Characterization of 6-hexadecanoylamino-4-methylumbelliferyl-beta-D- galactopyranoside as fluorogenic substrate of galactocerebrosidase for the diagnosis of Krabbe disease

Late-onset Krabbe disease presenting as spastic paraplegia - implications of GCase and CTSB/D

OBJECTIVE

Krabbe disease (KD) is a multisystem neurodegenerative disorder with severe disability and premature death, mostly with an infancy/childhood onset. In rare cases of late-onset phenotypes, symptoms are often milder and difficult to diagnose. We here present a translational approach combining diagnostic and biochemical analyses of a male patient with a progressive gait disorder starting at the age of 44 years, with a final diagnosis of late-onset KD (LOKD).

METHODS

Additionally to cerebral MRI, protein structural analyses of the β-galactocerebrosidase protein (GALC) were performed. Moreover, expression, lysosomal localization, and activities of β-glucocerebrosidase (GCase), cathepsin B (CTSB), and cathepsin D (CTSD) were analyzed in leukocytes, fibroblasts, and lysosomes of fibroblasts.

RESULTS

Exome sequencing revealed biallelic likely pathogenic variants: GALC exons 11-17: 33 kb deletion; exon 4: missense variant (c.334A>G, p.Thr112Ala). We detected a reduced GALC activity in leukocytes and fibroblasts. While histological KD phenotypes were absent in fibroblasts, they showed a significantly decreased activities of GCase, CTSB, and CTSD in lysosomal fractions, while expression levels were unaffected.

INTERPRETATION

The presented LOKD case underlines the age-dependent appearance of a mildly pathogenic GALC variant and its interplay with other lysosomal proteins. As GALC malfunction results in reduced ceramide levels, we assume this to be causative for the here described decrease in CTSB and CTSD activity, potentially leading to diminished GCase activity. Hence, we emphasize the importance of a functional interplay between the lysosomal enzymes GALC, CTSB, CTSD, and GCase, as well as between their substrates, and propose their conjoined contribution in KD pathology.

Functional analysis of two SLC9A6 frameshift variants in lymphoblastoid cells from patients with Christianson syndrome

BACKGROUND

Christianson syndrome (CS) is caused by mutations in SLC9A6 and is characterized by global developmental delay, epilepsy, hyperkinesis, ataxia, microcephaly, and behavioral disorder. However, the molecular mechanism by which these SLC9A6 mutations cause CS in humans is not entirely understood, and there is no objective method to determine the pathogenicity of single SLC9A6 variants.

METHODS

Trio-based whole exome sequencing (WES) was carried out on two individuals with suspicion of CS. qRT-PCR, western blot analysis, filipin staining, lysosomal enzymatic assays, and electron microscopy examination, using EBV-LCLs established from the two patients, were performed.

RESULTS

Trio-based WES identified a hemizygous SLC9A6 c.1560dupT, p.T521Yfs*23 variant in proband 1 and a hemizygous SLC9A6 c.608delA, p.H203Lfs*10 variant in proband 2. Both children exhibited typical phenotypes associated with CS. Expression analysis in EBV-LCLs derived from the two patients showed a significant decrease in mRNA levels and no detectable normal NHE6 protein. EBV-LCLs showed a statistically significant increase in unesterified cholesterol in patient 1, but only non-significant increase in patient 2 when stained with filipin. Activities of lysosomal enzymes (β-hexosaminidase A, β-hexosaminidase A + B, β-galactosidase, galactocerebrosidase, arylsulfatase A) of EBV-LCLs did not significantly differ between the two patients and six controls. Importantly, by electron microscopy we detected an accumulation of lamellated membrane structures, deformed mitochondria, and lipid droplets in the patients' EBV-LCLs.

CONCLUSIONS

The SLC9A6 p.T521Yfs*23 and p.H203Lfs*10 variants in our patients result in loss of NHE6. Alterations of mitochondria and lipid metabolism may play a role in the pathogenesis of CS. Moreover, the combination of filipin staining with electron microscopy examination of patient lymphoblastoid cells can serve as a useful complementary diagnostic method for CS.

From Lysosomal Storage Disorders to Parkinson's Disease - Challenges and Opportunities

Lysosomes are specialized organelles with an acidic pH that act as recycling hubs for intracellular and extracellular components. They harbour numerous different hydrolytic enzymes to degrade substrates like proteins, peptides, and glycolipids. Reduced catalytic activity of lysosomal enzymes can cause the accumulation of these substrates and loss of lysosomal integrity, resulting in lysosomal dysfunction and lysosomal storage disorders (LSDs). Post-mitotic cells, such as neurons, seem to be highly sensitive to damages induced by lysosomal dysfunction, thus LSDs often manifest with neurological symptoms. Interestingly, some LSDs and Parkinson's disease (PD) share common cellular pathomechanisms, suggesting convergence of aetiology of the two disease types. This is further underlined by genetic associations of several lysosomal genes involved in LSDs with PD. The increasing number of lysosome-associated genetic risk factors for PD makes it necessary to understand functions and interactions of lysosomal proteins/enzymes both in health and disease, thereby holding the potential to identify new therapeutic targets. In this review, we highlight genetic and mechanistic interactions between the complex lysosomal network, LSDs and PD, and elaborate on methodical challenges in lysosomal research.

Reliable and Fast Genotyping Protocol for Galactosylceramidase (Galc) in the Twitcher (Twi) Mouse

Twitcher (Twi) is a neurological Krabbe disease (KD, or globoid cell leukodystrophy) spontaneous mutant line in mice. The genome of the Twi mouse presents a single nucleotide polymorphism (SNP), leading to an enzymatically inactive galactosylceramidase (Galc) protein that causes KD. In this context, mouse Twi genotyping is an essential step in KD research. To date, the genotyping method used is labor-intensive and often has ambiguous results. Here, we evaluated a novel protocol for the genotype determination of Galc mutation status in Twi mice based on the allele-discrimination real-time polymerase chain reaction (PCR). Here, DNA is extracted from Twi mice (n = 20, pilot study; n = 120, verification study) and control group (n = 10, pilot study; n = 30 verification study) and assessed by allele-discrimination real-time PCR to detect SNP c.355G>A. Using the allele-discrimination PCR, all of the samples are identified correctly with the genotype GG (wild-type, WT), GA (heterozygote, HET), or AA (homozygote, HOM) using the first analysis and no animals are not genotyped. We demonstrated that this novel method can be used to distinguish KD timely, accurately, and without ambiguity in HOM, WT, and HET animals. This protocol represents a great opportunity to increase accuracy and speed in KD research.

Galactosylceramidase deficiency and pathological abnormalities in cerebral white matter of Krabbe disease

Krabbe Disease (KD) is an autosomal recessive disorder that results from loss-of-function mutations in the GALC gene, which encodes lysosomal enzyme galactosylceramidase (GALC). Functional deficiency of GALC is toxic to myelin-producing cells, which leads to progressive demyelination in both the central and peripheral nervous systems. It is hypothesized that accumulation of psychosine, which can only be degraded by GALC, is a primary initiator of pathologic cascades. Despite the central role of GALC in KD pathomechanism, investigations of GALC deficiency at a protein level are largely absent, due in part, to the lack of sensitive antibodies in the field. Leveraging two custom antibodies that can detect GALC at endogenous levels, we demonstrated that GALC protein is predominantly localized to oligodendrocytes in cerebral white matter of an infant brain, consistent with its functional role in myelination. Mature GALC could also be quantitatively detected as a 26 kDa band by western blotting and correlated to enzyme activity in brain tissues. The p.Ile562Thr polymorphic variant, which is over-represented in the KD population, was associated with reduced mature GALC protein and activity. In three infantile KD cases, homozygous null mutations in GALC lead to deficiency in total GALC protein and activity. Interestingly, although GALC activity was absent, normal levels of total GALC protein were detected by a sandwich ELISA using our custom antibodies in a later-onset KD brain, which suggests that the assay has the potential to differentiate infantile- and later-onset KD cases. Among the infantile KD cases, we quantified a 5-fold increase in psychosine levels, and observed increased levels of acid ceramidase, a key enzyme for psychosine production, and hyperglycosylated lysosomal-associated membrane protein 1, a marker for lysosomal activation, in periventricular white matter, a major pathological brain region, when compared with age-matched normal controls. While near complete demyelination was observed in these cases, we quantified that an early-infantile case (age of death at 10 months) had about 3-fold increases in both globoid cells, a pathological hallmark for KD, and CD8-positive T lymphocytes, a pathological marker for multiple sclerosis, in the white matter when compared with a slower progressing infantile case (age of death at 21 months), which suggests a positive correlation between clinical severity and neuropathology. Taken together, our findings have advanced the understanding of GALC protein biology in the context of normal and KD brain white matter. We also revealed new neuropathological changes that may provide insights to understand KD pathogenesis.

Chronic lithium administration in a mouse model for Krabbe disease

Krabbe disease (KD; or globoid cell leukodystrophy) is an autosomal recessive lysosomal storage disorder caused by deficiency of the galactosylceramidase (GALC) enzyme. No cure is currently available for KD. Clinical applied treatments are supportive only. Recently, we demonstrated that two differently acting autophagy inducers (lithium and rapamycin) can improve some KD hallmarks in-vitro, laying the foundation for their in-vivo pre-clinical testing. Here, we test lithium carbonate in-vivo, in the spontaneous mouse model for KD, the Twitcher (TWI) mouse. The drug is administered ad libitum via drinking water (600 mg/L) starting from post natal day 20. We longitudinally monitor the mouse motor performance through the grip strength, the hanging wire and the rotarod tests, and a set of biochemical parameters related to the KD pathogenesis [i.e., GALC enzymatic activity, psychosine (PSY) accumulation and astrogliosis]. Additionally, we investigate the expression of some crucial markers related to the two pathways that could be altered by lithium: the autophagy and the β-catenin-dependent pathways. Results demonstrate that lithium has not a significant rescue effect on the TWI phenotype, although it can slightly and transiently improves muscle strength. We also show that lithium, with this administration protocol, is unable to stimulate autophagy in the TWI mice central nervous system, whereas results suggest that it can restore the β-catenin activation status in the TWI sciatic nerve. Overall, these data provide intriguing inputs for further evaluations of lithium treatment in TWI mice.

Compound heterozygous pathogenic variants in the GALC gene cause infant-onset Krabbe disease

BACKGROUND

Krabbe disease, also called globoid cell leukodystrophy, is an autosomal recessive disease caused by a deficiency of lysosomal galactocerebrosidase. Infantile Krabbe occurring before 12 months of age accounts for most cases. Typical clinical features include irritability, seizures, peripheral neuropathy, and progressive neurodegeneration.

METHODS

We collected and summarized the clinical and genetic data of an 8-month-old boy who demonstrated Krabbe disease onset at around 6 months. Potential pathogenic variants were screened by whole exome sequencing, and effects of candidate variants on alternative transcript and truncated protein were further validated at the RNA and protein level.

RESULTS

Galactocerebrosidase activity was nearly absent in his blood, and whole exome sequencing revealed compound heterozygous variants [NM_000153.4: (c.658C>T); (c.328+5G>T)] in galactosylceramidase (GALC). The variant c.328+5G>T was predicted to alter splicing, and the abnormal isoform transcript was validated by observation of abnormal RNA isoforms. The variant c.658C>T was predicted to cause truncation of the protein, which was validated by western blotting.

CONCLUSIONS

Our findings revealed compound heterozygous variants with solid experimental results for Krabbe disease and provides strong evidence for further Krabbe disease screening and clinical consulting. As a rare inherited systemic disorder, genetic variants in Krabbe disease should be investigated, as experimental validation for clinical diagnosis is needed.

Comprehensive clinical, biochemical, radiological and genetic analysis of 28 Turkish cases with suspected metachromatic leukodystrophy and their relatives

Metachromatic leukodystrophy (MLD) is a glycosphingolipid storage disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ASA) or its activator protein saposin B. MLD can affect all age groups in severity varying from a severe fatal form to milder adult onset forms. Diagnosis is usually made by measuring leukocyte ASA activity. However, this test can give false negative or false positive laboratory results due to pseudodeficiency of ASA and saposin B deficiency, respectively. Therefore, we aimed to evaluate patients with suspected MLD in a Turkish population by comprehensive clinical, biochemical, radiological, and genetic analyses for molecular and phenotypic characterization. We analyzed 28 suspected MLD patients and 41 relatives from 24 families. ASA activity was found to be decreased in 21 of 28 patients. Sixteen patients were diagnosed as MLD (11 late infantile, 2 juvenile and 3 adult types), 2 MSD, 2 pseudodeficiency (PD) and the remaining 8 patients were diagnosed as having other leukodystrophies. Enzyme analysis showed that the age of onset of MLD did not correlate with residual ASA activity. Sequence analysis showed 11 mutations in ARSA, of which 4 were novel (p.Trp195GlyfsTer5, p.Gly298Asp, p.Arg301Leu, and p.Gly311Asp), and 2 mutations in SUMF1 causing multiple sulfatase deficiency, and confirmed the diagnosis of MLD in 2 presymptomatic relatives. All individuals with confirmed mutations had low ASA activity and urinary sulfatide excretion. Intra- and inter-familial variability was high for the same ARSA missense genotypes, indicating the contribution of other factors to disease expression. Imaging findings were evaluated through a modified brain MRI scoring system which indicated patients with protein-truncating mutations had more severe MRI findings and late-infantile disease onset. MRI findings were not specific for the diagnosis. Anti-sulfatide IgM was similar to control subjects, and IgG, elevated in multiple sulfatase deficiency. In conclusion, the knowledge on the biochemical, clinical and genetic basis of MLD was expanded, a modified diagnostic laboratory algorithm for MLD based on integrated evaluation of ASA activity, urinary sulfatide excretion and genetic tests was devised.

Discovery of a CNS penetrant small molecule SMN2 splicing modulator with improved tolerability for spinal muscular atrophy

Spinal muscular atrophy (SMA) is a motor neuron disease, typically resulting from loss-of-function mutations in the survival motor neuron 1 (SMN1) gene. Nusinersen/SPINRAZA, a splice-switching oligonucleotide that modulates SMN2 (a paralog of SMN1) splicing and consequently increases SMN protein levels, has a therapeutic effect for SMA. Previously reported small-molecule SMN2 splicing modulators such as risdiplam/EVRYSDI and its analog SMN-C3 modulate not only the splicing of SMN2 but also that of secondary splice targets, including forkhead box protein M1 (FOXM1). Through screening SMA patient-derived fibroblasts, a novel small molecule, designated TEC-1, was identified that selectively modulates SMN2 splicing over three secondary splice targets. TEC-1 did not strongly affect the splicing of FOXM1, and unlike risdiplam, did not induce micronucleus formation. In addition, TEC-1 showed higher selectively on galactosylceramidase and huntingtin gene expression compared to previously reported compounds (e.g., SMN-C3) due to off-target effects on cryptic exon inclusion and nonsense-mediated mRNA decay. Moreover, TEC-1 significantly ameliorated the disease phenotype in an SMA murine model in vivo. Thus, TEC-1 may have promising therapeutic potential for SMA, and our study demonstrates the feasibility of RNA-targeting small-molecule drug development with an improved tolerability profile.

Fluorimetric assay with a novel substrate for quantification of galactocerebrosidase activity in dried blood spot specimens

Background

Decreased galactocerebrosidase (GALC) enzyme activity is causative for Krabbe disease, a lysosomal storage disorder with devastating neurodegenerative consequences. Quantitative fluorimetric assays for GALC activity in isolated blood and skin cells have been described; however, no such assay has been described using dried blood spot (DBS) specimens.

Methods

GALC enzyme activity was measured quantitatively using fluorescence from a novel glycosidic substrate: carboxy derived from 6-hexadecanoylamino-4-methylumbelliferone. GALC activity was demonstrated on newborn DBS specimens, known Krabbe disease patient specimens, proficiency testing and quality control samples.

Results

We present data on characterization of the novel substrate and assay, including pH optimization and enzyme kinetics using a fluorimetric profile. Single and multi-day precision analyses revealed tight analytical measurements with %CV ranging from 5.2% to 14.1%. GALC enzyme activity was linear over the range of 0.31 - 12.04 μmol/l/h with a limit of detection of 0.066 μmol/l/h. Our results with this assay show a clear discrimination between GALC activities in samples from Krabbe disease patients versus presumed normal newborn samples.

Conclusions

A fluorimetric assay for GALC enzyme activity measurement on dried blood spot specimens is feasible. Improvements to the assay including novel substrate design, increased substrate concentration and removal of sodium chloride maximize the specificity of the assay and minimize interference from β-galactosidase.

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First fluorescent assay to measure GALC enzyme activity in dried blood spots.

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Linear range covers the activity normally seen in newborn dried blood spots.

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Successfully discriminates deficient from normal enzyme activity in DBS specimens.

Brain-targeted enzyme-loaded nanoparticles: A breach through the blood-brain barrier for enzyme replacement therapy in Krabbe disease

Lysosomal storage disorders (LSDs) result from an enzyme deficiency within lysosomes. The systemic administration of the missing enzyme, however, is not effective in the case of LSDs with central nervous system (CNS)-involvement. Here, an enzyme delivery system based on the encapsulation of cross-linked enzyme aggregates (CLEAs) into poly-(lactide-co-glycolide) (PLGA) nanoparticles (NPs) functionalized with brain targeting peptides (Ang2, g7 or Tf2) is demonstrated for Krabbe disease, a neurodegenerative LSD caused by galactosylceramidase (GALC) deficiency. We first synthesize and characterize Ang2-, g7- and Tf2-targeted GALC CLEA NPs. We study NP cell trafficking and capability to reinstate enzymatic activity in vitro. Then, we successfully test our formulations in the Twitcher mouse. We report enzymatic activity measurements in the nervous system and in accumulation districts upon intraperitoneal injections, demonstrating activity recovery in the brain up to the unaffected mice level. Together, these results open new therapeutic perspectives for all LSDs with major CNS-involvement.

Genotype and phenotype classification of 29 patients affected by Krabbe disease

Krabbe disease is a rare neurodegenerative lysosomal storage disorder caused by mutations in the galactocerebrosidase gene, GALC. Krabbe disease usually affects infants, but has also been reported in older children and adults. Different phenotypes are described based on age at onset. The gene encoding the galactocerebrosidase enzyme was cloned and expressed in 1993, and up until today 117 mutations have been described. In a patient population of Northern European origin, a 30-kb deletion and two missense mutations, c.1586C>T; p.T529M and c.1700A>C; p.Y567S, are expected to account for 50%-60% of pathogenic alleles. In this study, we present information on genetic variation, enzyme activity, and phenotypes of 29 patients affected by Krabbe disease. Patient data were collected from patient files at the Department of Clinical Genetics, Rigshospitalet. Ten previously unreported mutations were identified, including four missense mutations; c.1142C>T; p.T381I, c.596G>T; p.R199M, c.443G>A; p.G148E, c.1858G>A; p.G620R, two nonsense mutations; c.863G>A; p.W288*, c.1214c>G; p.S405*, one splice site mutation; c.442+1G>A, one insertion; c.293insT and two deletions; c.1003_1004del, c.887delA. For all of the new mutations, we were able to classify them in phenotype groups. Furthermore, we present a combined allele frequency of the three frequent mutations p.T529M, p.Y567S, and the 30-kb deletion of 62%, and we describe a broadening of the phenotypes associated with the mutations p.T529M and p.Y567S.

Exonic deletions in GALC are frequent in Japanese globoid-cell leukodystrophy patients

Globoid-cell leukodystrophy is an autosomal-recessive lysosomal storage disorder. Single-base substitutions and small indel mutations in the GALC gene are common in Japanese patients. In this study, we identified three novel deletions, in exons 1, 8, and 11-12, in three patients using Multiplex Ligation-dependent Probe Amplification. We suggest that some patients in whom no or only a single pathogenic mutation is detected by Sanger sequencing may have exon deletions.

Utility of amniotic fluid chitotriosidase in the prenatal diagnosis of lysosomal storage disorders

OBJECTIVE

Plasma chitotriosidase is a documented biomarker for certain lysosomal storage disorders. However, its clinical utility for prenatal samples is not elucidated yet.

METHODS

We have established Reference intervals for amniotic fluid chitotriosidase using control amniotic fluids (n = 47) and compared the activity with amniotic fluids affected by lysosomal storage disorders (n = 25).

RESULTS

The reference interval established was 0-6.76 nmol/h/ml. The amniotic fluids affected with LSDs exhibited elevation of chitotriosidase. The area under the curve (AUC) of receiver operating characteristic curve for affected vs. healthy was 0.987 indicating 98.6% accuracy of chitotriosidase in identifying pregnancies affected with LSDs. Among the different LSDs, Gaucher (202.00 ± 35.27 nmol/h/ml) and Niemann-pick A/B (60.33 ± 21.59 nmol/h/ml) showed very high levels of chitotriosidase.

CONCLUSION

Amniotic fluid chitotriosidase has the potential to serve as a diagnostic marker for lysosomal storage disorders, more specifically for Gaucher and Niemann-Pick A/B.

Unfolded protein response is activated in Krabbe disease in a manner dependent on the mutation type

Krabbe disease, one of the autosomal-recessive lysosomal storage disorders (LSDs), is caused by a deficiency of galactocerebrosidase (GALC) activity, resulting in the intracellular accumulation of psychosine, which is cytotoxic for neuronal cells. Genetically pathogenic mutations result in conformational changes in GALC and disrupt the lysosmal trafficking of cargos, which subsequently accumulate in the endoplasmic reticulum (ER). Recently, ER stress together with the activation of the unfolded protein response (UPR) has been suggested to play a key role in the pathogenesis of LSDs. In this study, we hence investigated whether the UPR is activated in Krabbe disease using COS-7 cells expressing pathogenic GALC mutants and skin fibroblasts (SFs) from Krabbe disease patients with various phenotypes, using a combination of semiquantitative and quantitative real-time polymerase chain reactions. We found that UPR activation in Krabbe disease depends on the mutations and cell types, and there is the possibility that multiple pathways, involving ER chaperones, inositol-requiring kinase 1, and protein kinase regulated by RNA-like ER kinase are activated by mutations associated with the infantile form. These results indicate that in Krabbe disease, each misfolded/unfolded protein evokes different UPR activation depending on the mutation, and that the activated pathways affect the phenotypes.

Prenatal Diagnosis of Lysosomal Storage Disorders Using Chorionic Villi

Prenatal enzymatic diagnosis for an array of lysosomal storage disorders (LSDs) can be performed accurately, provided that a confirmed diagnosis by biochemical/molecular study in the index case is available and a strict defined protocol, specific to each individual disorder is followed. The present chapter describes the protocols for reliable and accurate prenatal enzymatic diagnoses by fluorometric and spectrophotometric methods of lysosomal storage disorders: Gaucher, Fabry, Pompe, Niemann Pick A/B, Tay Sach, Sandhoff, GM1, Mucoplysaccharidoses, Wolman, Krabbe, Metachromatic leukodystrophy, and Batten diseases using uncultured chorionic villi samples. The biological reference intervals for enzyme levels in normal and affected fetuses are given for interpretation of prenatal results. It is imperative to establish normal reference interval in each laboratory to take into account the local environment, technical variations, and different ethnicities. Besides, enzyme activity in the fetus should be represented as percentage of the mean activity of enzyme of normal fetuses. The pitfalls and challenges in prenatal diagnosis as well as technical problems in performing enzyme assays are also discussed to help the reader in standardization and performing the assays for correct diagnosis.

Suppression of galactocerebrosidase premature termination codon and rescue of galactocerebrosidase activity in twitcher cells

Krabbe's disease (KD) is a degenerative lysosomal storage disease resulting from deficiency of β-galactocerebrosidase activity. Over 100 mutations are known to cause the disease, and these usually occur in compound heterozygote patterns. In affected patients, nonsense mutations leading to a nonfunctional enzyme are often found associated with other mutations. The twitcher mouse is a naturally occurring model of KD, containing in β-galactocerebrosidase a premature stop codon, W339X. Recent studies have shown that selected compounds may induce the ribosomal bypass of premature stop codons without affecting the normal termination codons. The rescue of β-galactocerebrosidase activity induced by treatment with premature termination codon (PTC) 124, a well-characterized compound known to induce ribosomal read-through, was investigated on oligodendrocytes prepared from twitcher mice and on human fibroblasts from patients bearing nonsense mutations. The effectiveness of the nonsense-mediated mRNA decay (NMD) inhibitor 1 (NMDI1), a newly identified inhibitor of NMD, was also tested. Incubation of these cell lines with PTC124 and NMDI1 increased the levels of mRNA and rescued galactocerebrosidase enzymatic activity in a dose-dependent manner. The low but sustained expression of β-galactocerebrosidase in oligodendrocytes was sufficient to improve the morphology of the differentiated cells. Our in vitro approach provides the basis for further investigation of ribosomal read-through as an alternative therapeutic strategy to ameliorate the quality of life in selected KD patients. © 2016 Wiley Periodicals, Inc.

New therapeutic approaches for Krabbe disease: The potential of pharmacological chaperones

Missense mutations in the lysosomal hydrolase β‐galactocerebrosidase (GALC) account for at least 40% of known cases of Krabbe disease (KD). Most of these missense mutations are predicted to disrupt the fold of the enzyme, preventing GALC in sufficient amounts from reaching its site of action in the lysosome. The predominant central nervous system (CNS) pathology and the absence of accumulated primary substrate within the lysosome mean that strategies used to treat other lysosomal storage disorders (LSDs) are insufficient in KD, highlighting the still unmet clinical requirement for successful KD therapeutics. Pharmacological chaperone therapy (PCT) is one strategy being explored to overcome defects in GALC caused by missense mutations. In recent studies, several small‐molecule inhibitors have been identified as promising chaperone candidates for GALC. This Review discusses new insights gained from these studies and highlights the importance of characterizing both the chaperone interaction and the underlying mutation to define properly a responsive population and to improve the translation of existing lead molecules into successful KD therapeutics. We also highlight the importance of using multiple complementary methods to monitor PCT effectiveness. Finally, we explore the exciting potential of using combination therapy to ameliorate disease through the use of PCT with existing therapies or with more generalized therapeutics, such as proteasomal inhibition, that have been shown to have synergistic effects in other LSDs. This, alongside advances in CNS delivery of recombinant enzyme and targeted rational drug design, provides a promising outlook for the development of KD therapeutics. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Hematopoietic Stem cell transplantation and lentiviral vector-based gene therapy for Krabbe's disease: Present convictions and future prospects

Currently, presymtomatic hematopoietic stem and progenitor cell transplantation (HSPCT) is the only therapeutic modality that alleviates Krabbe's disease (KD)‐induced central nervous system damage. However, all HSPCT‐treated patients exhibit severe deterioration in peripheral nervous system function characterized by major motor and expressive language pathologies. We hypothesize that a combination of several mechanisms contribute to this phenomenon, including 1) nonoptimal conditioning protocols with consequent inefficient engraftment and biodistribution of donor‐derived cells and 2) insufficient uptake of donor cell‐secreted galactocerebrosidease (GALC) secondary to a naturally low expression level of the cation‐independent mannose 6‐phosphate‐receptor (CI‐MPR). We have characterized the effects of a busulfan (Bu) based conditioning regimen on the efficacy of HSPCT in prolonging twi mouse average life span. There was no correlation between the efficiency of bone marrow engraftment of donor cells and twi mouse average life span. HSPCT prolonged the average life span of twi mice, which directly correlated with the aggressiveness of the Bu‐mediated conditioning protocols. HSPC transduced with lentiviral vectors carrying the GALC cDNA under control of cell‐specific promoters were efficiently engrafted in twi mouse bone marrow. To facilitate HSPCT‐mediated correction of GALC deficiency in target cells expressing low levels of CI‐MPR, a novel GALC fusion protein including the ApoE1 receptor was developed. Efficient cellular uptake of the novel fusion protein was mediated by a mannose‐6‐phosphate‐independent mechanism. The novel findings described here elucidate some of the cellular mechanisms that impede the cure of KD patients by HSPCT and concomitantly open new directions to enhance the therapeutic efficacy of HSPCT protocols for KD. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Large-scale study of clinical and biochemical characteristics of Chinese patients diagnosed with Krabbe disease

Krabbe disease (KD) is a rare disease caused by the deficiency of β-galactocerebrosidase. This study investigated 22 unrelated Chinese patients, including their clinical presentations, plasma psychosine levels and β-galactocerebrosidase gene mutations. We found the late-onset form of KD present in 82% of the patients in our study, which was more prevalent than in patients from other populations. Plasma psychosine levels were elevated in KD, which were correlated with the severity of clinical presentations. Sanger sequencing identified 8 novel mutations, including 7 missense mutations, p.H253Y, p.S259L, p.P318L, p.F350V, p.T428A, p.L530P, p.G586D, and 1 splicing mutation, c.1251+1G>A. Quantitative real-time polymerase chain reaction (PCR) and multiplex ligation-dependent probe amplification identified a novel exon 12 and 14 deletion, separately. Next generation sequencing, applied at the final step, revealed 2 missense mutant alleles missed using Sanger sequencing. The most common mutation in Chinese population is p.P154H, which accounts for 20.5% of alleles. Consistent with the higher prevalence of the late-onset form of KD, missense mutations predominated in our study, different with the common mutation types in Europe and Japan. This work was the first large-scale study of Chinese KD patients describing their clinical, biochemical and genetic characteristics, which furthered our understanding of this classical neurological lysosomal storage disease.

Cell-based high-throughput screening identifies galactocerebrosidase enhancers as potential small-molecule therapies for Krabbe's disease

Krabbe's disease, also known as globoid cell leukodystrophy (GLD), is a lysosomal storage disease caused by the deficiency of the lysosomal enzyme β-galactocerebrosidase (GALC), resulting in severe neurological manifestations related to demyelination secondary to elevated galactosylsphingosine (psychosine) with its subsequent cytotoxicity. The only available treatment is hematopoietic stem cell transplantation, which delays disease onset but does not prevent long-term neurological manifestations. This article describes the identification of small molecules that enhance mutant GALC activity, identified by quantitative cell-based high-throughput screening (qHTS). Using a specific neurologically relevant murine cell line (145M-Twi) modified to express common human hGALC-G270D mutant, we were able to detect GALC activity in a 1,536-well microplate format. The qHTS of approximately 46,000 compounds identified three small molecules that showed significant enhancements of residual mutant GALC activity in primary cell lines from GLD patients. These compounds were shown to increase the levels of GALC-G270D mutant in the lysosomal compartment. In kinetic assessments, these small molecules failed to disturb the GALC kinetic profile under acidic conditions, which is highly desirable for folding-assisting molecules operating in the endoplasmic reticulum and not affecting GALC catalytic properties in the lysosomal compartment. In addition, these small molecules rescued the decreased GALC activity at neutral pH and partially stabilized GALC under heat-denaturating conditions. These drug-like compounds can be used as the starting point to develop novel small-molecule agents to treat the progressive neurodegenerative course of GLD. © 2016 Wiley Periodicals, Inc.

The Spectrum of Krabbe Disease in Greece: Biochemical and Molecular Findings

Krabbe disease is an autosomal recessive neurodegenerative lysosomal storage disease caused by the deficiency of β-galactocerebrosidase. This deficiency results in the impaired degradation of β-galactocerebroside, a major myelin lipid, and of galactosylsphingosine. Based on the age of onset of neurological symptoms, an infantile form (90% patients) and late-onset forms (10% patients) of the disease are recognized. Over 130 disease-causing mutations have been identified in the β-galactocerebrosidase gene. We present the biochemical and molecular findings in 19 cases of Krabbe disease, 17 of them unrelated, diagnosed in Greece over the last 30 years. β-Galactocerebrosidase activity assayed in leukocyte homogenates using either the tritium-labeled or the fluorescent substrate was diagnostic for all. Increased plasma chitotriosidase activity was found in 11/15 patients.Mutational analysis, carried out in 11 unrelated cases, identified seven different mutations, four previously described (p.I250T, c.1161+6532_polyA+9kbdel, p.K139del, p.D187V) and three novel mutations (p.D610A, c.583-1 G>C, p.W132X), and seven distinct genotypes. The most prevalent mutation was mutation p.I250T, first described in a patient of Greek origin. It accounted for 36.4% (8/22) of the mutant alleles. The second most frequent mutation was c.1161+6532_polyA+9kbdel that accounted for 22.7% (5/22) of the mutant alleles. The observed frequency was lower than that described in Northern European countries and closer to that described in Italian patients.

Krabbe Disease in the Arab World

The autosomal recessive inherited Krabbe disease (KD) is a devastating pediatric lysosomal storage disorder affecting white matter of the brain. It is caused by mutations in the gene coding for the lysosomal enzyme galactocerebrosidase. While most patients present with symptoms within the first 6 months of life, others present later in life throughout adulthood. The early infantile form of KD (EIKD) is frequent in the Muslim Arab population in Israel, with a very high prevalence of approximately 1/100 to 1/150 live births. The homozygous variant c.1582G > A (p.D528N) was found to be responsible for EIKD in Palestinian Arab patients. KD was reported in different Arab countries with much lower frequency. While most Arab patients presented with EIKD, late infantile and late onset KD forms were also reported. Most Arab patients presented with variable symptoms ranging from EIKD to late onset KD, with variable clinical findings. Based on literature studies, this review focuses on the clinical and molecular findings of KD patients with Arab ancestry, and highlights the need for developing universal genetic screening programs to overcome the under-reported status of KD prevalence in Arabia. This is expected to improve the prognosis of the disease and promote targeted molecular diagnostics to the Arab patients.

Pharmacological chaperones increase residual β-galactocerebrosidase activity in fibroblasts from Krabbe patients

Krabbe disease or globoid cell leukodystrophy is a degenerative, lysosomal storage disease resulting from the deficiency of β-galactocerebrosidase activity. This enzyme catalyzes the lysosomal hydrolysis of galactocerebroside and psychosine. Krabbe disease is inherited as an autosomal recessive trait, and many of the 70 disease-causing mutations identified in the GALC gene are associated with protein misfolding. Recent studies have shown that enzyme inhibitors can sometimes translocate misfolded polypeptides to their appropriate target organelle bypassing the normal cellular quality control machinery and resulting in enhanced activity. In search for pharmacological chaperones that could rescue the β-galactocerebrosidase activity, we investigated the effect of α-Lobeline or 3',4',7-trihydroxyisoflavone on several patient-derived fibroblast cell lines carrying missense mutations, rather than on transduced cell lines. Incubation of these cell lines with α-lobeline or 3',4',7-trihydroxyisoflavone leads to an increase of β-galacocerebrosidase activity in p.G553R + p.G553R, in p.E130K + p.N295T and in p.G57S + p.G57S mutant forms over the critical threshold. The low but sustained expression of β-galactocerebrosidase induced by these compounds is a promising result; in fact, it is known that residual enzyme activity of only 15-20% is sufficient for clinical efficacy. The molecular interaction of the two chaperones with β-galactocerebrosidase is also supported by in silico analysis. Collectively, our combined in silico-in vitro approach indicate α-lobeline and 3',4',7-trihydroxyisoflavone as two potential pharmacological chaperones for the treatment or improvement of quality of life in selected Krabbe disease patients.

Glycobiology: progress, problems, and perspectives

This review highlights different aspects of glycobiology with analysis of recent progress in the study of biosynthesis, degradation, and biological role of glycoconjugates and of hereditary diseases related to the metabolism of these compounds. In addition, the review presents some analysis of the papers of other authors who have contributed to this special issue.

Characterization and application of a disease-cell model for a neurodegenerative lysosomal disease

Disease-cell models that recapitulate specific molecular phenotypes are essential for the investigation of molecular pathogenesis of neurodegenerative diseases including lysosomal storage diseases (LSDs) with predominant neurological manifestations. Herein we report the development and characterization of a cell model for a rapid neurodegenerative LSDs, globoid-cell leukodystrophy (GLD), mostly known as Krabbe disease. GLD is caused by the deficiency of β-galactocerebrosidase (GALC), a lysosomal enzyme that hydrolyzes two glycosphingolipids, psychosine and galactosylceramide. Unfortunately, the available culture fibroblasts from GLD patients consist of a limited research tool as these cells fail to accumulate psychosine, the central pathogenic glycosphingolipid in this LSD that results in severe demyelination. Firstly, we obtained brain samples from the Twitcher (Twi) mice (GALC(twi/twi)), the natural mouse model with GALC deficiency. We immortalized the primary neuroglial cultured cells with SV40 large T antigen, generating the 145M-Twi and the 145C-Wt cell lines from the Twi and control mice, respectively. Both cell lines expressed specific oligodendrocyte markers including A2B5 and GalC. The 145M-Twi cells showed biochemical and cellular disturbances related to GLD neuropathogenesis including remarkable caspase-3 activation, release of cytochrome C into the cytosol and expansion of the lysosomal compartment. Under treatment with glycosphingolipids, 145M-Twi cells showed increased LC3B levels, a marker of autophagy. Using the LC-MS/MS method that we developed, the 145M-Twi cells showed significantly higher levels of psychosine. The 145M-Twi and 145C-Wt lines allowed the development of a robust throughput LC-MS/MS assay to measure cellular psychosine levels. In this throughput assay, l-cycloserine showed to significantly reduce the 145M-Twi cellular levels of psychosine. The established 145M-Twi cells are powerful research tools to investigate the neurologically relevant pathogenic pathways as well as to develop primary screening assays for the identification of therapeutic agents for GLD and potentially other glycosphingolipid disorders.

Enzymatic Screening and Diagnosis of Lysosomal Storage Diseases

Lysosomal storage diseases (LSDs) are a group of more than 50 genetic disorders. Clinical symptoms are caused by the deficiency of specific enzyme (enzymes) function and resultant substrate accumulation in the lysosomes, which leads to impaired cellular function and progressive tissue and organ dysfunction. Measurement of lysosomal enzyme activity plays an important role in the clinical diagnosis of LSDs. The major enzymatic testing methods include fluorometric assays using artificial 4-methylumbelliferyl (4-MU) substrates, spectrophotometric assays and radioactive assays with radiolabeled natural substrates. As many effective treatment options have become available, presymptomatic diagnosis and early intervention are imperative. Many methods were developed in the past decade for newborn screening (NBS) of selective LSDs in dried blood spot (DBS) specimens. Modified fluorometric assays with 4-MU substrates, MS/MS or LC-MS/MS multiplex enzyme assays, digital microfluidic fluorometric assays, and immune-quantification assays for enzyme contents have been reported in NBS of LSDs, each with its own advantages and limitations. Active technical validation studies and pilot screening studies have been conducted or are ongoing. These studies have provided insight in the efficacy of various methodologies. In this review, technical aspects of the enzyme assays used in clinical diagnosis and NBS are summarized. The important findings from pilot NBS studies are also reviewed.

A high-throughput screening assay using Krabbe disease patient cells

Globoid cell leukodystrophy (GLD) or Krabbe disease is a lysosomal disease caused by β-galactocerebrosidase (GALC) deficiency resulting in a rapidly progressive neurodegenerative disorder. Unfortunately, the only available treatment is hematopoietic bone marrow transplantation, which prevents its fulminant manifestation but without treating further neurological manifestations. Here, we describe the development of a cellular high-throughput screening (HTS) assay using GLD patient fibroblasts to screen for small molecules that enhance the residual mutant GALC enzymatic activity. Small molecules have substantial therapeutic potential in GLD because they are more prone to cross the blood-brain barrier, reaching the neuronal affected cells. The transformation of primary skin fibroblasts with SV40 large T antigen has been shown to maintain the biochemical characteristics of the GLD cells and generates sufficient cells for the HTS. Using a specific fluorescent substrate, residual GALC activity from an SV40-transformed GLD patient fibroblast was measurable in high-density microplates. The pilot quantitative HTS against a small compound collection showed robust statistics. The small molecules that showed active concentration-response curves were further studied in primary GLD fibroblasts. This cell-based HTS assay demonstrates the feasibility of employing live GLD patient cells to identify therapeutic agents that can potentially be used for the treatment of this progressive neurodegenerative disease.

Persistence of psychosine in brain lipid rafts is a limiting factor in the therapeutic recovery of a mouse model for Krabbe disease

Sphingolipids are intrinsic components of membrane lipid rafts. The abnormal accumulation of these molecules may introduce architectural and functional changes in these domains, leading to cellular dysfunction. Galactosylsphingosine (psychosine) is a pathogenic lipid raft-associated molecule whose accumulation leads to brain deterioration and irreversible neurological handicap in the incurable leukodystrophy Krabbe disease (KD). The relevance of clearing excessive levels of pathogenic psychosine from lipid rafts in therapy for KD has not been investigated. The work presented here demonstrates that psychosine inhibits raft-mediated endocytosis in neural cells. In addition, although in vitro enzyme reconstitution is sufficient for the reversal of related endocytic defects in affected neural cells, traditional in vivo enzyme therapies in the mouse model of KD appear to be insufficient for complete removal of pathogenic levels of raft-associated psychosine. This work describes a mechanism that may contribute to limiting the in vivo efficacy of traditional therapies for KD.

Induced pluripotent stem cells derived from mouse models of lysosomal storage disorders

Most lysosomal storage diseases (LSDs) are life-threatening genetic diseases. The pathogenesis of these diseases is poorly understood. Induced pluripotent stem (iPS) cell technology offers new opportunities for both mechanistic studies and development of stem cell- based therapies. Here we report the generation of disease-specific iPS cells from mouse models of Fabry disease, globoid cell leukodystrophy (GLD), and mucopolysaccharidosis VII (MPSVII). These mouse model-derived iPS cells showed defects in disease-specific enzyme activities and significant accumulation of substrates for these enzymes. In the lineage-directed differentiation studies, Fabry-iPS and GLD-iPS cells were efficiently differentiated into disease-relevant cell types, such as cardiomyocytes and neural stem cells, which might be useful in mechanistic and therapeutic studies. Notably, MPSVII-iPS cells demonstrated a markedly impaired ability to form embryoid bodies (EBs) in vitro. MPSVII-EBs exibited elevated levels of hyaluronan and its receptor CD44, and markedly reduced expression levels of E-cadherin and cell-proliferating marker. Partial correction of enzyme deficiency in MSPVII-iPS cells led to improved EB formation and reversal of aberrant protein expression. These data indicate a potential mechanism for the partial lethality of MPSVII mice in utero, and suggest a possible abnormality of embryonic development in MPSVII patients. Thus, our study demonstrates the unique promise of iPS cells for studying the pathogenesis and treatment of LSDs.

Specific Determination of β-Galactocerebrosidase Activity via Competitive Inhibition of β-Galactosidase

Background: The determination of cellular β-galactocerebrosidase activity is an established procedure to diagnose Krabbe disease and monitor the efficacy of gene/stem cell-based therapeutic approaches aimed at restoring defective enzymatic activity in patients or disease models. Current biochemical assays for β-galactocerebrosidase show high specificity but generally require large protein amounts from scanty sources such as hematopoietic or neural stem cells. We developed a novel assay based on the hypothesis that specific measurements of β-galactocerebrosidase activity can be performed following complete inhibition of β-galactosidase activity.

Methods: We performed the assay using 2–7.5 μg of sample proteins with the artificial fluorogenic substrate 4-methylumbelliferone-β-galactopyranoside (1.5 mmol/L) resuspended in 0.1/0.2 mol/L citrate/phosphate buffer, pH 4.0, and AgNO3. Reactions were incubated for 30 min at 37 °C. Fluorescence of liberated 4-methylumbelliferone was measured on a spectrofluorometer (λex 360 nm, λem 446 nm).

Results: AgNO3 was a competitive inhibitor of β-galactosidase [inhibition constant (Ki) = 0.12 μmol/L] and completely inhibited β-galactosidase activity when used at a concentration of 11 μmol/L. Under this condition, the β-galactocerebrosidase activity was preserved and could be specifically and accurately measured. The assay can detect β-galactocerebrosidase activity in as little as 2 μg cell protein extract or 7.5 μg tissue. Assay validation was performed using (a) brain tissues from wild-type and twitcher mice and (b) murine GALC−/− hematopoietic stem cells and neural precursor cells transduced by GALC-lentiviral vectors.

Conclusions: The procedure is straightforward, rapid, and reproducible. Within a clinical context, our method unequivocally discriminated cells from healthy subjects and Krabbe patients and is therefore suitable for diagnostic applications.

Biochemical analysis of cultured chorionic villi for the prenatal diagnosis of peroxisomal disorders: biochemical thresholds and molecular sensitivity for maternal cell contamination detection

OBJECTIVES

The prenatal diagnosis of peroxisomal disorders is most often performed by biochemical analysis of cultured chorionic villus sample (CVS) or amniocytes. We aimed to (a) highlight the risk of maternal cell contamination (MCC) in biochemical prenatal diagnosis, (b) establish the threshold of these biochemical assays to MCC, and (c) document the sensitivity of PCR based genotyping of microsatellites for the detection of MCC in prenatal diagnosis of inborn errors by biochemical analysis.

METHODS

The threshold of each biochemical assay was assessed by co-cultivating fibroblasts from known affected and normal individuals. Genotypes for three polymorphic loci were determined by PCR and GeneScan analysis. The sensitivity of the molecular test was determined by DNA mixing experiments and isolation of DNA from co-cultivated fibroblasts.

RESULTS

MCC was detected in 2.5% of at risk CVS cultures (n = 79). Co-cultivation of defective and normal fibroblasts demonstrated that the peroxisomal biochemical assays were accurate at 25% contamination. Very low level DNA or cell contamination (1-5%) was detectable by genotyping, but an allele did not yield a definitive peak based on morphology until approximately 10% contamination. Furthermore, we demonstrated that other inborn errors of metabolism might be more susceptible to diagnostic error by low level MCC.

CONCLUSION

The sensitivity of the microsatellite analysis (> or =10%) is well within the threshold of peroxisomal biochemical assays. Although peroxisomal biochemical assays would not be predicted to introduce a false positive or negative result if MCC <10% were present but not recognised by molecular analysis, the same may not be true for other inborn errors of metabolism.

Reconstitution of lymphocyte subpopulations in children with inherited metabolic storage diseases after haematopoietic cell transplantation

We prospectively evaluated the reconstitution of lymphocyte subpopulations in nine children with lysosomal diseases who underwent 11 allogeneic haematopoietic cell transplants (HCTs) following CD34(+) immunomagnetic enrichment, limited T-cell addback and in vivo B-cell depletion. Absolute lymphocyte count recovery was slow to cross the 5th percentile, occurring at a median of 10 months after HCT in patients with full chimaerism. Natural killer cells represented up to 90% of the total lymphoid population during the first 3 months. CD4(+) lymphocyte recovery occurred 9-18 months after HCT. In most patients, CD8(+) lymphocyte recovery was slow and comparable with that of CD4(+) lymphocytes. The CD4(+)/CD8(+) ratio normalised by 3-7 months after HCT in 50% of the patients. CD8(+) lymphocyte recovery was enhanced in patients with viral reactivation. Reconstitution of B-lymphocytes was particularly delayed in patients treated with rituximab. Declining chimaerism, rejection and viral reactivation were the most common problems in our series. Because of the unique graft manipulation, the pace of lymphocyte reconstitution was particularly slow, suggesting that these patients are at a significantly increased risk of infections for up to 2 years after HCT.

External quality assurance programme for enzymatic analysis of lysosomal storage diseases: a pilot study

Inborn errors of metabolism are rare and laboratories performing diagnostic tests in this field must participate in external quality assurance (EQA) schemes to demonstrate their competence and also to maintain sufficient experience with patient material. EQA schemes for metabolite analyses are available (ERNDIM), but corresponding EQA schemes for enzyme analyses are nonexistent. In this paper we describe a pilot study on lysosomal enzyme testing by four centres in The Netherlands. Quantitative aspects of EQA were studied by interlaboratory comparison of activities of six lysosomal enzymes in a series of buffy coat samples. Interlaboratory variance was enormous. To reduce variance caused by methodological differences, participants reported enzyme activities relative to mean normal values. Beta-D-Galactosidase activities compared well between the participating laboratories (average interlaboratory CV 13%), but for other enzymes large differences were observed, e.g. sphingomyelinase (average CV 38%). Diagnostic proficiency was tested with cultured fibroblasts. In 45 out of a total of 48 tests (12 cell lines, 4 participants) the correct diagnosis was accomplished on the basis of merely biochemical investigations, i.e. without clinical data of the patients. In a survey using blood of a late-onset Pompe disease patient, less conclusive results were obtained. A stable enzyme source was developed for easy distribution. Most lysosomal enzymes were stable upon lyophilization of leukocyte homogenates and during subsequent storage of the freeze-dried material at room temperature, in particular when cryolyoprotectant was added. Shipment of such lyophilized samples is simple and cheap and ideal for an EQA scheme. Our study shows that an EQA programme for enzymatic testing of lysosomal storage diseases is necessary to accomplish reliable diagnostic procedures for lysosomal storage diseases. We recommend that EQA for lysosomal enzymes be implemented through ERNDIM.

Globoid cell leukodystrophy (Krabbe disease): normal umbilical cord blood galactocerebrosidase activity and polymorphic mutations

Globoid cell leukodystrophy is an inherited metabolic disorder of the central nervous system caused by deficiency of the lysosomal enzyme galactocerebrosidase. Haematopoietic stem cell transplantation is the only available effective treatment. The engraftment from normal donors provides competent cells able to correct the metabolic defect. Umbilical cord blood cells have proved to significantly decrease complications and improve engraftment rate compared to adult marrow cells in haematopoietic stem cell transplantation. Umbilical cord blood cells must be of sufficient activity to provide central nervous system recovery after engraftment is obtained. Galactocerebrosidase activity is known to be affected by two polymorphic alleles found at nucleotides 502 and 1637 of the cDNA for this gene. This enzyme activity and the polymorphic alleles noted above were analysed in 83 random samples of umbilical cord blood. The activity, assayed with the fluorogenic substrate 6-hexadecanoylamino-4-methylumbelliferyl-beta-galactopyranoside, in those with neither polymorphic allele was 4.6 +/- 1.7 units (nmol/h per mg protein). This optimal choice of cord blood was found in only 24% of specimens. Homozygotes for 1637T > C with activity of only 1.5 +/- 0.4 units represented 16% of the samples. Those heterozygous for 1637T > C with slightly better activity (2.3 +/- 0.7 units) represented 52% of the samples. Choice of umbilical cord blood for haematopoietic stem cell transplantation, therefore, requires consideration not only of cell quantity and HLA compatibility but also selection for normal alleles to obtain maximal enzymatic activity for central nervous system correction.

Allogeneic bone marrow stem cell transplantation following CD34+ immunomagnetic enrichment in patients with inherited metabolic storage diseases

T-cell depletion is an essential step in reducing the risk of graft-versus-host disease (GVHD) in patients with inherited metabolic storage diseases (IMSD) undergoing hematopoietic stem cell transplantation. This goal can be achieved either by selective removal of T cells or by positive selection of CD34+ cells. Large-scale preparations of purified CD34+ cells from bone marrow products have not been extensively described. We report our results with bone marrow CD34+ cell enrichment using the CliniMACS system in eight children with IMSD. The median recovery of positively selected CD34+ cells was 46.2% with a purity of 97.5%, and a residual T cell content of 0.04 x 10(6). A median of 5.5 x 10(6)/kg of CD34+ cells was infused. All patients engrafted at a median time of 12 days and none of the patients developed GVHD. This method is technically feasible and can be successfully used to transplant children with IMSD.

The enzymatic hydrolysis of 6-acylamino-4-methylumbelliferyl-beta-D-glucosides: identification of a novel human acid beta-glucosidase

Fluorogenic 6-acylamino-4-methylumbelliferyl-beta-D-glucosides were found to be poor substrates for the three known human beta-glucosidases, i.e., lysosomal and non-lysosomal glucocerebrosidases and cytosolic broad-specificity beta-glucosidase. However, homogenates of human tissues and human cell types showed significant enzymatic hydrolysis of 6-ethanoylamino-4-methylumbelliferyl-beta-D-glucoside (EMGlc) due to the activity of a hitherto undescribed beta-glucosidase, called here EMGlc-ase. It was shown that the isozyme is hardly active towards 4-methylumbelliferyl-beta-D-glucoside or glucosylceramide. EMGlc-ase exhibits maximal activity at pH 4.5 and 5.0 in the absence and presence of sodium taurocholate respectively. It is a soluble lysosomal enzyme with a discrete isoelectric point of about 5.0. EMGlc-ase is not inhibited by conduritol B-epoxide, is activated by sodium taurocholate and binds strongly to Concanavalin A. This enzyme is not deficient in relation to Gaucher disease.