Lower Exposure to Busulfan Allows for Stable Engraftment of Donor Hematopoietic Stem Cells in Children with Mucopolysaccharidosis Type I: A Case Report of Four Patients.

Busulfan is an alkylating agent routinely used in conditioning regimens prior to allogeneic hematopoietic cell transplantation (HCT) for various nonmalignant disorders, including inborn errors of metabolism. The combination of model-based dosing and therapeutic drug monitoring (TDM) of busulfan pharmacokinetics (PK) to a lower exposure target has the potential to reduce the regimen-related toxicity while opening marrow niches sufficient for engraftment in diseases such as mucopolysaccharidosis type I (MPS I). We present four cases of the severe form of MPS I or Hurler syndrome, demonstrating successful and stable CD14/15 donor chimerism following the prospective application of model-based dosing and TDM aimed to achieve lower busulfan exposure. All patients received a busulfan-based conditioning regimen with a median cumulative area-under-the-curve (cAUC) target of 63.7 mg h/L (range, 62.4 to 65.0) in protocol-specific combination of chemotherapeutic regimen. The donor source was unrelated umbilical cord blood for three patients and matched sibling donor bone marrow for one patient. The observed median busulfan cAUC was 66.1 mg h/L (range, 65.2 to 70.6) and was within 10% of the intended target. Stable, full donor myeloid chimerism was achieved for three patients, while one patient achieved a stable mixed chimerism (76% donor CD14/15 at 53 months) without a recurring need for enzyme replacement. The normalization of α-L-iduronidase enzyme levels followed the attainment of successful donor myeloid chimerism in all patients. Regimen-related toxicity remained low with no evidence of acute graft-versus-host disease (GVHD) grades II to IV and chronic GVHD.

The combined use of enzyme activity and metabolite assays as a strategy for newborn screening of mucopolysaccharidosis type I.

Objectives Mucopolysaccharidosis type I (MPS I) was added to our expanded screening panel in 2015. Since then, 127,869 newborns were screened by measuring α-L-iduronidase (IDUA) enzyme activity with liquid chromatography tandem mass spectrometry (LC-MS/MS). High false positives due to frequent pseudodeficiency alleles prompted us to develop a second-tier test to quantify glycosaminoglycan (GAG) levels in dried blood spot (DBS). Methods Heparan-sulfate (HS) and dermatan-sulfate (DS) were measured with LC-MS/MS after methanolysis. DBSs were incubated with methanolic-HCl 3 N at 65 °C for 45 min. Chromatographic separation used an amide column with a gradient of acetonitrile and water with 10 mM ammonium acetate in a 9-min run. The method was validated for specificity, linearity, lower limit of quantification (LOQ), accuracy and precision. Results Intra- and inter-day coefficients of variation were <15% for both metabolites. Reference values in 40 healthy newborns were: HS mean 1.0 mg/L, 0-3.2; DS mean 1.5 mg/L, 0.5-2.7). The two confirmed newborn MPS I patients had elevated HS (4.9-10.4 mg/L, n.v. <3.2) and DS (7.4-8.8 mg/L, n.v. <2.7). Since its introduction in February 2019, the second-tier test reduced the recall rate from 0.046% to 0.006%. Among 127,869 specimens screened, the incidence was 1:63,935 live births. Both patients started enzyme replacement therapy (ERT) within 15 days of birth and one of them received allogenic hematopoietic stem cell transplantation (HSCT) at ht age of 6 months. Conclusions GAGs in DBS increased the specificity of newborn screening for MPS I by reducing false-positives due to heterozygosity or pseudodeficiency. Early diagnosis and therapeutical approach has improved the outcome of our patients with MPS I.

Estimated birth prevalence of mucopolysaccharidoses in Brazil.

Several studies have been published on the frequency of the mucopolysaccharidoses (MPS) in different countries. The objective of the present study was to estimate the birth prevalence (BP) of MPS in Brazil. MPS diagnosis registered at MPS-Brazil Network and in Instituto Vidas Raras were reviewed. BP was estimated by (a) the number of registered patients born between 1994 and 2015 was divided by the number of live births (LBs), and (b) a sample of 1,000 healthy individuals was tested for the most frequent variant in IDUA gene in MPS I (p.Trp402Ter) to estimate the frequency of heterozygosity and homozygosity. (a) The BP based on total number of LBs was (cases per 100,000 LBs): MPS overall: 1.25; MPS I: 0.24; MPS II: 0.37; MPS III: 0.21; MPS IV: 0.14; MPS VI: 0.28; MPS VII: 0.02. (b) The overall frequency of p.Trp402Ter was 0.002. Considering the frequency of heterozygotes for the p.Trp402Ter IDUA variant in the RS state, the frequency of this variant among MPS I patients and the relative frequency of the different MPSs, we estimated the birth prevalence of MPS in total and of each MPS type, as follows: MPS overall: 4.62; MPS I: 0.95; MPS II: 1.32; MPS III: 0.56; MPS IV: 0.57; MPS VI: 1.02; MPS VII: 0.05. This study provided original data about BP and relative frequency of the MPS types, in Brazil, based on the frequency of the commonest IDUA pathogenic variant and in the records of two large patient databases.

A novel compound mutation in alpha-L-iduronidase gene causes mucopolysaccharidosis type I.

Mucopolysaccharidosis type I (MPSI) is a rare autosomal recessive disorder caused by mutations in alpha-L-iduronidase (IDUA) gene. IDUA contributes to the degradation of the glycosaminoglycans, including heparan sulphate and dermatan sulphate. Deficient activity of IDUA generates accumulation of glycosaminoglycans in lysosomes leading to MPS I. Here, we identified two boys with MPS I caused by a compound heterozygote of a reported c.265C > T (p.R89W) missense mutation in exon 2 and a novel c.1633G > T (p.E545*, 109) nonsense mutation in exon 11 of IDUA gene in a Chinese family. R89 is close to the active site and its replacement will affect the structure and function of IDUA. Besides, termination from E545 deletes one of the prominent domains and alters the spatial structure of IDUA. In conclusion, our study demonstrates a previously unrecognized mutation in IDUA gene and this report adds to the mutational spectrum observed.

In search of causal pathways in diabetes: a study using proteomics and genotyping data from a cross-sectional study.

AIMS/HYPOTHESIS: The pathogenesis of type 2 diabetes is not fully understood. We investigated whether circulating levels of preselected proteins were associated with the outcome 'diabetes' and whether these associations were causal. METHODS: In 2467 individuals of the population-based, cross-sectional EpiHealth study (45-75 years, 50% women), 249 plasma proteins were analysed by the proximity extension assay technique. DNA was genotyped using the Illumina HumanCoreExome-12 v1.0 BeadChip. Diabetes was defined as taking glucose-lowering treatment or having a fasting plasma glucose of ≥7.0 mmol/l. The associations between proteins and diabetes were assessed using logistic regression. To investigate causal relationships between proteins and diabetes, a bidirectional two-sample Mendelian randomisation was performed based on large, genome-wide association studies belonging to the DIAGRAM and MAGIC consortia, and a genome-wide association study in the EpiHealth study. RESULTS: Twenty-six proteins were positively associated with diabetes, including cathepsin D, retinal dehydrogenase 1, α-L-iduronidase, hydroxyacid oxidase 1 and galectin-4 (top five findings). Three proteins, lipoprotein lipase, IGF-binding protein 2 and paraoxonase 3 (PON-3), were inversely associated with diabetes. Fourteen of the proteins are novel discoveries. The Mendelian randomisation study did not disclose any significant causal effects between the proteins and diabetes in either direction that were consistent with the relationships found between the protein levels and diabetes. CONCLUSIONS/INTERPRETATION: The 29 proteins associated with diabetes are involved in several physiological pathways, but given the power of the study no causal link was identified for those proteins tested in Mendelian randomisation. Therefore, the identified proteins are likely to be biomarkers for type 2 diabetes, rather than representing causal pathways.

The North Carolina Experience with Mucopolysaccharidosis Type I Newborn Screening.

OBJECTIVE: To evaluate the performance of a 2-tiered newborn screening method for mucopolysaccharidosis type I (MPS I) in North Carolina. STUDY DESIGN: The screening algorithm included a flow injection analysis-tandem mass spectrometry assay as a first-tier screening method to measure α-L-iduronidase (IDUA) enzyme activity and Sanger sequencing of the IDUA gene on dried blood spots as a second-tier assay. The screening algorithm was revised to incorporate the Collaborative Laboratory Integrated Reports, an analytical interpretive tool, to reduce the false-positive rate. A medical history, physical examination, IDUA activity, and urinary glycosaminoglycan (GAG) analysis were obtained on all screen-positive infants. RESULTS: A total of 62 734 specimens were screened with 54 screen-positive samples using a cut-off of 15% of daily mean IDUA activity. The implementation of Collaborative Laboratory Integrated Reports reduced the number of specimens that screened positive to 19 infants. Of the infants identified as screen-positive, 1 had elevated urinary GAGs and a homozygous pathogenic variant associated with the severe form of MPS I. All other screen-positive infants had normal urinary GAG analysis; 13 newborns had pseudodeficiency alleles, 3 newborns had variants of unknown significance, and 2 had heterozygous pathogenic variants. CONCLUSIONS: An infant with severe MPS I was identified and referred for a hematopoietic stem cell transplant. Newborn IDUA enzyme deficiency is common in North Carolina, but most are due to pseudodeficiency alleles in infants with normal urinary GAG analysis and no evidence of disease. The pilot study confirmed the need for second-tier testing to reduce the follow-up burden.

Fast, sensitive method for trisaccharide biomarker detection in mucopolysaccharidosis type 1.

Certain recessively inherited diseases result from an enzyme deficiency within lysosomes. In mucopolysaccharidoses (MPS), a defect in glycosaminoglycan (GAG) degradation leads to GAG accumulation followed by progressive organ and multiple system dysfunctions. Current methods of GAG analysis used to diagnose and monitor the diseases lack sensitivity and throughput. Here we report a LC-MS method with accurate metabolite mass analysis for identifying and quantifying biomarkers for MPS type I without the need for extensive sample preparation. The method revealed 225 LC-MS features that were >1000-fold enriched in urine, plasma and tissue extracts from untreated MPS I mice compared to MPS I mice treated with iduronidase to correct the disorder. Levels of several trisaccharides were elevated >10000-fold. To validate the clinical relevance of our method, we confirmed the presence of these biomarkers in urine, plasma and cerebrospinal fluid from MPS I patients and assessed changes in their levels after treatment.

Plasma Pharmacokinetics of Valanafusp Alpha, a Human Insulin Receptor Antibody-Iduronidase Fusion Protein, in Patients with Mucopolysaccharidosis Type I.

BACKGROUND: Mucopolysaccharidosis type I (MPSI) is caused by mutations in the gene encoding the α-L-iduronidase (IDUA) lysosomal enzyme and the majority of MPSI patients have severe central nervous system (CNS) involvement. Enzyme replacement therapy (ERT) with recombinant IDUA does not treat the CNS, due to the lack of transport of the enzyme across the blood-brain barrier (BBB). Human IDUA has been re-engineered as an IgG-IDUA fusion protein, valanafusp alpha, where the IgG domain is a monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb domain binds the endogenous insulin receptor on the human BBB to trigger receptor-mediated transport across the BBB, and acts as a molecular Trojan horse to ferry the fused IDUA into the brain of patients with MPSI. METHODS: The present investigation describes the initial dosing, plasma pharmacokinetics, and plasma glucose response to the intravenous infusion of doses of valanafusp alpha ranging from 0.3 to 3 mg/kg in five adults and from 1 to 6 mg/kg in 13 pediatric subjects with MPSI. RESULTS: Valanafusp alpha plasma clearance is increased four-fold in children, and shows a linear pharmacokinetic response over the dose range of 0.3-3 mg/kg with a stable plasma elimination half-life (t½). The plasma pharmacokinetic parameters for valanafusp alpha overlapped with the same parameters previously reported for recombinant human IDUA (laronidase). The majority of the tested subjects had been receiving laronidase ERT for years, and some showed high levels of anti-drug antibodies (ADAs). However, the presence of these ADAs did not generally alter the rate of plasma clearance of valanafusp alpha in MPSI. The infusion of 0.3-6 mg/kg doses of valanafusp alpha had no effect on plasma glucose for up to 24 h after the drug infusion. CONCLUSION: The plasma clearance of valanafusp alpha is increased four-fold in children with MPSI compared with adult subjects at a dose of 1-3 mg/kg. The plasma pharmacokinetic profile of valanafusp alpha, at a dose of 1-3 mg/kg, is comparable to that of laronidase in children with MPSI.

Clinical features of Mexican patients with Mucopolysaccharidosis type I.

Mucopolysaccharidosis type I (MPS-I) is an autosomal recessive lysosomal storage disorder caused by a deficiency or absence of α--iduronidase, which is involved in the catabolism of glycosaminoglycans (GAGs). This deficiency leads to the accumulation of GAGs in several organs. Given the wide spectrum of the disease, MPS-I has historically been classified into 3 clinical subtypes - severe (Hurler syndrome), intermediate (Hurler-Scheie syndrome), and mild (Scheie syndrome) - none of which is determined by residual enzyme activity. Eleven Mexican patients with MPS-I from northwestern México were evaluated. Diagnoses were confirmed through quantification of GAGs in urine and enzyme assay for α--iduronidase. Regardless of phenotype, all patients had various degrees of infiltrated facies, short stature, dysostosis multiplex, joint contractures, and corneal opacity typical of the disease. A better understanding of the spectrum of this disease can assist in diagnosis, treatment, and improvement in the quality of life for these patients.

Alpha-l-iduronidase and arylsulfatase B in dried blood spots on filter paper: Biochemical parameters and time stability.

BACKGROUND: The goal of this study was to assess the biochemical parameters of the enzymes α-l-iduronidase (IDUA) and arylsulfatase B (ASB), which are deficient in mucopolysaccharidosis (MPS) I and VI, respectively, in dried blood spot (DBS) samples impregnated on filter paper. METHODS AND RESULTS: The optimal pH, Km, and Vmax of IDUA and ASB in DBS are hereby presented. After these analyses, the reference values for the activities of these enzymes in DBS with cutoff of 3.65nmol/h/mL for IDUA and 6.80nmol/h/mL for ASB were established. The research also showed that the stability (21days) of the IDUA activity is lower than ASB, which maintained its enzymatic activity stable up until 60days of analysis, after impregnating the filter paper with blood. CONCLUSION: Currently, DBS ensures important advantages in handling storage and transportation of samples with respect to neonatal screening programs. This study contributes to characterizing and differentiating the biochemistry of deficient enzymes in MPSs I and VI of DBS samples.

Pilot study of newborn screening for six lysosomal storage diseases using Tandem Mass Spectrometry.

BACKGROUND: There is current expansion of newborn screening (NBS) programs to include lysosomal storage disorders because of the availability of treatments that produce an optimal clinical outcome when started early in life. OBJECTIVE: To evaluate the performance of a multiplex-tandem mass spectrometry (MS/MS) enzymatic activity assay of 6 lysosomal enzymes in a NBS laboratory for the identification of newborns at risk for developing Pompe, Mucopolysaccharidosis-I (MPS-I), Fabry, Gaucher, Niemann Pick-A/B, and Krabbe diseases. METHODS AND RESULTS: Enzyme activities (acid α-glucosidase (GAA), galactocerebrosidase (GALC), glucocerebrosidase (GBA), α-galactosidase A (GLA), α-iduronidase (IDUA) and sphingomyeline phosphodiesterase-1 (SMPD-1)) were measured on ~43,000 de-identified dried blood spot (DBS) punches, and screen positive samples were submitted for DNA sequencing to obtain genotype confirmation of disease risk. The 6-plex assay was efficiently performed in the Washington state NBS laboratory by a single laboratory technician at the bench using a single MS/MS instrument. The number of screen positive samples per 100,000 newborns were as follows: GAA (4.5), IDUA (13.6), GLA (18.2), SMPD1 (11.4), GBA (6.8), and GALC (25.0). DISCUSSION: A 6-plex MS/MS assay for 6 lysosomal enzymes can be successfully performed in a NBS laboratory. The analytical ranges (enzyme-dependent assay response for the quality control HIGH sample divided by that for all enzyme-independent processes) for the 6-enzymes with the MS/MS is 5- to 15-fold higher than comparable fluorimetric assays using 4-methylumbelliferyl substrates. The rate of screen positive detection is consistently lower for the MS/MS assay compared to the fluorimetric assay using a digital microfluidics platform.

Chitotriosidase and lysosomal enzymes as potential biomarkers of disease progression in amyotrophic lateral sclerosis: a survey clinic-based study.

The aim of this study was to determine if blood chitotriosidase (Chit) activity and lysosomal enzyme levels might represent markers of disease activity and progression in amyotrophic lateral sclerosis (ALS). It is a survey clinic-based study performed in a tertiary ALS centre. Blood samples were obtained from 76 patients with ALS in different stages of the disease and from 106 healthy individuals serving as controls. Chit activity and the levels of acid alpha-glucosidase, acid alpha-galattosidase A, beta-glucocerebrosidase, and alpha-l-iduronidase were detected using the dried blood spots (DBS) technique. The CHIT1 genotype for exon 10 duplication and for the p.G102S variant was also determined. Chit activity was significantly higher in ALS patients than in healthy individuals. This difference was independent of the genotypes at CHIT1 functional variants. Chit were significantly higher in 34 rapidly progressing patients as compared to 42 with slowly progressive disease. Acid alpha-glucosidase was higher than normal and significantly correlated with the severity of the disease. Glucocerebrosidase and alpha-l-iduronidase activity were significantly lower in patients than in the controls. Alpha-galactosidase A was higher than normal only in rapidly progressing patients. We have employed a very simple and affordable laboratory test to measure blood Chit and lysosomal enzymes activity which could be easily included in the screening of ALS patients recruited in clinical trials. Remarkably, high levels of chitinase and alpha-galactosidase A could help to distinguish patients with fast progression from those with slow progression of the disease and possibly to follow the effects of treatments on neuroinflammation and autophagy.

Liver-directed gene therapy corrects cardiovascular lesions in feline mucopolysaccharidosis type I.

Patients with mucopolysaccharidosis type I (MPS I), a genetic deficiency of the lysosomal enzyme α-l-iduronidase (IDUA), exhibit accumulation of glycosaminoglycans in tissues, with resulting diverse clinical manifestations including neurological, ocular, skeletal, and cardiac disease. MPS I is currently treated with hematopoietic stem cell transplantation or weekly enzyme infusions, but these therapies have significant drawbacks for patient safety and quality of life and do not effectively address some of the most critical clinical sequelae, such as life-threatening cardiac valve involvement. Using the naturally occurring feline model of MPS I, we tested liver-directed gene therapy as a means of achieving long-term systemic IDUA reconstitution. We treated four MPS I cats at 3-5 mo of age with an adeno-associated virus serotype 8 vector expressing feline IDUA from a liver-specific promoter. We observed sustained serum enzyme activity for 6 mo at ∼ 30% of normal levels in one animal, and in excess of normal levels in three animals. Remarkably, treated animals not only demonstrated reductions in glycosaminoglycan storage in most tissues, but most also exhibited complete resolution of aortic valve lesions, an effect that has not been previously observed in this animal model or in MPS I patients treated with current therapies. These data point to clinically meaningful benefits of the robust enzyme expression achieved with hepatic gene transfer that extend beyond the economic and quality of life advantages over lifelong enzyme infusions.

Intrathecal gene therapy corrects CNS pathology in a feline model of mucopolysaccharidosis I.

Enzyme replacement therapy has revolutionized the treatment of the somatic manifestations of lysosomal storage diseases (LSD), although it has been ineffective in treating central nervous system (CNS) manifestations of these disorders. The development of neurotrophic vectors based on novel serotypes of adeno-associated viruses (AAV) such as AAV9 provides a potential platform for stable and efficient delivery of enzymes to the CNS. We evaluated the safety and efficacy of intrathecal delivery of AAV9 expressing α-l-iduronidase (IDUA) in a previously described feline model of mucopolysaccharidosis I (MPS I). A neurological phenotype has not been defined in these animals, so our analysis focused on the biochemical and histological CNS abnormalities characteristic of MPS I. Five MPS I cats were dosed with AAV9 vector at 4-7 months of age and followed for 6 months. Treated animals demonstrated virtually complete correction of biochemical and histological manifestations of the disease throughout the CNS. There was a range of antibody responses against IDUA in this cohort which reduced detectable enzyme without substantially reducing efficacy; there was no evidence of toxicity. This first demonstration of the efficacy of intrathecal gene therapy in a large animal model of a LSD should pave the way for translation into the clinic.

A column-switching HPLC-MS/MS method for mucopolysaccharidosis type I analysis in a multiplex assay for the simultaneous newborn screening of six lysosomal storage disorders.

Lysosomal storage disorders comprise a group of rare genetic diseases in which a deficit of specific hydrolases leads to the storage of undegraded substrates in lysosomes. Impaired enzyme activities can be assessed by MS/MS quantification of the reaction products obtained after incubation with specific substrates. In this study, a column-switching HPLC-MS/MS method for multiplex screening in dried blood spot of the lysosomal enzymes activities was developed. Mucopolysaccharidosis type I, Fabry, Gaucher, Krabbe, Niemann-Pick A/B and Pompe diseases were simultaneously assayed. Dried blood spots were incubated with substrates and internal standards; thereafter, supernatants were collected with minor manipulations. Samples were injected, trapped into an online perfusion column and, by a six-port valve, switched online through the C18 analytical column to perform separation of metabolites followed by MS/MS analysis. A total of 1136 de-identified newborn screening samples were analyzed to determine references for enzymes activity values. As positive controls, we analyzed dried blood spots from three patients with Pompe, one with Fabry, one with Krabbe disease and two with MPS I, and in all cases the enzyme activities were below the cutoff values measured for newborns, except for an MPS I patient after successful hematopoietic stem cell transplantation.

Identification of mucopolysaccharidosis I heterozygotes based on biochemical characteristics of L-iduronidase from dried blood spots.

BACKGROUND: Mucopolysaccharidosis I (MPS I) is a genetic disorder caused by deficiency of L-iduronidase (IDUA) activity. Heterozygote screening is a highly requested service by risk families; however, determination of IDUA activity alone is not sufficient to discriminate between heterozygotes and normal individuals because a significant overlap occurs between them. The aim of this study was to characterize the enzyme eluted from heterozygote's dried blood samples and determine if there are differences with that of normal individuals. METHODS: We determined Km, Vmax and the thermal stability of the enzyme at 50 °C. RESULTS: Vmax from heterozygotes (7.28 ± 2.72 µmol/l blood/h) was significantly different than the obtained in controls (10.52 ± 2.05 µmol/l blood/h), while their Km were similar: 0.633 ± 0.339 mmol/l and 0.672 ± 0.246 mmol/l, respectively. After a 12 h pre-incubation period, IDUA activity in controls was significantly lower compared to heterozygotes. CONCLUSIONS: IDUA eluted from dried blood spots of heterozygotes differs from that of controls in terms of Vmax and thermal stability. These parameters can be used as an important tool for the detection of carriers for MPS I. This is the first report describing a differential behavior of these parameters for a lysosomal enzyme obtained from dried blood.

High-dose enzyme replacement therapy in murine Hurler syndrome.

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disease that is systemic, including progressive neurodegeneration, mental retardation and death before the age of 10 years. MPS I results from deficiency of α-L-iduronidase (IDUA) in lysosomes and subsequent accumulation of glycosaminoglycans (GAG). Clinical enzyme replacement therapy (ERT) with intravenous laronidase reverses some aspects of MPS I disease (e.g., hepatomegaly, splenomegaly, glycosaminoglycanuria) and ameliorates others (e.g., pulmonary function, cardiac disease, arthropathy, exercise tolerance). However, neurologic benefits are thought to be negligible because the blood-brain barrier (BBB) blocks enzyme from reaching the central nervous system (CNS). We considered the possibility that a very high dose of intravenous laronidase might be able to traverse the BBB in small quantities, and provide some metabolic correction in the brain. To address this question, high-dose laronidase was administered (11.6 mg/kg, once per week, 4 weeks) to adult MPS I mice. IDUA enzyme activity in the cortex of treated mice increased to 97% of that in wild type mice (p<0.01). GAG levels in cortex were reduced by 63% of that from untreated MPS I mice (p<0.05). Further, immunohistochemical analysis showed that treatment reduced secondary GM3-ganglioside accumulation in treated MPS I mice. Water T-maze tests showed that the learning abnormality in MPS I mice was reduced (p<0.0001). In summary, repeated, high-dose ERT facilitated laronidase transit across the BBB, reduced GAG accumulation within the CNS, and rescued cognitive impairment.

Rapid assays for Gaucher and Hurler diseases in dried blood spots using digital microfluidics.

OBJECTIVE: Easy tool for newborn screening of Gaucher and Hurler diseases. METHODS: Method comparison between fluorometric enzymatic activity assay on a digital microfluidic platform and micro-titer plate bench assay was performed on normal (n = 100), Gaucher (n = 10) and Hurler (n = 7) dried blood spot samples. RESULTS: Enzymatic activity analysis of glucocerebrosidase (Gaucher) and α-l-iduronidase (Hurler) revealed similar discrimination between normal and affected samples on both platforms. CONCLUSIONS: Digital microfluidics is suitable for Gaucher and Hurler newborn screening.

Optimization of enzymatic diagnosis for mucopolysaccharidosis I in dried blood spots on filter paper.

OBJECTIVES: The aim of this study was to validate an ultramicroassay with a reduced interference of hemoglobin for the enzymatic diagnosis of mucopolysaccharidosis I in dried blood spots on filter paper. DESIGN AND METHODS: A matrix of dried blood was incorporated within the calibration system. In addition, trichloroacetic acid was added to precipitate hemoglobin. Linearity, precision, accuracy and limits of detection and quantification were determined and α-l-iduronidase activity was obtained from 6 patients, 9 heterozygotes, 25 healthy adults and 500 neonates. RESULTS: The ultramicroassay was linear, precise (coefficients of variation less than 10%) and accurate (recovery between 91 and 98%). The interference of hemoglobin was decreased within the hematocrit range of clinical interest: 35-55%. CONCLUSIONS: This ultramicroassay increases in 2.5 times the difference between healthy individuals and patients with respect to the reference assay; optimizing enzymatic quantification and confirmatory biochemical diagnosis for mucopolysaccharidosis I.