Hepatomegaly and Splenomegaly: An Approach to the Diagnosis of Lysosomal Storage Diseases

Clinical findings of hepatomegaly and splenomegaly, the abnormal enlargement of the liver and spleen, respectively, should prompt a broad differential diagnosis that includes metabolic, congestive, neoplastic, infectious, toxic, and inflammatory conditions. Among the metabolic diseases, lysosomal storage diseases (LSDs) are a group of rare and ultrarare conditions with a collective incidence of 1 in 5000 live births. LSDs are caused by genetic variants affecting the lysosomal enzymes, transporters, or integral membrane proteins. As a result, abnormal metabolites accumulate in the organelle, leading to dysfunction. Therapeutic advances, including early diagnosis and disease-targeted management, have improved the life expectancy and quality of life of people affected by certain LSDs. To access these new interventions, LSDs must be considered in patients presenting with hepatomegaly and splenomegaly throughout the lifespan. This review article navigates the diagnostic approach for individuals with hepatosplenomegaly particularly focusing on LSDs. We provide hints in the history, physical exam, laboratories, and imaging that may identify LSDs. Additionally, we discuss molecular testing, arguably the preferred confirmatory test (over biopsy), accompanied by enzymatic testing when feasible.

Neurotoxic stimulation alters prosaposin levels in the salivary systems of rats

Prosaposin (PSAP), a potent neurotrophic factor, is found in neuronal and non-neuronal tissues and various biological fluids. Neuropathological conditions often alter PSAP production in neural tissues. However, little is known about its alterations in non-neural tissues, particularly in the salivary glands, which are natural reservoirs of various neurotrophic factors. In this study, we explored whether neurotoxic stimulation by kainic acid (KA), a glutamate analog, altered PSAP levels in the salivary system of rats. The results revealed that KA injection did not alter total saliva production. However, KA-induced neurotoxic stimulation significantly increased the PSAP level in the secreted saliva but decreased it in the serum. In addition, KA-induced elevated immunoreactivities of PSAP and its receptors have been observed in the granular convoluted tubule (GCT) cells of the submandibular gland (SMG), a major salivary secretory organ. Indeed, a large number of PSAP-expressing immunogold particles were observed in the secretory granules of the SMG. Furthermore, KA-induced overexpression of PSAP was co-localized with secretogranin in secretory acini (mostly in GCT cells) and the ductal system of the SMG, suggesting the release of excess PSAP from the salivary glands into the oral cavity. In conclusion, the salivary system produces more PSAP during neurotoxic conditions, which may play a protective role in maintaining the secretory function of the salivary glands and may work in distant organs.

Choroid plexus mis-splicing and altered cerebrospinal fluid composition in myotonic dystrophy type 1

Myotonic dystrophy type 1 is a dominantly inherited multisystemic disease caused by CTG tandem repeat expansions in the DMPK 3' untranslated region. These expanded repeats are transcribed and produce toxic CUG RNAs that sequester and inhibit activities of the MBNL family of developmental RNA processing factors. Although myotonic dystrophy is classified as a muscular dystrophy, the brain is also severely affected by an unusual cohort of symptoms, including hypersomnia, executive dysfunction, as well as early onsets of tau/MAPT pathology and cerebral atrophy. To address the molecular and cellular events that lead to these pathological outcomes, we recently generated a mouse Dmpk CTG expansion knock-in model and identified choroid plexus epithelial cells as particularly affected by the expression of toxic CUG expansion RNAs. To determine if toxic CUG RNAs perturb choroid plexus functions, alternative splicing analysis was performed on lateral and hindbrain choroid plexi from Dmpk CTG knock-in mice. Choroid plexus transcriptome-wide changes were evaluated in Mbnl2 knockout mice, a developmental-onset model of myotonic dystrophy brain dysfunction. To determine if transcriptome changes also occurred in the human disease, we obtained post-mortem choroid plexus for RNA-seq from neurologically unaffected (two females, three males; ages 50-70 years) and myotonic dystrophy type 1 (one female, three males; ages 50-70 years) donors. To test that choroid plexus transcriptome alterations resulted in altered CSF composition, we obtained CSF via lumbar puncture from patients with myotonic dystrophy type 1 (five females, five males; ages 35-55 years) and non-myotonic dystrophy patients (three females, four males; ages 26-51 years), and western blot and osmolarity analyses were used to test CSF alterations predicted by choroid plexus transcriptome analysis. We determined that CUG RNA induced toxicity was more robust in the lateral choroid plexus of Dmpk CTG knock-in mice due to comparatively higher Dmpk and lower Mbnl RNA levels. Impaired transitions to adult splicing patterns during choroid plexus development were identified in Mbnl2 knockout mice, including mis-splicing previously found in Dmpk CTG knock-in mice. Whole transcriptome analysis of myotonic dystrophy type 1 choroid plexus revealed disease-associated RNA expression and mis-splicing events. Based on these RNA changes, predicted alterations in ion homeostasis, secretory output and CSF composition were confirmed by analysis of myotonic dystrophy type 1 CSF. Our results implicate choroid plexus spliceopathy and concomitant alterations in CSF homeostasis as an unappreciated contributor to myotonic dystrophy type 1 CNS pathogenesis.

Expression patterns of prosaposin and its receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in the mouse olfactory organ

Prosaposin is a glycoprotein conserved widely in vertebrates, because it is a precursor for saposins that are required for normal lysosomal function and thus for autophagy, and acts as a neurotrophic factor. Most tetrapods possess two kinds of olfactory neuroepithelia, namely, the olfactory epithelium (OE) and the vomeronasal epithelium (VNE). This study examined the expression patterns of prosaposin and its candidate receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in mouse OE and VNE by immunofluorescence and in situ hybridization. Prosaposin immunoreactivity was observed in the olfactory receptor neurons, vomeronasal receptor neurons, Bowman's gland (BG), and Jacobson's gland (JG). Prosaposin expression was mainly observed in mature neurons. Prosaposin mRNA expression was observed not only in these cells but also in the apical region of the VNE. GPR37 and GPR37L1 immunoreactivities were found only in the BG and/or the JG. Prosaposin was suggested to secrete and facilitate the autophagic activities of the neurons and modulate the mucus secretion in mouse olfactory organ.

Combined saposin deficiency: A rare occurrence

Combined saposin deficiency (OMIM #611721), an exceedingly rare lysosomal storage disorder, is caused by a mutation in the gene PSAP. This gene encodes a protein, prosaposin, that cleaves into four constituent proteins, each of which has a role as a cofactor for the enzymes whose deficiency results in Krabbe disease, metachromatic leukodystrophy, Gaucher disease, and Farber disease, respectively. Intact prosaposin itself is essential for neuronal survival. The typical manifestation of combined saposin deficiency is of severe neurological features in the neonatal period, hepatosplenomegaly, thrombocytopenia, and early death. We report, to the best of our knowledge, the first Indian case with these clinical manifestations and confirmation by genetic and enzymatic testing.

Gene Therapy of Sphingolipid Metabolic Disorders

Sphingolipidoses are defined as a group of rare hereditary diseases resulting from mutations in the genes encoding lysosomal enzymes. This group of lysosomal storage diseases includes more than 10 genetic disorders, including GM1-gangliosidosis, Tay-Sachs disease, Sandhoff disease, the AB variant of GM2-gangliosidosis, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease, Farber disease, etc. Enzyme deficiency results in accumulation of sphingolipids in various cell types, and the nervous system is also usually affected. There are currently no known effective methods for the treatment of sphingolipidoses; however, gene therapy seems to be a promising therapeutic variant for this group of diseases. In this review, we discuss gene therapy approaches for sphingolipidoses that are currently being investigated in clinical trials, among which adeno-associated viral vector-based approaches and transplantation of hematopoietic stem cells genetically modified with lentiviral vectors seem to be the most effective.

Patient centered guidelines for the laboratory diagnosis of Gaucher disease type 1

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder due to the deficient activity of the acid beta-glucosidase (GCase) enzyme, resulting in the progressive lysosomal accumulation of glucosylceramide (GlcCer) and its deacylated derivate, glucosylsphingosine (GlcSph). GCase is encoded by the GBA1 gene, located on chromosome 1q21 16 kb upstream from a highly homologous pseudogene. To date, more than 400 GBA1 pathogenic variants have been reported, many of them derived from recombination events between the gene and the pseudogene. In the last years, the increased access to new technologies has led to an exponential growth in the number of diagnostic laboratories offering GD testing. However, both biochemical and genetic diagnosis of GD are challenging and to date no specific evidence-based guidelines for the laboratory diagnosis of GD have been published. The objective of the guidelines presented here is to provide evidence-based recommendations for the technical implementation and interpretation of biochemical and genetic testing for the diagnosis of GD to ensure a timely and accurate diagnosis for patients with GD worldwide. The guidelines have been developed by members of the Diagnostic Working group of the International Working Group of Gaucher Disease (IWGGD), a non-profit network established to promote clinical and basic research into GD for the ultimate purpose of improving the lives of patients with this disease. One of the goals of the IWGGD is to support equitable access to diagnosis of GD and to standardize procedures to ensure an accurate diagnosis. Therefore, a guideline development group consisting of biochemists and geneticists working in the field of GD diagnosis was established and a list of topics to be discussed was selected. In these guidelines, twenty recommendations are provided based on information gathered through a systematic review of the literature and two different diagnostic algorithms are presented, considering the geographical differences in the access to diagnostic services. Besides, several gaps in the current diagnostic workflow were identified and actions to fulfill them were taken within the IWGGD. We believe that the implementation of recommendations provided in these guidelines will promote an equitable, timely and accurate diagnosis for patients with GD worldwide.

Prosaposin Reduces α-Synuclein in Cells and Saposin C Dislodges it from Glucosylceramide-enriched Lipid Membranes

Parkinson's disease (PD) is the second most common progressive neurodegenerative disorder affecting over 1% of the 65 + age population. Saposin C, a lysosomal protein required for the normal activity of glucocerebrosidase (GCase), may serve as a disease modifier in PD. Saposin C is cleaved from its precursor, Prosaposin (PSAP), which is secreted as an uncleaved protein and exerts neuroprotective effects. In this study, we aim to elucidate the neuroprotective roles of PSAP and saposin C in PD by evaluating their effects on α-synuclein accumulation in human neuroblastoma cells. Stable overexpression of PSAP reduced monomeric α-synuclein levels in SH-SY5Y cells, while PSAP knockdown by small interfering RNA led to the opposite effect, and those effects were independent of GCase activity. Autophagy flux was decreased by stable PSAP overexpression. Furthermore, a flow-through assay revealed that recombinant saposin C was able to detach α-synuclein from artificial glucosylceramide-enriched lipid membranes at the lysosomal pH. Taken together, our findings provide further evidence that PSAP and saposin C as key proteins involved in α-synuclein clearance by dislodging it from lipid membranes.

Plasma Globotriaosylsphingosine and α-Galactosidase A Activity as a Combined Screening Biomarker for Fabry Disease in a Large Japanese Cohort

Fabry disease is an X-linked disorder of α-galactosidase A (GLA) deficiency. Our previous interim analysis (1 July 2014 to 31 December 2015) revealed plasma globotriaosylsphingosine as a promising primary screening biomarker for Fabry disease probands. Herein, we report the final results, including patients enrolled from 1 January to 31 December 2016 for evaluating the potential of plasma globotriaosylsphingosine and GLA activity as a combined screening marker. We screened 5691 patients (3439 males) referred from 237 Japanese specialty clinics based on clinical findings suggestive of Fabry disease using plasma globotriaosylsphingosine and GLA activity as primary screening markers, and GLA variant status as a secondary screening marker. Of the 14 males who tested positive in the globotriaosylsphingosine screen (≥2.0 ng/mL), 11 with low GLA activity (<4.0 nmol/h/mL) displayed GLA variants (four classic, seven late-onset) and one with normal GLA activity and no pathogenic variant displayed lamellar bodies in affected organs, indicating late-onset biopsy-proven Fabry disease. Of the 19 females who tested positive in the globotriaosylsphingosine screen, eight with low GLA activity displayed GLA variants (six classic, two late-onset) and five with normal GLA activity displayed a GLA variant (one classic) and no pathogenic variant (four late-onset biopsy-proven). The combination of plasma globotriaosylsphingosine and GLA activity can be a primary screening biomarker for classic, late-onset, and late-onset biopsy-proven Fabry disease probands.

Bi-allelic VPS16 variants limit HOPS/CORVET levels and cause a mucopolysaccharidosis-like disease

Lysosomal storage diseases, including mucopolysaccharidoses, result from genetic defects that impair lysosomal catabolism. Here, we describe two patients from two independent families presenting with progressive psychomotor regression, delayed myelination, brain atrophy, neutropenia, skeletal abnormalities, and mucopolysaccharidosis-like dysmorphic features. Both patients were homozygous for the same intronic variant in VPS16, a gene encoding a subunit of the HOPS and CORVET complexes. The variant impaired normal mRNA splicing and led to an ~85% reduction in VPS16 protein levels in patient-derived fibroblasts. Levels of other HOPS/CORVET subunits, including VPS33A, were similarly reduced, but restored upon re-expression of VPS16. Patient-derived fibroblasts showed defects in the uptake and endosomal trafficking of transferrin as well as accumulation of autophagosomes and lysosomal compartments. Re-expression of VPS16 rescued the cellular phenotypes. Zebrafish with disrupted vps16 expression showed impaired development, reduced myelination, and a similar accumulation of lysosomes and autophagosomes in the brain, particularly in glia cells. This disorder resembles previously reported patients with mutations in VPS33A, thus expanding the family of mucopolysaccharidosis-like diseases that result from mutations in HOPS/CORVET subunits.

The Role of Microglia in Inherited White-Matter Disorders and Connections to Frontotemporal Dementia

Microglia play a critical but poorly understood role in promoting white-matter homeostasis. In this review, we leverage advances in human genetics and mouse models of leukodystrophies to delineate our current knowledge and identify outstanding questions regarding the impact of microglia on central nervous system white matter. We first focus on the role of pathogenic mutations in genes, such as TREM2, TYROBP, and CSF1R, that cause leukodystrophies in which the primary deficit is thought to originate in microglia. We next discuss recent advances in disorders such as adrenoleukodystrophy and Krabbe disease, in which microglia play an increasingly recognized role. We conclude by reviewing the roles of GRN and related genes, such as TMEM106B, PSAP, and SORT1, that affect microglial biology and associate with several types of disease, including multiple leukodystrophies as well as forms of frontotemporal dementia (FTD) presenting with white-matter abnormalities. Taken together, mouse and human data support the notion that loss of microglia-facilitated white-matter homeostasis plays an important role in the development of leukodystrophies and suggest novel mechanisms contributing to FTD.

Age- and sex-associated changes in prosaposin and its receptors in the lacrimal glands of rats

Prosaposin, a saposin precursor, is a potent neurotrophic factor found in several tissues and various biological fluids. Saposin-deficient patients have different ophthalmic disorders, indicating a relationship between ocular health and prosaposin. However, there is little information about prosaposin on the ocular surface. Because ocular functions are diverse and depend on age and sex, we examined whether prosaposin and its receptors, G protein-coupled receptor 37 (GPR37) and GPR37L1, are expressed in the major ocular glands, the extra orbital lacrimal gland (ELG), and harderian gland (HG) of rats and whether sex and aging affect their expression. Immunohistochemical analyses revealed that prosaposin and its receptors were expressed in the ELGs and HGs of rats, although their expression varied based on the type of gland, age, and sex. Prosaposin, GPR37, and GPR37L1 were expressed in the basolateral membranes and cytoplasm of acinar cells of the ELGs, and their immunoreactivities were higher in female rats of menopausal age than age-matched male rats. However, such age- and sex-related differences in the immunoreactivities of prosaposin, GPR37, and GPR37L1 were not observed in the HGs. Triple immunofluorescence labelling revealed that prosaposin, GPR37, and GPR37L1 were co-localised in the acinar and ductal cells in the ELGs, although the degrees of colocalization varied according to the age and sex of the rats. Together, the present results showed that prosaposin and its receptors were expressed in the major ocular glands of rats, and their immunoreactivities to the ELGs differed considerably with age and sex.

Inherited monogenic defects of ceramide metabolism: Molecular bases and diagnoses

Ceramides are membrane lipids implicated in the regulation of numerous biological functions. Recent evidence suggests that specific subsets of molecular species of ceramide may play distinct physiological roles. The importance of this family of molecules in vertebrates is witnessed by the deleterious consequences of genetic alterations in ceramide metabolism. This brief review summarizes the clinical presentation of human disorders due to the deficiency of enzymes involved either in the biosynthesis or the degradation of ceramides. Information on the possible underlying pathophysiological mechanisms is also provided, based on knowledge gathered from animal models of these inherited rare conditions. When appropriate, tools for chemical and molecular diagnosis of these disorders and therapeutic options are also presented.

Plasma and dried blood spot lysosphingolipids for the diagnosis of different sphingolipidoses: a comparative study

Background

Lysosphingolipids, the N-deacylated forms of sphingolipids, have been identified as potential biomarkers of several sphingolipidoses, such as Gaucher, Fabry, Krabbe and Niemann-Pick diseases and in GM1 and GM2 gangliosidoses. To date, different methods have been developed to measure various lysosphingolipids (LysoSLs) in plasma. Here, we present a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for a simultaneous quantification of LysoSLs (HexSph, LysoGb3, LysoGM1, LysoGM2, LysoSM and LysoSM509) in dried blood spot (DBS). This LC-MS/MS method was used to compare the levels of LysoSLs in DBS and plasma in both affected patients and healthy controls.

Methods

Lysosphingolipids were extracted from a 3.2 mm diameter DBS with a mixture of methanol:acetonitrile:water (80:15:5, v/v) containing internal stable isotope standards. Chromatographic separation was performed using a C18 column with a gradient of water and acetonitrile both with 0.1% formic acid in a total run time of 4 min. The compounds were detected in the positive ion mode electrospray ionization (ESI)-MS/MS by multiple reaction monitoring (MRM).

Results

The method was validated on DBS to demonstrate specificity, linearity, lowest limit of quantification, accuracy and precision. The reference ranges were determined in pediatric and adult populations. The elevated levels of LysoSLs were identified in Gaucher disease (HexSph), Fabry disease (LysoGb3), prosaposin deficiency (HexSph and LysoGb3) and Niemann-Pick disease types A/B and C (LysoSM and LysoSM509). The correlation in the levels between DBS and plasma was excellent for LysoGb3 and HexSph but poor for LysoSM and LysoSM509.

Conclusions

Despite the fact that plasma LysoSLs determination remains the gold standard, our LC-MS/MS method allows a rapid and reliable quantification of lysosphingolipids in DBS. The method is a useful tool for the diagnosis of different sphingolipidoses except for Niemann-Pick type C.

Recent advances in the genetics of frontotemporal dementia

Purpose of review

In this review we highlight recent advances in the human genetics of frontotemporal dementia (FTD). In addition to providing a broad survey of genes implicated in FTD in the last several years, we also discuss variation in genes implicated in both hereditary leukodystrophies and risk for FTD (e.g., TREM2, TMEM106B, CSF1R, AARS2, NOTCH3).

Recent findings

Over the past five years, genetic variation in approximately 50 genes has been confirmed or suggested to cause or influence risk for FTD and FTD-spectrum disorders. We first give background and discuss recent findings related to C9ORF72, GRN and MAPT, the genes most commonly implicated in FTD. We then provide a broad overview of other FTD-associated genes and go on to discuss new findings in FTD genetics in East Asian populations, including pathogenic variation in CHCHD10, which may represent a frequent cause of disease in Chinese populations. Finally, we consider recent insights gleaned from genome-wide association and genetic pleiotropy studies.

Summary

Recent genetic discoveries highlight cellular pathways involving autophagy, the endolysosomal system and neuroinflammation, and reveal an intriguing overlap between genes that confer risk for leukodystrophy and FTD.

Genotypes and phenotypes in 20 Chinese patients with type 2 Gaucher disease

BACKGROUND

Gaucher disease (GD) is one of the most common lysosomal storage diseases resulting from a deficiency of glucocerebrosidase. Three main types have been described, with type 2 being the most rare and severe form. Here we investigated the clinical symptoms and mutation spectrum in 20 unrelated type 2 GD patients.

METHOD

The diagnosis of GD was based on the acid β-glucocerebrosidase (GBA) enzyme activity and direct sequencing of the GBA gene. GBA activity was measured in leukocytes and the GBA gene was amplified by a polymerase chain reaction (PCR). For patient 7, the GBA gene was analyzed by PCR as well as quantitative real-time PCR.

RESULTS

The age of onset was under 12 months for all patients. All patients experienced severe neurological involvement. A total of 19 different GBA gene mutations were identified, including 6 novel mutations: two were exonic point mutations, c.1127T > C (p.Phe376Ser), c.1418T > G (p.Val473Gly); one was splicing error, ISV7-1G > C; one was insertion, c.717_718insACAG; and the other two were a gross deletion that involved exon 6 and a recombinant allele. The most prevalent mutation was Leu483Pro, which constituted 42.5% of all mutant alleles and was associated with a neurological form in Chinese GD patients as calculated by a Fisher's exact test.

CONCLUSION

The clinical characteristics of Chinese type 2 GD were consistent with reports from other ethnic populations. We identified 6 novel mutations that contribute to the spectrum of GBA gene mutations. Our study confirmed that GD patients with the Leu483Pro allele were prone to experience neurological symptoms.

Prosaposin promotes the proliferation and tumorigenesis of glioma through toll-like receptor 4 (TLR4)-mediated NF-κB signaling pathway

Background

As a neurotrophic factor, prosaposin (PSAP) can exert neuroprotective and neurotrophic effects. It is involved in the occurrence and development of prostate and breast cancer. However, there is no research about the role of PSAP in glioma.

Methods

The PSAP overexpressed or silenced glioma cells or glioma stem cells were established based on Lentiviral vector transfection. Cell viability assay, Edu assay, neurosphere formation assay and xenograft experiments were used to detect the proliferative ability. Western blot, Elisa and luciferase reporter assays were used to detect the possible mechanism.

Findings

Our study firstly found that PSAP was highly expressed and secreted in clinical glioma specimens, glioma stem cells, and glioma cell lines. It was associated with poor prognosis. We found that PSAP significantly promoted the proliferation of glioma stem cells and cell lines. Moreover, PSAP promoted tumorigenesis in subcutaneous and orthotopic models of this disease. Furthermore, GSEA and KEGG analysis predicted that PSAP acts through the TLR4 and NF-κB signaling pathways, which was confirmed by western blot, immunoprecipitation, immunofluorescence, and use of the TLR4-specific inhibitor TAK-242.

Interpretation

The findings of this study suggest that PSAP can promote glioma cell proliferation via the TLR4/NF-κB signaling pathway and may be an important target for glioma treatment.

Fund

This work was funded by National Natural Science Foundation of China (Nos. 81101917, 81270036, 81201802, 81673025), Program for Liaoning Excellent Talents in University (No. LR2014023), and Liaoning Province Natural Science Foundation (Nos. 20170541022, 20172250290). The funders did not play a role in manuscript design, data collection, data analysis, interpretation nor writing of the manuscript.

Acute Gaucher Disease-Like Condition in an Indian Infant with a Novel Biallelic Mutation in the Prosaposin Gene

This is the first reported case of prosaposin ( PSAP ) mutation from India manifesting as an acute neuronal Gaucher disease-like condition. A 2-month-old male baby presented with encephalopathy, resistant tonic-clonic seizures, moderate hepatosplenomegaly, hypotonia, and cherry red spot in the retinae. The child had anemia, thrombocytopenia, elevated chitotriosidase, and normal activity of acid sphingomyelinase and low normal activity of β-glucosidase 1 (β-glucocerebrosidase 1, GBA). The child succumbed in the fourth month of life due to persistent respiratory distress and refractory seizures. The clinical phenotype, cherry red spots, elevated chitotriosidase, and lysosomal assays led to the suspicion of Gaucher disease. Exome sequencing revealed a homozygous stop codon mutation in the PSAP gene (c.G1228T, p.Glu410ter). Prenatal diagnosis in the next pregnancy revealed a carrier fetus, who was unaffected postnatally. The diagnosis of specific activator deficiency such as saposin C and saposin D deficiency (in the current study) should be considered and tested for when Gaucher disease is suspected in an infant with partially deficient or near normal GBA activity.

A HILIC-MS/MS method for simultaneous quantification of the lysosomal disease markers galactosylsphingosine and glucosylsphingosine in mouse serum

Deficiencies of galactosylceramidase and glucocerebrosidase result in the accumulation of galactosylsphingosine (GalSph) and glucosylsphingosine (GluSph) in Krabbe and Gaucher diseases, respectively. GalSph and GluSph are useful biomarkers for both diagnosis and monitoring of treatment effects. We have developed and validated a sensitive, accurate, high-throughput assay for simultaneous determination of the concentration of GalSph and GluSph in mouse serum. GalSph and GluSph and their deuterated internal standards were extracted by protein precipitation in quantitative recoveries, baseline separated by hydrophilic interaction chromatography and detected by positive-ion electrospray mass spectrometry in multiple reaction monitoring mode. Total run time was 7 min. The lower limit of quantification was 0.2 ng/mL for both GalSph and GluSph. Sample stability, assay precision and accuracy, and method robustness were demonstrated. This method has been successfully applied to measurement of these lipid biomarkers in a natural history study in twitcher (Krabbe) mice.

Contribution of tandem mass spectrometry to the diagnosis of lysosomal storage disorders

Tandem mass spectrometry (MS/MS) is a highly sensitive and specific technique. Thanks to the development of triple quadrupole analyzers, it is becoming more widely used in laboratories working in the field of inborn errors of metabolism. We review here the state of the art of this technique applied to the diagnosis of lysosomal storage disorders (LSDs) and how MS/MS has changed the diagnostic rationale in recent years. This fine technology brings more sensitive, specific, and reliable methods than the previous biochemical ones for the analysis of urinary glycosaminoglycans, oligosaccharides, and sialic acid. In sphingolipidoses, the quantification of urinary sphingolipids (globotriaosylceramide, sulfatides) is possible. The measurement of new plasmatic biomarkers such as oxysterols, bile acids, and lysosphingolipids allows the screening of many sphingolipidoses and related disorders (Niemann-Pick type C), replacing tedious biochemical techniques. Applied to amniotic fluid, a more reliable prenatal diagnosis or screening of LSDs is now available for fetuses presenting with antenatal manifestations. Applied to enzyme measurements, it allows high throughput assays for the screening of large populations, even newborn screening. The advent of this new method can modify the diagnostic rationale behind LSDs.

Prosaposin and its receptors are differentially expressed in the salivary glands of male and female rats

Salivary glands produce various neurotrophins that are thought to regulate salivary function during normal and pathological conditions. Prosaposin (PSAP) is a potent neurotrophin found in several tissues and various biological fluids and may play roles in the regulation of salivary function. However, little is known about PSAP in salivary glands. As the functions of salivary glands are diverse based on age and sex, this study examines whether PSAP and its receptors, G protein-coupled receptor 37 (GPR37) and GPR37L1, are expressed in the salivary glands of rats and whether sex and aging affect their expression. Immunohistochemical analysis revealed that PSAP and its receptors were expressed in the major salivary glands of rats, although their expression varied considerably based on the type of gland, acinar cells, age and sex. In fact, PSAP, GPR37 and GPR37L1 were predominantly expressed in granular convoluted tubule cells of the submandibular gland and the intensity of their immunoreactivity was higher in young adult female rats than age-matched male rats, which was more prominent at older ages (mature adult to menopause). On the other hand, weak PSAP, GPR37 and GPR37L1 immunoreactivity was observed mainly in the basal layer of mucous cells of the sublingual gland. Triple label immunofluorescence analysis revealed that PSAP, GPR37 and GPR37L1 were co-localized in the basal layer of acinar and ductal cells in the major salivary glands. The present findings indicate that PSAP and its receptors, GPR37 and GPR37L1, are expressed in the major salivary glands of rats and their immunoreactivities differ considerably with age and sex.

Rapid screening for lipid storage disorders using biochemical markers. Expert center data and review of the literature

BACKGROUND

In patients suspected of a lipid storage disorder (sphingolipidoses, lipidoses), confirmation of the diagnosis relies predominantly on the measurement of specific enzymatic activities and genetic studies. New UPLC-MS/MS methods have been developed to measure lysosphingolipids and oxysterols, which, combined with chitotriosidase activity may represent a rapid first tier screening for lipid storage disorders.

MATERIAL AND METHODS

A lysosphingolipid panel consisting of lysoglobotriaosylceramide (LysoGb3), lysohexosylceramide (LysoHexCer: both lysoglucosylceramide and lysogalactosylceramide), lysosphingomyelin (LysoSM) and its carboxylated analogue lysosphingomyelin-509 (LysoSM-509) was measured in control subjects and plasma samples of predominantly untreated patients affected with lipid storage disorders (n=74). In addition, the oxysterols cholestane-3β,5α,6β-triol and 7-ketocholesterol were measured in a subset of these patients (n=36) as well as chitotriosidase activity (n=43). A systematic review of the literature was performed to assess the usefulness of these biochemical markers.

RESULTS

Specific elevations of metabolites, i.e. without overlap between controls and other lipid storage disorders, were found for several lysosomal storage diseases: increased LysoSM levels in acid sphingomyelinase deficiency (Niemann-Pick disease type A/B), LysoGb3 levels in males with classical phenotype Fabry disease and LysoHexCer (i.e. lysoglucosylceramide/lysogalactosylceramide) in Gaucher and Krabbe diseases. While elevated levels of LysoSM-509 and cholestane-3β,5α,6β-triol did not discriminate between Niemann Pick disease type C and acid sphingomyelinase deficiency, LysoSM-509/LysoSM ratio was specifically elevated in Niemann-Pick disease type C. In Gaucher disease type I, mild increases in several lysosphingolipids were found including LysoGb3 with levels in the range of non-classical Fabry males and females. Chitotriosidase showed specific elevations in symptomatic Gaucher disease, and was mildly elevated in all other lipid storage disorders. Review of the literature identified 44 publications. Most findings were in line with our cohort. Several moderate elevations of biochemical markers were found across a wide range of other, mainly inherited metabolic, diseases.

CONCLUSION

Measurement in plasma of LysoSLs and oxysterols by UPLC-MS/MS in combination with activity of chitotriosidase provides a useful first tier screening of patients suspected of lipid storage disease. The LysoSM-509/LysoSM ratio is a promising parameter in Niemann-Pick disease type C. Further studies in larger groups of untreated patients and controls are needed to improve the specificity of the findings.

LC-MS/MS multiplex analysis of lysosphingolipids in plasma and amniotic fluid: A novel tool for the screening of sphingolipidoses and Niemann-Pick type C disease

Background

The biological diagnosis of sphingolipidoses currently relies on the measurement of specific enzymatic activities and/or genetic studies. Lysosphingolipids have recently emerged as potential biomarkers of sphingolipidoses and Niemann-Pick type C in plasma.

Methodology

We developed a sensitive and specific method enabling the simultaneous quantification of lysosphingolipids by LC-MS/MS: lysoglobotriaosylceramide for Fabry disease, lysohexosylceramide (i.e. lysoglucosylceramide and/or lysogalactosylceramide) for Gaucher and Krabbe diseases, lysosphingomyelin and its carboxylated analogue lysosphingomyelin-509 for Niemann-Pick type A or B, and C diseases, lysoGM1 ganglioside for GM1gangliosidosis and lysoGM2 ganglioside for GM2 gangliosidosis.

Findings

The diagnostic performances were validated in plasma samples analysing a large series of patients affected with sphingolipidoses and Niemann-Pick type C disease (n = 98), other inborn errors of metabolism (n = 23), and controls (n = 228). The multiplex measurement of lysosphingolipids allowed the screening of Fabry (including female patients and late-onset variants), Gaucher and infantile Krabbe, Niemann-Pick type A/B and C diseases with high sensitivity and specificity. LysoGM1 and LysoGM2 were elevated in most of the patients affected with GM1 and GM2 gangliosidosis respectively.

In amniotic fluid supernatant from pregnancies presenting non-immune hydrops fetalis (n = 77, including previously diagnosed Gaucher (n = 5), GM1 gangliosidosis (n = 4) and galactosialidosis (n = 4) fetuses) and from normal pregnancies (n = 15), a specific and dramatic increase of lysohexosylceramide was observed only in the Gaucher amniotic fluid samples.

Interpretation

This multiplex assay which allows the simultaneous measurement of lysosphingolipids in plasma modifies the diagnostic strategy of sphingolipidoses and Niemann-Pick type C. Furthermore, in pregnancies presenting non-immune hydrops fetalis, lysohexosylceramide measurement in amniotic fluid offers a rapid screening of fetal Gaucher disease without waiting for glucocerebrosidase activity measurement in cultured amniocytes.

A rare form of Gaucher disease resulting from saposin C deficiency

Gaucher disease is mainly caused by the deficiency of lysosomal acid β-glucosidase. Gaucher disease caused by the deficiency of saposin C is rare. Here we report a patient mainly presenting with hepatosplenomegaly, thrombocytopenia and anemia. EEG examination revealed increased theta waves. Gaucher cells identified in his bone marrow and the highly elevated plasma chitotriosidase activity and glucosylsphingosine supported a diagnosis of Gaucher disease. However, the leukocyte β-glucosidase activity was in a normal range. Sanger sequencing revealed a novel maternal exonic mutation c.1133C>G (p.Pro378Arg) in exon 10 of the PSAP gene, which codes the Sap C domain of PSAP protein. To search for other underlying mutations in this patient, whole genome sequencing was applied and revealed a deletion involving exon 2 to 7 of PSAP gene. The deletion appears as a de novo event on paternal chromosome. We concluded that biallelic mutations of PSAP gene were the cause of this patient's Gaucher disease. Our finding expands the mutation spectrum of Gaucher disease with saposin C deficiency.

Differentially expressed proteins underlying childhood cortical dysplasia with epilepsy identified by iTRAQ proteomic profiling

Cortical dysplasia accounts for at least 14% of epilepsy cases, and is mostly seen in children. However, the understanding of molecular mechanisms and pathogenesis underlying cortical dysplasia is limited. The aim of this cross-sectional study is to identify potential key molecules in the mechanisms of cortical dysplasia by screening the proteins expressed in brain tissues of childhood cortical dysplasia patients with epilepsy using isobaric tags for relative and absolute quantitation-based tandem mass spectrometry compared to controls, and several differentially expressed proteins that are not reported to be associated with cortical dysplasia previously were selected for validation using real-time polymerase chain reaction, immunoblotting and immunohistochemistry. 153 out of 3340 proteins were identified differentially expressed between childhood cortical dysplasia patients and controls. And FSCN1, CRMP1, NDRG1, DPYSL5, MAP4, and FABP3 were selected for validation and identified to be increased in childhood cortical dysplasia patients, while PRDX6 and PSAP were identified decreased. This is the first report on differentially expressed proteins in childhood cortical dysplasia. We identified differential expression of FSCN1, CRMP1, NDRG1, DPYSL5, MAP4, FABP3, PRDX6 and PSAP in childhood cortical dysplasia patients, these proteins are involved in various processes and have various function. These results may provide new directions or targets for the research of childhood cortical dysplasia, and may be helpful in revealing molecular mechanisms and pathogenesis and/or pathophysiology of childhood cortical dysplasia if further investigated.

Diagnostic tests for Niemann-Pick disease type C (NP-C): A critical review

Niemann-Pick disease type C (NP-C) is a neurovisceral lysosomal cholesterol trafficking and lipid storage disorder caused by mutations in one of the two genes, NPC1 or NPC2. Diagnosis has often been a difficult task, due to the wide range in age of onset of NP-C and clinical presentation of the disease, combined with the complexity of the cell biology (filipin) laboratory testing, even in combination with genetic testing. This has led to substantial delays in diagnosis, largely depending on the access to specialist centres and the level of knowledge about NP-C of the physician in the area. In recent years, advances in mass spectrometry has allowed identification of several sensitive plasma biomarkers elevated in NP-C (e.g. cholestane-3β,5α,6β-triol, lysosphingomyelin isoforms and bile acid metabolites), which, together with the concomitant progress in molecular genetic technology, have greatly impacted the strategy of laboratory testing. Specificity of the biomarkers is currently under investigation and other pathologies are being found to also result in elevations. Molecular genetic testing also has its limitations, notably with unidentified mutations and the classification of new variants. This review is intended to increase awareness on the currently available approaches to laboratory diagnosis of NP-C, to provide an up to date, comprehensive and critical evaluation of the various techniques (cell biology, biochemical biomarkers and molecular genetics), and to briefly discuss ongoing/future developments. The use of current tests in proper combination enables a rapid and correct diagnosis in a large majority of cases. However, even with recent progress, definitive diagnosis remains challenging in some patients, for whom combined genetic/biochemical/cytochemical markers do not provide a clear answer. Expertise and reference laboratories thus remain essential, and further work is still required to fulfill unmet needs.