Lysosomal storage disorders: Molecular basis and laboratory testing

Abstract

Lysosomal storage disorders (LSDs) are a large group of more than 50 different inherited metabolic diseases which, in the great majority of cases, result from the defective function of specific lysosomal enzymes and, in cases, of non-enzymatic lysosomal proteins or non-lysosomal proteins involved in lysosomal biogenesis. The progressive lysosomal accumulation of undegraded metabolites results in generalised cell and tissue dysfunction, and, therefore, multi-systemic pathology. Storage may begin during early embryonic development, and the clinical presentation for LSDs can vary from an early and severe phenotype to late-onset mild disease. The diagnosis of most LSDs--after accurate clinical/paraclinical evaluation, including the analysis of some urinary metabolites--is based mainly on the detection of a specific enzymatic deficiency. In these cases, molecular genetic testing (MGT) can refine the enzymatic diagnosis. Once the genotype of an individual LSD patient has been ascertained, genetic counselling should include prediction of the possible phenotype and the identification of carriers in the family at risk. MGT is essential for the identification of genetic disorders resulting from non-enzymatic lysosomal protein defects and is complementary to biochemical genetic testing (BGT) in complex situations, such as in cases of enzymatic pseudodeficiencies. Prenatal diagnosis is performed on the most appropriate samples, which include fresh or cultured chorionic villus sampling or cultured amniotic fluid. The choice of the test--enzymatic and/or molecular--is based on the characteristics of the defect to be investigated. For prenatal MGT, the genotype of the family index case must be known. The availability of both tests, enzymatic and molecular, enormously increases the reliability of the entire prenatal diagnostic procedure. To conclude, BGT and MGT are mostly complementary for post- and prenatal diagnosis of LSDs. Whenever genotype/phenotype correlations are available, they can be helpful in predicting prognosis and in making decisions about therapy.

Burden of Lysosomal Storage Disorders in India: Experience of 387 Affected Children from a Single Diagnostic Facility

“…The screening study was carried out from urine samples for glycosaminoglycans (GAGs) [both quantitative and qualitative] (Dembure and Roesel 1991;Hopwood and Harrison 1982) and plasma was analyzed for chitotriosidase activity (Aerts et al 2008;Sheth et al 2010) and mucolipidosis II/III [ML II/III] screening . Leukocytes were isolated from whole blood and were processed by standard protocol for enzyme assay using 4-MU fluorometric assay or PNCS spectrophotometric synthetic substrate as outlined by Shapria et al (1989); Filocamo and Morrone (2011);and Sheth et al (2004). Niemann-Pick disease-C (NPC) study was carried out on cultured skin fibroblasts in lipid-deficient medium using filipin stain (Kruth and Vaughan 1980;Sheth et al 2008).…”

Selective Screening for Lysosomal Storage Diseases with Dried Blood Spots Collected on Filter Paper in 4,700 High-Risk Colombian Subjects

“…The phenotypic expression of these diseases is so diverse and heterogeneous that their definitive identification and diagnosis must be made through specialized clinical and laboratory studies (Wenger et al 2002) The laboratory diagnostic approach, directed at high-risk populations, first uses protocols typically based on the detection of metabolites that are excreted in the urine after accumulating in tissues as a result of enzymatic deficiencies. Lysosomal storage disorders usually involve an accumulation of three groups of compounds: sphingolipids, mucopolysaccharides, and oligosaccharides, molecules that may be detected in affected individuals but do not offer specific diagnostic clues (Futerman et al 2004;Filocamo and Morrone 2011). Next, these preliminary tests were followed by specific enzymatic studies -which involved plasma, leukocytes, or cultured fibroblasts samples -aimed to provide definitive diagnosis (Civallero et al 2006).…”

Anderson-Fabry, the Histrionic Disease: From Genetics to Clinical Management

“…77 The GLA gene sequence analysis should always be performed and correctly interpreted, in order to reveal polymorphisms, that potentially lead to an enzymatic pseudodeficiency. 78 Biochemical diagnosis may be unreliable in heterozygous females, as they can have a normal or only mildly reduced a-gal A activity, due to random X-chromosome inactivation. Therefore, it is crucial to combine biochemical assays with appropriate molecular analyses of the GLA gene in order to attribute or exclude the AFD heterozygous status in females.…”