Gabriel Civallero

Reliable detection of mucopolysacchariduria in dried-urine filter paper samples.

BACKGROUND The mucopolysaccharidoses (MPS) are inherited metabolic disorders with bone, joint, and visceral abnormalities, leading to multi-organ dysfunction and, sometimes, neurological manifestations. These diseases are caused by storage of glycosaminoglycans (GAGs) and other complex molecules in tissues, among other pathogenic mechanisms. Definitive diagnosis of the affected individual is mainly based on the identification of the specific enzyme deficiency. New therapies are available or are in development for these pathologies, and early diagnosis seems to be important for the therapy outcomes. Almost all MPS patients have increased levels of GAGs in urine being their evaluation usually the first step in the screening of these conditions. Test on urine may be challenging as transportation of liquid urine samples in appropriate conditions for long distances, especially across international borders, could be difficult. METHODS With the aim of overcoming the difficulties related to the use of liquid samples, we extended and validated previous studies about colorimetric determination of GAGs in dried-urine filter paper (DUFP) samples. RESULTS In the conditions we described, there are no differences in the concentration of GAGs between urine and DUFP samples. Untreated patients with MPS and normal controls were well discriminated using any of the samples. CONCLUSIONS Dried-urine filter paper is a suitable sample for the colorimetric quantitation of GAGs, and that its incorporation as an additional tool for screening of MPS should be considered by reference laboratories.

Extended use of a selective inhibitor of acid lipase for the diagnosis of Wolman disease and cholesteryl ester storage disease.

Lysosomal acid lipase (LAL) deficiency produces two well defined inborn disorders, Wolman disease (WD) and cholesteryl ester storage disease (CESD). WD is a severe, early-onset condition involving massive storage of triglycerides and cholesteryl esters in the liver, with death usually occurring before one year of life. CESD is a more attenuated, later-onset disease that leads to a progressive and variable liver dysfunction. Diagnosis of LAL deficiency is mainly based on the enzyme assay of LAL activity in fibroblasts. Recently, a selective acid lipase inhibitor was used for the determination of enzyme activity in dried-blood filter paper (DBFP) samples. To extend and to validate these studies, we tested LAL activity with selective inhibition on DBFP samples, leukocytes and fibroblasts. Our results showed a clear discrimination between patients with LAL deficiency and healthy controls when using DBFP, leukocytes or fibroblasts (p<0.001). Deficiency of LAL was also demonstrated in individuals referred to our laboratory with suspected clinical diagnosis of WD, CESD, and Niemann-Pick type B. We conclude that the assay of LAL using selective inhibitor is a reliable and useful method for the identification of LAL deficiency, not only in DBFP samples but also in leukocytes and fibroblasts. This is important as enzyme replacement therapy for LAL deficiency is currently being developed, making the correct diagnosis a critical issue.

Diagnosis and therapy options in mucopolysaccharidosis II (Hunter syndrome)

Introduction: Hunter syndrome (Mucopolysaccharidosis II, MPS II) is a lysosomal storage disease inherited as an X-linked trait. The disease is progressive, affects multiple systems and is clinically heterogeneous. Patients with the so-called ‘attenuated’ form have somatic manifestations affecting bone, joints, respiratory, cardiac, auditory and other systems. Patients with the ‘severe form’ have, in addition to the somatic manifestations, neurocognitive decline. Areas covered: Diagnosis is reached with biochemical tests (urinary glycosaminoglycans [GAGs] and enzyme assay), usually complemented with genetic analysis. Mutation identification could play a role in phenotype prediction and could help to identify carriers, which is very important in an X-linked disease. Specific treatment with enzyme replacement therapy (ERT) became available few years ago and improved significantly the natural course of the disease. However, treatment with intravenous ERT has limitations, and the possibility of alternative therapies such as hematopoietic stem cell transplantation and substrate reduction therapy with genistein is being considered. Novel therapies mainly designed to address the CNS manifestations (intrathecal ERT, ERT with fusion proteins, gene therapy and others) are also in development. Expert opinion: The combination of effective therapies with early diagnosis (newborn screening is feasible and could be available shortly) could completely change the prospect for MPS II patients in few years.

Extended use of dried-leukocytes impregnated in filter paper samples for detection of Pompe, Gaucher, and Morquio A diseases

BACKGROUND Lysosomal storage diseases (LSD) are a group of genetic conditions which could present a vast spectrum of abnormalities that may include skeletal abnormalities, organ dysfunction, neuronal involvement, and tissue accumulation of complex molecules, among other manifestations. Definitive diagnosis of LSD is generally obtained by specific enzyme assays performed in leukocytes, fibroblasts, or more recently, dried-blood filter paper (DBFP) samples. METHODS We recently introduced dried-leukocytes filter paper (DLFP) as an alternative source of enzyme to assay heparan sulfamidase and galactocerebrosidase activities, which could not be measured in DBFP samples using fluorometric methods. We present a new fluorometric methods on DLFP samples, for evaluation of α-glucosidase (GAA), β-glucosidase (GBA), and N-acetylgalactosamine-6-sulfatase (GALNS) activities, key enzyme assays for the identification of patients with Pompe disease (PD), Gaucher disease (GD), and Morquio A disease (MD), respectively. RESULTS We show a clear discrimination between confirmed PD, GD, and MD patients and healthy controls. CONCLUSIONS We conclude that the assays of GAA, GBA, and GALNS on DLFP are reliable and useful methods for the identification of PD, GD, and MD diseases, respectively. As sample preparation is feasible in standard biochemical laboratories and transportation is very simple, it could enable patients living in remote areas to be investigated, diagnosed and eventually treated with the specific therapies available for these diseases.

High-Risk Screening and Diagnosis of Inborn Errors of Metabolism: A Practical Guide for Laboratories

Inborn errors of metabolism (IEM) are a large and heterogeneous group of genetic diseases. In most of these conditions, the presence of variants in specific genes leads to enzyme deficiencies that ...

Validation of a Multiplex Tandem Mass Spectrometry Method for the Detection of Selected Lysosomal Storage Diseases in Dried Blood Spots

Background:Interest in screening methods for lysosomal storage diseases (LSDs) has increased in recent years, since early diagnosis and treatment are essential to prevent or attenuate the onset of symptoms and the complications of these diseases. In the current work, we evaluated the performance of tandem mass spectrometry (MS/MS) for the detection of some LSDs, aiming the future use of this methodology for the screening of these disorders.Methods:Standard curves and quality control dried blood spots were assayed to evaluate the precision, linearity, and accuracy. A total of 150 controls were grouped according to age and subjected to measurement of lysosomal enzymes deficient in Niemann-Pick A/B, Krabbe, Gaucher, Fabry, Pompe, and Mucopolysaccharidosis type I diseases. Samples from 59 affected patients with a diagnosis of LSDs previously confirmed by fluorimetric methods were analyzed.Results:Data from standard calibration demonstrated good linearity and accuracy and the intra- and interassay precisions v...