Treatment for Lysosomal Storage Disorders

Development, validation and application of single molecule molecular inversion probe based novel integrated genetic screening method for 29 common lysosomal storage disorders in India

BACKGROUND

Current clinical diagnosis pathway for lysosomal storage disorders (LSDs) involves sequential biochemical enzymatic tests followed by DNA sequencing, which is iterative, has low diagnostic yield and is costly due to overlapping clinical presentations. Here, we describe a novel low-cost and high-throughput sequencing assay using single-molecule molecular inversion probes (smMIPs) to screen for causative single nucleotide variants (SNVs) and copy number variants (CNVs) in genes associated with 29 common LSDs in India.

RESULTS

903 smMIPs were designed to target exon and exon-intron boundaries of targeted genes (n = 23; 53.7 kb of the human genome) and were equimolarly pooled to create a sequencing library. After extensive validation in a cohort of 50 patients, we screened 300 patients with either biochemical diagnosis (n = 187) or clinical suspicion (n = 113) of LSDs. A diagnostic yield of 83.4% was observed in patients with prior biochemical diagnosis of LSD. Furthermore, diagnostic yield of 73.9% (n = 54/73) was observed in patients with high clinical suspicion of LSD in contrast with 2.4% (n = 1/40) in patients with low clinical suspicion of LSD. In addition to detecting SNVs, the assay could detect single and multi-exon copy number variants with high confidence. Critically, Niemann-Pick disease type C and neuronal ceroid lipofuscinosis-6 diseases for which biochemical testing is unavailable, could be diagnosed using our assay. Lastly, we observed a non-inferior performance of the assay in DNA extracted from dried blood spots in comparison with whole blood.

CONCLUSION

We developed a flexible and scalable assay to reliably detect genetic causes of 29 common LSDs in India. The assay consolidates the detection of multiple variant types in multiple sample types while having improved diagnostic yield at same or lower cost compared to current clinical paradigm.

Unraveling the link between neuropathy target esterase NTE/SWS, lysosomal storage diseases, inflammation, abnormal fatty acid metabolism, and leaky brain barrier

Mutations in Drosophila Swiss cheese (SWS) gene or its vertebrate orthologue neuropathy target esterase (NTE) lead to progressive neuronal degeneration in flies and humans. Despite its enzymatic function as a phospholipase is well established, the molecular mechanism responsible for maintaining nervous system integrity remains unclear. In this study, we found that NTE/SWS is present in surface glia that forms the blood-brain barrier (BBB) and that NTE/SWS is important to maintain its structure and permeability. Importantly, BBB glia-specific expression of Drosophila NTE/SWS or human NTE in the sws mutant background fully rescues surface glial organization and partially restores BBB integrity, suggesting a conserved function of NTE/SWS. Interestingly, sws mutant glia showed abnormal organization of plasma membrane domains and tight junction rafts accompanied by the accumulation of lipid droplets, lysosomes, and multilamellar bodies. Since the observed cellular phenotypes closely resemble the characteristics described in a group of metabolic disorders known as lysosomal storage diseases (LSDs), our data established a novel connection between NTE/SWS and these conditions. We found that mutants with defective BBB exhibit elevated levels of fatty acids, which are precursors of eicosanoids and are involved in the inflammatory response. Also, as a consequence of a permeable BBB, several innate immunity factors are upregulated in an age-dependent manner, while BBB glia-specific expression of NTE/SWS normalizes inflammatory response. Treatment with anti-inflammatory agents prevents the abnormal architecture of the BBB, suggesting that inflammation contributes to the maintenance of a healthy brain barrier. Considering the link between a malfunctioning BBB and various neurodegenerative diseases, gaining a deeper understanding of the molecular mechanisms causing inflammation due to a defective BBB could help to promote the use of anti-inflammatory therapies for age-related neurodegeneration.

Living Cell as a Self-Synchronized Chemical Reactor

Thermal fluctuations power all processes inside living cells. Therefore, these processes are inherently random. However, myriad multistep chemical reactions act in concerto inside a cell, finally leading to this chemical reactor's self-replication. We speculate that an underlying mechanism in nature must exist that allows all of these reactions to synchronize at multiple time and length scales, overcoming in this way the random nature of any single process in a cell. This Perspective discusses what type of research is needed to understand this undiscovered synchronization law.

Lysosomal storage disorders identified in adult population from India: Experience of a tertiary genetic centre and review of literature

Lysosomal storage disorders (LSDs) in adults have milder phenotype and variable age at presentation. Several studies have described the phenotype, genotype and treatment outcomes for adult-onset LSDs like Gaucher, Fabry, Pompe disease and others. We describe the first systematic study on the occurrence of LSDs in an adult population from India. It describes, the key clinical signs seen in these patients and those from literature review that can aid in early detection. Of 2102 biochemically diagnosed LSDs cases, 32 adult patients were identified with LSDs. Based on the clinical suspicion, screening test and enzyme study was carried out. Twenty-two patients were subjected to a genetic study to identify the causative variant in a respective gene. Of the 32 adult patients, we observed a maximum percentage of 37.5% (n = 12) cases with Gaucher disease, followed by 13% (n = 4) with Fabry disease. We found 10% of cases with MPS IVA and MPS I, and 9% cases with Pompe. Single case of adult mucolipidosis III and two cases each of Type 1 Sialidosis, Niemann-Pick disease B and metachromatic leukodystrophy were identified. We observed two common variants p.Leu483Pro and p.Ala487Thr in the GBA1 gene in 23% of Indian patients with adult Gaucher disease. No common variants were observed in other aforementioned LSDs. Study identified 50% of Fabry patients and 4% of Gaucher patients diagnosed at our centre to be adults. The prevalence of adult Pompe patients was low (3.4%) as compared to 80% reported in the Caucasian population. Adult LSDs such as, MPS III, GM1/GM2 gangliosidosis and Krabbe disease were not identified in our cohort.

Evaluation, in a highly specialised enzyme laboratory, of a digital microfluidics platform for rapid assessment of lysosomal enzyme activity in dried blood spots

Lysosomal storage disorders (LSDs) are predominantly enzyme deficiencies leading to substrate accumulation, causing progressive damage to multiple organs. To date, a crucial part of diagnosing LSDs is measuring enzymatic activity in leucocytes, plasma, or dried blood spots (DBS). Here, we present results from a proof-of-principle study, evaluating an innovative digital microfluidics (DMF) platform, referred to as SEEKER®, that can measure the activity of the following four lysosomal enzymes from DBS: α-L-iduronidase (IDUA) for mucopolysaccharidosis I (MPS I), acid α-glucosidase (GAA) for Pompe disease, β-glucosidase (GBA) for Gaucher disease, and α-galactosidase A (GLA) for Fabry disease. Over 900 DBS were analysed from newborns, children, and adults. DMF successfully detected known patients with MPS I, Pompe disease, and Gaucher disease, and known males with Fabry disease. This is the first demonstration of this multiplexed DMF platform for identification of patients with LSDs in a specialised diagnostic enzyme laboratory environment. We conclude that this DMF platform is relatively simple, high-throughput, and could be readily accommodated into a specialised laboratory as a first-tier test for MPS I, Pompe disease, and Gaucher disease for all patients, and Fabry disease for male patients only.

An Overview of Canine Inherited Neurological Disorders with Known Causal Variants

Hereditary neurological conditions documented in dogs encompass congenital, neonatal, and late-onset disorders, along with both progressive and non-progressive forms. In order to identify the causal variant of a disease, the main two approaches are genome-wide investigations and candidate gene investigation. Online Mendelian Inheritance in Animals currently lists 418 Mendelian disorders specific to dogs, of which 355 have their likely causal genetic variant identified. This review aims to summarize the current knowledge on the canine nervous system phenes and their genetic causal variant. It has been noted that the majority of these diseases have an autosomal recessive pattern of inheritance. Additionally, the dog breeds that are more prone to develop such diseases are the Golden Retriever, in which six inherited neurological disorders with a known causal variant have been documented, and the Belgian Shepherd, in which five such disorders have been documented. DNA tests can play a vital role in effectively managing and ultimately eradicating inherited diseases.

Evaluation of dried-blood spots and a hematocrit-independent procedure in lysosomal diseases screening using multiplexed tandem mass spectrometry assays

BACKGROUND

Dried blood spots (DBS) are widely used as a non-invasive sampling method, especially in newborn screening (NBS). Despite its numerous advantages, conventional DBS might be limited by the hematocrit effect when analyzing a punch, depending on its position in the blood spot. This effect could be avoided using hematocrit-independent sampling devices such as the hemaPEN®. This device collects blood through integrated microcapillaries, and a fixed blood volume is deposited on a pre-punched paper disc. NBS programs are increasingly poised to include lysosomal disorders, given the availability of treatments that improve clinical outcomes if detected early. In this study, the effect of hematocrit and punch position in the DBS on the assay of 6 lysosomal enzymes was evaluated on 3 mm discs pre-punched in hemaPEN® devices compared to 3 mm punches from the PerkinElmer 226 DBS.

METHODS

The enzyme activities were measured by multiplexed tandem mass spectrometry coupled to ultra-high performance liquid chromatography. Three hematocrit levels (23%, 35%, and 50%) and punching positions (center, intermediary, and border) were tested. Three replicates have been performed for each condition. A multivariate approach has been used along with a univariate method to assess the effect of the experimental design on each enzyme activity.

RESULTS

Hematocrit, punch position, and whole blood sampling method do not affect the assessment of enzyme activity using the NeoLSD® assay.

CONCLUSION

The results obtained from conventional DBS and the volumetric device HemaPEN® are comparable. These results underline the reliability of DBS for this test.

Lysosomal storage disorders: from biology to the clinic with reference to India

Lysosomal storage disorders (LSDs) are a group of seventy different metabolic storage diseases due to accumulation of substrate mainly in the form of carbohydrate, lipids, proteins, and cellular debris. They occur due to variant in different genes that regulate lysosomal enzymes synthesis, transport, and secretion. In recent years, due to an increased availability of various therapies to treat these disorders, and increased diagnostic tools, there has been an escalated awareness of LSDs. Due to heterogeneous population and various social reasons, India is likely to have a high frequency of LSDs. Therefore, to understand the burden of various LSDs, its molecular spectrum, and understanding the phenotype-genotype correlation, Indian Council of Medical Research (ICMR) and Department of Health Research (DHR), Government of India had set up a task force in the year 2015. It has resulted in identifying common LSDs, and founder variant for some of the storage disorders and molecular spectrum of various LSDs across the country. This review describes in detail the spectrum of LSDs, its molecular epidemiology and prevention in context to Indian population.

Ferroptosis and Its Modulation by Autophagy in Light of the Pathogenesis of Lysosomal Storage Diseases

Ferroptosis is one of the recently described types of cell death which is dependent on many factors, including the accumulation of iron and lipid peroxidation. Its induction requires various signaling pathways. Recent discovery of ferroptosis induction pathways stimulated by autophagy, so called autophagy-dependent ferroptosis, put our attention on the role of ferroptosis in lysosomal storage diseases (LSD). Lysosome dysfunction, observed in these diseases, may influence ferroptosis efficiency, with as yet unknown consequences for the function of cells, tissues, and organisms, due to the effects of ferroptosis on physiological and pathological metabolic processes. Modulation of levels of ferrous ions and enhanced oxidative stress, which are primary markers of ferroptosis, are often described as processes associated with the pathology of LSD. Inhibition of autophagy flux and resultant accumulation of autophagosomes in neuronopathic LSD may induce autophagy-dependent ferroptosis, indicating a considerable contribution of this process in neurodegeneration. In this review article, we describe molecular mechanisms of ferroptosis in light of LSD, underlining the modulation of levels of ferroptosis markers in these diseases. Furthermore, we propose a hypothesis about the possible involvement of autophagy-dependent ferroptosis in these disorders.