Analysis and classification of 304 mutant alleles in patients with type 1 and type 3 Gaucher disease

Disease-causing mutations within the lysosomal integral membrane protein type 2 (LIMP-2) reveal the nature of binding to its ligand beta-glucocerebrosidase

Action myoclonus-renal failure syndrome (AMRF) is caused by mutations in the lysosomal integral membrane protein type 2 (LIMP-2/SCARB2). LIMP-2 was identified as a sorting receptor for beta-glucocerebrosidase (beta-GC), which is defective in Gaucher disease. To date, six AMRF-causing mutations have been described, including splice site, missense and nonsense mutations. All mutations investigated in this study lead to a retention of LIMP-2 in the endoplasmic reticulum (ER) but affect the binding to beta-GC differentially. From the three nonsense mutations, only the Q288X mutation was still able to bind to beta-GC as efficiently as compared with wild-type LIMP-2, whereas the W146SfsX16 and W178X mutations lost their beta-GC-binding capacity almost completely. The LIMP-2 segment 145-288, comprising the nonsense mutations, contains a highly conserved coiled-coil domain, which we suggest determines beta-GC binding. In fact, disruption of the helical arrangement and amphiphatic nature of the coiled-coil domain abolishes beta-GC binding, and a synthetic peptide comprising the coiled-coil domain of LIMP-2 displays pH-selective multimerization properties. In contrast to the reduced binding properties of the nonsense mutations, the only missense mutation (H363N) found in AMRF leads to increased binding of beta-GC to LIMP-2, indicating that this highly conserved histidine modifies the affinity of LIMP-2 to its ligand. With the present study, we demonstrate that disruption of the coiled-coil structure or AMRF disease-causing mutations abolish beta-GC binding, indicating the importance of an intact coiled-coil structure for the interaction of LIMP-2 and beta-GC.

Phenotype determining alleles in GM1 gangliosidosis patients bearing novel GLB1 mutations

GM1 gangliosidosis manifests with progressive psychomotor deterioration and dysostosis of infantile, juvenile, or adult onset, caused by alterations in the structural gene coding for lysosomal acid beta-galactosidase (GLB1). In addition, allelic variants of this gene can result in Morquio B disease (MBD), a phenotype with dysostosis multiplex and entire lack of neurologic involvement. More than 100 sequence alterations in the GLB1 gene have been identified so far, but only few could be proven to be predictive for one of the GM1 gangliosidosis subtypes or MBD. We performed genotype analyses in 16 GM1 gangliosidosis patients of all phenotypes and detected 28 different genetic lesions. Among these, p.I55FfsX16, p.W65X, p.F107L, p.H112P, p.C127Y, p.W161X, p.I181K, p.C230R, p.W273X, p.R299VfsX5, p.A301V, p.F357L, p.K359KfsX23, p.L389P, p.D448V, p.D448GfsX8, and the intronic mutation IVS6-8A>G have not been published so far. Due to their occurrence in homozygous patients, four mutations could be correlated to a distinct GM1 gangliosidosis phenotype. Furthermore, the missense mutations from heteroallelic patients and three artificial nonsense mutations were characterized by overexpression in COS-1 cells, and the subcellular localization of the mutant proteins in fibroblasts was assessed. The phenotype specificity of 10 alleles can be proposed on the basis of our results and previous data.

Neuronopathic Gaucher disease in the mouse: viable combined selective saposin C deficiency and mutant glucocerebrosidase (V394L) mice with glucosylsphingosine and glucosylceramide accumulation and progressive neurological deficits

Gaucher disease is caused by defective acid β-glucosidase (GCase) function. Saposin C is a lysosomal protein needed for optimal GCase activity. To test the in vivo effects of saposin C on GCase, saposin C deficient mice (C−/−) were backcrossed to point mutated GCase (V394L/V394L) mice. The resultant mice (4L;C*) began to exhibit CNS abnormalities ∼30 days: first as hindlimb paresis, then progressive tremor and ataxia. Death occurred ∼48 days due to neurological deficits. Axonal degeneration was evident in brain stem, spinal cord and white matter of cerebellum accompanied by increasing infiltration of the brain stem, cortex and thalamus by CD68 positive microglial cells and activation of astrocytes. Electron microscopy showed inclusion bodies in neuronal processes and degenerating cells. Accumulation of p62 and Lamp2 were prominent in the brain suggesting the impairment of autophagosome/lysosome function. This phenotype was different from either V394L/V394L or C−/− alone. Relative to V394L/V394L mice, 4L;C* mice had diminished GCase protein and activity. Marked increases (20- to 30-fold) of glucosylsphingosine (GS) and moderate elevation (1.5- to 3-fold) of glucosylceramide (GC) were in 4L;C* brains. Visceral tissues had increases of GS and GC, but no storage cells were found. Neuronal cells in thick hippocampal slices from 4L;C* mice had significantly attenuated long-term potentiation, presumably resulting from substrate accumulation. The 4L;C* mouse mimics the CNS phenotype and biochemistry of some type 3 (neuronopathic) variants of Gaucher disease and is a unique model suitable for testing pharmacological chaperone and substrate reduction therapies, and investigating the mechanisms of neuronopathic Gaucher disease.

Type 2 Gaucher disease occurs in Ashkenazi Jews but is surprisingly rare

Patients with Gaucher disease (GD) are divided into three types based on the presence and rate of progression of the neurologic manifestations. While type 1 GD has a strong predilection in the Jewish Ashkenazi population, both other types lack such a propensity. We report the occurrence of type 2 GD (GD2) in four pregnancies in two Jewish families in Israel (in one case the mother was not Ashkenazi but was from a Sfaradi Jewish family) and also review seven additional cases of GD2 in Ashkenazi Jewish families reported in the literature. Phenotypically, GD2 in Ashkenazi Jews does not differ significantly from this form in other ethnic groups. Genotypic analysis of probands from the two Israeli families demonstrates that each carried two heterozygous glucocerebrosidase mutations. We could find no explanation why GD2 is so rare in the Jewish Ashkenazi population but we could hypothesize that homozygosity for certain Ashkenazi alleles might be lethal, leading to a lower than expected frequency of GD2 and noted that no cases of homozygous L444P has ever been described in Ashkenazi Jews.

Identification and characterization of ambroxol as an enzyme enhancement agent for Gaucher disease

Gaucher disease (GD), the most prevalent lysosomal storage disease, is caused by a deficiency of glucocerebrosidase (GCase). The identification of small molecules acting as agents for enzyme enhancement therapy is an attractive approach for treating different forms of GD. A thermal denaturation assay utilizing wild type GCase was developed to screen a library of 1,040 Food and Drug Administration-approved drugs. Ambroxol (ABX), a drug used to treat airway mucus hypersecretion and hyaline membrane disease in newborns, was identified and found to be a pH-dependent, mixed-type inhibitor of GCase. Its inhibitory activity was maximal at neutral pH, found in the endoplasmic reticulum, and undetectable at the acidic pH of lysosomes. The pH dependence of ABX to bind and stabilize the enzyme was confirmed by monitoring the rate of hydrogen/deuterium exchange at increasing guanidine hydrochloride concentrations. ABX treatment significantly increased N370S and F213I mutant GCase activity and protein levels in GD fibroblasts. These increases were primarily confined to the lysosome-enriched fraction of treated cells, a finding confirmed by confocal immunofluorescence microscopy. Additionally, enhancement of GCase activity and a reduction in glucosylceramide storage was verified in ABX-treated GD lymphoblasts (N370S/N370S). Hydrogen/deuterium exchange mass spectrometry revealed that upon binding of ABX, amino acid segments 243-249, 310-312, and 386-400 near the active site of GCase are stabilized. Consistent with its mixed-type inhibition of GCase, modeling studies indicated that ABX interacts with both active and non-active site residues. Thus, ABX has the biochemical characteristics of a safe and effective enzyme enhancement therapy agent for the treatment of patients with the most common GD genotypes.

Apparent diffusion coefficient vale of the brain in patients with Gaucher's disease type II and type III

INTRODUCTION

The aim of this work is to assess the usefulness of apparent diffusion coefficient (ADC) value of the brain for diagnosis of patients with Gaucher's disease type II and type III.

METHODS

Prospective study was conducted upon 13 patients (nine boys and four girls aged 8 months-14 years: mean 6.1 years) with Gaucher's disease type II and III and for age-matched control group (n = 13). Diffusion-weighted magnetic resonance imaging using a single-shot echo-planar imaging with a diffusion-weighted factor b of 0, 500, and 1,000 s/mm(2) was done for all patients and volunteers. The ADC value was calculated in ten regions of the brain parenchyma and correlated with genotyping.

RESULTS

There was significantly lower ADC value of the cortical frontal (P = 0.003), cortical temporal (P = 0.04), frontal subcortical white matter (P = 0.02), corticospinal tract (P = 0.001), cerebellum (P = 0.001), medulla (P = 0.002), and midbrain (P = 0.02) between patients and volunteers. There was significant difference in the ADC value of the frontal and temporal gray matter (P = 0.04 and 0.05, respectively) between patients with heterozygous and homozygous gene mutation.

CONCLUSION

We concluded that ADC value is a new promising quantitative imaging parameter that can be used for the detection of brain abnormalities in patients with Gaucher's disease type II and type III and has a correlation with genotyping.

Diltiazem, a L-type Ca(2+) channel blocker, also acts as a pharmacological chaperone in Gaucher patient cells

Recently, inhibition of L-type Ca(2+) channels, using either Diltiazem or Verapamil, has been reported to partially restore mutant glucocerebrosidase activity in cells from patients with Gaucher disease homozygous for the N370S or L444P alleles, as well as cells from patients with two other lysosomal storage diseases. It was hypothesized that these drugs act on the endoplasmic reticulum, increasing its folding efficiency, inhibited due to altered calcium homeostasis. Several other laboratories have reported that cells carrying either the N370S or the F213I alleles are amenable to enzyme enhancement therapy with pharmacological chaperones, whereas cells homozygous for L444P respond poorly. We found that Verapamil treatment does not enhance mutant enzyme activity in any of the cell lines tested, while Diltiazem moderately increases activity in normal cells, and in N370S/N370S and F213I/L444P, but not in L444P/L444P Gaucher cells, or in either of two adult Tay-Sachs disease cell lines. Since the mode of action of pharmacological chaperones and Diltiazem are believed to be different, we examined the possibility that they could act in concert. Diltiazem co-administered with known chaperones failed to increase enzyme activities above that reached by chaperone-treatment alone in any of the patient cell lines. Thus, we re-examined the possibility that Diltiazem acts as a pharmacological chaperone. We found that, at the acidic pH of lysosomes, Diltiazem was not an inhibitor, nor did its presence increase the heat stability of glucocerebrosidase. However, at neutral pH, found in the endoplasmic reticulum, Diltiazem exhibited both of these properties. Thus Diltiazem exhibits the biochemical characteristics of a glucocerebrosidase pharmacological chaperone.

Phenotypic heterogeneity of N370S homozygotes with type I Gaucher disease: an analysis of 798 patients from the ICGG Gaucher Registry

Gaucher disease is a lysosomal storage disorder caused by a deficiency of the enzyme acid beta-glucosidase. The most prevalent mutant genotype in type I Gaucher disease, N370S/N370S, is commonly thought to confer a mild phenotype presenting in adulthood. To characterize a subset of more severely affected N370S homozygotes, we assessed the phenotypes at or near the time of diagnosis of all N370S homozygotes with available data enrolled in the International Collaborative Gaucher Group Gaucher Registry. N370S compound heterozygotes were analyzed for comparison, as they are expected to present with a more severe phenotype. Of 798 N370S homozygotes and 1,278 N370S compound heterozygotes identified, 32% (251/788) and 65% (820/1269), respectively, were diagnosed before age 20 years. At diagnosis, N370S homozygotes as compared to N370S compound heterozygotes had the following clinical characteristics: irreversible skeletal lesions 17% (34/198) for N370S homozygotes versus 26% (76/290) for N370S compound heterozygotes; anaemia 18% (59/327) versus 29% (145/494); thrombocytopenia 52% (170/327) versus 62% (281/453); hepatomegaly 44% (83/190) versus 72% (141/195); splenomegaly 73% (142/194) versus 91% (178/195); and osteopenia or osteoporosis 48.6% (34/70) versus 51% (25/49). Some N370S homozygotes exhibited more severe clinical manifestations: 9% (29/327) had severe thrombocytopenia; 3% (5/190) had severe hepatomegaly; 11% (22/194) had severe splenomegaly; 7% (18/255) reported bone crises; 11% (8/70) had osteoporosis. In conclusion, N370S homozygosity does not consistently confer a mild, adult-onset phenotype. Gaucher disease patients with the N370S/N370S genotype exhibit a high degree of phenotypic heterogeneity and some may be at risk for early disease onset and severe clinical manifestations.

Isofagomine induced stabilization of glucocerebrosidase

Structurally destabilizing mutations in acid beta-glucosidase (GCase) can result in Gaucher disease (GD). The iminosugar isofagomine (IFG), a competitive inhibitor and a potential pharmacological chaperone of GCase, is currently undergoing clinical evaluation for the treatment of GD. An X-ray crystallographic study of the GCase-IFG complex revealed a hydrogen bonding network between IFG and certain active site residues. It was suggested that this network may translate into greater global stability. Here it is demonstrated that IFG does increase the global stability of wild-type GCase, shifting its melting curve by approximately 15 degrees C and that it enhances mutant GCase activity in pre-treated N370S/N370S and F213I/L444P patient fibroblasts. Additionally, amide hydrogen/deuterium exchange mass spectroscopy (H/D-Ex) was employed to identify regions within GCase that undergo stabilization upon IFG-binding. H/D-Ex data indicate that the binding of IFG not only restricts the local protein dynamics of the active site, but also propagates this effect into surrounding regions.

Identification of pharmacological chaperones for Gaucher disease and characterization of their effects on beta-glucocerebrosidase by hydrogen/deuterium exchange mass spectrometry

Point mutations in beta-glucocerebrosidase (GCase) can result in a deficiency of both GCase activity and protein in lysosomes thereby causing Gaucher Disease (GD). Enzyme inhibitors such as isofagomine, acting as pharmacological chaperones (PCs), increase these levels by binding and stabilizing the native form of the enzyme in the endoplasmic reticulum (ER), and allow increased lysosomal transport of the enzyme. A high-throughput screen of the 50,000-compound Maybridge library identified two, non-carbohydrate-based inhibitory molecules, a 2,4-diamino-5-substituted quinazoline (IC(50) 5 microM) and a 5-substituted pyridinyl-2-furamide (IC(50) 8 microM). They raised the levels of functional GCase 1.5-2.5-fold in N370S or F213I GD fibroblasts. Immunofluorescence confirmed that treated GD fibroblasts had decreased levels of GCase in their ER and increased levels in lysosomes. Changes in protein dynamics, monitored by hydrogen/deuterium-exchange mass spectrometry, identified a domain III active-site loop (residues 243-249) as being significantly stabilized upon binding of isofagomine or either of these two new compounds; this suggests a common mechanism for PC enhancement of intracellular transport.

Lipidomics in diagnosis of lipidoses

A review is presented of the major clinical features of a number of glycolipidoses including Fabry, Gaucher, Tay-Sachs, metachromatic leukodystrophy as well as CeroidLipofucinosis and Sjogren-Larsson syndrome. The possibilities offered by lipidomics for diagnosis and follow-up after enzyme replacement therapy are presented from a practical perspective. The contribution of HPLC coupled with tandem mass spectrometry has considerably simplified the detection and assay of abnormal metabolites. Corresponding internal standards consisting of weighed mixtures of the stable-isotope labeled metabolites required to calibrate and quantitate lipid components of these orphan diseases standards have yet to become commercially available. A lipidomics approach has been found to compare favorably with DNA-sequence analysis for the rapid diagnosis of pre-birth syndromes resulting from these multiple gene defects. The method also seems to be suitable for screening applications in terms of a high throughput combined with a low rate of false diagnoses based on the wide differences in metabolite concentrations found in affected patients as compared with normal subjects. The practical advantages of handling samples for lipidomic diagnoses as compared to enzyme assay are presented for application to diagnosis during pregnancy.

Gaucher disease: New developments in treatment and etiology

Gaucher disease (GD) is an autosomal recessive disease which if undiagnosed or diagnosed late results in devastating complications. Because of the heterozygous nature of GD, there is a wide spectrum of clinical presentation. Clinicians should be aware of this rare but potentially treatable disease in patients who present with unexplained organomegaly, anemia, massive splenomegaly, ascites and even cirrhosis of unknown origin. The treatment options for adult type GD include enzyme replacement treatment (ERT) and substrate reduction treatment (SRT) depending on the status of the patient. Future treatment options are gene therapy and “smart molecules” which provide specific cure and additional treatment options. In this review, we present the key issues about GD and new developments that gastroenterologists should be aware of.

Molecular analysis of Turkish Gaucher disease patients: identification of novel mutations in glucocerebrosidase (GBA) gene

Gaucher disease (GD) is the most frequent lysosomal glycolipid storage disorder due to autosomal recessive deficiency of acid beta-glucosidase and is characterized by the accumulation of glucocerebroside. In this work we carried out molecular analysis of the glucocerebrosidase gene (GBA) in 57 unrelated patients and the alleleic frequencies of gene mutations in Turkish patients are reported. The most prevalent are L444P and N370S accounting for 42% and 30% in our patients. We identified three novel genetic alterations: two missense changes S356F, L296V that are associated with the severe phenotype of type 1 GD. 303-305delCAC was identified in a homozygous state in one patient type 1 or type 3.

Management of non-neuronopathic Gaucher disease with special reference to pregnancy, splenectomy, bisphosphonate therapy, use of biomarkers and bone disease monitoring

Enzyme replacement was introduced as treatment for non-neuronopathic Gaucher disease more than 15 years ago. To ensure the best use of this costly ultra-orphan agent, a systematic disease management approach has been proposed by an international panel; this includes the development, by consensus, of achievable treatment goals. Here we critically review these goals and monitoring guidelines and incorporate emerging experience of the disease in the therapeutic era, as well as contemporary clinical research. This review makes recommendations related specifically to the management of pregnancy; the appropriate use of splenectomy and bisphosphonate treatment; the relevance of biochemical markers to disease monitoring; and the use of semi-quantitative methods for assessing bone marrow infiltration. In addition, we identify key areas for development, including the requirement for a validated index of disease severity; the need to correlate widely used biomarkers with long-term disease outcomes, and the desirability of establishing agreed standards for monitoring of bone disease particularly in infants and children with Gaucher disease.

An evolutionary and structure-based docking model for glucocerebrosidase-saposin C and glucocerebrosidase-substrate interactions - relevance for Gaucher disease

Gaucher disease, the most prevalent lysosomal storage disorder, is principally caused by malfunction of the lysosomal enzyme glucocerebrosidase (GBA), a 497-amino acid membrane glycoprotein that catalyzes the hydrolysis of glucosylceramide to ceramide and glucose in the presence of an essential 84-residue activator peptide named saposin C (SapC). Knowledge of the GBA structure, a typical (beta/alpha)(8) TIM barrel, explains the effect of few mutations, directly affecting or located near the catalytic site. To identify new regions crucial for proper GBA functionality, we analyzed the interactions of the enzyme with a second (substrate) and a third (cofactor) partner. We build 3D docking models of the GBA-SapC and the GBA-ceramide interactions, by means of methodologies that integrate both evolutive and structural information. The GBA-SapC docking model confirm the implication of three spatially closed regions of the GBA surface (TIM barrel-helix 6 and helix 7, and the Ig-like domain) in binding the SapC molecule. This model provides new basis to understand the pathogenicity of several mutations, such as the prevalent Leu444Pro, and the additive effect of Glu326Lys in the double mutant Glu326Lys-Leu444Pro. Overall, 39 positions in which amino acid changes are known to cause Gaucher disease were localized in the GBA regions identified in this work. Our model is discussed in relation to the phenotype (pathogenic effect) of these mutations, as well as to the enzymatic activity of the recombinant proteins when available. Both data fully correlates with the proposed model, which will provide a new tool to better understand Gaucher disease and to design new therapy strategies.

Neurological and brain MRS findings in patients with Gaucher disease type 1

Gaucher disease type 1 (GD1) is an autosomal recessive lysosomal storage disorder, characterised by accumulation of glycosphingolipids in visceral organs. Although considered non-neuronopathic neurological involvement has been reported in single cases. The aim of our study was to investigate central and peripheral nervous system involvement in patients with GD1. We investigated nine unrelated patients with GD1 by three-dimensional cerebral 1H-magnetic resonance spectroscopic imaging and clinical and neurophysiological tests. We found an increased choline level on MRS in four patients. One of these patients had mixed axonal neuropathy and subclinical involvement of the central somatosensory tract as well as monoclonal gammopathy. One patient with normal cerebral choline levels had evidence of bilateral carpal tunnel syndrome upon neurophysiological exam. The N370S mutation was found in 11 out of 18 alleles. Three patients were compound heterozygous for the L444P mutation. There was no correlation between increased cerebral choline levels and type of mutations. MRS findings suggest that in patients with classical non-neuronopathic GD1, the brain is involved at a subclinical level in some patients.

High frequency of mutation G377S in Brazilian type 3 Gaucher disease patients

Gaucher disease (GD), the most prevalent lysosome storage disorder, presents an autosomal recessive mode of inheritance. It is a paradigm for therapeutic intervention in medical genetics due to the existence of effective enzyme replacement therapy. We report here the analysis of GD in 262 unrelated Brazilian patients, carried out in order to establish the frequency of the most common mutations and to provide prognostic information based on genotype-phenotype correlations. Among 247 type 1 GD patients, mutation N370S was detected in 47% of all the alleles, but N370S/N370S homozygosity was found in only 10% of the patients, a much lower frequency than expected, suggesting that most individuals presenting this genotype may not receive medical attention. Recombinant alleles were detected at a high frequency: 44% of the chromosomes bearing mutation L444P had other mutations derived from the pseudogene sequence, present in 25% of patients. Three neuronopathic type 2 patients were homozygous for L444P, all presenting additional mutations (E326K or recombinant alleles) that probably lead to the more severe phenotypes. Six children, classified as type 1 GD patients, had a L444P/L444P genotype, showing that neuronopathic symptoms may only manifest later in life. This would indicate the need for a higher treatment dose during enzyme replacement therapy. Finally, mutation G377S was present in 4 homozygous type 1 patients and also in compound heterozygosity in 5 (42%) type 3 patients. These findings indicate that G377S cannot be unambiguously classified as mild and suggest an allele-dose effect for this mutation.

Oral Aspects of Gaucher's Disease: A Literature Review and Case Report

BACKGROUND

Gaucher's disease (GD) is a lysosomal storage disease with a high incidence in Ashkenazi Jews. The disease is caused by an autosomally recessive inherited deficiency of the lysosomal enzyme glucocerebrosidase, leading to the accumulation of glucocerebroside in macrophages. The lipid-laden macrophages, called Gaucher cells, can be detected in liver, spleen, and bone marrow tissues.

METHODS

A case report of periodontal treatment of a 47-year-old female patient with GD with recurrent gingival hemorrhage and toothache is presented. Periapical radiographs revealed cyst-like lesions in the mandibular premolar-molar regions accompanied by severe apical root resorption, enlargement of the periodontal ligament and bone-marrow spaces, and loss of trabecular structure and radiopaque appearance of bone. An abnormally narrow and sharp coronoid process and effacement of the cortical borders of the mandibular canal were noted.

RESULTS

The patient was diagnosed as having generalized severe chronic periodontitis. Treatment included oral hygiene motivation and instructions, scaling, root planing, and access flap therapy, resulting in resolution of periodontal signs and symptoms and a marked improvement in the patient's feeling of well being.

CONCLUSIONS

Periodontal treatment can be effective in patients with GD. Oral findings may lead to early detection of GD, especially in the absence of clinical symptoms. Dentists should be aware of possible oral and radiographic manifestations of the disease and the role of periodontal treatment in improving patient's oral health and quality of life.

Detection of 12 new mutations in Gaucher disease Brazilian patients

Gaucher disease is the most frequent lysosome storage disease and presents an autosomal recessive mode of inheritance. It is caused by mutations at the GBA gene leading to deficient activity of the glucocerebrosidase enzyme. This report describes 12 new mutations [c.38A>G (K-27R), c.220G>A (G35S), c.448G>A (E111K), IVS4+1G>A, c.746C>T (A210V), c.776A>G (Y220C), c.793delC (Q226_fs4X), c.1102C>T (R329C), c.1300C>T (R395C), c.1309G>A (V398I), c.1324-1326delATT (delI403) and c.1583T>C (I489T)] and 4 novel silent alterations [c.342C>T (F75), c.528C>T (D137), c.1011C>T (D298) and c.1092G>A (G325)] detected among 40 unrelated Brazilian type 1 Gaucher disease patients by a combination of RFLP, dHPLC and DNA sequencing procedures. The R329C mutation, previously described in a Parkinson's disease patient (A. Lwin, E. Orvisky, O. Goker-Alpan, M.E. LaMarca, E. Sidransky. Glucocerebrosidase mutations in subjects with Parkinsonism. Mol. Genet. Metab. 81 (2004) 70-73), is described here for the first time in a Gaucher disease patient. Several genotype-phenotype correlations could be established, contributing significantly to the panel of reported mutations and conferring predictive value to their detection.

Inborn errors of metabolism: the flux from Mendelian to complex diseases

Inborn errors of metabolism are characterized by dysregulation of the metabolic networks that underlie development and homeostasis, and constitute an important and expanding group of genetic disorders in humans. Diagnostic methods that are based on molecular genetic tools have a limited ability to correlate phenotypes with subtle changes in metabolic fluxes. We argue that the direct and dynamic measurement of metabolite flux will facilitate the integration of environmental, genetic and biochemical factors with phenotypic information. Ultimately, this integration will lead to new diagnostic and therapeutic approaches that are focused on the manipulation of these pathways.

Analyses of variant acid beta-glucosidases: effects of Gaucher disease mutations

Acid beta-glucosidase (GCase) is a 497-amino acid, membrane-associated lysosomal exo-beta-glucosidase whose defective activity leads to the Gaucher disease phenotypes. To move toward a structure/function map for disease mutations, 52 selected single amino acid substitutions were introduced into GCase, expressed in an insect cell system, purified, and characterized for basic kinetic, stability, and activator response properties. The variant GCases from Gaucher disease patients and selected variant GCases from the mouse had decreased relative k(cat) and differential effects on active site binding and/or attachment of mechanism-based covalent (conduritol B epoxide) or reversible (deoxynojirimycin derivatives) inhibitors. A defect in negatively charged phospholipid activation was present in the majority of variant GCases but was increased in two, N370S and V394L. Deficits in saposin C enhancement of k(cat) were present in variant GCases involving residues 48-122, whereas approximately 2-fold increases were obtained with the L264I GCase. About 50% of variant GCases each had wild-type or increased sensitivity to in vitro cathepsin D digestion. Mapping of these properties onto the crystal structures of GCase indicated wide dispersion of functional properties that can affect catalytic function and stability. Site-directed mutagenesis of cysteine residues showed that the disulfide bonds, Cys(4)-Cys(16) and Cys(18)-Cys(23), and a free Cys(342) were essential for activity; the free Cys(126) and Cys(248) were not. Relative k(cat) was highly sensitive to a His substitution at Arg(496) but not at Arg(495). These studies and high phylogenetic conservation indicate localized and general structural effects of Gaucher disease mutations that were not obvious from the nature of the amino acid substitution, including those predicted to be nondisruptive (e.g. Val --> Leu). These results provide initial studies for the engineering of variant GCases and, potentially, molecular chaperones for therapeutic use.

Use of fluorescent substrates for characterization of Gaucher disease mutations

Gaucher disease results from impaired activity of the lysosomal enzyme beta-glucocerebrosidase. More than 200 mutations within the glucocerebrosidase gene have been associated with this disease. In this study we tested the effect of several mutations (K157Q, D140H, E326K, D140H+E326K, V394L and R463C) on RNA stability, protein stability and activity toward four different fluorescent substrates (LR-12-GC, Bodipy-12-GC, LR-0-PAP-glucose and 4-MUG), using the vaccinia-derived expression system. The results indicated that the K157Q mutation leads to RNA instability, causing low protein levels and a concomitant reduction in beta-glucocerebrosidase activity. All other tested mutations led to production of glucocerebrosidase RNA and protein with stabilities comparable to those of the normal counterpart. The D140H variant exhibited a high activity toward the tested substrates while the variant enzymes containing either the E326K or D140H and E326k mutations together expressed low beta-glucocerebrosidase activity. The V394L variant exhibited low activity toward the tested substrates, while a higher activity was presented by the R463C containing glucocerebrosidase variant. Our results strongly indicated that the LR-12-GC substrate distinguishes between severities of different mutant glucocerebrosidase variants overexpressed in a heterologous system.

Perinatal lethal Gaucher disease: a distinct phenotype along the neuronopathic continuum

Gaucher disease, the inherited deficiency of glucocerebrosidase, is characterized by significant genetic and phenotypic heterogeneity. At the extreme end of the phenotypic continuum is the perinatal lethal variant, typically presenting in utero or during the neonatal period as hydrops and/orcongenital ichthyosis, with severe and progressive neurological involvement. Insights from the null-allele Gaucher mouse model contributed to the identification of this distinct phenotype, which has unique epidermal involvement. While multiple mutations are encountered, many affected infants are homozygous for recombinant alleles. The diagnosis is often missed due to the early lethality and the failure to recognize the association between lysosomal disorders and hydrops fetalis. The incidence of severe perinatal Gaucher disease may prove more common than currently appreciated with greater physician awareness of the disorder.

Analysis of the glucocerebrosidase gene in Parkinson's disease

Parkinson's disease (PD) is a common progressive neurodegenerative disorder characterized clinically by a combination of motor symptoms. Identifying novel PD genetic risk factors is important for understanding its pathogenesis. A recent study suggested that up to 21% of subjects with PD may have mutations in the glucocerebrosidase (GBA) gene. We investigated the GBA gene for mutations in 88 PD cases and 122 normal controls and detected the presence of heterozygous GBA mutations in 5 PD cases and in 1 control. Sequencing of the entire open reading frame of the GBA gene in a subset of 25 cases with early-onset PD (<50 years of age) uncovered no additional mutations. Our results demonstrate a marginally significant association of GBA mutations with PD and suggest that variations in the GBA gene may constitute a rare susceptibility factor for PD (P = 0.048).

Therapeutic goals in the treatment of Gaucher disease

Gaucher disease, the most common lysosomal storage disorder, is a heterogeneous multisystem condition. Patients with non-neuronopathic (type 1) Gaucher disease may suffer from hepatomegaly, splenomegaly, thrombocytopenia, bleeding tendencies, anemia, hypermetabolism, skeletal pathology, growth retardation, pulmonary disease, and decreased quality of life. Enzyme replacement therapy (ERT) with mannose-terminated glucocerebrosidase reverses or ameliorates many of the manifestations of type 1 Gaucher disease. However, the variable disease pattern and severity, and the uncertain manner of progression, render the decision to initiate ERT difficult. Thus, implementation of treatment and evaluation of the therapeutic response must be tailored to the individual patient. To obtain an evidence-based consensus on contemporary therapeutic goals, an international panel of physicians with extensive clinical experience in Gaucher disease met to review the extant literature on its treatment. The panel adopted an integrated system-based approach to arrive at a comprehensive guide to individualized management. Here we establish goals of treatment in Gaucher disease and propose a comprehensive schedule of monitoring of all relevant aspects to confirm the achievement, maintenance, and continuity of the therapeutic response.

Molecular screening for diseases frequent in Ashkenazi Jews: lessons learned from more than 100,000 tests performed in a commercial laboratory

PURPOSE

To determine the frequency of carriers of Ashkenazi Jewish (AJ) genetic diseases in the US population and compare these numbers with previously published frequencies reported in smaller more isolated cohorts.

METHODS

A database containing more than 100,000 genotyping assays was queried. Assays for 10 separate AJ genetic diseases where comparisons were made with published data.

RESULTS

As expected, we observed lower carrier frequencies in a general, US population than those reported in literature. In 2427 patients tested for a panel of 8 AJ diseases, 20 (1:121) were carriers of two diseases and 331 (1:7) were carriers of a single disease. Fifty-three of 7184 (1:306) individuals tested for Gaucher disease had 2 Gaucher Disease mutations indicating a potentially affected phenotype.

CONCLUSIONS

As the number of AJ diseases increases, progressively more individuals will be identified as carriers of at least one disease.

Gaucher disease type 1: Revised recommendations on evaluations and monitoring for adult patients

For patients with type 1 Gaucher disease, challenges to patient care posed by clinical heterogeneity, variable progression rates, and potential permanent disability that can result from untreated or suboptimally treated hematologic, skeletal, and visceral organ involvement dictate a need for comprehensive, serial monitoring. An updated consensus on minimum recommendations for effective monitoring of all adult patients with type 1 Gaucher disease has been developed by the International Collaborative Gaucher Group (ICGG) Registry coordinators. These recommendations provide a schedule for comprehensive and reproducible evaluation and monitoring of all clinically relevant aspects of this disease. The initial assessment should include confirmation of deficiency of beta-glucocerebrosidase, genotyping, and a complete family medical history. Other assessments to be performed initially and at regular intervals include a complete physical examination, patient-reported quality of life using the SF-36 survey, and assessment of hematologic (hemoglobin and platelet count), visceral, and skeletal involvement, and biomarkers. Specific radiologic imaging techniques are recommended for evaluating visceral and skeletal pathology. All patients should undergo comprehensive regular assessment, the frequency of which depends on treatment status and whether therapeutic goals have been achieved. Additionally, reassessment should be performed whenever enzyme therapy dose is altered, or in case of significant clinical complication.

Prevalence of lysosomal storage diseases in Portugal

Lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders individually considered as rare, and few data on its prevalence has been reported in the literature. The overall birth prevalence of the 29 different LSDs studied in the Portuguese population was calculated to be 25/100000 live births, twice the prevalence previously described in Australia and in The Netherlands. The comparison of the prevalence profile of the LSDs presenting a prevalence higher than 0.5/100000 in the Portuguese, Dutch and Australian populations showed, in the Portuguese, the existence of a higher prevalence of GM2 gangliosidoses (B variant), mucolipidoses (II and III), Niemman-Pick type C and metachromatic leukodystrophy (MLD), and a lower prevalence of Pompe and Fabry. The highest prevalence value for a single LSD is the one of GM2 gangliosidoses (B variant), corresponding to 3/100000, a value which is significantly higher than the prevalence of the most frequent LSD in Dutch, Pompe disease (2/100000) and Australians, Gaucher's disease (GD) (1.8/100000). It is worth noting that the highest prevalence of GM2 gangliosidoses found in the Portuguese is mainly due to the existence of a unique subtype, the rare juvenile B1 variant.

Early Visual Seizures and Progressive Myoclonus Epilepsy in Neuronopathic Gaucher Disease Due to a Rare Compound Heterozygosity (N188S/S107L)

PURPOSE

Gaucher disease, the inherited deficiency of the lysosomal enzyme glucocerebrosidase, is characterized by genotypic and phenotypic heterogeneity. We recently characterized the glucocerebrosidase alleles of a patient with an unusual clinical presentation of type 3 Gaucher disease.

METHODS

Initial clinical manifestations appeared at age 11 years as visual seizures.

RESULTS

Subsequent progressive myoclonus and generalized seizures were consistent with an adolescent-onset form of progressive myoclonus epilepsy. However, a specific diagnosis was established only at age 16, because of the absence of hematologic abnormalities and a fairly moderate hepatomegaly. Bone marrow aspirate was slightly positive for Gaucher cells. Demonstration of reduced glucocerebrosidase in the fibroblasts confirmed the diagnosis. The child died at age 19 years. Postmortem sequencing of the glucocerebrosidase gene from cultured fibroblasts demonstrated a rare compound heterozygote for N188S/S107L.

CONCLUSIONS

This unusual presentation of Gaucher disease indicates that if clinical and neurophysiological findings in adolescents with initial visual seizures and myoclonus suggest a progressive disorder, enzymatic assay is mandatory, even in the absence of the classic neurologic and systemic signs of the disease. Early differential diagnosis from other forms of progressive myoclonus epilepsy with similar clinical presentation may help provide appropriate genetic counseling.

Gaucher disease: complexity in a "simple" disorder

Gaucher disease, the recessively inherited deficiency of the enzyme glucocerebrosidase and the most common sphingolipidosis, has both non-neurological and neuronopathic forms and a continuum of diverse clinical manifestations. Studies of genotype-phenotype correlations reveal significant genotypic heterogeneity among clinically similar patients, and vastly different phenotypes among patients with the same mutations. The region surrounding the glucocerebrosidase gene (GBA) on chromosome 1q is particularly gene-rich, with a highly homologous pseudogene sequence 16 kb downstream. Recombination events within the GBA locus contribute to the etiology of some mutations in Gaucher disease. Studies of patients with Gaucher disease and atypical manifestations, including parkinsonism, myoclonic epilepsy, cardiac involvement and collodion skin, seek to define other genetic or environmental factors contributing to the phenotypes. Recent reports demonstrating an association between Gaucher disease and parkinsonism provide an example of heterozygosity for a Mendelian disorder acting as a risk factor for a complex disease. There are rare patients with Gaucher disease and differing genotypes who develop early onset, treatment-refractory parkinsonism. Neuropathology in a group of these patients showed alpha-synuclein-reactive Lewy bodies in brain regions specifically associated with Gaucher disease. Family studies of these probands suggested that the incidence of parkinsonism might be more frequent in obligate heterozygotes. In a complementary finding, the examination of GBA in autopsy samples from individuals with sporadic Parkinson disease identified alterations in the GBA sequence in 14% of the cohort. These studies provide evidence that altered glucocerebrosidase may contribute to a vulnerability to parkinsonism. Moreover, this research demonstrates how insights from rare, single gene disorders like Gaucher disease can provide a window into the etiology of more common, multifactorial genetic diseases.

Twin pairs showing discordance of phenotype in adult Gaucher's disease

BACKGROUND

Non-neuronopathic (type 1) Gaucher's disease, a recessive disorder caused by glucocerebrosidase deficiency, shows marked variability in the severity and extent of clinical expression: many individuals who harbour two mutant alleles remain mildly affected or asymptomatic. Despite much effort, it is not possible accurately to predict disease severity from the genotype, or to identify those patients destined to develop severe disease and meriting early treatment.

AIM

To determine the degree to which variance in Gaucher disease is determined by non-heritable factors.

DESIGN

Case reports of monozygotic and dizygotic twin pairs.

RESULTS

For the monozygotic twin pair, homozygous for the frequent N370S glucocerebrosidase allele, there was no evidence that significant lipid storage was ever initiated in the unaffected twin. In contrast, pathological storage of glucocerebroside has been present in the macrophages of both members of the dizygotic twin pair (compound heterozygotes for the N370S and L444P alleles) from an early age but, by the age of 57 years, only one has developed symptoms.

DISCUSSION

Non-heritable factors influence Gaucher disease expression in genetically predisposed individuals. Understanding the interactions between heritable and non-heritable factors will be critical for an analysis of pathogenesis, and the treatment of individuals predisposed to Gaucher disease.

A novel alteration in metaxin 1, F202L, is associated with N370S in Gaucher disease

The gene for glucocerebrosidase ( GBA), the enzyme deficient in Gaucher disease, is located in a gene-rich region on 1q21. Metaxin 1( MTX1) is a convergently transcribed gene contiguous to the 3' end of the GBA pseudogene. A single nucleotide alteration in MTX1, 628T-->C, resulting in the amino acid change F202L, was identified in patients with Gaucher disease in association with the common N370S mutation in GBA. The polymorphism was also present on 4.6% of 152 control alleles, but could have functional consequences that have a modifying role in Gaucher disease.

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.

Gaucher disease: variability in phenotype among siblings

Although many mutations of the GBA gene have been described as causing Gaucher disease, there is generally poor correlation between genotype and phenotype, with a few exceptions. However, most previous reports of genotype-phenotype correlation have involved unrelated individuals, who, even if they share the same mutations, are not as genetically close as siblings. We have studied 24 groups (mostly pairs) of Canadian siblings with type I (non-neuronopathic) Gaucher disease. Since most Canadian provinces have adopted similar criteria for instituting enzyme replacement therapy (ERT), the age at which ERT is begun can serve as a rough surrogate for disease severity, and concordance (or lack of concordance) can be examined between siblings. In 14 of the 24 sibling families, there was sibling concordance: either both siblings were not on ERT, or both were on ERT and had begun at roughly the same age. In these families, there was also much similarity in the clinical features of the disease between siblings. In the other 10 families there was lack of sibling concordance, with only one sibling receiving ERT (or, in one family with three affected siblings, two of three on ERT). In these families, there was also much discrepancy between siblings in the clinical features (as might be expected in a setting where the guidelines for starting ERT are relatively uniform). Possible reasons for the discordances between siblings include macro-environmental and microenvironmental differences. The latter may include micro-environments at the level of the cell (e.g. lysosomal pH, alternative substrates) or at the level of the chromosome (contiguous genes, modifier genes, neutral polymorphisms in GBA).

Diagnostic and treatment challenges of neuronopathic Gaucher disease: two cases with an intermediate phenotype

Gaucher disease (GD) is a lysosomal storage disorder with a broad, overlapping clinical spectrum. The presented two case reports highlight the clinical evaluation required in neuronopathic GD to assist with medical management and genetic counselling.

The concomitant occurrence of multiple epidermal cysts, osteomas and thyroid gland nodules is not diagnostic for Gardner syndrome in the absence of intestinal polyposis: a clinical and genetic report

Gardner syndrome, a phenotypic variant of familial adenomatous polyposis, is characterized by the classical clinical triad of skin and soft tissue tumours, osteomas and intestinal polyposis, but disease patterns with pairs of these findings have also been reported. Different mutations in the adenomatous polyposis coli (APC) gene have been shown to be associated with Gardner syndrome disease phenotypes. A 36-year-old patient presented with multiple epidermal cysts on the face, left ear lobe and neck, and the possible diagnosis of Gardner syndrome was based on the additional findings of two classical osteomas in the left radius and ulna and a cold non-malignant nodule of the thyroid gland. Intestinal polyposis was lacking at the time of examination. Major deletions but not microdeletions were excluded by a cytogenetic analysis with 650 chromosomal bands per haploid set. Systematic sequencing of the entire coding region of the APC gene (> 8500 bp) of the patient and five healthy controls was also performed. As a results, new APC gene polymorphisms were identified in exons 13 [A545A (A/G)] and 15 [G1678G (A/G), S1756S (G/T), P1960P (A/G)]. We also detected D1822V (A/T) which has recently been reported to be potentially related to colorectal carcinoma, and genotyped 194 randomly chosen healthy individuals from the Glasgow area for this as well as for the above variants in exons 13 and 15. Interestingly, of the 194 controls, 112 carried the DD (57.7%), 71 the DV (36.6%), and the remaining 11 (5.7%), including our patient, the VV genotype. It is therefore unlikely that APC D1822V serves as an important marker for colorectal carcinoma. In conclusion, we failed to identify obvious germline candidate mutations in > 8500 bp of the coding region of the APC gene in a patient with multiple epidermal cysts, osteomas and a thyroid gland nodule; major chromosomal deletions were excluded. Therefore, we assume that only the presence of intestinal polyposis is a marker for Gardner syndrome.

Gaucher's disease: identification of novel mutant alleles and genotype-phenotype relationships

A sequencing protocol for the acid beta-glucosidase (GCase) gene (GBA) was developed using a long-range PCR template. This protocol has an advantage of greater DNA yields over similar strategies. Seven Gaucher's disease patients had four novel and five other rare alleles. A non-pseudogene in-frame deletion (g.2600-2602delTAC) and a new complex mutation (null allele) were identified in Gaucher's disease type 1, i.e. the g.2600-2602delTAC deletion is associated with the non-neuronopathic variant. An F251L allele was found in a baby with the collodion skin phenotype. Three mutant alleles were identified in a single primary family with type 3. The patients' father at 45 years is healthy and is heteroallelic for the G202R and E326K alleles. Family studies indicated that E326K is in trans to G202R and L444P, and that isolated E326K is non-pathogenic in this family. A rare mutation R257Q was identified in a type 2 patient, providing an association with neuronopathic disease. A genotype L444P/L444P was noted in a 22-year-old non-neuronopathic patient. Complete gene sequencing showed a new complex allele consisting of L444P and g.7741T > C in the 3' UTR. Three additional complex alleles also involved the 3' UTR. Complete gene characterization in Gaucher's disease should allow greater insights into the correlation of specific alleles with phenotype.

Myoclonic epilepsy in Gaucher disease: genotype-phenotype insights from a rare patient subgroup

Gaucher disease, the inherited deficiency of lysosomal glucocerebrosidase, presents with a wide spectrum of manifestations. Although Gaucher disease has been divided into three clinical types, patients with atypical presentations continue to be recognized. A careful phenotypic and genotypic assessment of patients with unusual symptoms may help define factors that modify phenotype in this disorder. One such example is a rare subgroup of patients with type 3 Gaucher disease who develop progressive myoclonic epilepsy. We evaluated 16 patients with myoclonic epilepsy, nine of whom were diagnosed by age 4 y with severe visceral involvement and myoclonus, and seven with a more chronic course, who were studied between ages 22 and 40. All of the patients had abnormal horizontal saccadic eye movements. Fourteen different genotypes were encountered, yet there were several shared alleles, including V394L (seen on two alleles), G377S (seen on three alleles), and L444P, N188S, and recombinant alleles (each found on four alleles). V394L, G377S, and N188S are mutations that have previously been associated with non-neuronopathic Gaucher disease. The spectrum of genotypes differed significantly from other patients with type 3 Gaucher disease, where genotypes L444P/L444P and R463C/null allele predominated. Northern blot studies revealed a normal glucocerebrosidase transcript, whereas Western studies showed that the patients studied lacked the processed 56 kD isoform of the enzyme, consistent with neuronopathic Gaucher disease. Brain autopsy samples from two patients demonstrated elevated levels of glucosylsphingosine, a toxic glycolipid, which could contribute to the development of myoclonus. Thus, although there were certain shared mutant alleles found in these patients, both the lack of a shared genotype and the variability in clinical presentations suggest that other modifiers must contribute to this rare phenotype.