Direct multiplex assay of lysosomal enzymes in dried blood spots for newborn screening

Successful screening for Gaucher disease in a high-prevalence population in tabuleiro do Norte (northeastern Brazil): a cross-sectional study

BACKGROUND

Gaucher disease (GD) is a hereditary lysosomal storage disorder characterized by the accumulation of glucosylceramide, mainly in the cells of the reticuloendothelial system, due to a deficiency of the enzyme acid β-glucosidase (GBA). Diagnosis is usually based on measurement of GBA activity in peripheral leukocytes. The purpose of this study was to evaluate the ability of screening for GBA and chitotriosidase activity using dried blood spots on filter paper (DBS-FP) to identify individuals at high risk for GD in high-risk populations such as that of Tabuleiro do Norte, a small town in Northeastern Brazil.

METHODS

Between 1 June 2007 and 31 May 2008, 740 consented residents and descendants of traditional families from Tabuleiro do Norte were submitted to screening with DBS-FP. Subjects with GBA activity < 2.19 nmol/h/mL were referred to the analysis of GBA and chitotriosidase activity in peripheral leukocytes and in plasma, respectively. Subjects at highest risk for GD (GBA activity in peripheral leukocytes < 5.6 nmol/h/mg protein) were referred to molecular analysis to confirm diagnosis.

RESULTS

Screening with DBS-FP identified 135 subjects (18.2%) with GBA activity < 2.19 nmol/h/mL, 131 of whom remained in the study. In ten of these (7.6%), GBA activity in leukocytes was 2.6-5.5 nmol/h/mg protein. Subsequent molecular analysis confirmed six cases of heterozygosity and four normals for GD.

CONCLUSION

DBS-FP assay was shown to be an effective initial GD-screening strategy for high-prevalence populations in developing regions. Diagnosis could not be established from GBA activity in leukocytes alone, but required confirmation with molecular analysis.

Effect of one year of cryopreservation on the activity of lysosomal hydrolases from EBV-transformed lymphocytes

Background. The Epstein-Barr virus (EBV) was used as an agent of B lymphocyte proliferation for subsequent diagnosis of lysosomal storage disease. Due to the constant handling of long-preserved samples in our cell bank, we decided to observe the behavior and then compare cultured and frozen samples for at least one year's cryopreservation. Methods. Twenty-five samples from healthy individuals were used to assess the possible changes in activity of enzymes β-galactosidase, β-glucosidase, α-iduronidase, α-galactosidase, and α-glucosidase. Transmission electron microscopy was used to confirm cell transformation of B lymphocytes into EBV-infected cells, generating lymphoblastoid cell lines. Results. Transmission electron microscopy findings confirmed previous reports in the literature that is, significant and evident morphological changes in the nucleus occur after day 12 and the consequent cell transformation into EBV-infected cells. After thawing and subsequent treatment with the five enzymes utilized, we observed no significant changes in samples cryopreserved for more than one year, as compared to samples cultured for 12 days.

Comparative triplex tandem mass spectrometry assays of lysosomal enzyme activities in dried blood spots using fast liquid chromatography: application to newborn screening of Pompe, Fabry, and Hurler diseases

We report a comparative study of triplex tandem mass spectrometry (MS/MS) based assays of lysosomal enzymes in dried blood spots for the early detection of Pompe, Fabry, and Hurler diseases in newborns. Four methods have been evaluated that differed in sample handling and the equipment used. A newly developed method uses assay quenching with acetonitrile to precipitate blood proteins followed by analysis on an LC-electrospray/MS/MS system capable of multiple consecutive sample injections on two parallel chromatographic columns. This method requires 1.5 min per a triplex analysis of enzyme products and internal standards, which matches the throughput of the previously reported flow injection method. LC separation reduces matrix effects and allows for more facile sample workup. The new LC-based method showed figures of merit that were superior to those of the currently used method based on liquid-liquid extraction into ethyl acetate and flow injection into the mass spectrometer. The other methods we investigated for comprehensive comparison involved liquid-liquid extraction into ethyl acetate followed by LC-ESI-MS/MS and acetonitrile quenching followed by direct flow injection. Both methods using acetonitrile quenching were found to be robust and provide good quality data while requiring fewer liquid transfer steps and less disposable material and labor than did the extraction methods. The individual merits of the new methods are discussed to present an evaluated alternative approach to high-throughput analysis in newborn screening laboratories.

Improved assay for differential diagnosis between Pompe disease and acid α-glucosidase pseudodeficiency on dried blood spots

The high frequency (3.3-3.9%) of acid α-glucosidase pseudodeficiency, c.[1726G>A; 2065G>A] homozygote (AA homozygote), in Asian populations complicates newborn screening for Pompe disease (glycogen storage disease type II or acid maltase deficiency) on dried blood spots, since AA homozygotes have a considerably low enzyme activity. We observed that hemoglobin in the enzyme reaction solution strongly interferes with the fluorescence of 4-methylumbelliferone released from 4-methylumbelliferyl α-D-glucopyranoside (4MU-αGlc) by acid α-glucosidase. Therefore, we have searched for a method to effectively eliminate hemoglobin in the reaction solution. Hemoglobin precipitation with barium hydroxide and zinc sulfate (Ba/Zn method) carried out after the enzyme reaction considerably enhances the fluorescence intensity while it does not reduce the intensity to any extent as can occur with conventional deproteinization agents like trichloroacetic acid. The Ba/Zn method greatly improved the separation between 18 Japanese patients with Pompe disease and 70 unaffected AA homozygotes in a population of Japanese newborns in the assay with 4MU-αGlc on dried blood spots. No overlap was observed between both groups. We further examined acid α-glucosidase activity in fibroblasts from 11 Japanese patients and 57 Japanese unaffected individuals including 31 c.[1726G; 2065G] homozygotes, 18 c.[1726G; 2065G]/[1726A; 2065A] heterozygotes and 8 AA homozygotes to confirm that fibroblasts can be used for definitive diagnosis. The patients were reliably distinguished from three control groups. These data provide advanced information for the development of a simple and reliable newborn screening program with dried blood spots for Pompe disease in Asian populations.

Newborn screening for galactosemia by a second-tier multiplex enzyme assay using UPLC-MS/MS in dried blood spots

Galactosemia is one of the most important inherited metabolic disorders detected by newborn screening tests. Abnormal results during screening should be confirmed by enzyme activity assays. Recently, we developed a multiplex enzyme assay for galactosemia in erythrocytes using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). In this study, we proposed a second-tier multiplex enzyme assay for galactosemia that can be directly applied to dried blood spots (DBSs). Supernatants from two rehydrated-punched 3.2-mm DBSs were incubated with a reaction mixture containing [¹³C6]galactose, [¹³C2]galactose-1-phosphate, and UDP-glucose as substrates for three galactose-metabolizing enzymes. After a 4-hour incubation, the end products from the combined reaction mixture, [¹³C6]galactose-1-phosphate, UDP-[¹³C2]galactose, and UDP-galactose, were simultaneously measured using UPLC-MS/MS. Substrates, products, and internal standards from the mixture of the three enzyme reactions were clearly separated in the UPLC-MS/MS system, with an injection cycle time of 10 min. Intra- and inter-assay imprecisions of the UPLC-MS/MS were 8.4-14.8% and 13.2-15.7% CV, respectively. Enzyme activities in DBSs from 37 normal individuals and 10 patients with enzyme deficiencies were analyzed. DBSs from galactosemia patients showed consistently lower enzyme activities as compared to those of normal individuals. In conclusion, multiplex enzyme assays using UPLC-MS/MS can be successfully applied to DBS analysis. This method allows a fast and effective second-tier test for newborns showing abnormal screening results.

α-Galactosidase A expressed in the salivary glands partially corrects organ biochemical deficits in the fabry mouse through endocrine trafficking

Fabry disease is caused by an X-linked deficiency of the lysosomal enzyme α-galactosidase A (GLA) and has been treated successfully with enzyme replacement therapy (ERT). Gene therapy has been proposed as an alternative to ERT due to the presumed advantages of continuous, endogenous production of the therapeutic enzyme. GLA production in the liver and its therapeutic efficacy in the Fabry mouse have been demonstrated previously with various viral vector systems. In consideration of the potential advantages of using the salivary glands as endogenous GLA biosynthesis sites, we explored the feasibility of this approach in the Fabry mouse. GLA -/0 or -/- mice received an adenoviral vector (2 × 10(10) or 1 × 10(9) viral particles) expressing GLA to the right submandibular gland via oral cannulation of the submandibular duct. Four days later, animals were sacrificed; saliva, plasma, kidney, liver, and brain were collected and assayed using ELISA, Western blot, and a GLA enzymatic activity assay using both traditional fluorescence methods and isotope dilution mass spectrometry by following the U.S. EPA Method 6800. GLA activity was significantly elevated in the serum and liver of both treatment groups, and improvement in the kidney was marginally significant (P < 0.069) in the high-dose group. Notably, we found that liver and salivary gland produce different glycoforms of the GLA transgene. Only small numbers of adenoviral genomes were observed in the livers of treated animals, but in four of 14 in the high-dose groups, liver levels of adenovirus exceeded 20 copies/μg, indicating that the sequestration in the salivary gland was imperfect at high doses. Taken together, these results indicate that the salivary gland-based gene therapy for Fabry disease is promising, and further studies with advanced viral vector gene delivery systems (e.g., adeno-associated virus) for long-term treatment appear to be warranted.

Efficient analysis of urinary glycosaminoglycans by LC-MS/MS in mucopolysaccharidoses type I, II and VI

Mucopolysaccharidoses (MPSs) are complex storage disorders caused by specific lysosomal enzyme deficiencies, resulting in the accumulation of glycosaminoglycans (GAGs) in urine, plasma, as well as in various tissues. We devised and validated a straightforward, but accurate and precise tandem mass spectrometry methodology coupled to high performance liquid chromatography (LC-MS/MS) for the quantification of GAGs in urine. The method is applicable to the investigation of patients with MPS I, II, and VI, by quantifying dermatan sulfate (DS) and heparan sulfate (HS) in urine. We analyzed urine samples from 28 MPS patients, aged 1 to 42 years, and 55 control subjects (41 days to 18 years old). Levels of DS and HS in urine from healthy controls of all ages were below the limit of quantification. The levels of DS and HS in urine from 6 treated patients with MPS I were lower than in 6 untreated patients in DS (0.7-45 vs 9.3-177 mg/mmol creat) and HS (0-123 mg/mmol creatinine vs 38-418 mg/mmol creatinine); similar results were obtained for 9 patients with MPS II and 7 patients with MPS VI. Analyses were performed on as little as 250 μL of urine. Methanolysis took 75 min per sample; the total analysis run time for each LC-MS/MS injection was 8 min. Results indicate that the method is applicable to a wide variety of situations in which high accuracy and precision are required, including the evaluation of the effectiveness of existing and emerging treatments.

Tandem mass spectrometry for the direct assay of lysosomal enzymes in dried blood spots: application to screening newborns for mucopolysaccharidosis II (Hunter Syndrome)

We have developed a tandem mass spectrometry based assay of iduronate-2-sulfatase (IdS) activity for the neonatal detection of mucopolysaccharidosis II (MPS-II, Hunter Syndrome). The assay uses a newly designed synthetic substrate (IdS-S) consisting of α-L-iduronate-2-sulfate, which is glycosidically conjugated to a coumarin and a linker containing a tert-butyloxycarbamido group. A short synthesis of the substrate has been developed that has the potential of being scaled to multigram quantities. Sulfate hydrolysis of IdS-S by IdS found within a 3 mm dried blood spot specifically produces a nonsulfated product (IdS-P) which is detected by electrospray tandem mass spectrometry and quantified using a deuterium-labeled internal standard, both carried out in positive ion mode. Analysis of DBS from 75 random human newborns showed IdS activities in the range of 4.8-16.2 (mean 9.1) μmol/(h L of blood), which were clearly distinguished from the activities measured for 14 MPS-II patients at 0.17-0.52 (mean 0.29) μmol/(h L of blood). The assay shows low blank activity, 0.15 ± 0.03 μmol/(h L of blood). The within-assay coefficient of variation (CV) was 3.1% while the interassay CV was 15%.

Fabry disease

Fabry disease (FD) is a progressive, X-linked inherited disorder of glycosphingolipid metabolism due to deficient or absent lysosomal α-galactosidase A activity. FD is pan-ethnic and the reported annual incidence of 1 in 100,000 may underestimate the true prevalence of the disease. Classically affected hemizygous males, with no residual α-galactosidase A activity may display all the characteristic neurological (pain), cutaneous (angiokeratoma), renal (proteinuria, kidney failure), cardiovascular (cardiomyopathy, arrhythmia), cochleo-vestibular and cerebrovascular (transient ischemic attacks, strokes) signs of the disease while heterozygous females have symptoms ranging from very mild to severe. Deficient activity of lysosomal α-galactosidase A results in progressive accumulation of globotriaosylceramide within lysosomes, believed to trigger a cascade of cellular events. Demonstration of marked α-galactosidase A deficiency is the definitive method for the diagnosis of hemizygous males. Enzyme analysis may occasionnally help to detect heterozygotes but is often inconclusive due to random X-chromosomal inactivation so that molecular testing (genotyping) of females is mandatory. In childhood, other possible causes of pain such as rheumatoid arthritis and 'growing pains' must be ruled out. In adulthood, multiple sclerosis is sometimes considered. Prenatal diagnosis, available by determination of enzyme activity or DNA testing in chorionic villi or cultured amniotic cells is, for ethical reasons, only considered in male fetuses. Pre-implantation diagnosis is possible. The existence of atypical variants and the availability of a specific therapy singularly complicate genetic counseling. A disease-specific therapeutic option - enzyme replacement therapy using recombinant human α-galactosidase A - has been recently introduced and its long term outcome is currently still being investigated. Conventional management consists of pain relief with analgesic drugs, nephroprotection (angiotensin converting enzyme inhibitors and angiotensin receptors blockers) and antiarrhythmic agents, whereas dialysis or renal transplantation are available for patients experiencing end-stage renal failure. With age, progressive damage to vital organ systems develops and at some point, organs may start to fail in functioning. End-stage renal disease and life-threatening cardiovascular or cerebrovascular complications limit life-expectancy of untreated males and females with reductions of 20 and 10 years, respectively, as compared to the general population. While there is increasing evidence that long-term enzyme therapy can halt disease progression, the importance of adjunctive therapies should be emphasized and the possibility of developing an oral therapy drives research forward into active site specific chaperones.

Tandem mass spectrometry for the direct assay of lysosomal enzymes in dried blood spots: application to screening newborns for mucopolysaccharidosis VI (Maroteaux-Lamy syndrome)

We report a new assay of N-acetylgalactosamine-4-sulfatase (aryl sulfatase B) activity in dried blood spots (DBS) for the early detection of mucopolysaccharidosis VI (Maroteaux-Lamy syndrome) in newborn screening. The assay uses a synthetic substrate consisting of N-acetylgalactosamine-4-sulfate moiety glycosidically linked to a hydrophobic residue and furnished with a tert-butyloxycarbamido group as a marker for specific mass spectrometric fragmentation. Incubation with aryl sulfatase B present in DBS converts the substrate to a desulfated product which is detected by electrospray tandem mass spectrometry and quantified using a homologous internal standard. Assay and workup procedures were optimized to be compatible with the work flow in newborn screening laboratories. Analysis of DBS from human newborns showed clear distinction of aryl sulfatase B activity from 89 healthy individuals where it ranged between 1.4 and 16.9 μmol/(h L of blood), with an average activity of 7.4 μmol/(h L of blood), and an MPS-VI patient that had an activity of 0.12 μmol/(h L of blood). Results are also reported for the aryl sulfatase B assay in DBS from groups of normal felines and felines affected with MPS-VI.

A review of clinical diagnostic applications of liquid chromatography-tandem mass spectrometry

Liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) technology is emerging as a complementary method to traditional methodology used for clinical applications. Enhanced specificity and high-throughput capabilities are providing significant benefits to clinical diagnostic laboratories conducting routine analyses. This technology is expected to expand rapidly as scientists focus on more complicated challenges that can be solved efficiently by adding LC/MS/MS to their arsenal of techniques.

Tandem mass spectrometry for the direct assay of lysosomal enzymes in dried blood spots: application to screening newborns for mucopolysaccharidosis IVA

BACKGROUND

Treatments are being developed for an increasing number of mucopolysaccharidoses, and early diagnosis is expected to be necessary to maximize the benefits of therapy. Therefore, we developed an assay for N-acetylgalactosamine-6-sulfate sulfatase (GALNS), the enzyme deficient in mucopolysaccharidosis IVA (Morquio A syndrome), that is applicable for clinical diagnosis.

METHODS

A novel substrate for GALNS was synthesized for a new enzyme activity assay that is based on tandem mass spectrometry and uses dried blood spots (DBSs) as the enzyme source. We optimized the assay conditions, including the substrate concentration, reaction pH, lead formate concentration, incubation time, punch size of the DBS, and mass spectrometer conditions. We also assessed inter- and intraassay variation.

RESULTS

The assay uses either solid-phase or liquid-phase extraction before analysis by mass spectrometry. An evaluation of blood spots from 90 randomly chosen healthy newborns and 9 patients with Morquio A syndrome showed a well-defined interval between their respective enzyme activities. Inter- and intraassay imprecision was <10%.

CONCLUSIONS

This tandem mass spectrometry assay requires a minimal number of sample-preparation steps, thus making it easy to implement. The assay has the potential to be adopted for early diagnosis of Morquio A syndrome. We believe this assay could be performed in a multiplex fashion with assays for other lysosomal enzymes.

A tandem mass spectrometry triplex assay for the detection of Fabry, Pompe, and mucopolysaccharidosis-I (Hurler)

BACKGROUND

We sought to develop a tandem mass spectrometry assay in which the enzymatic activities of 3 lysosomal enzymes (α-glucosidase, α-galactosidase A, and α-l-iduronidase) could be quantified in dried blood spots by using a single assay buffer.

METHODS

A 3-mm dried blood spot punch was incubated in a single assay buffer with 3 different substrates and internal standards. The sample was processed by a simple liquid-liquid extraction by using ethyl acetate. The extract was dried down and resuspended in solvent for injection into the tandem mass spectrometer. Products and internal standards were monitored by multiple reaction monitoring.

RESULTS

Assay for the 3 lysosomal enzymes was successfully achieved with acceptable statistics. The assay can be performed by using a minimal quantity of disposable supplies and equipment. The entire procedure fits into a 48-h cycle including data analysis. Data from 5990 anonymous newborn dried blood spots showed an approximate bell-shaped distribution of enzymatic activities (mean values of 19.0, 11.5, and 3.5 μmol · h(-1) · (L blood)(-1) for α-glucosidase, α-galactosidase A, and α-l-iduronidase, respectively. Blank values obtained in the absence of blood were 0.13, 0.24, and 0.45 μmol · h(-1) · (L blood)(-1), respectively). By assaying 3 enzymes at once, problematic samples are spotted for reanalysis if enzyme activity values are low for all enzymes (for example, if insufficient blood is present in the assay).

CONCLUSIONS

This method demonstrates that a triplex assay in a single buffer and with minimal supplies and labor can be adapted to a high-throughput newborn screening laboratory for the analysis of Pompe, Fabry, and mucopolysaccharidosis-I (Hurler) diseases.

Reference values for lysosomal enzymes activities using dried blood spots samples - a Brazilian experience

Background

Lysosomal storage diseases (LSD) are inherited disorders caused by deficiency of lysosomal enzymes in which early diagnosis is essential to provide timely treatment. This study reports interval values for the activity of lysosomal enzymes that are deficient in Mucopolysaccharidosis type I, Fabry, Gaucher and Pompe disease, using dried blood spots on filter paper (DBS) samples in a Brazilian population.

Results

Reference activity values were obtained from healthy volunteers samples for alpha-galactosidase A (4.57 ± 1.37 umol/L/h), beta-glucosidase (3.06 ± 0.99 umol/L/h), alpha-glucosidase (ratio: 13.19 ± 4.26; % inhibition: 70.66 ± 7.60), alpha-iduronidase (3.45 ± 1.21 umol/L/h) and beta-galactosidase (14.09 ± 4.36 umol/L/h).

Conclusion

Reference values of five lysosomal enzymes were determined for a Brazilian population sample. However, as our results differ from other laboratories, it highlights the importance of establishing specific reference values for each center.

Fabry disease: a review of current management strategies

Fabry disease is an X-linked inherited condition due to the absence or reduction of alpha-galactosidase activity in lysosomes, that results in accumulation of globotriaosylceramide (Gb3) and related neutral glycosphingolipids. Manifestations of Fabry disease include serious and progressive impairment of renal and cardiac function. In addition, patients experience pain, gastrointestinal disturbance, transient ischaemic attacks and strokes. Additional effects on the skin, eyes, ears, lungs and bones are often seen. The first symptoms of classic Fabry disease usually appear in childhood. Despite being X-linked, females can suffer the same severity of symptoms as males, and life expectancy is reduced in both females and males. Enzyme replacement therapy (ERT) can stabilize the progression of the disease. The rarity of the classic form of Fabry disease, however, means that there is a need to improve the knowledge and understanding that the majority of physicians have concerning Fabry disease, in order to avoid misdiagnosis and/or delayed diagnosis. This review aims to raise awareness of the signs and symptoms of Fabry disease; to provide a general diagnostic algorithm and to give an overview of the effects of ERT and concomitant treatments. We highlight a need to develop comprehensive international guidelines to optimize ERT and adjunctive therapy in patients with Fabry disease, including females and children.

Newborn screening for neuropathic lysosomal storage disorders

Interest in newborn screening (NBS) for lysosomal storage disorders (LSDs) has increased significantly due to newly developed enzyme replacement therapy (ERT), the need for early diagnosis, and advances in technical developments. Since the central nervous system cannot be treated by ERT, neuronopathic LSDs are generally not the primary target of NBS. An exception is Krabbe disease, in which hematopoietic stem cell transplantation before the onset of symptoms has benefits. However, NBS for LSD relies on measuring enzyme activities, so the most severely affected individuals (usually patients with neuronopathic subtypes) will be detected together with patients with less severe disease. In the near future, NBS is likely to be developed for diseases such as Gaucher, Niemann-Pick A/B, and certain mucopolysaccharidoses. The ability to predict phenotypes (neuronopathic or not) by enzyme activity and genotyping will therefore be critical for adequate patient management. This article reviews the status of LSD screening and issues concerning detection of neuronopathic LSDs by screening.

Newborn Screening of Lysosomal Storage Disorders

Background: Newborn screening is a state-based public health program established as a means for the early detection and treatment of certain medical conditions to minimize developmental disability and mortality. The program was initiated more than 40 years ago to detect and prevent phenylketonuria. Recent technological advances have expanded the scope of newborn screening to include more than 30 inborn errors of metabolism. Consideration is now being given to inclusion of screening for lysosomal storage disorders (LSDs).

Content: Some lysosomal storage disorders (LSDs) express early in infancy or childhood and are treatable. Initiation of treatment in presymptomatic patients or in syptomatic patients before important symptoms are present may improve the long-term outcome. Therefore, early diagnosis is critical. Based on the availability of therapy and development of a screening method, 6 of the more than 40 known LSDs are candidates for newborn screening in the US: Gaucher disease, Pompe disease, Fabry disease, Niemann-Pick disease, mucopolysaccharidosis I, and Krabbe disease. This report reviews the history of newborn screening, the technology that has allowed for expanded screening during the last decade, LSDs and their treatment, and the evolving methods that might allow additional expansion of newborn screening to include certain LSDs.

Summary: Recent and evolving technological advances may be implemented for newborn screening for LSDs. This screening will identify presymptomatic newborns, allowing for early treatment and prevention or limitation of morbidity otherwise associated with these inherited rare diseases.

Feasibility of using cryopreserved lymphoblastoid cells to diagnose some lysosomal storage diseases

OBJECTIVE

The Epstein-Barr virus (EBV) is utilized as a tool in the study of cellular biology because of its capacity to transform B-lymphocytes. For this reason, EBV is used in conservation of human B-lymphocytes for long periods for subsequent evaluation of lysosomal hydrolase activity. Lymphoblastoid cell lines have several advantages for use over other cell types, such as prompt availability and possibility to develop, characterize and standardize cell banks, to test effects of promising pharmaceutical reagents. The study below presents biochemical data that demonstrate validity of lymphoblastoid cell lines for diagnosis of GM1-gangliosidosis, Gaucher, Fabry and Pompe diseases and mucopolysaccharidosis type I.

MATERIALS AND METHODS

Cultures were prepared from peripheral blood, collected from 25 normal subjects and 13 affected individuals. Enzyme activities and immunohistochemistry (IHC) were measured. Activities of enzymes beta-galactosidase, beta-glucosidase, alpha-iduronidase, alpha-galactosidase and alpha-glucosidase were measured before and after cryopreservation for 180 days. Enzymatic activity was measured when transformation was confirmed by IHC.

RESULTS

We observed some significant alterations in enzymatic activity of non-cultured cells when compared to others that had been cultured for 12 days and kept frozen for 180 days.

CONCLUSIONS

However, these alterations did not invalidate use of the technology of transformation of lymphoblastoid cell lines with EBV, to diagnose the diseases mentioned above, in view of the fact that the cultured cells, before and after freezing, demonstrated similar enzymatic activities.

Multiplex Enzyme Assay for Galactosemia Using Ultraperformance Liquid Chromatography–Tandem Mass Spectrometry

Background: Galactosemia is one of the most important inherited disorders detected by newborn screening tests. Abnormal results in screening tests should be confirmed by enzyme activity assays, but existing methods are time and labor intensive. We developed a novel multiplex enzyme assay for galactosemia using ultraperformance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS).

Methods: [13C6]-galactose, [13C2]-galactose-1-phosphate, and UDP-glucose were used as substrates for 3 galactose-metabolizing enzymes. The end products from the combined reaction mixtures, [13C6]-galactose-1-phosphate, UDP-[13C2]-galactose, and UDP-galactose, were simultaneously measured using UPLC-MS/MS. Linearity, imprecision, ion suppression, and the effects of substrate were evaluated to determine assay performance. Enzyme activities from 35 healthy individuals, 8 patients with enzyme deficiency, and 18 mutant cells were analyzed.

Results: Substrates, products, and internal standards from the mixture of 3 enzyme reactions were clearly separated by using UPLC-MS/MS, with an injection cycle time of 10 min. Ion suppression was 0.1%–2.5%, the interassay imprecision of UPLC-MS/MS was 3.3%–10.6% CV, and the linearity of each system was good (R2 = 0.994–0.999). Patient samples and mutated cells showed consistently low enzyme activities compared with those of normal individuals and wild-type cells.

Conclusions: This method allows for a high-throughput and reproducible multiplex enzyme assay for galactosemia in erythrocytes.

The application of multiplexed, multi-dimensional ultra-high-performance liquid chromatography/tandem mass spectrometry to the high-throughput screening of lysosomal storage disorders in newborn dried bloodspots

Lysozomal storage disorders are just beginning to be routinely screened using enzyme activity assays involving dried blood spots and tandem mass spectrometry (MS/MS). This paper discusses some of the analytical challenges associated with published assays including complex sample preparation and potential interference from excess residual substrate. Solutions to these challenges are presented in the form of on-line two-dimensional chromatography to eliminate off-line liquid-liquid extraction (LLE) and solid-phase extraction (SPE), the use of ultra-high-performance liquid chromatography (UHPLC) to separate excess substrate from all other analytes and multiplexed sample introduction for higher throughput required of a population screening assay. High sensitivity, specificity and throughput were demonstrated using this novel method.

Mucopolysaccharidosis VI

Mucopolysaccharidosis VI (MPS VI) is a lysosomal storage disease with progressive multisystem involvement, associated with a deficiency of arylsulfatase B leading to the accumulation of dermatan sulfate. Birth prevalence is between 1 in 43,261 and 1 in 1,505,160 live births. The disorder shows a wide spectrum of symptoms from slowly to rapidly progressing forms. The characteristic skeletal dysplasia includes short stature, dysostosis multiplex and degenerative joint disease. Rapidly progressing forms may have onset from birth, elevated urinary glycosaminoglycans (generally >100 microg/mg creatinine), severe dysostosis multiplex, short stature, and death before the 2nd or 3rd decades. A more slowly progressing form has been described as having later onset, mildly elevated glycosaminoglycans (generally <100 microg/mg creatinine), mild dysostosis multiplex, with death in the 4th or 5th decades. Other clinical findings may include cardiac valve disease, reduced pulmonary function, hepatosplenomegaly, sinusitis, otitis media, hearing loss, sleep apnea, corneal clouding, carpal tunnel disease, and inguinal or umbilical hernia. Although intellectual deficit is generally absent in MPS VI, central nervous system findings may include cervical cord compression caused by cervical spinal instability, meningeal thickening and/or bony stenosis, communicating hydrocephalus, optic nerve atrophy and blindness. The disorder is transmitted in an autosomal recessive manner and is caused by mutations in the ARSB gene, located in chromosome 5 (5q13-5q14). Over 130 ARSB mutations have been reported, causing absent or reduced arylsulfatase B (N-acetylgalactosamine 4-sulfatase) activity and interrupted dermatan sulfate and chondroitin sulfate degradation. Diagnosis generally requires evidence of clinical phenotype, arylsulfatase B enzyme activity <10% of the lower limit of normal in cultured fibroblasts or isolated leukocytes, and demonstration of a normal activity of a different sulfatase enzyme (to exclude multiple sulfatase deficiency). The finding of elevated urinary dermatan sulfate with the absence of heparan sulfate is supportive. In addition to multiple sulfatase deficiency, the differential diagnosis should also include other forms of MPS (MPS I, II IVA, VII), sialidosis and mucolipidosis. Before enzyme replacement therapy (ERT) with galsulfase (Naglazyme), clinical management was limited to supportive care and hematopoietic stem cell transplantation. Galsulfase is now widely available and is a specific therapy providing improved endurance with an acceptable safety profile. Prognosis is variable depending on the age of onset, rate of disease progression, age at initiation of ERT and on the quality of the medical care provided.

Multiplex enzyme assays and inhibitor screening by mass spectrometry

Current methods for high-throughput screening (HTS) use a serial process to evaluate compounds as inhibitors toward a single therapeutic target, but as the demand to reduce screening time and cost continues to grow, one solution is the development of multiplex technology. In this communication, the multiplex assay capability of a mass spectrometry (MS)-based readout system is verified using a kinase and esterase reaction simultaneously. Furthermore, the MS-based readout is shown to be compatible with a typical HTS workflow by identifying and validating several new inhibitors for each enzyme from a small library of compounds. These data confirm that it is possible to monitor inhibition of multiple therapeutic targets with one pass through the compound repository, thus demonstrating the potential for MS-based methods to become a method of choice for HTS of isolated enzymes.

Biochemical profiling to predict disease severity in metachromatic leukodystrophy

Metachromatic leukodystrophy is a neurodegenerative disease that is characterized by a deficiency of arylsulfatase A, resulting in the accumulation of sulfatide and other lipids in the lysosomal network of affected cells. Accumulation of sulfatide in the nervous system leads to severe impairment of neurological function with a fatal outcome. Prognosis is often poor unless treatment is carried out before the onset of clinical symptoms. Pre-symptomatic detection of affected individuals may be possible with the introduction of newborn screening programs. The ability to accurately predict clinical phenotype and rate of disease progression in asymptomatic individuals will be essential to assist selection of the most appropriate treatment strategy. Biochemical profiling, incorporating the determination of residual enzyme protein/activity using immune-based assays, and metabolite profiling using electrospray ionization-tandem mass spectrometry, was performed on urine and cultured skin fibroblasts from a cohort of patients representing the clinical spectrum of metachromatic leukodystrophy and on unaffected controls. Residual enzyme protein/activity in fibroblasts was able to differentiate unaffected controls, arylsulfatase A pseudo-deficient individuals, pseudo-deficient compound heterozygotes and affected patients. Metachromatic leukodystrophy phenotypes were distinguished by quantification of sulfatide and other secondarily altered lipids in urine and skin fibroblasts; this enabled further differentiation of the late-infantile form of the disorder from the juvenile and adult forms. Prediction of the rate of disease progression for metachromatic leukodystrophy requires a combination of information on genotype, residual arylsulfatase A protein and activity and the measurement of sulfatide and other lipids in urine and cultured skin fibroblasts.

Multiplex lysosomal enzyme activity assay on dried blood spots using tandem mass spectrometry

Deficiencies in any of the 50 degradative enzymes found in lysosomes results in the accumulation of undegraded material and subsequently cellular dysfunction. Early identification of deficiencies before irreversible organ and tissue damages occur leads to better clinical outcomes. In the method which follows, lysosomal alpha-glucosidase, alpha-galactosidase, beta-glucocerebrosidase, acid sphingomyelinase, and galactocerebrosidase are extracted from dried blood spots and incubated individually with an enzyme-specific cocktail containing the corresponding substrate and internal standard. Each enzyme cocktail is prepared using commercially available mixture of substrate and internal standard at the predetermined optimized molar ratio. After incubation, the enzymatic reactions are quenched using an ethyl acetate/methanol solution and all five enzyme solutions are combined. The mixtures of the reaction products are prepared using liquid-liquid and solid-phase extractions and quantified simultaneously using selected ion monitoring on LC-MS-MS system.

Pompe disease in infants: improving the prognosis by newborn screening and early treatment

OBJECTIVE

Pompe disease causes progressive, debilitating, and often life-threatening musculoskeletal, respiratory, and cardiac symptoms. Favorable outcomes with early intravenous enzyme-replacement therapy and alglucosidase alfa have been reported, but early clinical diagnosis before the development of severe symptoms has rarely been possible in infants.

METHODS

We recently conducted a newborn screening pilot program in Taiwan to improve the early detection of Pompe disease. Six of 206088 newborns screened tested positive and were treated for Pompe disease. Five had the rapidly progressive form of Pompe disease, characterized by cardiac and motor involvement, and were treated soon after diagnosis. The sixth patient was started on treatment at 14 months of age because of progressive muscle weakness. Outcomes were compared with treated patients whose disease was diagnosed clinically and with untreated historical control subjects.

RESULTS

At the time of this report, patients had been treated for 14 to 32 months. The 5 infants who had early cardiac involvement demonstrated normalization of cardiac size and muscle pathology with normal physical growth and age-appropriate gains in motor development. The infant without cardiac involvement also achieved normal motor development with treatment. Survival in patients who had newborn screening was significantly improved compared with those in the untreated reference cohort (P = .001). Survival in the treated clinical comparators was reduced but not statistically different from that in the newborn screening group (P = .48).

CONCLUSIONS

Results from this study indicate that early treatment can benefit infants with Pompe disease and highlight the advantages of early diagnosis, which can be achieved by newborn screening.

High incidence of the cardiac variant of Fabry disease revealed by newborn screening in the Taiwan Chinese population

BACKGROUND

Fabry disease is a treatable lysosomal storage disorder, which is often misdiagnosed or belatedly diagnosed.

METHODS AND RESULTS

To determine the disease incidence in the Taiwan Chinese population, a Fabry disease newborn screening study was initiated. A total of 110 027 newborns were screened by assaying the alpha-galactosidase A (alpha-Gal A) activity using dry blood spots. Low plasma alpha-Gal A activity and presence of a Fabry mutation was demonstrated in 45 neonates (3 females). Eight different mutations were identified, including 3 known missense mutations (R112H, A143T, and R356W), 4 novel missense mutations (G104V, M296L, G360C, and K391T), and one known intronic mutation (IVS4+919G-->A). The IVS4+919G-->A mutation was most common (82% of patients). A total of 20 maternal grandparents of infants harboring this intronic mutation were evaluated by echocardiography, mutation analysis and alpha-Gal A activity assay. The intronic mutation was found in 9 grandfathers and 11 grandmothers. Of these grandparents, 3 grandfathers (33%) but none of the grandmothers had hypertrophic cardiomyopathy. Additionally, 16 males who had been diagnosed with idiopathic hypertrophic cardiomyopathy were screened by mutation analysis and alpha-Gal A activity; 4 (25%) showed deficient plasma alpha-Gal A activity in combination with the intronic mutation.

CONCLUSIONS

We found an unexpected high prevalence of the cardiac variant Fabry mutation IVS4+919G-->A among both newborns (approximately 1 in 1600 males) and patients with idiopathic hypertrophic cardiomyopathy in the Taiwan Chinese population. The early identification of undiagnosed patients allows timely therapeutic intervention providing a better clinical outcome.

National academy of clinical biochemistry laboratory medicine practice guidelines: follow-up testing for metabolic disease identified by expanded newborn screening using tandem mass spectrometry; executive summary

BACKGROUND

Almost all newborns in the US are screened at birth for multiple inborn errors of metabolism using tandem mass spectrometry. Screening tests are designed to be sufficiently sensitive so that cases are not missed. The NACB recognized a need for standard guidelines for laboratory confirmation of a positive newborn screen such that all babies would benefit from equal and optimal follow-up by confirmatory testing.

METHODS

A committee was formed to review available data pertaining to confirmatory testing. The committee evaluated previously published guidelines, published methodological and clinical studies, clinical case reports, and expert opinion to support optimal confirmatory testing. Grading was based on guidelines adopted from criteria derived from the US Preventive Services Task Force and on the strength of recommendations and the quality of the evidence. Three primary methods of analyte measurement were evaluated for confirmatory testing including measurement of amino acids, organic acids, and carnitine esters. The committee graded the evidence for diagnostic utility of each test for the screened conditions.

RESULTS

Ample data and experience were available to make strong recommendations for the practice of analyzing amino acids, organic acids, and acylcarnitines. Likewise, strong recommendations were made for the follow-up test menu for many disorders, particularly those with highest prevalence. Fewer data exist to determine the impact of newborn screening on patient outcomes in all but a few disorders. The guidelines also provide an assessment of developing technology that will fuel a refinement of current practice and ultimate expansion of the diseases detectable by tandem mass spectrometry.

CONCLUSIONS

Guidelines are provided for optimal follow-up testing for positive newborn screens using tandem mass spectrometry. The committee regards these tests as reliable and currently optimal for follow-up testing. .

Enzyme analysis for Pompe disease in leukocytes; superior results with natural substrate compared with artificial substrates

Enzyme analysis for Pompe disease in leukocytes has been greatly improved by the introduction of acarbose, a powerful inhibitor of interfering alpha-glucosidases, which are present in granulocytes but not in lymphocytes. Here we show that the application of acarbose in the enzymatic assay employing the artificial substrate 4-methylumbelliferyl-alpha-D: -glucoside (MU-alphaGlc) is insufficient to clearly distinguish patients from healthy individuals in all cases. Also, the ratios of the activities without/with acarbose only marginally discriminated Pompe patients and healthy individuals. By contrast, when the natural substrate glycogen is used, the activity in leukocytes from patients (n = 82) with Pompe disease is at most 17% of the lowest control value. The use of artificial substrate in an assay with isolated lymphocytes instead of total leukocytes is a poor alternative as blood samples older than one day invariably yield lymphocyte preparations that are contaminated with granulocytes. To diagnose Pompe disease in leukocytes we recommend the use of glycogen as substrate in the presence of acarbose. This assay unequivocally excludes Pompe disease. To also exclude pseudo-deficiency of acid alpha-glucosidase caused by the sequence change c.271G>A (p.D91N or GAA2; homozygosity in approximately 1:1000 caucasians), a second assay employing MU-alphaGlc substrate plus acarbose or DNA analysis is required.

Development and Evaluation of Quality Control Dried Blood Spot Materials in Newborn Screening for Lysosomal Storage Disorders

Background: Lysosomal storage disorders (LSDs) comprise more than 40 genetic diseases that result in the accumulation of products that would normally be degraded by lysosomal enzymes. A tandem mass spectrometry (MS/MS)-based method is available for newborn screening for 5 LSDs, and many laboratories are initiating pilot studies to evaluate the incorporation of this method into their screening panels. We developed and evaluated dried blood spot (DBS) QC materials for LSDs and used the MS/MS method to investigate their suitability for LSD QC monitoring.

Methods: We incubated 3.2-mm punches from DBS controls for 20–24 h with assay cocktails containing substrate and internal standard. Using MS/MS, we quantified the resulting product and internal standard. Samples were run in triplicate for 3 consecutive days, and results were reported as product-to-internal standard ratios and enzyme activity units (μmol/L/h).

Results: Enzyme activity interday imprecision (CV) for the high, medium, and low series were 3.4%–14.3% for galactocerebroside α-galactosidase, 6.8%–24.6% for acid α-galactosidase A, 7.36%–22.1% for acid sphingomyelinase, 6.2%–26.2% for acid α-glucocerebrosidase, and 7.0%–24.8% for lysosomal acid α-glucosidase (n = 9). In addition, DBS stored at −20° and 4 °C showed minimal enzyme activity loss over a 187-d period. DBS stored at 37° and 45 °C had lower activity values over the 187-day evaluation time.

Conclusions: Suitable QC materials for newborn screening of LSDs were developed for laboratories performing DBS LSD screening. Good material linearity was observed, with goodness-of-fit values of 0.953 and higher. The QC materials may be used by screening laboratories that perform LSD analysis by MS and/or more conventional fluorescence-based screening methods.

Tandem Mass Spectrometry for the Direct Assay of Lysosomal Enzymes in Dried Blood Spots: Application to Screening Newborns for Mucopolysaccharidosis I

Background: Treatments now available for mucopolysaccharidosis I require early detection for optimum therapy. Therefore, we have developed an assay appropriate for newborn screening of the activity of the relevant enzyme, α-L-iduronidase.

Methods: We synthesized a new α-L-iduronidase substrate that can be used to assay the enzyme by use of tandem mass spectrometry together with an internal standard or by fluorometry. The assay uses a dried blood spot on a newborn screening card as the enzyme source. The assay protocol uses a simple liquid-liquid extraction step before mass spectrometry. We optimized enzyme reaction conditions and procedures for the assay, including the concentration of substrate, the reaction pH, the incubation time, and mass spectrometer operation. We also assessed inter- and intraassay imprecision.

Results: When the assay was tested on dried blood spots, the α-L-iduronidase activity measured for 5 patients with mucopolysaccharidosis I was well below the interval found for 10 randomly chosen newborns. Inter- and intraassay imprecision were &lt;10%. The synthesis of the α-L-iduronidase substrate is practical for use on a scale needed to support newborn screening demands.

Conclusions: This newly developed tandem mass spectrometry assay has the potential to be adopted for newborn screening of mucopolysaccharidosis I. This assay has advantages over a previously reported assay also developed in this laboratory and has the potential to be performed in a multiplex fashion to measure several lysosomal enzymes relevant to treatable lysosomal storage diseases.

Pompe's disease

Pompe's disease, glycogen-storage disease type II, and acid maltase deficiency are alternative names for the same metabolic disorder. It is a pan-ethnic autosomal recessive trait characterised by acid alpha-glucosidase deficiency leading to lysosomal glycogen storage. Pompe's disease is also regarded as a muscular disorder, but the generalised storage of glycogen causes more than mobility and respiratory problems. The clinical spectrum is continuous and broad. First symptoms can present in infants, children, and adults. Cardiac hypertrophy is a key feature of classic infantile Pompe's disease. For a long time, there was no means to stop disease progression, but the approval of enzyme replacement therapy has substantially changed the prospects for patients. With this new development, the disease is now among the small but increasing number of lysosomal storage disorders, for which treatment has become a reality. This review is meant to raise general awareness, to present and discuss the latest insights in disease pathophysiology, and to draw attention to new developments about diagnosis and care. We also discuss the developments that led to the approval of enzyme replacement therapy with recombinant human alpha-glucosidase from Chinese hamster ovary cells (alglucosidase alfa) by the US Food and Drug Administration and European Medicines Agency in 2006, and review clinical practice.

Newborn Screening for Pompe Disease by Measuring Acid α-Glucosidase Activity Using Tandem Mass Spectrometry

background: Pompe disease, caused by the deficiency of acid α-glucosidase (GAA), is a lysosomal storage disorder that manifests itself in its most severe form within the first months of life. Early detection by newborn screening is warranted, since prompt initiation of enzyme replacement therapy may improve morbidity and mortality. We evaluated a tandem mass spectrometry (MS/MS) method to measure GAA activity for newborn screening for Pompe disease.

methods: We incubated 3.2-mm punches from dried blood spots (DBS) for 22 h with the substrate [7-benzoylamino-heptyl)-{2-[4-(3,4,5-trihydroxy-6-hydroxymethyl-tetrahydro-pyran-2-yloxy)-phenylcarbamoyl]- ethyl}-carbamic acid tert-butyl ester] and internal standard [7-d5-benzoylamino-heptyl)-[2-(4-hydroxy-phenylcarbamoyl)-ethyl]-carbamic acid tertbutyl ester]. We quantified the resulting product and internal standard using MS/MS. We assessed inter- and intrarun imprecision, carryover, stability, and correlation between enzyme activities and hematocrit and punch location and generated a Pompe disease–specific cutoff value using routine newborn screening samples.

results: GAA activities in DBS from 29 known Pompe patients were &lt;2 μmol/h/L. GAA activities in routine newborn screening samples were [mean (SD)] 14.7 (7.2) μmol/h/L (n = 10 279, median 13.3, 95% CI 14.46–14.74 μmol/h/L) and in normal adult samples 9.3 (3.3) μmol/h/L (n = 229, median 9, 95% CI 8.88–9.72 μmol/h/L). GAA activity was stable for 28 days between 37 °C and −80 °C. Carryover could not be observed, whereas intrarun and interrun imprecision were &lt;10%. The limit of detection was 0.26 μmol/h/L and limit of quantification 0.35 μmol/h/L.

conclusions: The measurement of GAA activities in dry blood spots using MS/MS is suitable for high-throughput analysis and newborn screening for Pompe disease.