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.

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.

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.

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.

Evaluation of α-iduronidase in dried blood spots is an accurate tool for mucopolysaccharidosis I diagnosis.

BACKGROUND: Mucopolysaccharidosis type I (MPS I) is caused by a deficiency of the α-L-iduronidase (IDUA), which leads to the accumulation of glycosaminoglycans in lysosomes. MPS I patients present a spectrum ranging from a severe to an attenuated phenotype. Once clinical suspicion is present, diagnosis of MPS I can be performed by enzyme activity determination and/or molecular analysis. The aim of this study was to establish a reference interval value to IDUA activity using a dried blood spots (DBS) assay and to evaluate whether this assay could be a secure tool to diagnose MPS I patients. RESULTS: IDUA activity range on HV DBS samples were 1.40-7.78 µmol/l blood/hr. Regarding the validation group, 11 of the 36 individuals clinically suspected of MPS I had the diagnosis confirmed by DBS and reference assay (leukocytes). When we considered the new proposed cutoff value of 1.5 µmol/l blood/hr, the sensitivity, specificity, and predictive values were 100%. CONCLUSIONS: Our results strongly suggest that the determination of IDUA activity using a DBS assay is a secure tool for MPS I diagnosis. However, it is extremely important to assure that all recommendations for collection, transport, and storage are correctly followed to guarantee the quality of the samples.

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.

Mixed donor chimerism and low level iduronidase expression may be adequate for neurodevelopmental protection in Hurler Syndrome.

Hurler syndrome is a lysosomal storage disease resulting in fatal cardiac or neurologic sequelae unless alpha-iduronidase production is reconstituted with hematopoietic stem cell transplantation. We report on a 4-year, 6-month-old boy with mixed donor chimerism and low enzyme levels but a normal neurodevelopmental trajectory.

Effect of CuCl2, NaCl and EDTA on the enzyme alpha-L-iduronidase in the plasma of normal individuals and heterozygotes for MPS I.

BACKGROUND: It has been previously demonstrated that the enzyme alpha-L-iduronidase (IDUA) of patients with MPS I shows a different biochemical behavior in each of the three clinical forms of these. In heterozygotes, its biochemical behavior has been recently established in leukocyte and plasma samples, demonstrating that it is possible to distinguish individuals heterozygous for MPS I within an unselected population. METHODS: We evaluated the effect of copper chloride, EDTA and sodium chloride on the activity of the enzyme alpha-L-iduronidase in the plasma of normal individuals and of MPS I heterozygotes and observed the type of inhibition caused, the Ki, the apparent Km and the apparent Vmax for each inhibitor. RESULTS: Sodium chloride inhibited the enzyme in normal individuals and in 40% of the heterozygotes evaluated and activated it in 60% of heterozygotes. The remaining compounds inhibited IDUA in both heterozygotes and normal individuals. CONCLUSIONS: We detected significant differences capable of differentiating MPS I heterozygotes from normal individuals by simply adding sodium chloride, EDTA or copper chloride to the incubation medium at the time of IDUA activity determination, with a potential use in carrier detection protocols.

Detection of mucopolysaccharidosis type I heterozygotes on the basis of the biochemical properties of plasma alpha-L-iduronidase.

BACKGROUND: Mucopolysaccharidosis type I (MPS I) is a disease caused by deficiency of the enzyme alpha-L-iduronidase (IDUA). Since no treatment is currently available for this disorder, the detection of heterozygotes is very important for genetic counseling and prenatal diagnosis. The objective of the present study was to characterize plasma IDUA from MPS I heterozygotes in an attempt to distinguish it from that of normal individuals. METHODS: We determined the optimum pH, Km, Vmax and Calpha (Vmax/Km) of the reaction and the thermal stability of IDUA at 50 degrees C. RESULTS: MPS I heterozygotes can be separated from normal individuals on the basis of Km, Calpha and thermal stability of the enzyme. CONCLUSIONS: Taking into consideration the clinical status of the homozygous offspring, we were able to subdivide the MPS I heterozygotes into various subgroups (Hurler, Scheie or Hurler/Scheie compound), and verified that the Hurler subgroup had a lower optimum pH for IDUA activity than controls and other MPS I subgroups, and that all MPS I subgroups had higher Km and lower Calpha when compared to controls.