management to minimize impairment of growth and development and prevent irreversible symptoms.

Patterns of human genetic diversity: implications for human evolutionary history and disease

Since the completion of the human genome sequencing project, the discovery and characterization of human genetic variation is a principal focus for future research. Comparative studies across ethnically diverse human populations and across human and nonhuman primate species is important for reconstructing human evolutionary history and for understanding the genetic basis of human disease. In this review, we summarize data on patterns of human genetic diversity and the evolutionary forces (mutation, genetic drift, migration, and selection) that have shaped these patterns of variation across both human populations and the genome. African population samples typically have higher levels of genetic diversity, a complex population substructure, and low levels of linkage disequilibrium (LD) relative to non-African populations. We discuss these differences and their implications for mapping disease genes and for understanding how population and genomic diversity have been important in the evolution, differentiation, and adaptation of humans.

Proposal for an allele nomenclature system based on the evolutionary divergence of haplotypes

The classical view of what constitutes an "allele" has been challenged by recent findings of a great deal of human genetic variability, i.e., we can expect, on average, one variant site every 100-250 bases of our haploid genome. The haplotype is defined as "the patterns of co-occurrence of variant sites on the same chromosome" (and therefore within each particular gene). Sufficient evidence exists for the divergence of haplotypes during evolution of Homo sapiens sapiens, and the total number of haplotypes per gene will reflect the amount of time any particular ethnic group has existed on the planet, e.g., greatest in Africans, fewer in East Asians, and still fewer in Caucasians. If the average gene spans 30 kb, we can expect approximately 170 polymorphic variant sites per gene in the world population. We do not see 2(170) haplotypes, however; we might find only 10 to 200 haplotypes (depending on the gene's size and degree of conservation of the gene product). This finite number allows for a reasonable haplotype nomenclature system for each gene, based on evolutionary divergence. For polymorphic variants (i.e., frequency > or = 0.01), I propose using Arabic numerals for the major clades (e.g., *1, *2, em leader *20, *21), capital letters for sublineages (e.g., *2A, *2B, *2C), and Arabic numerals for sub-sublineages (e.g., *22G12, *22G13); additional subcategories may be added, in an alternating number/letter/number/letter sequence, depending on the complexity of present-day haplotypes of a particular gene. Web sites with a web master and external advisory committee should be set up for each gene superfamily, family, or individual gene (depending on complexity), and an international haplotype nomenclature committee, perhaps comprised of several dozen of these web masters, should oversee haplotype nomenclature for the entire human genome. The higher heterozygosity and multiallelic nature makes haplotypes more informative than biallelic SNPs. Ultimately, our knowledge of haplotype patterns, rather than single variant sites, of perhaps several hundred genes will likely be helpful in finding associations between genotype and any multiplex phenotype (e.g., complex diseases including cancer, and/or toxicity of pharmaceutical agents or environmental pollutants).

Skeletal aspects of Gaucher disease: a review

In Gaucher disease, a genetic deficiency in the activity of the lysosomal enzyme beta-glucocerebrosidase (acid beta-glucosidase) causes monocytes and macrophages to store excessive amounts of glucocerebroside in lysosomes. The resulting distended cells are called Gaucher cells, and the pathology associated with this condition stems from the accumulation of Gaucher cells in organ systems. The skeletal manifestations are probably the most disabling aspect of the disease. Patients commonly experience bone pain, some suffer bone crises, and up to 20% have impaired mobility. Radiological findings include Erlenmeyer flask deformity, osteopenia, osteosclerosis, osteonecrosis, fractures and bone marrow infiltration. Findings from the Gaucher Registry show that nearly all patients with Gaucher disease have radiological evidence of skeletal involvement, and the majority have a history of serious skeletal complications. Skeletal involvement follows three basic processes: focal disease (irreversible lesions such as osteonecrosis and osteosclerosis), local disease (reversible abnormalities adjacent to heavily involved marrow such as cortical thinning and long bone deformity) and generalized osteopenia. Infarctions are involved in some of the skeletal manifestations, but the mechanisms causing high rates of bone turnover and failure of remodelling are not known. The availability of a beta-glucocerebrosidase-deficient mouse model of Gaucher disease with long-term survival should help elucidate the skeletal pathology in Gaucher disease and may ultimately lead to improved management of skeletal complications.

Evaluation of the positional candidate gene CHRNA7 at the juvenile myoclonic epilepsy locus (EJM2) on chromosome 15q13-14

A previous study of 34 nuclear pedigrees segregating juvenile myoclonic epilepsy (JME) gave significant evidence of linkage with heterogeneity to marker loci on chromosome 15q13-14 close to the candidate gene CHRNA7 (Hum. Mol. Genet. 6 (1997) 1329). The aim of this work was to further evaluate the putative aetiological role of CHRNA7 in JME within the 34 families originally described, and to assess the contribution of this locus to a broader phenotype of idiopathic generalised epilepsy (IGE). Multipoint linkage analysis and intrafamilial association studies were performed with microsatellite markers that encompass both CHRNA7 and its partial duplication (CHRFAM7A). A maximum HLOD of 3.45 [alpha=0.58; (Zall=2.88, P=0.0008)] was observed 8 cM distal to D15S1360, a CHRNA7 intragenic marker. Significant exclusion lod scores were obtained across the region in 12 mixed phenotype JME/IGE families. Mutation screening of the CHRNA7 gene (and consequently exons 5-10 of CHRFAM7A) and its putative promoter sequence identified a total of 13 sequence variants across 23 of 34 JME-affected families. Two variants (c.1354G>A and c.1466C>T) are predicted to result in amino acid changes and one (IVS9+5G>A) is predicted to result in aberrant transcript splicing. However, none of the variants alone appeared either necessary or sufficient to cause JME in the families in which they occurred. In conclusion, linkage analyses continue to support the existence of a locus on chromosome 15q13-14 that confers susceptibility to JME but not to a broader IGE phenotype. Causal sequence variants in the positional candidate CHRNA7 have not been identified but the presence of multiple segmental duplications in this region raises the possibility of undetected disease-causing genomic rearrangements.

Systematic approach to the diagnosis of lysosomal storage disorders

Disorders that arise as a result of lysosomal dysfunction represent some of the most challenging diagnostic problems in medicine. Not only are these disorders infrequently seen, but they may also present with signs and symptoms that mimic perinatal injury, food intolerance, or the sequellae of neonatal infection. Misidentification can lead to significant delay in diagnosis. Ironically, as the prevailing economic climate places increasing time constraints on practicing physicians, medical research is providing treatment strategies and management techniques that are most effective if applied early in the course of the disease. Most lysosomal storage disorders can now be definitively diagnosed once the signs are recognized. In many cases the benefits of early diagnosis, enlightened management, and appropriate referral are considerable. The aim of this paper is to demystify this elusive class of diseases, to promote clinical vigilance in their detection, and to provide a systematic approach to diagnosis when clinical suspicion is aroused.

A genome scan for type 2 diabetes susceptibility loci in a genetically isolated population

A total of 896 individuals of Ashkenazi Jewish descent were ascertained in Israel from 267 multiplex families, including 472 sib-pairs affected with type 2 diabetes. A genome-wide scan with average marker spacing of 9.5 cM revealed five regions on four chromosomes (4q, 8q, 14q, and 20q) that exhibited nominal evidence for linkage (P < 0.05). The highest observed nonparametric linkage Z score was 2.41 (equivalent to a logarithm of odds score of 1.26) at marker D4S1501. A maximal signal, with a Z score of 2.05, was observed on chromosome 20 near marker D20S195, and another on 20p near marker D20S103 (Z 1.80). A single marker on chromosome 8 (D8S593) and two adjacent markers on chromosome 14 (D14S749 and D14S605) also attained evidence of linkage. To explore the hypothesis that the signals on chromosomes 4 and 20 are differentially attributable to variation in BMI or age of onset, an ordered subset analysis was conducted. This analysis revealed that only when the families were ranked by BMI (in increasing order) did a subset attain nominal significance, and only for chromosome 4. The findings reported here lend credence to the hypothesis, now supported by four studies of Caucasian populations and most recently by a combined analysis of 1,852 pedigrees, that a type 2 diabetes susceptibility locus resides on chromosome 20q. This population, because of its unique genetic attributes, may facilitate identification of this and other genes contributing to type 2 diabetes.

Mutational analysis of patients with p47-phox-deficient chronic granulomatous disease: The significance of recombination events between the p47-phox gene (NCF1) and its highly homologous pseudogenes

OBJECTIVE

The aim of this study was to determine the molecular basis of p47-phox-deficient chronic granulomatous disease (CGD), the most common autosomal recessive form of the disease. CGD is an inherited condition characterized by defective oxygen radical production due to defects in the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Mutational analysis of p47-phox-deficient CGD patients previously demonstrated that the majority of patients have a GT dinucleotide (Delta GT) deletion at the start of exon 2, a signature sequence also observed in the highly homologous pseudogenes of NCF1.

MATERIALS AND METHODS

We performed genetic analysis of NCF1 and its pseudogenes using genomic DNA in 29 p47-phox-deficient CGD patients from 22 separate families. First-strand cDNA analysis was performed in 17 of the 29 patients.

RESULTS

We confirmed the significance of the Delta GT mutation; in 27 of 29 patients, only the Delta GT sequence was detectable. All but one of the 27 had at least one additional signature sequence, specific to the pseudogene, in either intron 1 and/or intron 2. We extended our analysis to look at signature sequence differences in exons 6 and 9 and detected both the wild-type and pseudogene sequences in all patients tested.

CONCLUSIONS

Although detection of only Delta GT sequence accounts for over 85% of affected patients, the molecular basis is most likely due to partial cross-over events between the wild-type and pseudogene(s) of p47-phox at different recombination sites. Our results suggest that complete gene conversion or deletion of the p47-phox gene (NCF1) occurs rarely, if it all.

Gene conversion-like missense mutations in the human cationic trypsinogen gene and insights into the molecular evolution of the human trypsinogen family

Over the past decade, gene conversion has been shown increasingly to be a cause of human disease. Through this process, a functional gene is converted into a mutant by a homologous, nonfunctional one. In this article, we demonstrate that gene conversion is a likely cause of the mutations of the human cationic trypsinogen (PRSS1) gene that are associated with hereditary or sporadic pancreatitis, including the R122H (CGC>CAT: c.365-366 GC>AT), N29I (AAC>ATC: c.86A>T), and A16V (GCC>GTC: c.47C>T) missense mutations. This hypothesis is strongly supported by four lines of observation. First, human group I trypsinogen genes are tandemly repeated and share a high sequence homology between them. Secondly, a possible donor sequence for each variant is present in the PRSS1 gene's paralog(s). Thirdly, there exist uninterrupted sequence tracts ranging from 30 to 114 bp in the putatively converted regions. Finally, Chi-like and palindromic sequences are found in the vicinity of these missense mutations. This theory, if correct, will make the pancreatitis-associated PRSS1 mutations a unique example, as it shows that a functional gene may be converted by several paralogs, and that such an event may even occur between two functional genes (i.e., the N29I mutation), resulting in disease. This adds further to the diversity of genetic mechanisms underlying human disease. In addition, this genetic finding provides, for the first time, concrete evidence of the contribution made by gene conversion to the molecular evolution of the human trypsinogen family.

Treatment of a lysosomal storage disease, mucopolysaccharidosis VII, with microencapsulated recombinant cells

Most lysosomal enzyme deficiencies are catastrophic illnesses with no generally available treatments. We have used the beta-glucuronidase-deficient mouse model of mucopolysaccharidosis type VII (MPS VII) to develop an alternative approach to therapy. A "universal" cell line engineered to secrete the missing enzyme is implanted in all recipients requiring the same enzyme replacement. The cells, although nonautologous, are rendered immunologically tolerant by encapsulation in microcapsules that provide protection from immune mediators. Using this strategy, we injected beta-glucuronidase-secreting fibroblasts enclosed in alginate microcapsules into mutant MPS VII mice. After 24 hr, beta-glucuronidase activity was detected in the plasma, reaching 66% of physiological levels by 2 weeks postimplantation. Significant beta-glucuronidase activity was detected in liver and spleen for the duration of the 8-week experiment. Concomitantly, the intralysosomal accumulation of undegraded glycosaminoglycans was dramatically reduced in liver and spleen tissue sections and urinary glycosaminoglycan content was reduced to normal levels. Elevated secondary lysosomal enzymes beta-hexosaminidase and alpha-galactosidase were also reduced. However, implanted mutant MPS VII mice developed antibodies against the murine beta-glucuronidase, demonstrating a potential obstacle in patients with a null mutation who react against the replaced enzyme as a foreign antigen. The antibody response was transiently circumvented with a single treatment of purified anti-CD4 antibody coadministered with the microcapsules. This resulted in increased levels and duration of beta-glucuronidase delivery. Similarly, treated heterozygous mice maintained elevated levels of beta-glucuronidase and did not develop antibodies. This novel cell-based therapy demonstrates a potentially cost-effective and nonviral treatment applicable to all lysosomal storage diseases.

Sphingolipids

A significant corpus of work over the last decade has firmly established an important role for sphingolipids in a variety of important biological processes. Such processes include signaling events related to cell growth, differentiation, programmed cell death, and stress responses. These processes not only involve those sphingolipids that accumulate as a result of a variety of inherited lysosomal storage disorders, but, in addition, sphingolipids associated with long-chain base metabolism. This article reviews the chemical properties, pathways, regulated metabolism, and signaling function of sphingolipids. In addition, the potential roles of sphingolipids in renal-specific processes are considered. While a variety of cellular functions have been ascribed to sphingolipids, in many cases proof of the concept has yet to be well established. Thus, a number of critical questions can be posed in interpreting these studies. Several of these questions are considered.

N-butyldeoxygalactonojirimycin: a more selective inhibitor of glycosphingolipid biosynthesis than N-butyldeoxynojirimycin, in vitro and in vivo

N-Butyldeoxynojirimycin (NB-DNJ) inhibits the ceramide glucosyltransferase which catalyses the first step in glycosphingolipid (GSL) biosynthesis. It has the potential to be used for the treatment of the GSL lysosomal storage diseases and is currently in clinical trials for the treatment of type 1 Gaucher's disease. However, NB-DNJ is also a potent inhibitor of other enzymes, including alpha-glucosidase I and II, which could potentially cause side effects in patients receiving life-long therapy. Wetherefore evaluated a potentially more selective GSL biosynthesis inhibitor, N-butyldeoxygalactonojirimycin (NB-DGJ), in vitro and in vivo. The distribution and degree of GSL depletion in the liver of mice treated with NB-DGJ or NB-DNJ were equivalent. Mice treated with NB-DGJ had normal body weights and lymphoid organ sizes, whereas NB-DNJ-treated mice showed weight loss and partial lymphoid organ shrinkage. NB-DNJ inhibited glycogen catabolism in the liver, whereas NB-DGJ did not. NB-DNJ was also a potent inhibitor of sucrase and maltase in vitro but not of lactase, while NB-DGJ inhibited lactase but not sucrase or maltase. NB-DGJ is therefore more selective than NB-DNJ, and deserves to be evaluated for human therapy.

Recombination events between the p47-phoxgene and its highly homologous pseudogenes are the main cause of autosomal recessive chronic granulomatous disease

Chronic granulomatous disease (CGD) is an inherited disease caused by defects in the superoxide-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidase of phagocytes. Genetic lesions in any of 4 components of this antimicrobial enzyme have been detected. Family-specific mutations are found in 3 of 4 forms of CGD due to deficiencies of the gp91-phox, p22-phox, andp67-phox genes. In p47-phox–deficient CGD (autosomal recessive form A47°) patients, a GT deletion (▵GT) at the beginning of exon 2 of the p47-phox gene has been reported in 19 of 20 alleles. This GT deletion is also characteristic for the recently identified p47-phox pseudogenes. To explore a possible link between these findings, a sequence analysis of 28 unrelated, racially diverse A47° CGD patients and 37 healthy individuals was performed. The GT deletion in exon 2 was present on all alleles in 25 patients. Only 3 patients but all healthy individuals contained the GTGT and ▵GT sequences. A total of 22 patients carried additional pseudogene-specific intronic sequences on all alleles, either only in intron 1 or in intron 1 and intron 2, which lead to different types of chimeric DNA strands. It is concluded that recombination events between the p47-phox gene and its highly homologous pseudogenes result in the incorporation of ▵GT into the p47-phox gene, thereby leading to the high frequency of GT deletion in A47° CGD patients.

Encapsulation for somatic gene therapy

With the human genome project approaching its completion date of 2005, gene-based technology will play an increasingly important role in health-care delivery. Non-autologous somatic gene therapy is a novel application in which non-autologous cell lines engineered to secrete a recombinant protein are enclosed within immunoisolation devices and implanted into all patients requiring the same product for therapy. The development of this technology requires a multi-disciplinary effort towards optimization of the biomaterial used to manufacture the implantable devices and selection of the appropriate cell lines for enclosure. The efficacy of this technology is illustrated in the treatment of dwarfism and lysosomal storage disease in murine models. The potential of a safe and cost-effective gene-based delivery method should have wide applications in treating both classical genetic disorders and non-Mendelian diseases.

Murine MHC class II locus control region drives expression of human beta-glucocerebrosidase in antigen presenting cells of transgenic mice

Gaucher disease is the most prevalent lysosomal storage disorder in humans, resulting from an inherited deficiency of the enzyme glucocerebrosidase. Although the enzyme is ubiquitously expressed, cells of the reticuloendothelial system are particularly affected since they accumulate the undigested glucosylceramide substrate through their role in scavenging and breaking down cell debris. Gaucher disease is an attractive target for somatic gene therapy. To test the ability to express the enzyme in the affected cell types we have generated transgenic mice expressing human glucocerebrosidase under the control of the murine major histocompatibility complex (MHC) class II Ead locus control region (LCR). The four transgenic lines express the human enzyme in a copy number-dependent manner, independent of the integration site of the transgene. Over-expression of the human enzyme in mice did not result in any abnormal phenotype or pathology during the period of observation (> 2 years). The enzyme is expressed in B cells, monocytes, dendritic cells, thymic epithelial cells, and macrophages in various tissues: the peritoneal cavity, bone marrow, spleen, kidney, gastrointestinal tract, Kupffer cells in the liver and alveolar macrophages in lungs. Expression in the brain was limited to perivascular macrophages and was not seen in microglial cells. Therefore, the MHC class II LCR could potentially be of use in somatic gene therapy for type 1 Gaucher disease.

Clinical and molecular characteristics of Japanese Gaucher disease

Clinical signs and symptoms of Gaucher disease are more severe in Japanese than in Jewish and other non-Japanese patients. A higher percentage of bone crises and splenectomy was demonstrated by Japanese patients, and there were five fatalities among patients with type 1 Gaucher disease. Additionally, neonatal Gaucher disease, clinically characterized by hydrops foetalis, was observed. Japanese patients with type 2 and type 3 disease also demonstrate clinical heterogeneity. About 100 alleles of patients with Japanese Gaucher disease were examined for genotype determination with the PCR and SSCP methods. About 18 different mutations, including several novel mutations in Japanese patients, were identified. The most common mutations in Japanese patients were 1448C(L444P), accounting for 41 (41%) of alleles. The second most prevalent mutation was 754A(F2131), accounting for 14 (14%) of alleles. Other alleles identified included the 1324C, IVS2 and other mutations. Unidentified alleles comprised 16% of the total number of alleles studied. To date, neither the 1226G (N370S) nor the 84GG mutation has been identified in the Japanese population, although these mutations account for about 70% and 10% of the mutations in Jewish and other non-Japanese populations, respectively. The phenotype-genotype correlation in Japanese patients is more complex compared with that of the Jewish population. In Japanese patients, the 1448C mutation, in either heteroallelic or homoallelic forms, exhibits both neurological and non-neurological phenotypes. Japanese patients with the 754A mutation also exhibit both neuronopathic and non-neuronopathic disease. On the other hand, patients with the D409H mutation show only type 3 neurological disease, and those with the 1447-1466 del 20 ins TG mutation have the severe, neonatal neurological form of Gaucher disease. The 1503T allele was present only in patients with type 1 non-neurological disease. However, since this correlation was observed only in young patients, we do not as yet know the final phenotypic outcome of this mutation. Probably, Japanese patients with Gaucher disease have few mutations that exhibit non-neurological signs and symptoms.

Identification and expression of acid beta-glucosidase mutations causing severe type 1 and neurologic type 2 Gaucher disease in non-Jewish patients

Gaucher disease, the most prevalent lysosomal storage disease, occurs in three subtypes, all resulting from mutations in the acid beta-glucosidase gene. Molecular studies in five severely affected type 1 and two type 2 Gaucher disease patients of non-Jewish descent identified six new mutations: K74X, W179X, G195E, S271N, V352L, and a two-base deletion in exon 10 (1450del2). Two additional mutations identified in these patients (R48W and G202R) have been reported previously, but were not expressed or characterized. Heterologous expression in Sf 9 cells using the baculovirus system revealed that the missense mutations, R48W and V352L, had 14 and 7%, respectively, of the specific activity based on cross-reacting immunologic material expressed by the normal allele. In contrast, the G195E, G202R, and S271N mutant alleles were more severely compromised with only 1-2% of the normal expressed specific activity based on cross-reacting immunologic material. Structural distortion at the active site was probed by comparing the interaction of the mutant enzymes with active site-directed inhibitors (castanospermine, conduritol B epoxide and deoxynojirimycin). R48W, G202R, and S271N were normally inhibited, whereas the V352L and G195E mutant enzymes had significantly decreased binding affinity. These mutations further expand the genetic heterogeneity in the lesions causing Gaucher disease types 1 and 2, and further delineate genotype/phenotype correlations and functional domains within the acid beta-glucosidase gene.

Radiographic findings in type 3b Gaucher disease

The purpose of this paper is to describe the radiographic findings in type 3 b Gaucher disease, a chronic neuronopathic form of the illness with severe systemic manifestations. Between 1980 and 1985 17 consecutive patients were evaluated with radiography of the chest, long bones and spine, CT of the head and chest, abdominal sonography, and MRI of the head, abdomen and spine. Clinical manifestations were severe, and led to death from hepatic, pulmonary or cardiac failure in nine patients. Type 3 b Gaucher disease shares the same spectrum of radiographic findings observed in type 1 disease, but the systemic manifestations are more severe. Pulmonary infiltrates, thoracic lymph node enlargement, vertebral compression fractures and osteonecrosis of the long bones occur much more frequently in patients with type 3 b disease.

In vitro accumulation of glucocerebroside in neuroblastoma cells: a model for study of Gaucher disease pathobiology

Gaucher disease is the most common lysosomal glycosphingolipid storage disease; decreased activity of glucosylceramide beta-glucosidase (GCase) results in the accumulation of glucocerebroside (GlcCer) in macrophage-derived cells. The most devastating types of Gaucher disease also involve neuronopathology, thought to be mediated by intracellular GlcCer accumulation in the brain. In this study, we developed an in vitro neuronal cell model for accumulation of endogenous GlcCer to enable studies on the cellular basis for the neuronopathology of this disease. A human neuroblastoma cell line (SH-SY5Y) was selected because it produced appreciable GCase. When these cells were treated with conduritol B epoxide (CBE), a competitive, irreversible inhibitor of this enzyme, GCase levels fell precipitously, while other lysosomal hydrolase levels were unaffected. Relative to untreated control cells, the CBE-treated cells accumulated higher levels of GlcCer, but not other related glycolipids, over time. Thus, this in vitro system displayed many essential biological parameters relevant for studies on cellular events responsible for the neurologic damage that occurs in some types of Gaucher disease. This model should also be useful in investigations of the normal role of sphingolipids in neuronal cell function.

Metaxin, a gene contiguous to both thrombospondin 3 and glucocerebrosidase, is required for embryonic development in the mouse: implications for Gaucher disease

We have identified a murine gene, metaxin, that spans the 6-kb interval separating the glucocerebrosidase gene (GC) from the thrombospondin 3 gene on chromosome 3E3-F1. Metaxin and GC are transcribed convergently; their major polyadenylylation sites are only 431 bp apart. On the other hand, metaxin and the thrombospondin 3 gene are transcribed divergently and share a common promoter sequence. The cDNA for metaxin encodes a 317-aa protein, without either a signal sequence or consensus for N-linked glycosylation. Metaxin protein is expressed ubiquitously in tissues of the young adult mouse, but no close homologues have been found in the DNA or protein data bases. A targeted mutation (A-->G in exon 9) was introduced into GC by homologous recombination in embryonic stem cells to establish a mouse model for a mild form of Gaucher disease. A phosphoglycerate kinase-neomycin gene cassette was also inserted into the 3'-flanking region of GC as a selectable marker, at a site later identified as the terminal exon of metaxin. Mice homozygous for the combined mutations die early in gestation. Since the same amino acid mutation in humans is associated with mild type 1 Gaucher disease, we suggest that metaxin protein is likely to be essential for embryonic development in mice. Clearly, the contiguous gene organization at this locus limits targeting strategies for the production of murine models of Gaucher disease.