Direct multiplex assay of enzymes in dried blood spots by tandem mass spectrometry for the newborn screening of lysosomal storage disorders

An update on multiplexed mass spectrometry-based lysosomal storage disease diagnosis

Lysosomal storage disorders (LSDs) are a type of inherited metabolic disorders in which biomolecules, accumulate as a specific substrate in lysosomes due to specific individual enzyme deficiencies. Despite the fact that LSDs are incurable, various approaches, including enzyme replacement therapy, hematopoietic stem cell transplantation, or gene therapy are now available. Therefore, a timely diagnosis is a critical initial step in patient treatment. The-state-of-the-art in LSD diagnostic uses, in the first stage, enzymatic activity determination by fluorimetry or by mass spectrometry (MS) with the aid of dry blood spots, based on different enzymatic substrate structures. Due to its sensitivity, high precision, and ability to screen for an unprecedented number of diseases in a single assay, multiplexed tandem MS-based enzyme activity assays for the screening of LSDs in newborns have recently received a lot of attention. Here, (i) we review the current approaches used for simultaneous enzymatic activity determination of LSDs in dried blood spots using multiplex-LC-MS/MS; (ii) we explore the need for designing novel enzymatic substrates that generate different enzymatic products with distinct molecular masses in multiplexed-MS studies; and (iii) we give examples of the relevance of affinity-MS technique as a basis for reversing undesirable immune-reactivity in enzyme replacement therapy.

Clinical insight meets scientific innovation to develop a next generation ERT for Pompe disease

Years of research into the structure, processing, and function of acid alpha-glucosidase led to the development and 2006 approval of alglucosidase alfa (recombinant human acid alpha-glucosidase, Myozyme®/Lumizyme®), an enzyme replacement therapy and the first approved treatment for Pompe disease. Alglucosidase alfa has been a lifesaving treatment for patients with infantile-onset Pompe disease and radically improved daily life for patients with late-onset Pompe disease; however, long-term experience with alglucosidase alfa unraveled key unmet needs in these populations. Despite treatment, Pompe disease continues to progress, especially from a skeletal muscle perspective, resulting in a multitude of functional limitations. Strong collaboration between the scientific and patient communities led to increased awareness of Pompe disease, a better understanding of disease pathophysiology, knowledge of the clinical course of the disease as patients surpassed the first decade of life, and the strengths and limitations of enzyme replacement therapy. Taken together, these advancements spurred the need for development of a next generation of enzyme replacement therapy and provided a framework for progress toward other novel treatments. This review provides an overview of the development of avalglucosidase alfa as a model to highlight the interaction between clinical experience with existing treatments, the role of the clinician scientist, translational research at both system and cellular levels, and the iterative and collaborative process that optimizes the development of therapeutics.

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.

Autophagy-lysosome pathway alteration in ocular surface manifestations in Fabry disease patients

Background

Fabry disease (FD) is a rare X-linked, lysosomal storage disorder caused by mutations in the alpha-galactosidase gene and characterized by neurological, cutaneous, renal, cardiovascular, cochleo-vestibular and ocular manifestations. The aim of this study is to characterize morphological, functional and autophagy-lysosome pathway alterations of the ocular surface in FD patients.

Methods

Eleven subjects with a diagnosis of FD and fifteen healthy control subjects were examined. All patients underwent ocular surface slit lamp examination, corneal aesthesiometry and in vivo confocal laser-scanning microscopy (CCM). Conjunctival impression cytology was performed in six FD patients and six controls, to assess for expression of two markers of the autophagy-lysosome pathway: the microtubule-associated protein light chain 3 (LC3) and lysosome-associated membrane protein 2 (LAMP2).

Results

Cornea verticillata and increased conjunctival vessel tortuosity were detected respectively in 67% and 33% of patients with FD. Compared with healthy subjects, patients affected by FD showed a significant reduction in corneal nerve fiber length, density and nerve branching on CCM and a significantly increased expression of LC3 on conjunctival impression cytology (p < 0.001). No changes were observed in the conjunctival expression of LAMP2 between the two groups.

Conclusions

This study shows that FD is associated with ocular surface alterations including corneal and conjunctival morphology, innervation and vascularization changes. Our data demonstrate an increased expression of LC3 protein in patients with FD, suggesting that alteration of the autophagy-lysosome pathway may play a role in the occurrence of ocular manifestations.

The Clinical Management of Pompe Disease: A Pediatric Perspective

Pompe disease (PD) is an inherited metabolic disorder caused by a deficiency of acid α-glucosidase (GAA), leading to lysosomal accumulation of glycogen, mainly in skeletal and cardiac muscles as well as the nervous system. Patients with PD develop cellular dysfunction and muscle damage. PD can be classified into two classic forms, namely infantile-onset PD (IOPD) and late-onset PD (LOPD). Delayed treatment, particularly in IOPD, would result in significant organ damage and early death. Nonetheless, early diagnosis and timely treatment are often hampered by the rarity of PD and its wide variety of, but overlapping, symptoms. This article reviews the common clinical presentations of PD and outlines the essentials of PD management. In particular, the implications of newborn screening (NBS) and clinical performance of enzyme replacement therapy (ERT) are highlighted.

Bone disease in early detected Gaucher Type I disease: A case report

Gaucher disease (GD) is a lysosomal disorder characterized by the storage of glucosylceramide in macrophages ("Gaucher cells"), particularly in the spleen, liver, and bone marrow. The most common phenotype, GD type 1, usually presents with hepatosplenomegaly, cytopenias, and sometimes bone involvement at variable age. Enzyme replacement therapy (ERT) is available and effective, but some severe manifestations are irreversible (e.g., osteonecrosis), so that early treatment is crucial. We describe a 4-year-old Albanian male with GD type 1, diagnosed through newborn screening (NBS), presented during follow up with multiple osteonecrotic areas in both femurs. He had no other symptoms or signs of disease, except for increasing of lyso-Gb1 biomarker. Early initiation of ERT allowed a partial improvement of bone lesions. Our case highlights the importance of NBS for GD and of close follow-up of presymptomatic patients, especially if biomarker levels are increasing. In the absence of NBS, GD should be considered in patients who present with bone lesions, also isolated. Early diagnosis and treatment improve the course of disease and avoid irreversible sequelae.

Insights into National Laboratory Newborn Screening and Future Prospects

Newborn screening (NBS) is a group of tests that check all newborns for certain rare conditions, covering several genetic or metabolic disorders. The laboratory NBS is performed through blood testing. However, the conditions that newborn babies are screened for vary from one country to another. Since NBS began in the 1960s, technological advances have enabled its expansion to include an increasing number of disorders, and there is a national trend to further expand the NBS program. The use of mass spectrometry (MS) for the diagnosis of inborn errors of metabolism (IEM) obviously helps in the expansion of the screening panels. This technology allows the detection of different metabolic disorders at one run, replacing the use of traditional techniques. Analysis of the targeted pathogenic gene variant is a routine application in the molecular techniques for the NBS program as a confirmatory testing to the positive laboratory screening results. Recently, a lot of molecular investigations, such as next generation sequencing (NGS), have been introduced in the routine NBS program. Nowadays, NGS techniques are widely used in the diagnosis of IMD where its results are rapid, confirmed and reliable, but, due to its uncertainties and the nature of IEM, it necessitates a holistic approach for diagnosis. However, various characteristics found in NGS make it a potentially powerful tool for NBS. A range of disorders can be analyzed with a single assay directly, and samples can reduce costs and can largely be automated. For the implementation of a robust technology such as NGS in a mass NBS program, the main focus should not be just technologically biased; it should also be tested for its long- and short-term impact on the family and the child. The crucial question here is whether large-scale genomic sequencing can provide useful medical information beyond what current NBS is already providing and at what economical and emotional cost? Currently, the topic of newborn genome sequencing as a public health initiative remains argumentative. Thus, this article seeks the answer to the question: NGS for newborn screening- are we there yet?

Newborn screening of mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I), a lysosomal storage disease caused by a deficiency of α-L-iduronidase, leads to storage of the glycosaminoglycans, dermatan sulfate and heparan sulfate. Available therapies include enzyme replacement and hematopoietic stem cell transplantation. In the last two decades, newborn screening (NBS) has focused on early identification of the disorder, allowing early intervention and avoiding irreversible manifestations. Techniques developed and optimized for MPS I NBS include tandem mass-spectrometry, digital microfluidics, and glycosaminoglycan quantification. Several pilot studies have been conducted and screening programs have been implemented worldwide. NBS for MPS I has been established in Taiwan, the United States, Brazil, Mexico, and several European countries. All these programs measure α-L-iduronidase enzyme activity in dried blood spots, although there are differences in the analytical strategies employed. Screening algorithms based on published studies are discussed. However, some limitations remain: one is the high rate of false-positive results due to frequent pseudodeficiency alleles, which has been partially solved using post-analytical tools and second-tier tests; another involves the management of infants with late-onset forms or variants of uncertain significance. Nonetheless, the risk-benefit ratio is favorable. Furthermore, long-term follow-up of patients detected by neonatal screening will improve our knowledge of the natural history of the disease and inform better management.

Diagnosis and Management of Cardiovascular Involvement in Fabry Disease

Fabry disease (FD, OMIM 301500) is an X-linked lysosomal storage disease caused by pathogenic variants in the GLA gene. Cardiac involvement is common in FD and is responsible for impaired quality of life and premature death. The classic cardiac involvement is a nonobstructive form of hypertrophic cardiomyopathy, usually manifesting as concentric left ventricular hypertrophy, with subsequent arrhythmogenic intramural fibrosis. Treatment of patients with FD should be directed to prevent the disease progression to irreversible organ damage and organ failure. The aim of this review is to describe the current state of knowledge regarding cardiovascular involvement in FD, focusing on clinical and instrumental features, cardiovascular management, and targeted therapy.

Newborn Screening for Fabry Disease in Northeastern Italy: Results of Five Years of Experience

Fabry disease (FD) is a progressive multisystemic lysosomal storage disease. Early diagnosis by newborn screening (NBS) may allow for timely treatment, thus preventing future irreversible organ damage. We present the results of 5.5 years of NBS for FD by α-galactosidase A activity and globotriaosylsphingosine (lyso-Gb₃) assays in dried blood spot through a multiplexed MS/MS assay. Furthermore, we report our experience with long-term follow-up of positive subjects. We screened more than 170,000 newborns and 22 males were confirmed to have a GLA gene variant, with an incidence of 1:7879 newborns. All patients were diagnosed with a variant previously associated with the later-onset phenotype of FD or carried an unclassified variant (four patients) or the likely benign p.Ala143Thr variant. All were asymptomatic at the last visit. Although lyso-Gb₃ is not considered a reliable second tier test for newborn screening, it can simplify the screening algorithm when its levels are elevated at birth. After birth, plasma lyso-Gb₃ is a useful marker for non-invasive monitoring of all positive patients. Our study is the largest reported to date in Europe, and presents data from long-term NBS for FD that reveals the current incidence of FD in northeastern Italy. Our follow-up data describe the early disease course and the trend of plasma lyso-Gb₃ during early childhood.

Galactocerebrosidase activity by liquid-chromatography tandem mass spectrometry for clinical diagnosis of Krabbe disease

BACKGROUND

Deficiency of galactosylcerebrosidase (GALC) causes Krabbe disease. Historically, a diagnosis is made by measuring GALC enzymatic activity with a radioisotope assay. To improve the workflow and performance, we developed and clinically validated a leukocyte enzymatic assay using liquid chromatography tandem mass spectrometry (LC-MS/MS).

MATERIALS

Extracted cell lysates were quantified and incubated with commercially available multiplexed substrates and internal standards. Liquid-liquid extraction was performed, and pre-analytical and analytical variability were evaluated and validated following clinical laboratory regulation guidelines.

RESULTS

Enzymatic reaction products were resolved from substrate breakdown products by a 3.5-minute column separation. Intra- and inter- assay imprecision were less than 15%. No matrix effects or carryover were observed. ACD anticoagulant tubes provide the best sample stability. Detection of product was linear with an R² of 0.99. Small differences in GALC activity were measurable near the anticipated disease range. Confirmed cases of Krabbe disease were well differentiated from carriers and non-Krabbe individuals (normal reference range).

CONCLUSION

An LC-MS/MS assay was developed, which can measure trace residual GALC activity in leukocytes and aid in the diagnosis of Krabbe disease. The multiplexed mixture allows for built-in sample quality control and enables a streamlined workflow for evaluation of multiple lysosomal storage diseases.

Mucopolysaccharidoses I and II: Brief Review of Therapeutic Options and Supportive/Palliative Therapies

Purpose. Mucopolysaccharidoses (MPS) are group of inherited lysosomal storage diseases caused by mutations of enzymes involved in catalyzing different glycosaminoglycans (GAGs). MPS I and MPS II exhibit both somatic and neurological symptoms with a relatively high disease incidence. Hematopoietic stem cell therapy (HSCT) and intravenous enzyme replacement therapy (ERT) have had a significant impact on the treatment and comprehension of disease. This review is aimed at providing a comprehensive evaluation of the pros and cons of HSCT and ERT, as well as an up-to-date knowledge of new drugs under development. In addition, multiple disease management strategies for the uncontrollable manifestations of MPS I and MPS II to improve patients' quality of life are presented. Findings. Natural history of MPS I and MPS II shows that somatic and neurological symptoms occur earlier in severe forms of MPS I than in MPS II. ERT increases life expectancy and alleviates some of the somatic symptoms, but musculoskeletal, ophthalmological, and central nervous system (CNS) manifestations are not controlled. Additionally, life-long treatment burdens and immunogenicity restriction are unintended consequences of ERT application. HSCT, another treatment method, is effective in controlling the CNS symptoms and hence has been adopted as the standard treatment for severe types of MPS I. However, it is ineffective in MPS II, which can be explained by the relatively late diagnosis. In addition, several factors such as transplant age limits or graft-versus-host disease in HSCT have limited its application for patients. Novel therapies, including BBB-penetrable-ERT, gene therapy, and substrate reduction therapy, are under development to control currently unmanageable manifestations. BBB-penetrable-ERT is being studied comprehensively in the hopes of being used in the near future as a method to effectively control CNS symptoms. Gene therapy has the potential to “cure” the disease with a one-time treatment rather than just alleviate symptoms, which makes it an attractive treatment strategy. Several clinical studies on gene therapy reveal that delivering genes directly into the brain achieves better results than intravenous administration in patients with neurological symptoms. Considering new drugs are still in clinical stage, disease management with close monitoring and supportive/palliative therapy is of great importance for the time being. Proper rehabilitation therapy, including physical and occupational therapy, surgical intervention, or medications, can benefit patients with uncontrolled musculoskeletal, respiratory, ophthalmological, and neurological manifestations.

Enzymatic diagnosis of Pompe disease: lessons from 28 years of experience

Pompe disease is a lysosomal and neuromuscular disorder caused by deficiency of acid alpha-glucosidase (GAA), and causes classic infantile, childhood onset, or adulthood onset phenotypes. The biochemical diagnosis is based on GAA activity assays in dried blood spots, leukocytes, or fibroblasts. Diagnosis can be complicated by the existence of pseudodeficiencies, i.e., GAA variants that lower GAA activity but do not cause Pompe disease. A large-scale comparison between these assays for patient samples, including exceptions and borderline cases, along with clinical diagnoses has not been reported so far. Here we analyzed GAA activity in a total of 1709 diagnostic cases over the past 28 years using a total of 2591 analyses and we confirmed the clinical diagnosis in 174 patients. We compared the following assays: leukocytes using glycogen or 4MUG as substrate, fibroblasts using 4MUG as substrate, and dried blood spots using 4MUG as substrate. In 794 individuals, two or more assays were performed. We found that phenotypes could only be distinguished using fibroblasts with 4MUG as substrate. Pseudodeficiencies caused by the GAA2 allele could be ruled out using 4MUG rather than glycogen as substrate in leukocytes or fibroblasts. The Asian pseudodeficiency could only be ruled out in fibroblasts using 4MUG as substrate. We conclude that fibroblasts using 4MUG as substrate provides the most reliable assay for biochemical diagnosis and can serve to validate results from leukocytes or dried blood spots.

A click-flipped enzyme substrate boosts the performance of the diagnostic screening for Hunter syndrome

We report on the unexpected finding that click modification of iduronyl azides results in a conformational flip of the pyranose ring, which led to the development of a new strategy for the design of superior enzyme substrates for the diagnostic assaying of iduronate-2-sulfatase (I2S), a lysosomal enzyme related to Hunter syndrome. Synthetic substrates are essential in testing newborns for metabolic disorders to enable early initiation of therapy. Our click-flipped iduronyl triazole showed a remarkably better performance with I2S than commonly used O-iduronates. We found that both O- and triazole-linked substrates are accepted by the enzyme, irrespective of their different conformations, but only the O-linked product inhibits the activity of I2S. Thus, in the long reaction times required for clinical assays, the triazole substrate substantially outperforms the O-iduronate. Applying our click-flipped substrate to assay I2S in dried blood spots sampled from affected patients and random newborns significantly increased the confidence in discriminating between these groups, clearly indicating the potential of the click-flip strategy to control the biomolecular function of carbohydrates.

An expert consensus document on the management of cardiovascular manifestations of Fabry disease

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by pathogenic variants in the α-galactosidase A (GLA) gene that leads to reduced or undetectable α-galactosidase A enzyme activity and progressive accumulation of globotriaosylceramide and its deacylated form globotriaosylsphingosine in cells throughout the body. FD can be multisystemic with neurological, renal, cutaneous and cardiac involvement or be limited to the heart. Cardiac involvement is characterized by progressive cardiac hypertrophy, fibrosis, arrhythmias, heart failure and sudden cardiac death. The cardiac management of FD requires specific measures including enzyme replacement therapy or small pharmacological chaperones in patients carrying amenable pathogenic GLA gene variants and more general management of cardiac symptoms and complications. In this paper, we summarize current knowledge of FD-related heart disease and expert consensus recommendations for its management.

Newborn screening of mucopolysaccharidoses: past, present, and future

Mucopolysaccharidoses (MPS) are a subtype of lysosomal storage disorders (LSDs) characterized by the deficiency of the enzyme involved in the breakdown of glycosaminoglycans (GAGs). Mucopolysaccharidosis type I (MPS I, Hurler Syndrome) was endorsed by the U.S. Secretary of the Department of Health and Human Services for universal newborn screening (NBS) in February 2016. Its endorsement exemplifies the need to enhance the accuracy of diagnostic testing for disorders that are considered for NBS. The progression of MPS disorders typically incudes irreversible CNS involvement, severe bone dysplasia, and cardiac and respiratory issues. Patients with MPS have a significantly decreased quality of life if untreated and require timely diagnosis and management for optimal outcomes. NBS provides the opportunity to diagnose and initiate treatment plans for MPS patients as early as possible. Most newborns with MPS are asymptomatic at birth; therefore, it is crucial to have biomarkers that can be identified in the newborn. At present, there are tiered methods and different instrumentation available for this purpose. The screening of quick, cost-effective, sensitive, and specific biomarkers in patients with MPS at birth is important. Rapid newborn diagnosis enables treatments to maximize therapeutic efficacy and to introduce immune tolerance during the neonatal period. Currently, newborn screening for MPS I and II has been implemented and/or in pilot testing in several countries. In this review article, historical aspects of NBS for MPS and the prospect of newborn screening for MPS are described, including the potential tiers of screening.

A Comparative Effectiveness Study of Newborn Screening Methods for Four Lysosomal Storage Disorders

Newborn screening for one or more lysosomal disorders has been implemented in several US states, Japan and Taiwan by multiplexed enzyme assays using either tandem mass spectrometry or digital microfluidics. Another multiplex assay making use of immunocapture technology has also been proposed. To investigate the potential variability in performance of these analytical approaches, we implemented three high-throughput screening assays for the simultaneous screening for four lysosomal disorders: Fabry disease, Gaucher disease, mucopolysaccharidosis type I, and Pompe disease. These assays were tested in a prospective comparative effectiveness study using nearly 100,000 residual newborn dried blood spot specimens. In addition, 2nd tier enzyme assays and confirmatory molecular genetic testing were employed. Post-analytical interpretive tools were created using the software Collaborative Laboratory Integrated Reports (CLIR) to determine its ability to improve the performance of each assay vs. the traditional result interpretation based on analyte-specific reference ranges and cutoffs. This study showed that all three platforms have high sensitivity, and the application of CLIR tools markedly improves the performance of each platform while reducing the need for 2nd tier testing by 66% to 95%. Moreover, the addition of disease-specific biochemical 2nd tier tests ensures the lowest false positive rates and the highest positive predictive values for any platform.

Validation of Liquid Chromatography-Tandem Mass Spectrometry-Based 5-Plex Assay for Mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are rare lysosomal storage diseases caused by the accumulation of undegraded glycosaminoglycans in cells and tissues. The effectiveness of early intervention for MPS has been reported. Multiple-assay formats using tandem mass spectrometry have been developed. Here, we developed a method for simultaneous preparation and better measurement of the activities of five enzymes involved in MPSs, i.e., MPS I, MPS II, MPS IIIB, MPS IVA, and MPS VI, which were validated using 672 dried blood spot samples obtained from healthy newborns and 23 patients with MPS. The mean values of the enzyme activities and standard deviations in controls were as follows: α-iduronidase (IDUA), 4.19 ± 1.53 µM/h; iduronate-2-sulfatase (I2S), 8.39 ± 2.82 µM/h; N-acetyl-α-glucosaminidase (NAGLU), 1.96 ± 0.57 µM/h; N-acetylgalactosamine-6-sulfatase (GALNS), 0.50 ± 0.20 µM/h; and N-acetylgalactosamine-4-sulfatase (ARSB), 2.64 ± 1.01 µM/h. All patients displayed absent or low enzyme activity. In MPS I, IIIB, and VI, each patient group was clearly separated from controls, whereas there was some overlap between the control and patient groups in MPS II and IVA, suggesting the occurrence of pseudo-deficiencies. Thus, we established a multiplex assay for newborn screening using liquid chromatography tandem mass spectrometry, allowing simultaneous pretreatment and measurement of five enzymes relevant to MPSs.

The First Year Experience of Newborn Screening for Pompe Disease in California

The California Department of Public Health started universal newborn screening for Pompe disease in August 2018 with a two-tier process including: (1) acid alpha-glucosidase (GAA) enzyme activity assay followed by, (2) GAA gene sequencing analysis. This study examines results from the first year of screening in a large and diverse screening population. With 453,152 screened newborns, the birth prevalence and GAA enzyme activity associated with various types of Pompe disease classifications are described. The frequency of GAA gene mutations and allele variants are reported. Of 88 screen positives, 18 newborns were resolved as Pompe disease, including 2 classic infantile-onset and 16 suspected late-onset form. The c.-32-13T>G variant was the most common pathogenic mutation reported. African American and Asian/Pacific Islander newborns had higher allele frequencies for both pathogenic and pseudodeficiency variants. After the first year of Pompe disease screening in California, the disease distribution in the population is now better understood. With the ongoing long-term follow-up system currently in place, our understanding of the complex genotype-phenotype relationships will become more evident in the future, and this should help us better understand the clinical significance of identified cases.

Implementation of Second-Tier Tests in Newborn Screening for Lysosomal Disorders in North Eastern Italy

The increasing availability of treatments and the importance of early intervention have stimulated interest in newborn screening for lysosomal storage diseases. Since 2015, 112,446 newborns in North Eastern Italy have been screened for four lysosomal disorders-mucopolysaccharidosis type I and Pompe, Fabry and Gaucher diseases-using a multiplexed tandem mass spectrometry (MS/MS) assay system. We recalled 138 neonates (0.12%) for collection of a second dried blood spot. Low activity was confirmed in 62 (0.06%), who underwent confirmatory testing. Twenty-five neonates (0.02%) were true positive: eight with Pompe disease; seven with Gaucher disease; eight with Fabry disease; and two with Mucopolysaccharidosis type I. The combined incidence of the four disorders was 1 in 4497 births. Except for Pompe disease, a second-tier test was implemented. We conclude that newborn screening for multiple lysosomal storage diseases combined with a second-tier test can largely eliminate false-positives and achieve rapid diagnosis.

Rapid and Modular Assembly of Click Substrates To Assay Enzyme Activity in the Newborn Screening of Lysosomal Storage Disorders

Synthetic substrates play a pivotal role in the development of enzyme assays for medical diagnostics. However, the preparation of these chemical tools often requires multistep synthetic procedures complicating structural optimization and limiting versatility. In particular, substrates for enzyme assays based on tandem mass spectrometry need to be designed and optimized to fulfill the requirements to finally enable the development of robust diagnostic assays. In addition, isotope-labeled standards need to be prepared to facilitate accurate quantification of enzyme assay products. Here we report the development of a building block strategy for rapid and modular assembly of enzyme substrates using click chemistry as a key step. These click substrates are made up of a sugar moiety as enzyme responsive unit, a linker that can easily be isotope-labeled for the synthesis of internal standards, and a modifier compound that can readily be exchanged for structural optimization and analytical/diagnostic tuning. Moreover, the building block assembly eliminates the need for extensive optimization of different glycosylation reactions as it enables the divergent synthesis of substrates using a clickable enzyme responsive unit. The outlined strategy has been applied to obtain a series of synthetic α-l-iduronates and sulfated β-d-galactosides as substrates for assaying α-l-iduronidase and N-acetylgalactosamine-6-sulfate sulfatase, enzymes related to the lysosomal storage disorders mucopolysaccharidosis type I and type IVa, respectively. Selected click substrates were finally shown to be suitable to assay enzyme activities in dried blood spot samples from affected patients and random newborns.

Clinical presentation and diagnosis of mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are estimated to affect1 in 25,000 live births although specific rates vary between the ethnic origin and country. MPS are a group of lysosomal storage disorders, which cause the buildup of GAG(s) due to insufficient or absent GAG-degrading enzymes. With seven types of MPS disorders and eleven subtypes, the MPS family presents unique challenges for early clinical diagnosis due to the molecular and clinical heterogeneity between groups and patients. Novel methods of early identification, particularly newborn screening through mass spectrometry, can change the flow of diagnosis, allowing enzyme and GAG quantification before the presentation of clinical symptoms improving outcomes. Genetic testing of patients and their families can also be conducted preemptively. This testing enables families to make informed decisions about family planning, leading to prenatal diagnosis. In this review, we discuss the clinical symptoms of each MPS type as they initially appear in patients, biochemical and molecular diagnostic methods, and the future of newborn screening for this group of disorders.

The New York pilot newborn screening program for lysosomal storage diseases: Report of the First 65,000 Infants

Purpose:

We conducted a consented pilot newborn screening (NBS) for Pompe, Gaucher, Niemann Pick A/B, Fabry, and MPS 1 to assess the suitability of these lysosomal storage disorders (LSD) for public health mandated screening.

Methods:

At five participating high-birth-rate, ethnically diverse New York City hospitals, recruiters discussed the study with post-partum parents and documented verbal consent. Screening on consented samples was performed using multiplexed tandem mass spectrometry. Screen-positive infants underwent confirmatory enzymology, DNA testing, and biomarker quantitation when available. Affected infants are being followed for clinical management and long term outcome.

Results:

65,605 infants participated over four years, representing an overall consent rate of 74%. Sixty-nine infants were screen-positive. Twenty-three were confirmed true positives, all of whom were predicted to have late-onset phenotypes. Six of the 69 currently have undetermined disease status.

Conclusion:

Our results suggest that NBS for LSDs is much more likely to detect individuals at risk for late-onset disease, similar to results from other NBS programs. This work has demonstrated the feasibility of using a novel consented pilot NBS study design that can be modified to include other disorders under consideration for public health implementation as a means to gather critical evidence for evidence-based NBS practices.

Newborn Screening for Pompe Disease

Started in 1963 by Robert Guthrie, newborn screening (NBS) is considered to be one of the great public health achievements. Its original goal was to screen newborns for conditions that could benefit from presymptomatic treatment, thereby reducing associated morbidity and mortality. With advances in technology, the number of disorders included in NBS programs increased. Pompe disease is a good candidate for NBS. Because decisions regarding which diseases should be included in NBS panels are made regionally and locally, programs and efforts for NBS for Pompe disease have been inconsistent both in the United States and globally. In this article, published in the "Newborn Screening, Diagnosis, and Treatment for Pompe Disease" guidance supplement, the Pompe Disease Newborn Screening Working Group, an international group of experts in both NBS and Pompe disease, review the methods used for NBS for Pompe disease and summarize results of current and ongoing NBS programs in the United States and other countries. Challenges and potential drawbacks associated with NBS also are discussed.

Newborn Screening for Lysosomal Storage Diseases: A Concise Review of the Literature on Screening Methods, Therapeutic Possibilities and Regional Programs

Newborn screening for lysosomal storage diseases (LSDs) is increasingly being considered as an option. The development of analytical screening methods, of second-tier methods, and of therapeutic possibilities, are paving the way for routine screening for LSDs in the coming years. Here, we give a brief description of the current status quo, what screening methods are currently available or are in the pipeline, what is the current status of therapeutic possibilities for LSDs, what LSDs are the most obvious candidates for introduction in screening programs, and what LSDs are already part of regional or national pilot or routine screening programs worldwide.

Age and gender-specific reference intervals for lysosomal enzymes in dried blood spot samples: A study in Indian population

OBJECTIVES

The study aimed to establish age and gender-specific reference values for the activities of lysosomal enzymes (acid α-galactosidase [GLA], acid β-glucocerebrosidase [GBA], acid α-glucosidase [GAA], acid sphingomyelinase [ASM] and galactocerebrosidase [GALC]) in dried blood spots (DBS) of Indian population.

DESIGN AND METHODS

A total of 3797 healthy Indian subjects (1456 females and 2341 males) aged from 2days to 60years were selected for the study. Activities of 5 lysosomal enzymes were determined by tandem mass spectrometry, for newborns (<30days), infants (>1month-1year), children (>1-5years) and (>5-18years) and adults (>18years).Variations in enzyme activities based on age and gender were studied. The reference interval was defined as the central 95% range, and was determined based on age and gender.

RESULTS

Highly significant differences in activities were observed for GAA (p=0.001), GLA (p<0.0001), GBA (p<0.0001), ASM (p<0.0001) and GALC (p<0.0001), between different age groups. Comparison of activities between genders showed significant difference for ASM in children aged 1-5years (p=0.03) with higher activity in females, and for GLA in children aged 5-18years (p=0.004) where the activity was higher in males. Reference intervals decreased with age for all enzymes, except GAA. The ranges of GLA and GALC were higher in females, whereas GBA was higher in males.

CONCLUSION

The study establishes age and gender-specific reference values for the screening and identification of lysosomal storage disorders in Indian population. Our data may facilitate establishment of mass screening programs for these disorders in India.

Effect of temperature on lysosomal enzyme activity during preparation and storage of dried blood spots

BACKGROUND

The use of dried blood spots (DBS) for the assay of lysosomal enzymes has facilitated the implementation of pilot studies for newborn screening for lysosomal storage disorders in various developed countries. The aim of the study was to determine the influence of ambient temperature during DBS preparation and storage on lysosomal enzyme activity in a developing, tropical country.

METHODS

Blood samples from 12 healthy subjects collected on a S&S 903 filter paper were dried and stored at different temperatures for different periods of time. Activities of five lysosomal enzymes (acid α-glucosidase, acid α-galactosidase, acid β-glucocerebrosidase, acid sphingomyelinase, and galactocerebrosidase) were determined by tandem mass spectrometric and fluorimetric (acid α-glucosidase and acid β-glucocerebrosidase only) assays.

RESULTS

The mean activities of all five enzymes decreased significantly when DBS was dried at temperatures above 24°C (P<.0001). DBS stored at 4°C, 24°C, 30°C, 37°C, and 45°C for 10 days and more, also showed significant reduction in activities of all five enzymes (P<.0001).

CONCLUSION

The results highlight the importance of maintaining the correct ambient temperature during DBS preparation and storage to avoid false positive results when screening for lysosomal storage disorders.

Newborn screening for mucopolysaccharidoses: a pilot study of measurement of glycosaminoglycans by tandem mass spectrometry

BACKGROUND

Mucopolysaccharidoses (MPS) are a group of inborn errors of metabolism that are progressive and usually result in irreversible skeletal, visceral, and/or brain damage, highlighting a need for early diagnosis.

METHODS

This pilot study analyzed 2862 dried blood spots (DBS) from newborns and 14 DBS from newborn patients with MPS (MPS I, n = 7; MPS II, n = 2; MPS III, n = 5). Disaccharides were produced from polymer GAGs by digestion with chondroitinase B, heparitinase, and keratanase II. Heparan sulfate (0S, NS), dermatan sulfate (DS) and mono- and di-sulfated KS were measured by liquid chromatography tandem mass spectrometry (LC-MS/MS). Median absolute deviation (MAD) was used to determine cutoffs to distinguish patients from controls. Cutoffs were defined as median + 7× MAD from general newborns.

RESULTS

The cutoffs were as follows: HS-0S > 90 ng/mL; HS-NS > 23 ng/mL, DS > 88 ng/mL; mono-sulfated KS > 445 ng/mL; di-sulfated KS > 89 ng/mL and ratio di-KS in total KS > 32 %. All MPS I and II samples were above the cutoffs for HS-0S, HS-NS, and DS, and all MPS III samples were above cutoffs for HS-0S and HS-NS. The rate of false positives for MPS I and II was 0.03 % based on a combination of HS-0S, HS-NS, and DS, and for MPS III was 0.9 % based upon a combination of HS-0S and HS-NS.

CONCLUSIONS

Combination of levels of two or more different GAGs improves separation of MPS patients from unaffected controls, indicating that GAG measurements are potentially valuable biomarkers for newborn screening for MPS.

Newborn screening for Fabry disease in the north-west of Spain

Fabry disease is an X-linked lysosomal storage disorder caused by the impairment of α-galactosidase A. Enzyme replacement therapy is available to treat patients, who often experience delayed diagnosis. A newborn screening for Fabry disease was performed to study the prevalence of the pathology and to evaluate the possibility to implement the test in systematic screenings. We collected 14,600 dried blood spot samples (7575 males and 7025 females) and carried out a diagnostic study by fluorometric measurement of α-galactosidase A enzymatic activity and GLA gene sequencing. We detected one patient with a mutation in GLA associated with classical Fabry Disease (M290I), ten subjects carrying genetic variants of uncertain diagnosis (S126G, R118C, A143T), and a girl with the non-characterized variant F18Y, which was not previously described. Additional 25 samples presented nucleotide substitutions described as polymorphisms (D313Y, rs2071225, and rs2071397). The estimated prevalence for Fabry disease in north-western Spanish males is of 0.013%.

CONCLUSION

These results confirm that the prevalence of Fabry disease is underestimated and systematic screening is feasible; however, further characterization of variants of uncertain clinical significance is necessary to establish protocols of patients' management. What is Known: • Fabry disease is a rare disease of delayed diagnosis, whose prevalence is underestimated. However, early diagnosis is important for better efficiency of the current available treatment. What is New: • This newborn screening for Fabry disease performed on Spanish population reveals a prevalence of genetic alterations in GLA of 0.1% in males (0.013% with classic Fabry disease) and also characterizes these modifications in order to discriminate between pathogenic mutations and genetic variants of unknown significance.

Tandem Mass Spectrometry of Sphingolipids: Applications for Diagnosis of Sphingolipidoses

In recent years, mass spectrometry (MS) has become the dominant technology in lipidomic analysis. It is widely used in diagnosis and research of lipid metabolism disorders including those characterized by impairment of lysosomal functions and storage of nondegraded-degraded substrates. These rare diseases, which include sphingolipidoses, have severe and often fatal clinical consequences. Modern MS methods have contributed significantly to achieve a definitive diagnosis, which is essential in clinical practice to begin properly targeted patient care. Here we summarize MS and tandem MS methods used for qualitative and quantitative analysis of sphingolipids (SL) relative to the diagnostic process for sphingolipidoses and studies focusing on alterations in cell functions due to these disorders. This review covers the following topics: Tandem MS is sensitive and robust in determining the composition of sphingolipid classes in various biological materials. Its ability to establish SL metabolomic profiles using MS bench-top analyzers, significantly benefits the first stages of a diagnosis as well as metabolic studies of these disorders. It can thus contribute to a better understanding of the biological significance of SL.

Fabry's disease: an example of cardiorenal syndrome type 5

Cardiorenal syndrome type 5 (CRS-5) includes conditions where there is a simultaneous involvement of the heart and kidney from a systemic disorder. This is a bilateral organ cross talk. Fabry's disease (FD) is a devastating progressive inborn error of metabolism with lysosomal glycosphingolipid deposition in variety of cell types, capillary endothelial cells, renal, cardiac and nerve cells. Basic effect is absent or deficient activity of lysosomal exoglycohydrolase a-galactosidase A. Renal involvement consists of proteinuria, isosthenuria, altered tubular function, presenting in second or third decade leading to azotemia and end-stage renal disease in third to fifth decade mainly due to irreversible changes to glomerular, tubular and vascular structures, especially highlighted by podocytes foot process effacement. Cardiac involvement consists of left ventricular hypertrophy, right ventricular hypertrophy, arrhythmias (sinus node and conduction system impairment), diastolic dysfunction, myocardial ischemia, infarction, transmural replacement fibrosis, congestive heart failure and cardiac death. Management of FD is based on enzymatic replacement therapy and control of renal (with anti-proteinuric agents such as angiotensin-converting enzyme inhibitors-and/or angiotensin II receptor blockers), brain (coated aspirin, clopidogrel and statin to prevent strokes) and heart complications (calcium channel blockers for ischemic cardiomyopathy, warfarin and amiodarone or cardioverter device for arrhythmias).

Activity of daily living for Morquio A syndrome

The aim of this study was to evaluate the activity of daily living (ADL) and surgical interventions in patients with mucopolysaccharidosis IVA (MPS IVA). The factor(s) that affect ADL are age, clinical phenotypes, surgical interventions, therapeutic effect, and body mass index. The ADL questionnaire comprises three domains: "Movement," "Movement with cognition," and "Cognition." Each domain has four subcategories rated on a 5-point scale based on the level of assistance. The questionnaire was collected from 145 healthy controls and 82 patients with MPS IVA. The patient cohort consisted of 63 severe and 17 attenuated phenotypes (2 were undefined); 4 patients treated with hematopoietic stem cell transplantation (HSCT), 33 patients treated with enzyme replacement therapy (ERT) for more than a year, and 45 untreated patients. MPS IVA patients show a decline in ADL scores after 10years of age. Patients with a severe phenotype have a lower ADL score than healthy control subjects, and lower scores than patients with an attenuated phenotype in domains of "Movement" and "Movement with cognition." Patients, who underwent HSCT and were followed up for over 10years, had higher ADL scores and fewer surgical interventions than untreated patients. ADL scores for ERT patients (2.5years follow-up on average) were similar with the-age-matched controls below 10years of age, but declined in older patients. Surgical frequency was higher for severe phenotypic patients than attenuated ones. Surgical frequency for patients treated with ERT was not decreased compared to untreated patients. In conclusion, we have shown the utility of the proposed ADL questionnaire and frequency of surgical interventions in patients with MPS IVA to evaluate the clinical severity and therapeutic efficacy compared with age-matched controls.

Improved sensitivity of an acid sphingomyelinase activity assay using a C6:0 sphingomyelin substrate

Short-chain C6-sphingomyelin is an artificial substrate that was used in an acid sphingomyelinase activity assay for a pilot screening study of patients with Niemann–Pick disease types A and B. Using previously published multiplex and single assay conditions, normal acid sphingomyelinase activity levels (i.e. false negative results) were observed in two sisters with Niemann–Pick B who were compound heterozygotes for two missense mutations, p.C92W and p.P184L, in the SMPD1 gene. Increasing the sodium taurocholate detergent concentration in the assay buffer lowered the activity levels of these two patients into the range observed with other patients with clear separation from normal controls.

Neonatal cellular and gene therapies for mucopolysaccharidoses: the earlier the better?

Mucopolysaccharidoses (MPSs) are a group of lysosomal storage disorders (LSDs). The increasing interest in newborn screening procedures for LSDs underlines the need for alternative cellular and gene therapy approaches to be developed during the perinatal period, supporting the treatment of MPS patients before the onset of clinical signs and symptoms. The rationale for considering these early therapies results from the clinical experience in the treatment of MPSs and other genetic disorders. The normal or gene-corrected hematopoiesis transplanted in patients can produce the missing protein at levels sufficient to improve and/or halt the disease-related abnormalities. However, these current therapies are only partially successful, probably due to the limited efficacy of the protein provided through the hematopoiesis. An alternative explanation is that the time at which the cellular or gene therapy procedures are performed could be too late to prevent pre-existing or progressive organ damage. Considering these aspects, in the last several years, novel cellular and gene therapy approaches have been tested in different animal models at birth, a highly early stage, showing that precocious treatment is critical to prevent long-term pathological consequences. This review provides insights into the state-of-art accomplishments made with neonatal cellular and gene-based therapies and the major barriers that need to be overcome before they can be implemented in the medical community.

Diagnosis of late-onset Pompe disease and other muscle disorders by next-generation sequencing

Background

Late-onset Pompe disease (LOPD) is a rare treatable lysosomal storage disorder characterized by progressive lysosomal glycogen accumulation and muscle weakness, with often a limb-girdle pattern. Despite published guidelines, testing for LOPD is often overlooked or delayed in adults, owing to its low frequency compared to other muscle disorders with similar muscle patterns. Next-generation sequencing has the capability to test concurrently for several muscle disorders. This could potentially lead to increased diagnosis of LOPD, disorders with non-specific muscle weakness or atypical patients.

Methods

We developed a gene panel to further study its clinical utility in a cohort of patients with suspected muscle disorders. We designed a gene panel to analyze the coding sequences and splice site junctions of GAA causing LOPD, along with 77 other genes causing muscle disorders with overlapping phenotypes.

Results

At a median coverage of ~200X (sequences per base), all GAA exons were successfully covered with >20X and only 0.3 % of exons across all genes were <20X. The panel showed an excellent sensitivity (100 %) and specificity (98 %) across all selected genes, using known variations in Pompe patients and controls. We determined its clinical utility by analyzing 34 patients with suspected muscle disorders of undetermined etiology and various muscle patterns, who were referred or followed in neuromuscular and genetics clinics. A putative diagnosis was found in up to 32 % of patients. The gene panel was instrumental in reaching a diagnosis in atypical patients, including one LOPD case. Acid alpha-glucosidase activity was used to confirm the molecular results in all patients.

Conclusion

This work highlights the high clinical utility of gene panels in patients with suspected muscle disorders and its potential to facilitate the diagnosis of patients showing non-specific muscle weakness or atypical phenotypes. We propose that gene panels should be used as a first-tier test in patients with suspected muscle disorders of undetermined etiology, which could further increase overall diagnosis of muscle conditions, and potentially reduce diagnostic delay. Further studies are necessary to determine the impact of first-tier gene panels on diagnostic delay and on treatment outcome for LOPD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0390-6) contains supplementary material, which is available to authorized users.

Expanded newborn screening by mass spectrometry: New tests, future perspectives

Tandem mass spectrometry (MS/MS) has become a leading technology used in clinical chemistry and has shown to be particularly sensitive and specific when used in newborn screening (NBS) tests. The success of tandem mass spectrometry is due to important advances in hardware, software and clinical applications during the last 25 years. MS/MS permits a very rapid measurement of many metabolites in different biological specimens by using filter paper spots or directly on biological fluids. Its use in NBS give us the chance to identify possible treatable metabolic disorders even when asymptomatic and the benefits gained by this type of screening is now recognized worldwide. Today the use of MS/MS for second-tier tests and confirmatory testing is promising especially in the early detection of new disorders such as some lysosomal storage disorders, ADA and PNP SCIDs, X-adrenoleucodistrophy (X-ALD), Wilson disease, guanidinoacetate methyltransferase deficiency (GAMT), and Duchenne muscular dystrophy. The new challenge for the future will be reducing the false positive rate by using second-tier tests, avoiding false negative results by using new specific biomarkers and introducing new treatable disorders in NBS programs.

Enzymatic diagnosis of Fabry disease using a fluorometric assay on dried blood spots: An alternative methodology

Fabry disease (FD, OMIM#301500) is an X-linked lysosomal storage disorder caused by the functional deficiency of α-galactosidase A, a lysosomal enzyme. A method to screen for FD in large populations has been developed using a fluorometric assay of α-galactosidase A activity in dried blood spots (DBS) on filter paper. However, results can be influenced by quenching of fluorescence by haemoglobin which, together with small sample size, may result in a low light emission signal. An alternative, simple and sensitive fluorometric assay was developed for the determination of α-galactosidase A activity in DBS. The assay uses 4-methylumbelliferyl-α-d-galactose as an artificial substrate. To minimize the risk of false-positives, zinc sulfate was used for protein precipitation to stop the enzymatic reaction and eliminate interfering species (hemoglobin). Samples from 209 individuals (60 hemizygotes, 68 heterozygotes, and 81 controls) were tested to establish reference values for the assay. The mean α-galactosidase A activity of the 81 controls was 9.1 ± 3.3 μmol h(-1) L(-1) (mean ± SD). All 60 hemizygotes affected with FD had AGAL activities below 1.7 μmol h(-1) L(-1) (0.2 ± 0.3 μmol h(-1) L(-1)). For the 68 heterozygous females, AGAL activity ranged from 0 to 12.6 μmol h(-1) L(-1) (3.5 ± 2.7 μmol h(-1) L(-1)). Two-thirds of the female patients could be identified using the enzymatic assay and a cut-off level of 40% of the median control value (<3.4 μmol h(-1) L(-1)). Our fluorometric assay using zinc sulfate protein precipitation was shown to have similar sensitivity and robustness while reducing the risk of false positive results due to quenching of 4-MU fluorescence by haemoglobin.

Identification and structural characterization of novel O- and N-glycoforms in the urine of a Schindler disease patient by Orbitrap mass spectrometry

Schindler disease is an inherited metabolic disorder caused by the deficient activity of α-N-acetylgalactosaminidase enzyme. An accurate diagnosis requires, besides clinical examination, complex and costly biochemical and molecular genetic tests. In the last years, mass spectrometry (MS) based on nanofluidics and high-resolution instruments has become a successful alternative for disease diagnosis based on the investigation of O-glycopeptides in patient urine. A complex mixture of glycoforms extracted from the urine of a 3-year-old patient was investigated by Orbitrap MS equipped with Nanospray Flex Ion Source in the negative ion mode. For structural characterization of several molecular species, collision-induced dissociation MS² -MS³ was carried out using collision energy values within 20-60 eV range. By our approach, 39 novel species associated to this condition were identified, among which O-glycopeptides, free O-glycans and one structure corresponding to an N-glycan never characterized in the context of Schindler disease. The experiments conducted at a resolution of 60 000 allowed the discrimination and identification of a total number of 69 different species with an average mass accuracy of 9.87 ppm, an in-run reproducibility of almost 100%, an experiment-to-experiment and day-to-day reproducibility of about 95%. This study brings contributions in the diagnosis of Schindler disease through the elucidation of potential biomarker species in urine. Our multistage MS results completed with 39 new glycoforms the inventory of potential biomarker structures associated to Schindler disease. For the first time, an N-glycan was identified and structurally characterized in Schindler patient urine, which opens new research directions in the field. Copyright © 2015 John Wiley & Sons, Ltd.

Newborn screening for lysosomal storage disorders

Every newborn in the U.S. is screened for at least 29 disorders, where evidence suggests that early detection is possible and beneficial. With new or improved treatment options and development of high-throughput screening tests, additional conditions have been proposed for inclusion in newborn screening programs. Among those are several lysosomal storage disorders that have been evaluated in limited pilot studies or that are already included in a few national or international newborn screening programs. These conditions include Pompe disease, Niemann-Pick type A/B disease, Fabry disease, Krabbe disease, Mucopolysaccharidoses types I and II, and Gaucher disease. Here, we review the current state of newborn screening for these lysosomal storage disorders.

Novel GAA mutations in patients with Pompe disease

Pompe disease is an autosomal recessive disorder linked to GAA gene that leads to a multi-system intralysosomal accumulation of glycogen. Mutation identification in the GAA gene can be very important for early diagnosis, correlation between genotype-phenotype and therapeutic intervention. For this purpose, peripheral blood from 57 individuals susceptible to Pompe disease was collected and all exons of GAA gene were amplified; the sequences and the mutations were analyzed in silico to predict possible impact on the structure and function of the human protein. In this study, 46 individuals presented 33 alterations in the GAA gene sequence, among which five (c.547-67C>G, c.547-39T>G, p.R437H, p.L641V and p.L705P) have not been previously described in the literature. The alterations in the coding region included 15 missense mutations, three nonsense mutations and one deletion. One insertion and other 13 single base changes were found in the non-coding region. The mutation p.G611D was found in homozygosis in a one-year-old child, who presented low levels of GAA activity, hypotonia and hypertrophic cardiomyopathy. Two patients presented the new mutation p.L705P in association with c.-32-13T>G. They had low levels of GAA activity and developed late onset Pompe disease. In our study, we observed alterations in the GAA gene originating from Asians, African-Americans and Caucasians, highlighting the high heterogeneity of the Brazilian population. Considering that Pompe disease studies are not very common in Brazil, this study will help to better understand the potential pathogenic role of each change in the GAA gene. Furthermore, a precise and early molecular analysis improves genetic counseling besides allowing for a more efficient treatment in potential candidates.