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Galactocerebrosidase (GALC)-catalyzed reaction and direct conversion of galactosylceramide to psychosine when GALC is deficient as proposed [4].
Source publication
Measurement of the absolute concentration of the biomarker psychosine in dried blood spots (DBS) is useful for diagnosis and prognosis of Krabbe disease and to support newborn screening of this leukodystrophy. As for assays for more common diseases, it is important to achieve congruence when multiple clinical laboratories provide testing. Four clin...
Contexts in source publication
Context 1
... glycosylsphingolipid psychosine has emerged as a biomarker for diagnosis and prognosis of Krabbe disease, a rare lysosomal storage disorder caused by deficiency of galactocerebrosidase (GALC) [1][2][3]. GALC removes galactose from galactosylceramide as part of the lysosomal re-cycling of glycosphingolipids that are rich in myelin (Figure 1). The next step in the breakdown pathway is release of the fatty acyl group from ceramide by acid ceramidase (Figure 1). ...
Context 2
... removes galactose from galactosylceramide as part of the lysosomal re-cycling of glycosphingolipids that are rich in myelin (Figure 1). The next step in the breakdown pathway is release of the fatty acyl group from ceramide by acid ceramidase (Figure 1). Recent studies have suggested that when GALC is deficient, acid ceramidase removes the fatty acyl chain from galactosylceramide to generate psychosine ( Figure 1) [4]. ...
Context 3
... next step in the breakdown pathway is release of the fatty acyl group from ceramide by acid ceramidase (Figure 1). Recent studies have suggested that when GALC is deficient, acid ceramidase removes the fatty acyl chain from galactosylceramide to generate psychosine ( Figure 1) [4]. Psychosine is thought to be a key cytotoxic agent that is responsible for loss of oligodendrocytes and Schwann cells that is the hallmark of Krabbe disease [4]. ...
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Objectives
Mucopolysaccharidosis type I (MPS I) was added to our expanded screening panel in 2015. Since then, 127,869 newborns were screened by measuring α-L-iduronidase (IDUA) enzyme activity with liquid chromatography tandem mass spectrometry (LC-MS/MS). High false positives due to frequent pseudodeficiency alleles prompted us to develop a secon...
Citations
... The MS standard contains equal moles of all internal disaccharides (available commercially) and the internal standard. Moles of each internal disaccharide and the internal standard are determined using quantitative proton nuclear magnetic resonance (qNMR) rather than using gravimetric analysis, which can be problematic for absolute quantification [23]. The injection of this standard in every LC-MS/MS run provides a response factor ratio, which is the measured signal per mole of analyte, divided by the measured signal per mole of internal standard. ...
All newborn screening (NBS) for mucopolysaccharidosis-I and -II (MPS-I and MPS-II) is carried out via the measurement of α-iduronidase (IDUA) and iduronate-2-sulfatase (IDS) enzymatic activity, respectively, in dried blood spots (DBS). The majority of low enzyme results are due to pseudodeficiencies, and data from recent MPS-II population screenings and studies from the Mayo Clinic show that the false positive rate can be dramatically reduced by the inclusion of a second-tier analysis of glycosaminoglycans (GAGs) in DBS as part of NBS. In the present study, which focused on MPS-II, we obtained newborn DBS from 17 patients with severe MPS-II, 1 with attenuated MPS-II, and 6 patients with various IDS pseudodeficiencies. These samples were submitted to two different GAG mass spectrometry analyses in a comparative study: (1) internal disaccharide biomarkers and (2) endogenous biomarkers. For both of these methods, the biomarker levels in six patients with pseudodeficiencies were below the range measured in MPS-II patients. One patient with attenuated MPS-II was not distinguishable from severe disease patients, but all MPS-II patients were distinguishable from the reference range using both methods. The minimal differential factor (lowest GAG marker level in MPS-II samples divided by highest level in the reference range of 60 random newborns) was 3.01-fold for the internal disaccharide method. The endogenous biomarker method demonstrated an improved minimum differential of 5.41-fold. The minimum differential factors between MPS-II patients and patients with pseudodeficiencies for the internal disaccharide and endogenous biomarker methods were 3.77-fold and 2.06-fold, respectively. This study supports use of the second-tier GAG analysis of newborn DBS, especially the endogenous disaccharide method, as part of NBS to reduce the false positive rate.
... Initially appearing healthy, affected infants experience rapid neurologic decline that leads to death at a median of 2 years of age. 1 Low GALC activity coupled with a high psychosine level (a prognostic biomarker) supports a neonatal diagnosis of IKD. [2][3][4] ...
... Testing used the Bayley Scales of Infant and Toddler Development, third edition (BSID-III), a comprehensive normreferenced assessment that provides composite scores (mean: 100; standard deviation [SD]: 15; range, 40-160) in cognitive, language, and motor developmental domains. 14 Five subscales provide cognitive, receptive language, expressive language, fine motor, and gross motor development scores (mean: 10; SD: 3; range, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Growth scores (mean: 500; SD: 100; range, 200-800) were calculated to reflect longitudinal growth independent of age. ...
... Similarly, subscale scores were all below the mean (10; SD: 3; range, 1-19; Figure 2B). In general, the children demonstrated stronger cognitive (range, 4-6), receptive (range, [3][4][5][6][7][8], and expressive language (range, 3-7) skills compared with motor skills. Fine motor skills (range, 1-7) varied between infants whereas gross motor scores were uniformly extremely low. ...
Infantile Krabbe Disease (IKD) can be treated with hematopoietic cell transplantation (HCT) if done during the first weeks of life before symptoms develop. To facilitate this, newborn screening (NBS) has been instituted in eight U.S. states. An application to add KD to the Recommended NBS Panel (RUSP) is currently under review. In this report, the outcomes of newborns with IKD diagnosed through NBS and treated with HCT are presented. The unique challenges associated with NBS for this disease are discussed including opportunities for earlier diagnosis and streamlining treatment referrals. This is a retrospective review of infants with IKD detected by NBS and referred for HCT. The timing from diagnosis to HCT were examined and both HCT and neurodevelopmental outcomes are described. Six infants were diagnosed and referred for HCT. Neurologic testing before HCT revealed evidence of active IKD in all infants. All underwent HCT between 24-40 days of age, successfully engrafted, and are alive 30-58 months later (median, 47.5 months). All are gaining developmental milestones albeit at a slower pace than unaffected age-matched peers. Gross motor function is most notably affected. NBS for these patients enabled early access to HCT, the only currently available treatment for infants with IKD. All children are alive and have derived developmental and neurologic benefits from timely HCT. Long-term follow up is ongoing. Optimization of HCT and further development of emerging therapies, all of which must be delivered early in life, are expected to further improve outcomes of infants with IKD.
... In fact, in 1980, Svennerholm et al. [16] called Krabbe disease a psychosine lipidosis. More about the significance of elevated psychosine as a second-tier test in the diagnosis of Krabbe disease has recently been published [17,18]. ...
... In individuals with a psychosine concentration over 2 nmol/L, mutation analysis and neuro-diagnostic studies may be indicated, but it is not a first priority [17,18]. ...
... Values under 2 nmol/L indicate that the individual probably will not develop Krabbe disease. In individuals with a psychosine concentration over 2 nmol/L, mutation analysis and neurodiagnostic studies may be indicated, but it is not a first priority [17,18]. Figure 1. ...
Krabbe disease is an autosomal recessive leukodystrophy caused by pathogenic variants in the galactocerebrosidase (GALC) gene. GALC activity is needed for the lysosomal hydrolysis of galactosylceramide, an important component of myelin. While most patients are infants, older patients are also diagnosed. Starting in 1970, a diagnosis could be made by measuring GALC activity in leukocytes and cultured cells. After the purification of GALC in 1993, the cDNA and genes were cloned. Over 260 disease-causing variants as well as activity lowering benign variants have been identified. While some pathogenic variants can be considered "severe," others can be considered "mild." The combination of alleles determines the type of Krabbe disease a person will have. To identify patients earlier, newborn screening (NBS) has been implemented in several states. Low GALC activity in this screening test may indicate a diagnosis of Krabbe disease. Second tier testing as well as neuro-diagnostic studies may be required to identify those individuals needing immediate treatment. Treatment of pre-symptomatic or mildly symptomatic patients at this time is limited to hematopoietic stem cell transplantation. Treatment studies using the mouse and dog models have shown that combining bone marrow transplantation with intra-venous gene therapy provides the best outcomes in terms of survival, behavior, and preservation of normal myelination in the central and peripheral nervous systems. With earlier diagnosis of patients through newborn screening and advances in treatment, it is hoped that more patients will have a much better quality of life.
... Psy levels provide invaluable information as part of NBS for KD and their measurement as a second-tier test has improved the specificity of NBS for KD. While the case presented here has led to the revision of Psy cutoffs in DBS and an attempt to standardize results between laboratories providing Psy testing [29], it is unlikely that 100% sensitivity can be achieved without considerable negative impact on specificity [8,30]. Finally, it cannot be overemphasized that Psy levels must be reviewed as just one of several important factors in determining the diagnosis and follow-up plan of a patient who screens positive. ...
Krabbe disease (KD) is a rare inherited neurodegenerative disorder caused by a deficiency in galactocerebrosidase enzyme activity, which can present in early infancy, requiring an urgent referral for hematopoietic stem cell transplantation, or later in life. Newborn screening (NBS) for KD requires identification and risk-stratification of patients based on laboratory values to predict disease onset in early infancy or later in life. The biomarker psychosine plays a key role in NBS algorithms to ascertain probability of early-onset disease. This report describes a patient who was screened positive for KD in New York State, had a likely pathogenic genotype, and showed markedly reduced enzyme activity but surprisingly low psychosine levels. The patient ultimately developed KD in late infancy, an outcome not clearly predicted by existing NBS algorithms. It remains critical that psychosine levels be evaluated alongside genotype, enzyme activity levels, and the patient’s evolving clinical presentation, ideally in consultation with experts in KD, in order to guide diagnosis and plans for monitoring.
... Recent studies by Guenzel et al. (2020) showed that infants suspected of having IKD disease have elevated PSY levels, whereas intermediate PSY levels warrant an evaluation for late-onset variants [11]. Considering PSY being an important marker for identifying IKD presumptive babies, Herbst et al. (2020) conducted studies using a common set of DBS calibrators. PSY levels in reference and participating laboratories adopted similar reference ranges and could identify presumptive IKD infants [12]. ...
... Considering PSY being an important marker for identifying IKD presumptive babies, Herbst et al. (2020) conducted studies using a common set of DBS calibrators. PSY levels in reference and participating laboratories adopted similar reference ranges and could identify presumptive IKD infants [12]. Escolar and colleagues reported an improved outcome by performing human stem cell transplantation (HSCT) in IKD-diagnosed infants during their pre-symptomatic stage as compared to infants' treatment after symptoms began [8]. ...
... In addition, our results also confirmed consensus guidelines for the diagnosis and initial referral for treatment of IKD suggested by Kwon et al. (2018) [10]. This observation highlights the importance of the utilization of a common set of DBS calibrators among reference laboratories such that similar PSY values for the limited number of presumed IKD specimens can be reported [12]. We are in the process of updating the PSY cut-off (to 10 nM) to reflect an agreed value among the testing/reference laboratories. ...
Population-based newborn screening for Krabbe disease was initiated by measurement of galactocerebrosidase (GALC) activity in the state of Illinois in December 2017. Due to the poor specificity of GALC for the diagnosis of Krabbe disease, second-tier testing services were provided to reduce the false positive rates for disease monitoring. Using ultra-pressure liquid chromatography coupled to mass spectrometry assay, a total of 497,147 newborns were screened. In total, 288 infants’ specimens (0.06%) having reduced GALC activity were sent out for second-tier testing to a reference laboratory. All newborns’ reduced GALC specimens were tested for psychosine levels, the presence of a 30-kb deletion and GALC sequencing. The results showed that two infants had elevated psychosine levels (10 and 35 nM) and were referred immediately for evaluation and treatment for Infantile Krabbe disease, and six infants had intermediate PSY levels (≥2 to 5 nM) and are under observation as suspected candidates for late-onset Krabbe disease. In addition, 178 infants had pseudodeficiency alleles, all having psychosine levels < 2.0 nM. Our data show that a high percentage of reduced GALC activity (62%) was due to the presence of pseudodeficiency alleles in the GALC gene. In conclusion, incorporation of psychosine measurements can identify infants with infantile Krabbe disease and probable late-onset Krabbe infants. Furthermore, Krabbe disease screening can be achieved at public health laboratories, and infants with infantile Krabbe disease can be diagnosed in timely manner for better outcome.
... Newborn screenings are available for Krabbe disease with measurement of GALC enzymatic activity in DBS and measurement of psychosine in DBS as second-tier test may help to differentiate infantile from late-onset KD variants, as well as from GALC variant and pseudodeficiency carriers [165]. Psychosine concentrations have also been evaluated as biomarker to predict the severity of disease considering patients with psychosine greater concentrations at high risk to develop early-onset KD [166]. ...
Inherited neuromuscular disorders (INMD) are a heterogeneous group of rare diseases that involve muscles, motor neurons, peripheral nerves or the neuromuscular junction. Several different lab abnormalities have been linked to INMD: sometimes they are typical of the disorder, but they usually appear to be less specific. Sometimes serum biomarkers can point out abnormalities in presymtomatic or otherwise asymptomatic patients (e.g., carriers). More often a biomarker of INMD is evaluated by multiple clinicians other than expert in NMD before the diagnosis, because of the multisystemic involvement in INMD. The authors performed a literature search on biomarkers in inherited neuromuscular disorders to provide a practical approach to the diagnosis and the correct management of INMD. A considerable number of biomarkers have been reported that support the diagnosis of INMD, but the role of an expert clinician is crucial. Hence, the complete knowledge of such abnormalities can accelerate the diagnostic workup supporting the referral to specialists in neuromuscular disorders.
... Before the development of the chromatographic separation method, we were aware of the existence of psychosine, a biomarker increased in Krabbe disease [32] which might interfere with the quantitation of lyso-Gb 1 considering that it is a molecule with physical and chemical properties similar to lyso-Gb 1 [33]. Therefore, in order to properly characterize the compound identified and better understand the physiopathology of Gaucher disease, a separation of psychosine and lyso-Gb 1 is preferred. ...
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.
Tandem mass spectrometry (MS/MS) is the most universal platform currently available for the analysis of enzymatic activities and biomarkers in dried blood spots (DBS) for applications in newborn screening (NBS). Among the MS/MS applications in NBS, the most common is flow-injection analysis (FIA-) MS/MS, where the sample is introduced as a bolus injection into the mass spectrometer without the prior fractionation of analytes. Liquid chromatography combined with MS/MS (LC-MS/MS) has been employed for second-tier tests to reduce the false-positive rate associated with several nonspecific screening markers, beginning two decades ago. More recently, LC-MS/MS has been applied to primary screening for new conditions for which FIA-MS/MS or other methods, including genomic screening, are not yet adequate. In addition to providing a list of the currently used LC-MS/MS-based assays for NBS, the authors share their experience regarding the maintenance requirements of LC-MS/MS vs. FIA-MS/MS systems. The consensus is that the maintenance of LC-MS/MS and FIA-MS/MS instrumentation is similar, and LC-MS/MS has the advantage of allowing for a larger number of diseases to be screened for in a multiplex, cost-effective fashion with a high throughput and an adequate turnaround time.
Sphingolipidoses is a cluster of genetic rare disorders regarding glycosphingolipid metabolism, classified as lysosomal storage disorders (LSD). Here, we focus on eight inheritable diseases, including GM1 gangliosidosis, GM2 gangliosidosis, Fabry disease, Gaucher’s disease, metachromatic leukodystrophy, Krabbe disease, Niemann–Pick disease A and B, and Farber disease. Mostly, pathogenic mutations in the key enzyme are loss-function, resulting in accumulation of substrates and deficiency of products. Thus, cellular overload of substrates causes lipotoxicity, which is deleterious to cellular and organ function. In the terms of clinical manifestations in sphingolipidoses, multiple systems and organs, especially central nervous system (CNS) are usually affected. As for diagnosis strategy, enzymatic activity assay and genetic sequencing are helpful. Up till now, limited treatment approaches have approved for treating sphingolipidoses, with some potential strategies for further evaluation. In general, enzyme replacement therapy (ERT), substrate reduction therapy (SRT), and molecular chaperones are feasible choices for enzyme deficiency disorders, but these therapies are limited to relieve CNS lesions and symptoms due to prevention from blood–brain barrier. Other possible treatments such as gene therapy, bone marrow transplantation (BMT), and hematopoietic stem cell transplantation (HSCT) need further evaluation.
Objective
To provide updated evidence and consensus-based recommendations for the classification of individuals who screen positive for Krabbe Disease (KD) and recommendations for long-term follow-up for those who are at risk for late onset Krabbe Disease (LOKD).
Methods
KD experts (KD NBS Council) met between July 2017 and June 2020 to develop consensus-based classification and follow-up recommendations. The resulting newly proposed recommendations were assessed in a historical cohort of 47 newborns from New York State who were originally classified at moderate or high risk for LOKD.
Results
Infants identified by newborn screening with possible KD should enter one of three clinical follow-up pathways (Early infantile KD, at-risk for LOKD, or unaffected), based on galactocerebrosidase (GALC) activity, psychosine concentration, and GALC genotype. Patients considered at-risk for LOKD based on low GALC activity and an intermediate psychosine concentration are further split into a high-risk or low-risk follow-up pathway based on genotype. Review of the historical New York State cohort found that the updated follow-up recommendations would reduce follow up testing by 88%.
Conclusion
The KD NBS Council has presented updated consensus recommendations for efficient and effective classification and follow-up of NBS positive patients with a focus on long-term follow-up of those at-risk for LOKD.
