Increased glucosylsphingosine levels and Gaucher disease in GBA1-associated Parkinson's disease.

INTRODUCTION: Gaucher's disease (GD) is caused by biallelic mutations in the GBA1 gene, leading to reduced glucocerebrosidase (GCase) activity and substrate (glucosylceramide and glucosylsphingosine, GlcSph) accumulation. GBA1 variant carriers are at risk of Parkinson's disease (PD), but only those with biallelic mutations cross the threshold of GCase reduction, leading to substrate accumulation and GD. The link between GBA1 mutations, GD and PD is not fully understood. Here we aimed at reporting the results of a large PD population screening with dried blood spot tests for GD. METHODS: We measured GCase activity and GlcSph levels in 1344 PD patients with dried blood spot tests, and performed GBA1 genetic sequencing. RESULTS: While the GCase activity was reduced in GBA1-PD carriers compared to wild type PD, GlcSph was increased in GBA1-PD compared to GBA1-controls, regardless of the underlying type of GBA1 variant. 13.6 % and 0.4 % of PD patients had mono- or biallelic GBA1 mutations respectively. GCase deficiency, lipid accumulation and clinical manifestations of GD was detected in five PD patients with biallelic GBA1 mutations, of whom four had a risk combined with a GD causing variant. CONCLUSIONS: GlcSph appearing higher in PD may represent a reliable biomarker of the disease and deserves to be further investigated. This study highlights the importance of screening PD patients for possible underlying GD, which is a treatable condition that should not be missed. We diagnosed GD cases carrying a "risk" variant in one allele, which is an unprecedented finding deserving further investigation.

Contribution of Glucosylsphingosine (Lyso-Gb1) to Treatment Decisions in Patients with Gaucher Disease.

Glucosylsphingosine (lyso-Gb1), the deacylated form of glucocerebroside, was shown to be the most specific and sensitive biomarker for diagnosing Gaucher disease (GD). The aim of this study is to assess the contribution of lyso-Gb1 at the time of diagnosis for treatment decisions in naïve patients with GD. Newly diagnosed patients from July 2014 to November 2022 were included in this retrospective cohort study. The diagnosis was done by sending a dry blood spot (DBS) sample for GBA1 molecular sequencing and lyso-Gb1 quantification. Treatment decisions were based on symptoms, signs, and routine laboratory tests. We diagnosed 97 patients (41 males), both type 1 (n = 87), and neuronopathic (n = 10). The median (range) age at diagnosis was 22 (1-78), with 36 children. In 65 patients, GD-specific therapy was started with a median (range) lyso-Gb1, 337 (60-1340) ng/mL, significantly higher than in patients who did not go on to treatment, 153.5 (9-442) ng/mL. Using a receiver operating characteristic (ROC) analysis, a cutoff of lyso-Gb1 > 250 ng/mL was associated with treatment with a sensitivity of 71% and specificity of 87.5%. Predictors of treatment were thrombocytopenia, anemia, and elevated lyso-Gb1 (>250 ng/mL). In conclusion, lyso-Gb1 levels contribute to the medical decision related to the initiation of treatment, mainly among mildly affected newly diagnosed patients. For patients with a severe phenotype, as for all patients, the main value of lyso-Gb1 would be to monitor response to therapy. The variable methodology and differences in the units of lyso-Gb1 measurements between laboratories prevent the adaptation of the exact cut-off we found in general practice. However, the concept is that a significant elevation, i.e., a several-fold increase from the diagnostic lyso-Gb1 cutoff, is related to a more severe phenotype and, accordingly, to the decision regarding the initiation of GD-specific therapy.

Gaucher Disease Diagnosis Using Lyso-Gb1 on Dry Blood Spot Samples: Time to Change the Paradigm?

For years, the gold standard for diagnosing Gaucher disease (GD) has been detecting reduced ß-glucocerebrosidase (GCase) activity in peripheral blood cells combined with GBA1 mutation analysis. The use of dried blood spot (DBS) specimens offers many advantages, including easy collection, the need for a small amount of blood, and simpler transportation. However, DBS has limitations for measuring GCase activity. In this paper, we recount our cross-sectional study and publish seven years of experience using DBS samples and levels of the deacylated form of glucocerebroside, glucosylsphingosine (lyso-Gb1), for GD diagnosis. Of 444 screened subjects, 99 (22.3%) were diagnosed with GD at a median (range) age of 21 (1-78) years. Lyso-Gb levels for genetically confirmed GD patients vs. subjects negative to GD diagnosis were 252 (9-1340) ng/mL and 5.4 (1.5-16) ng/mL, respectively. Patients diagnosed with GD1 and mild GBA1 variants had lower median (range) lyso-Gb1, 194 (9-1050), compared to GD1 and severe GBA1 variants, 447 (38-1340) ng/mL, and neuronopathic GD, 325 (116-1270) ng/mL (p = 0.001). Subjects with heterozygous GBA1 variants (carrier) had higher lyso-Gb1 levels, 5.8 (2.5-15.3) ng/mL, compared to wild-type GBA1, 4.9 (1.5-16), ng/mL (p = 0.001). Lyso-Gb1 levels, median (range), were 5 (2.7-10.7) in heterozygous GBA1 carriers with Parkinson's disease (PD), similar to lyso-Gb1 levels in subjects without PD. We call for a paradigm change for the diagnosis of GD based on lyso-Gb1 measurements and confirmatory GBA1 mutation analyses in DBS. Lyso-Gb1 levels could not be used to differentiate between heterozygous GBA1 carriers and wild type.

Impact of Long-Term Enzyme Replacement Therapy on Glucosylsphingosine (Lyso-Gb1) Values in Patients with Type 1 Gaucher Disease: Statistical Models for Comparing Three Enzymatic Formulations.

For three decades, enzyme replacement therapy (ERT), and more recently, substrate reduction therapy, have been the standard-of-care for type I Gaucher disease (GD1). Since 2012, three different ERTs have been available. No clinical trial or academic study has ever compared these ERTs beyond one year. Herein we compare the impact of the ERTs on repeated measurements of glucosylsphingosine (lyso-Gb1; the most sensitive and GD-specific biomarker). A total of 135 adult patients (77 (57%) female) with GD1, followed from July 2014 to March 2020 and treated with a single ERT (imiglucerase (n = 41, 30.4%), taliglucerase alfa (n = 21, 15.6%) and velaglucerase alfa (n = 73, 54.1%)), were included. Disease severity was defined by genotypes (mild: N370S (c.1226A>G) homozygous and N370S/R496H (c.1604G) compound heterozygous; severe: all other genotypes) and by the severity score index (SSI; mild: <7; severe: ≥7). Lyso-Gb1 testing was performed at Centogene™ on dry blood spot samples collected during routine visits. Patients treated with imiglucerase had higher lyso-Gb1 levels at different time points. A huge variation in lyso-Gb1 levels was noticeable both inter-individually and intra-individually for all three ERTs. A steeper and faster decrease of lyso-Gb1 levels was shown in velaglucerase alfa. Nevertheless, the differences between medications were not very large, and bigger numbers and more pretreatment data are required for more powerful conclusions.

Elevated glucosylsphingosine in Gaucher disease induced pluripotent stem cell neurons deregulates lysosomal compartment through mammalian target of rapamycin complex 1.

Gaucher disease (GD) is a lysosomal storage disorder caused by mutations in GBA1, the gene that encodes lysosomal ß-glucocerebrosidase (GCase). Mild mutations in GBA1 cause type 1 non-neuronopathic GD, whereas severe mutations cause types 2 and 3 neuronopathic GD (nGD). GCase deficiency results in the accumulation of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph). GlcSph is formed by deacylation of GlcCer by the lysosomal enzyme acid ceramidase. Brains from patients with nGD have high levels of GlcSph, a lipid believed to play an important role in nGD, but the mechanisms involved remain unclear. To identify these mechanisms, we used human induced pluripotent stem cell-derived neurons from nGD patients. We found that elevated levels of GlcSph activate mammalian target of rapamycin (mTOR) complex 1 (mTORC1), interfering with lysosomal biogenesis and autophagy, which were restored by incubation of nGD neurons with mTOR inhibitors. We also found that inhibition of acid ceramidase prevented both, mTOR hyperactivity and lysosomal dysfunction, suggesting that these alterations were caused by GlcSph accumulation in the mutant neurons. To directly determine whether GlcSph can cause mTOR hyperactivation, we incubated wild-type neurons with exogenous GlcSph. Remarkably, GlcSph treatment recapitulated the mTOR hyperactivation and lysosomal abnormalities in mutant neurons, which were prevented by coincubation of GlcSph with mTOR inhibitors. We conclude that elevated GlcSph activates an mTORC1-dependent pathogenic mechanism that is responsible for the lysosomal abnormalities of nGD neurons. We also identify acid ceramidase as essential to the pathogenesis of nGD, providing a new therapeutic target for treating GBA1-associated neurodegeneration.

Detection of glucosylsphingosine in dried blood spots for diagnosis of Gaucher disease by LC-MS/MS.

INTRODUCTION: Gaucher disease (GD) is caused by a deficiency of ß-glucosidase (GCase), leading to accumulation of glucosylceramide (GlcC) and glucosylsphingosine (Lyso-Gb1). Lyso-Gb1 is a reliable biomarker for GD. OBJECTIVES: This study aims to develop a simple, effective and accurate method for the screening and diagnosis of GD using dried blood spot (DBS) samples. METHODS: Lyso-Gb1 in DBS was extracted by 50% acetonitrile aqueous solution containing isotope-labeled internal standard and analyzed using liquid chromatography tandem mass spectrometry (LC-MS/MS). A reference interval was established by analyzing samples from 277 healthy controls. Lyso-Gb1 was detected in the residual DBS samples from 142 high-risk patients with splenomegaly and/or thrombocytopenia. Based on GCase activity in DBS, samples were classified into four groups: confirmed GD patients (n = 52), GD carriers (n = 5), false positive (n = 36) and negative (n = 49). RESULTS: The optimized Lyso-Gb1 assay showed intra- and inter-assay variations ranged between 2.0%-8.2% and 3.8%-10.2%, respectively. Accuracies ranged from 93.5% to 112.6%. The lowest limit of quantification was 1 ng/mL. The normal reference interval of Lyso-Gb1 in DBS ranged from 2.1 to 9.9 ng/mL. Among the 142 subjects, except for one GD patient (Lyso-Gb1 > 2500 ng/mL), the Lyso-Gb1 concentrations in 51 GD patients ranged from 190.5 to 2380.6 ng/mL (the median 614.8 ng/mL). Also, one negative patient was found to have an elevated Lyso-Gb1 level (684.5 ng/mL), while the other patients were normal. The negative case was then confirmed to be an atypical GD patient with a c.1091A > G (p.Y364C) homozygous variant in PSAP gene by next generation sequencing. CONCLUSIONS: The optimized method to determine Lyso-Gb1 in DBS was demonstrated as a useful tool for the screening and diagnosis of GD.

Value of Glucosylsphingosine (Lyso-Gb1) as a Biomarker in Gaucher Disease: A Systematic Literature Review.

The challenges in the diagnosis, prognosis, and monitoring of Gaucher disease (GD), an autosomal recessive inborn error of glycosphingolipid metabolism, can negatively impact clinical outcomes. This systematic literature review evaluated the value of glucosylsphingosine (lyso-Gb1), as the most reliable biomarker currently available for the diagnosis, prognosis, and disease/treatment monitoring of patients with GD. Literature searches were conducted using MEDLINE, Embase, PubMed, ScienceOpen, Science.gov, Biological Abstracts, and Sci-Hub to identify original research articles relevant to lyso-Gb1 and GD published before March 2019. Seventy-four articles met the inclusion criteria, encompassing 56 related to pathology and 21 related to clinical biomarkers. Evidence for lyso-Gb1 as a pathogenic mediator of GD was unequivocal, although its precise role requires further elucidation. Lyso-Gb1 was deemed a statistically reliable diagnostic and pharmacodynamic biomarker in GD. Evidence supports lyso-Gb1 as a disease-monitoring biomarker for GD, and some evidence supports lyso-Gb1 as a prognostic biomarker, but further study is required. Lyso-Gb1 meets the criteria for a biomarker as it is easily accessible and reliably quantifiable in plasma and dried blood spots, enables the elucidation of GD molecular pathogenesis, is diagnostically valuable, and reflects therapeutic responses. Evidentiary standards appropriate for verifying inter-laboratory lyso-Gb1 concentrations in plasma and in other anatomical sites are needed.

Identification of a Reliable Biomarker Profile for the Diagnosis of Gaucher Disease Type 1 Patients Using a Mass Spectrometry-Based Metabolomic Approach.

Gaucher disease (GD) is a rare autosomal recessive multisystemic lysosomal storage disorder presenting a marked phenotypic and genotypic variability. GD is caused by a deficiency in the glucocerebrosidase enzyme. The diagnosis of GD remains challenging because of the large clinical spectrum associated with the disease. Moreover, GD biomarkers are often not sensitive enough and can be subject to polymorphic variations. The main objective of this study was to perform a metabolomic study using an ultra-performance liquid chromatography system coupled to a time-of-flight mass spectrometer to identify novel GD biomarkers. Following the analysis of plasma samples from patients with GD, and age- and gender-matched control samples, supervised statistical analyses were used to find the best molecules to differentiate the two groups. Targeted biomarkers were structurally elucidated using accurate mass measurements and tandem mass spectrometry. This metabolomic study was successful in highlighting seven biomarkers associated with GD. Fragmentation tests revealed that these latter biomarkers were lyso-Gb1 (glucosylsphingosine) and four related analogs (with the following modifications on the sphingosine moiety: -C2H4, -H2, -H2+O, and +H2O), sphingosylphosphorylcholine, and N-palmitoyl-O-phosphocholineserine. Based on the plasma biomarker distribution, we suggest the evaluation of this GD biomarker profile, which might facilitate early diagnosis, monitoring, and follow-up of patients.

Effects of sphingolipids overload on red blood cell properties in Gaucher disease.

Gaucher disease (GD) is a genetic disease with mutations in the GBA gene that encodes glucocerebrosidase causing complications such as anaemia and bone disease. GD is characterized by accumulation of the sphingolipids (SL) glucosylceramide (GL1), glucosylsphingosine (Lyso-GL1), sphingosine (Sph) and sphingosine-1-phosphate (S1P). These SL are increased in the plasma of GD patients and the associated complications have been attributed to the accumulation of lipids in macrophages. Our recent findings indicated that red blood cells (RBCs) and erythroid progenitors may play an important role in GD pathophysiology. RBCs abnormalities and dyserythropoiesis have been observed in GD patients. Moreover, we showed higher SL levels in the plasma and in RBCs from untreated GD patients compared with controls. In this study, we quantified SL in 16 untreated GD patients and 15 patients treated with enzyme replacement therapy. Our results showed that the treatment significantly decreases SL levels in the plasma and RBCs. The increased SL content in RBCs correlates with abnormal RBC properties and with markers of disease activity. Because RBCs lack glucocerebrosidase activity, we investigated how lipid overload could occur in these cells. Our results suggested that SL overload in RBCs occurs both during erythropoiesis and during its circulation in the plasma.

Treatment Efficiency in Gaucher Patients Can Reliably Be Monitored by Quantification of Lyso-Gb1 Concentrations in Dried Blood Spots.

Gaucher disease (GD) is a lysosomal storage disorder that responds well to enzyme replacement therapy (ERT). Certain laboratory parameters, including blood concentration of glucosylsphingosine (Lyso-Gb1), the lyso-derivate of the common glycolipid glucocerebroside, correlate with clinical improvement and are therefore considered candidate-monitoring biomarkers. Whether they can indicate a reduction or loss of treatment efficiency, however, has not been systematically addressed for obvious reasons. We established and validated measurement of Lyso-Gb1 from dried blood spots (DBSs) by mass spectrometry. We then characterized the assay's longitudinal performance in 19 stably ERT-treated GD patients by dense monitoring over a 3-year period. The observed level of fluctuation was accounted for in the subsequent development of a unifying data normalization concept. The resulting approach was eventually applied to data from Lyso-Gb1 measurements after an involuntary treatment break for all 19 patients. It enabled separation of the "under treatment" versus "not under treatment" conditions with high sensitivity and specificity. We conclude that Lyso-Gb1 determination from DBSs indicates treatment issues already at an early stage before clinical consequences arise. In addition to its previously shown diagnostic utility, Lyso-Gb1 thereby qualifies as a monitoring biomarker in GD patients.

8-Plex stable isotope labeling absolute quantitation strategy combined with dual-targeted recognizing function material for simultaneous separation and determination of glucosylsphingosine and galactosylsphingosine in human plasma.

Glucosylsphingosine (GlcS) in plasma is considered to be a reliable biomarker of Gaucher disease. The detection difficulty of GlcS is that it is difficult to achieve simultaneous separation and quantification with its isomer galactosylsphingosine (GalS), a biomarker of Krabbe disease. In this work, a multiplexed stable isotope labeling absolute quantization strategy coupled with magnetic dispersive solid phase extraction using new prepared dummy magnetic molecularly imprinted polymers (DMMIPs) has been developed for this purpose by ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). 8-Plex Amine-reactive Mass Difference Tags (M360/361/362/363/373/375/376/378-AMDTs), were designed, synthesized and used to label GalS and GlcS in different 8 plasma samples, respectively. Synchronously, M359-AMDTs was prepared and used to label mixed standards of GalS and GlcS, which served as internal standards in UHPLC-MS/MS quantitation. Then DMMIPs possessing dual recognition function were applied for specific enrichment and purification of all GlcS and GalS derivatives from a combined solution of labeled 8-plex plasma samples and mixed standards before UHPLC-MS/MS injection. The labeling efficiency, chromatographic retention and mass spectrometry responses of all the 9 AMDTs reagents were consistent for GlcS and GalS. The established and validated method enabled 8-plex plasma samples quantification in a single UHPLC-MS/MS run (<2.0 min). Good linearity of AMDTs-GlcS/GalS derivatives was obtained in the range of 0.02-800 nM. LODs of GlcS and GalS were both 0.005 nM. The recoveries were in the range of 96.1-107.2%. The method was successfully applied for multiplex quantitative analysis of GlcS and GalS in human plasma samples. The results indicated that this method was capable of better realizing the simultaneous separation and quantification of GalS and GlcS compared to reported methods.

LC-MS/MS analysis of plasma glucosylsphingosine as a biomarker for diagnosis and follow-up monitoring in Gaucher disease in the Spanish population.

Background Gaucher disease (GD), caused by a deficiency in acid ß-glucosidase, leads to the accumulation of glucosylsphingosine (GluSph), which has been used as a powerful biomarker for the diagnosis and follow-up of GD. Our aim was to perform the first retrospective study of GluSph in Spanish patients, analyzing its relationship with classical biomarkers and other parameters of disease and its utility regarding treatment monitoring. Methods Classical biomarkers were evaluated retrospectively by standard methods in a total of 145 subjects, including 47 GD patients, carriers, healthy controls and patients suffering from other lysosomal lipidoses. GluSph was also measured using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method developed as part of the present study. Results The optimized method presented intra- and inter-assay variations of 3.1 and 11.5%, respectively, overall recovery higher than 96% and linearity up to plasma concentrations of 1000 ng/mL with 100% specificity and sensitivity. Only GD patients displayed GluSph levels above 5.4 ng/mL at diagnosis and this was significantly correlated with the classical biomarkers chitotriosidase (r = 0.560) and the chemokine CCL18/PARC (CCL18/PARC) (ρ = 0.515), as well as with the Spanish magnetic resonance imaging index (S-MRI, r = 0.364), whereas chitotriosidase correlated with liver volume (r = 0.372) and CCL18/PARC increased in patients with bone manifestations (p = 0.005). GluSph levels decreased with treatment in naïve patients. Conclusions Plasma GluSph is the most disease-specific biomarker for GD with demonstrated diagnostic value and responsiveness to therapy. GluSph in the present series of patients failed to demonstrate better correlations with clinical characteristics at onset than classical biomarkers.

Rare Saposin A deficiency: Novel variant and psychosine analysis.

Saposin A is a post-translation product of the prosaposin (PSAP) gene that serves as an activator protein of the galactocerebrosidase (GALC) enzyme, and is necessary for the degradation of certain glycosphingolipids. Deficiency of saposin A leads to a clinical picture identical to that of early-infantile Krabbe disease caused by GALC enzyme deficiency. Galactosylsphingosine, also known as psychosine, is a substrate of the GALC enzyme that is known to be elevated in classic Krabbe disease. We present the case of an 18-month-old male with clinical and radiological findings concerning for Krabbe disease who had preserved GALC enzyme activity and negative GALC gene sequencing, but was found to have a homozygous variant, c.257 T > A (p.I86N), in the saposin A peptide of PSAP. Psychosine determination on dried blood spot at 18 months of age was elevated to 12 nmol/L (normal <3 nmol/L). We present this case to add to the literature on the rare diagnosis of atypical Krabbe disease due to saposin A deficiency, to report a novel presumed pathogenic variant within PSAP, and to suggest that individuals with saposin A deficiency may have elevated levels of psychosine, similar to children with classic Krabbe disease due to GALC deficiency.

Cerebrospinal fluid and serum glycosphingolipid biomarkers in canine globoid cell leukodystrophy (Krabbe Disease).

Globoid cell leukodystrophy (GLD, Krabbe disease, Krabbe's disease) is caused by genetic mutations in the gene encoding, galactosylceramidase (GALC). Deficiency of this enzyme results in central and peripheral nervous system pathology, and is characterized by loss of myelin and an infiltration of globoid cells. The canine model of GLD provides a translational model which faithfully recapitulates much of the human disease pathology. Targeted lipidomic analysis was conducted in serum and cerebrospinal fluid (CSF) over the lifetime of GLD affected and normal canines, and in brain tissue at humane endpoint to better understand disease progression and identify potential biomarkers of disease. Psychosine, a substrate of GALC and primary contributor to the pathology in GLD, was observed to be significantly elevated in the serum and CSF by 2 or 4 weeks of age, respectively, and steadily increased over the lifetime of affected animals. Importantly, psychosine concentration strongly correlated with disease severity. Galactosylceramide, glucosylceramide, and lactosylceramide were also found to be elevated in the CSF of affected animals and increased with age. Psychosine and galactosylceramide were found to be significantly increased in brain tissue at humane endpoint. This study identified several biomarkers which may be useful in the development of therapeutics for GLD.

Expanding the clinical utility of glucosylsphingosine for Gaucher disease.

Gaucher disease (GD) is an inherited metabolic disorder characterised by impaired catabolism of the glycosphingolipid, glucosylceramide. The deacetylated derivative, glucosylsphingosine (GluSph, lyso-Gb1) has materialised as a biomarker for GD. Further appraisal of the clinical utility of GluSph is required in terms of its prognostic power to inform disease course and pre-symptomatic testing. In this study, we show that plasma GluSph concentrations are significantly higher in GD patients with neuronopathic disease compared with non-neuronopathic disease, even in the neonatal period. A neonate diagnosed at 1 day of age (homozygous for N370S) due to an affected older sibling, returned GluSph of 70 nmol/L compared with 1070-2620 nmol/L for four neuronopathic patients diagnosed <20 days of age. Given this result shows promise for newborn screening, we developed a rapid, simple, and robust assay for GluSph in dried filter paper blood spots (DBS) and were able to detect 23 GD patients from 220 unaffected individuals. Neuronopathic GD patients also had significantly higher DBS concentrations of GluSph than their non-neuronopathic counterparts. We went on to measure GluSph in tissue extracts prepared from chorionic villus sampling and confirmed concentrations were undetectable in unaffected tissue but elevated in GD tissue demonstrating utility in the prenatal setting. Additionally, GluSph is a pharmacodynamic biomarker, revealing a precipitous drop following initiation of enzyme replacement therapy. In conclusion, GluSph is a reliable and specific biomarker for GD and shows promise for prenatal diagnosis and DBS screening programmes.

Glucosylsphingosine (lyso-Gb1) as a Biomarker for Monitoring Treated and Untreated Children with Gaucher Disease.

The role of glucosylsphingosine (lyso-Gb1), a downstream metabolic product of glucosylceramide, for monitoring treated and untreated children with Gaucher disease (GD) has not yet been studied. We reviewed the clinical charts of 81 children (<18 years), 35 with mild type 1 GD (GD1), 34 with severe GD1 and 12 with type 3 GD (GD3), followed at Shaare Zedek Medical Center between 2014-2018. Disease severity for GD1 was based on genotypes. Forty children (87%) with severe GD1 and GD3 received enzyme replacement therapy (ERT) compared to two children (6%) with mild GD1. Lyso-Gb1 measurements were conducted on dried blood spot samples taken at each clinic visit. Lyso-Gb1 levels were significantly lower in children with mild compared to severe GD1 (p = 0.009). In untreated children, lyso-Gb1 levels were inversely correlated with platelet counts. During follow-up, lyso-Gb1 increased in almost 50% of untreated children, more commonly in younger children. In treated children, lyso-Gb1 levels were inversely correlated with hemoglobin levels. The increase of lyso-Gb1 while receiving ERT, seen in eight children, was partly associated with compliance and weight gain. Lyso-Gb1 seems to be a useful biomarker for monitoring children with GD and should be included in the routine follow-up. Progressive increase in lyso-Gb1 levels in untreated children suggests ERT initiation.

Galactosylsphingosine does not interfere with the quantitation of plasma glucosylsphingosine levels in Gaucher patients.

It has been shown that the plasma level of glucosylsphingosine (Lyso GL-1) is a useful biomarker for the diagnosis and monitoring of Gaucher disease. Potentially interfering with the quantitation of Lyso GL-1 is its isobaric structural isomer, galactosylsphingosine (psychosine). The contribution of psychosine is generally not accounted for in the determination of Lyso GL-1, due to the difficulty in separating these two isomers. Few methods have been presented in the literature to distinguish the two isomers, and those available tend to be tedious and time-consuming. Here, we developed a LC/MS/MS method able to chromatographically separate Lyso GL-1 and psychosine reproducibly and combine it with a simple, high-throughput sample preparation technique. We also show that the separation of these two isomers in the plasma of Gaucher patients is not necessary for the quantitation of Lyso GL-1 levels, as the relative psychosine level is <3% of Lyso GL-1.

Ophthalmic manifestations of Gaucher disease: the most common lysosomal storage disorder.

Gaucher disease (GD) results from a deficiency of glucocerebrosidase activity and the subsequent accumulation of the enzyme's metabolites, principally glucosylsphingosine and glucosylceramide. There are three principal forms: Type I, which is the most common, is usually considered non-neuronopathic. Type II, III and IIIc manifest earlier and have neurological sequelae due to markedly reduced enzyme activity. Gaucher's can be associated with ophthalmological sequelae but these have not been systematically reviewed. We therefore performed a comprehensive literature review of all such ophthalmic abnormalities associated with the different types of Gaucher disease. We systematically searched the literature (1950 - present) for functional and structural ocular abnormalities arising in patients with Gaucher disease and found that all subtypes can be associated with ophthalmic abnormalities; these range from recently described intraocular lesions to disease involving the adnexae, peripheral nerves and brain. In summary, Gaucher can affect most parts of the eye. Rarely is it sight-threatening; some but not all manifestations are amenable to treatment, including with enzyme replacement and substrate reduction therapy. Retinal involvement is rare but patients with ocular manifestations should be monitored and treated early to reduce the risk of progression and further complications. As Gaucher disease is also associated with Parkinsons disease and may also confer an increased risk of malignancy (particularly haematological forms and melanoma), any ocular abnormalities should be fully investigated to exclude these potential underlying conditions.

Development of a newborn screening tool based on bivariate normal limits: using psychosine and galactocerebrosidase determination on dried blood spots to predict Krabbe disease.

PURPOSE: Newborn screening for Krabbe disease (KD) originated in New York State in 2006 but has proven to have a high false positive rate and low positive predictive value. To improve accuracy of presymptomatic prediction, we propose a screening tool based on two biomarkers, psychosine and galactocerebrosidase enzyme activity (GalC). METHODS: We developed the tool using measures from dried blood spots of 166 normal newborns and tested it on dried blood spot measures from 15 newborns who later developed KD, 8 newborns identified as "high risk" by the New York screening protocol but were disease-free at follow-up, and 3 symptomatic children with onset before 4 years of age. The tool was developed from the (1-10-6)100% prediction region of the natural logarithms of psychosine and GalC measures, assuming bivariate normality, and their univariate normal limits. RESULTS: Krabbe disease was predicted correctly for every patient who developed symptoms in infancy or early childhood. None of the high-risk patients were incorrectly identified as having early KD. CONCLUSION: Bivariate analysis of psychosine and GalC in newborn blood spots can accurately predict early Krabbe symptoms, control false positive rates, and permit presymptomatic treatment.