Tay-Sachs disease: current perspectives from Australia

Lipid-Lowering Drug Gemfibrozil Protects Mice from Tay-Sachs Disease via Peroxisome Proliferator-Activated Receptor α

Tay-Sachs disease (TSD) is a progressive heritable neurodegenerative disorder characterized by the deficiency of the lysosomal β-hexosaminidase enzyme (Hex-/-) and the storage of GM2 ganglioside, as well as other related glycoconjugates. Along with motor difficulties, TSD patients also manifest a gradual loss of skills and behavioral problems, followed by early death. Unfortunately, there is no cure for TSD; however, research on treatments and therapeutic approaches is ongoing. This study underlines the importance of gemfibrozil (GFB), an FDA-approved lipid-lowering drug, in inhibiting the disease process in a transgenic mouse model of Tay-Sachs. Oral administration of GFB significantly suppressed glial activation and inflammation, while also reducing the accumulation of GM2 gangliosides/glycoconjugates in the motor cortex of Tay-Sachs mice. Furthermore, oral GFB improved behavioral performance and increased the life expectancy of Tay-Sachs mice. While investigating the mechanism, we found that oral administration of GFB increased the level of peroxisome proliferator-activated receptor α (PPARα) in the brain of Tay-Sachs mice, and that GFB remained unable to reduce glycoconjugates and improve behavior and survival in Tay-Sachs mice lacking PPARα. Our results indicate a beneficial function of GFB that employs a PPARα-dependent mechanism to halt the progression of TSD and increase longevity in Tay-Sachs mice.

Therapeutic Strategies For Tay-Sachs Disease

Tay-Sachs disease (TSD) is an autosomal recessive disease that features progressive neurodegenerative presentations. It affects one in 100,000 live births. Currently, there is no approved therapy or cure. This review summarizes multiple drug development strategies for TSD, including enzyme replacement therapy, pharmaceutical chaperone therapy, substrate reduction therapy, gene therapy, and hematopoietic stem cell replacement therapy. In vitro and in vivo systems are described to assess the efficacy of the aforementioned therapeutic strategies. Furthermore, we discuss using MALDI mass spectrometry to perform a high throughput screen of compound libraries. This enables discovery of compounds that reduce GM2 and can lead to further development of a TSD therapy.

Gene Therapy for Rare Neurological Disorders

There are over 7 000 diseases that are individually rare, but collectively affect missions of people worldwide. They are very commonly neurologic single-gene disorders. Recent advances in recombinant adeno-associated virus (rAAV) vectors have enabled breakthroughs, including FDA-approved gene therapies for Inherited Retinal Dystrophy due to RPE65 mutation and spinal muscular atrophy. A range of other gene therapies for rare neurologic diseases are at various stages of development. Future development of gene editing technologies promises further to broaden the potential for more patients with these disorders to benefit from innovative therapies.

Serum Cytokine Profile, Beta-Hexosaminidase A Enzymatic Activity and GM2 Ganglioside Levels in the Plasma of a Tay-Sachs Disease Patient after Cord Blood Cell Transplantation and Curcumin Administration: A Case Report

Tay-Sachs disease (TSD) is a progressive neurodegenerative disorder that occurs due to a deficiency of a β hexosaminidase A (HexA) enzyme, resulting in the accumulation of GM₂ gangliosides. In this work, we analyzed the effect of umbilical cord blood cell transplantation (UCBCT) and curcumin administration on the course of the disease in a patient with adult TSD. The patient’s serum cytokine profile was determined using multiplex analysis. The level of GM₂ gangliosides in plasma was determined using mass spectrometry. The enzymatic activity of HexA in the plasma of the patient was assessed using a fluorescent substrate assay. The HexA α-subunit (HexA) concentration was determined using ELISA. It was shown that both UCBCT and curcumin administration led to a change in the patient’s cytokine profile. The UCBCT resulted in an increase in the concentration of HexA in the patient’s serum and in an improvement in the patient’s neurological status. However, neither UCBCT nor curcumin were able to alter HexA activity and the level of GM₂ in patient’s plasma. The data obtained indicate that UCBCT and curcumin administration can alter the immunity of a patient with TSD, reduce the level of inflammatory cytokines and thereby improve the patient’s condition.

In-silico screening and microsecond molecular dynamics simulations to identify single point mutations that destabilize β-hexosaminidase A causing Tay-Sachs disease

β-hexosaminidase A (HexA) protein is responsible for the degradation of GM2 gangliosides in the central and peripheral nervous systems. Tay-Sachs disease occurs when HexA within Hexosaminidase does not properly function and harmful GM2 gangliosides begin to build up within the neurons. In this study, in silico methods such as SIFT, PolyPhen-2, PhD-SNP, and MutPred were utilized to analyze the effects of nonsynonymous single nucleotide polymorphisms (nsSNPs) on HexA in order to identify possible pathogenetic and deleterious variants. Molecular dynamics (MD) simulations showed that two mutants, P25S and W485R, experienced an increase in structural flexibility compared to the native protein. Particularly, there was a decrease in the overall number and frequencies of hydrogen bonds for the mutants compared to the wildtype. MM/GBSA calculations were performed to help assess the change in binding affinity between the wildtype and mutant structures and a mechanism-based inhibitor, NGT, which is known to help increase the residual activity of HexA. Both of the mutants experienced a decrease in the binding affinity from -23.8 kcal/mol in wildtype to -20.9 and -18.7 kcal/mol for the P25S and W485R variants of HexA, respectively.

Novel HEXA variants in Korean children with Tay-Sachs disease with regression of neurodevelopment from infancy

Background

Tay–Sachs disease (TSD) is a lysosomal storage disease caused by mutations in the HEXA gene that encodes the HexosaminidaseA (HEXA) enzyme. As HEXA normally functions to degrade the protein GM2‐ganglioside in lysosomes, decreased levels of HEXAcauses an accumulation of the protein and leads to neurological toxicity. Typical clinical manifestations of TSD include neurodevelopmental regression, muscle weakness, hypotonia, hyperreflexia, ataxia, seizures, and other neurological symptoms. It is quite rare in Asian populations, wherein only two cases have been reported in Korea to date.

Methods

Clinical records, radiological assessments, and laboratory findings, such as plasma hexosaminidase assay and HEXA analysis, were extracted from the medical records of three (1 male and 2 female) independent Korean children with infantile form of Tay–Sachs disease.

Results

All three children presented with neurodevelopmental regression and strabismus at around 8 months of age. Presence of cherry‐red spots in the macula led to conduction of biochemical and genetic studies for TSD confirmation. The plasma hexosaminidase assay revealed decreased HEXA activity and low to normal total hexosaminidase activity. Similarly, genetic analysis revealed 4 variants from 6 alleles, including 2 previously reported and 2 novel variants, in the HEXA gene.

Conclusion

We presented three Korean children, who were recently diagnosed with infantile‐type TSDvia enzyme assay and genetic analysis. Furthermore, results showed that fundus examination can be helpful for early diagnosis of children with neurodevelopmental regression.

CRISPR-Cas9 for treating hereditary diseases

This chapter analyzes to use of the genome editing tool to the treatment of various genetic diseases. The genome editing method could be used to change the DNA in cells or organisms to understand their physiological response. Therefore, a key objective is to present general information about the use of the genome editing tool in a pertinent way. An emerging genome editing technology like a clustered regularly short palindromic repeats (CRISPR) is an extensively expended in biological sciences. CRISPR and CRISPR-associated protein 9 (CRISPR-Cas9) technique is being utilized to edit any DNA mutations associated with hereditary diseases to study in cells (in vitro) and animals (in vivo). Interestingly, CRISPR-Cas9 could be used to the investigation of treatments of various human hereditary diseases such as hemophila, β-thalassemia, cystic fibrosis, Alzheimer's, Huntington's, Parkinson's, tyrosinemia, Duchnene muscular dystrophy, Tay-Sachs, and fragile X syndrome disorders. Furthermore, CRISPR-Cas9 could also be used in other diseases to the improvement of human health. Finally, this chapter discuss current progress to treatment for hereditary diseases using CRISPR-Cas9 technology and highlights associated challenges and future prospects.

A feasibility study of mHealth and wearable technology in late onset GM2 gangliosidosis (Tay-Sachs and Sandhoff Disease)

Background

As part of a late onset GM2 gangliosidosis natural history study, digital health technology was utilized to monitor a group of patients remotely between hospital visits. This approach was explored as a means of capturing continuous data and moving away from focusing only on episodic data captured in traditional study designs. A strong emphasis was placed on real-time capture of symptoms and mobile Patient Reported Outcomes (mPROs) to identify the disease impact important to the patients themselves; an impact that may not always correlate with the measured clinical outcomes assessed during patient visits. This was supported by passive, continuous data capture from a wearable device.

Results

Adherence rate for wearing the device and completing the mPROs was 84 and 91%, respectively, resulting in a rich multidimensional dataset. As expected for a six-month proof-of-concept study in a disease that progresses slowly, statistically significant changes were not expected or observed in the clinical, mPROs, or wearable device data.

Conclusions

The study demonstrated that patients were very enthusiastic and motivated to engage with the technology as demonstrated by excellent compliance. The combination of mPROs and wearables generates feature-rich datasets that could be a useful and feasible way to capture remote, real-time insight into disease burden.

Metabolomics for Investigating Physiological and Pathophysiological Processes

Metabolomics uses advanced analytical chemistry techniques to enable the high-throughput characterization of metabolites from cells, organs, tissues, or biofluids. The rapid growth in metabolomics is leading to a renewed interest in metabolism and the role that small molecule metabolites play in many biological processes. As a result, traditional views of metabolites as being simply the "bricks and mortar" of cells or just the fuel for cellular energetics are being upended. Indeed, metabolites appear to have much more varied and far more important roles as signaling molecules, immune modulators, endogenous toxins, and environmental sensors. This review explores how metabolomics is yielding important new insights into a number of important biological and physiological processes. In particular, a major focus is on illustrating how metabolomics and discoveries made through metabolomics are improving our understanding of both normal physiology and the pathophysiology of many diseases. These discoveries are yielding new insights into how metabolites influence organ function, immune function, nutrient sensing, and gut physiology. Collectively, this work is leading to a much more unified and system-wide perspective of biology wherein metabolites, proteins, and genes are understood to interact synergistically to modify the actions and functions of organelles, organs, and organisms.

Screening for Tay-Sachs disease carriers by full-exon sequencing with novel variant interpretation outperforms enzyme testing in a pan-ethnic cohort

Background

Pathogenic variants in HEXA that impair β‐hexosaminidase A (Hex A) enzyme activity cause Tay‐Sachs Disease (TSD), a severe autosomal‐recessive neurodegenerative disorder. Hex A enzyme analysis demonstrates near‐zero activity in patients affected with TSD and can also identify carriers, whose single functional copy of HEXA results in reduced enzyme activity relative to noncarriers. Although enzyme testing has been optimized and widely used for carrier screening in Ashkenazi Jewish (AJ) individuals, it has unproven sensitivity and specificity in a pan‐ethnic population. The ability to detect HEXA variants via DNA analysis has evolved from limited targeting of a few ethnicity‐specific variants to next‐generation sequencing (NGS) of the entire coding region coupled with interpretation of any discovered novel variants.

Methods

We combined results of enzyme testing, retrospective computational analysis, and variant reclassification to estimate the respective clinical performance of TSD screening via enzyme analysis and NGS. We maximized NGS accuracy by reclassifying variants of uncertain significance and compared to the maximum performance of enzyme analysis estimated by calculating ethnicity‐specific frequencies of variants known to yield false‐positive or false‐negative enzyme results (e.g., pseudodeficiency and B1 alleles).

Results

In both AJ and non‐AJ populations, the estimated clinical sensitivity, specificity, and positive predictive value were higher by NGS than by enzyme testing. The differences were significant for all comparisons except for AJ clinical sensitivity, where NGS exceeded enzyme testing, but not significantly.

Conclusions

Our results suggest that performance of an NGS‐based TSD carrier screen that interrogates the entire coding region and employs novel variant interpretation exceeds that of Hex A enzyme testing, warranting a reconsideration of existing guidelines.

S. Dawkins H, Nowak KJ, Weeramanthri TS. Genomic Testing for Human Health and Disease Across the Life Cycle: Applications and Ethical, Legal, and Social Challenges

The expanding use of genomic technologies encompasses all phases of life, from the embryo to the elderly, and even the posthumous phase. In this paper, we present the spectrum of genomic healthcare applications, and describe their scope and challenges at different stages of the life cycle. The integration of genomic technology into healthcare presents unique ethical issues that challenge traditional aspects of healthcare delivery. These challenges include the different definitions of utility as applied to genomic information; the particular characteristics of genetic data that influence how it might be protected, used and shared; and the difficulties applying existing models of informed consent, and how new consent models might be needed.

New Approaches to Tay-Sachs Disease Therapy

Tay-Sachs disease belongs to the group of autosomal-recessive lysosomal storage metabolic disorders. This disease is caused by β-hexosaminidase A (HexA) enzyme deficiency due to various mutations in α-subunit gene of this enzyme, resulting in GM2 ganglioside accumulation predominantly in lysosomes of nerve cells. Tay-Sachs disease is characterized by acute neurodegeneration preceded by activated microglia expansion, macrophage and astrocyte activation along with inflammatory mediator production. In most cases, the disease manifests itself during infancy, the “infantile form,” which characterizes the most severe disorders of the nervous system. The juvenile form, the symptoms of which appear in adolescence, and the most rare form with late onset of symptoms in adulthood are also described. The typical features of Tay-Sachs disease are muscle weakness, ataxia, speech, and mental disorders. Clinical symptom severity depends on residual HexA enzymatic activity associated with some mutations. Currently, Tay-Sachs disease treatment is based on symptom relief and, in case of the late-onset form, on the delay of progression. There are also clinical reports of substrate reduction therapy using miglustat and bone marrow or hematopoietic stem cell transplantation. At the development stage there are methods of Tay-Sachs disease gene therapy using adeno- or adeno-associated viruses as vectors for the delivery of cDNA encoding α and β HexA subunit genes. Effectiveness of this approach is evaluated in α or β HexA subunit defective model mice or Jacob sheep, in which Tay-Sachs disease arises spontaneously and is characterized by the same pathological features as in humans. This review discusses the possibilities of new therapeutic strategies in Tay-Sachs disease therapy aimed at preventing neurodegeneration and neuroinflammation.

Progranulin associates with hexosaminidase A and ameliorates GM2 ganglioside accumulation and lysosomal storage in Tay-Sachs disease

Tay-Sachs disease (TSD) is a lethal lysosomal storage disease (LSD) caused by mutations in the HexA gene, which can lead to deficiency of β-hexosaminidase A (HexA) activity and consequent accumulation of its substrate, GM2 ganglioside. Recent reports that progranulin (PGRN) functions as a chaperone of lysosomal enzymes and its deficiency is associated with LSDs, including Gaucher disease and neuronal ceroid lipofuscinosis, prompted us to screen the effects of recombinant PGRN on lysosomal storage in fibroblasts from 11 patients affected by various LSDs, which led to the isolation of TSD in which PGRN demonstrated the best effects in reducing lysosomal storage. Subsequent in vivo studies revealed significant GM2 accumulation and the existence of typical TSD cells containing zebra bodies in both aged and ovalbumin-challenged adult PGRN-deficient mice. In addition, HexA, but not HexB, was aggregated in PGRN-deficient cells. Furthermore, recombinant PGRN significantly reduced GM2 accumulation and lysosomal storage in these animal models. Mechanistic studies indicated that PGRN bound to HexA through granulins G and E domain and increased the enzymatic activity and lysosomal delivery of HexA. More importantly, Pcgin, an engineered PGRN derivative bearing the granulin E domain, also effectively bound to HexA and reduced the GM2 accumulation. Collectively, these studies not only provide new insights into the pathogenesis of TSD but may also have implications for developing PGRN-based therapy for this life-threatening disorder. KEY MESSAGES: GM2 accumulation and the existence of typical TSD cells containing zebra bodies are detected in both aged and ovalbumin-challenged adult PGRN deficient mice. Recombinant PGRN significantly reduces GM2 accumulation and lysosomal storage both in vivo and in vitro, which works through increasing the expression and lysosomal delivery of HexA. Pcgin, an engineered PGRN derivative bearing the granulin E domain, also effectively binds to to HexA and reduces GM2 accumulation.

Measuring the impact of genetic knowledge on intentions and attitudes of the community towards expanded preconception carrier screening

BACKGROUND

Preconception carrier screening (PCS) provides the potential to empower couples to make reproductive choices before having an affected child. An important question is what factors influence the decision to use or not use PCS.

METHODS

We analysed the relationship between knowledge, attitudes and intentions to participate in PCS using logistic regression in 832 participants in Western Australia.

RESULTS

Two-thirds of participants said they would take the test, with 92% of these supporting screening for diseases reducing the lifespan of children and infants. Those who had good genetic knowledge were seven times more likely to intend to use PCS (p≤0.001), while those with high genetic knowledge were four times more likely to (p=0.002) and raised concerns such as insurance and confidentiality.Decreasing genetic knowledge correlated positively with religiosity and apprehension (p≤0.001), which correlated negatively with intention to use PCS (p≤0.001). Increasing genetic knowledge correlated positively with factors representing positive attitudes (p≤0.001), which correlated positively with intention to use PCS (p≤0.001). Many participants with good genetic knowledge nevertheless answered questions that tested understanding incorrectly.80% of participants stated they would prefer to access the test through their general practitioners and 30% would pay up to $A200.

CONCLUSIONS

Knowledge is instrumental in influencing participation. Having good genetic knowledge may not be enough to understand core concepts of PCS and may impact informed decision-making. This study recommends that continuous education of health professionals and thus the community, in PCS is crucial to reduce misconceptions.

Genetics and Therapies for GM2 Gangliosidosis

Tay-Sachs disease, caused by impaired β-N-acetylhexosaminidase activity, was the first GM2 gangliosidosis to be studied and one of the most severe and earliest lysosomal diseases to be described. The condition, associated with the pathological build-up of GM2 ganglioside, has acquired almost iconic status and serves as a paradigm in the study of lysosomal storage diseases. Inherited as a classical autosomal recessive disorder, this global disease of the nervous system induces developmental arrest with regression of attained milestones; neurodegeneration progresses rapidly to cause premature death in young children. There is no effective treatment beyond palliative care, and while the genetic basis of GM2 gangliosidosis is well established, the molecular and cellular events, from diseasecausing mutations and glycosphingolipid storage to disease manifestations, remain to be fully delineated. Several therapeutic approaches have been attempted in patients, including enzymatic augmentation, bone marrow transplantation, enzyme enhancement, and substrate reduction therapy. Hitherto, none of these stratagems has materially altered the course of the disease. Authentic animal models of GM2 gangliodidosis have facilitated in-depth evaluation of innovative applications such as gene transfer, which in contrast to other interventions, shows great promise. This review outlines current knowledge pertaining the pathobiology as well as potential innovative treatments for the GM2 gangliosidoses.

Mutation Frequency of Three Neurodegenerative Lysosomal Storage Diseases: From Screening to Treatment?

BACKGROUND

The ascertainment of mutation frequencies in the general population may have impact on the population's wellbeing and respective healthcare services. Furthermore, it may help define which approaches will be more effective for certain patients based on the genetic cause of disease.

AIM OF THE STUDY

Determine the frequency of three mutations, known to be a major cause of three distinct Lysosomal Storage Diseases (LSDs).

METHODS

The following pre-requisites were met: each mutation accounted for over 55% of the disease alleles among previously reported unrelated patients, all three diseases were among the most prevalent LSDs in the population under study, they all involved devastating deterioration of the nervous system, lacked curative treatment and may be fatal in childhood or adolescence. The anonymous samples used in this study were representative of the whole population; mutations were tested by PCR based methods, positive results were further confirmed. The diseases studied were Mucopolysaccharidosis type I (Hurler, MIM 607014), Tay Sachs disease variant B1 (TS, MIM 272800) and Metachromatic Leukodystrophy (MLD, MIM 250100); the mutations were, respectively, p.W402X, p.R178C and c.465+1G>A.

RESULTS AND CONCLUSION

Increased carrier frequencies were found for Tay Sachs disease variant B1 HEXA p.R178C mutation (1:340) and for the infantile MLD ARSA c.465+1G> A mutation (1:350) denoting higher risk for these sub-types of disease in Portugal and possibly in individuals of Iberian ancestry. Carrier screening in target populations may provide the foundations for more effective approaches to precision medicine.

Harnessing the Flow of Excitation: TRP, Voltage-Gated Na(+), and Voltage-Gated Ca(2+) Channels in Contemporary Medicine

Cellular signaling in both excitable and nonexcitable cells involves several classes of ion channels. Some of them are of minor importance, with very specialized roles in physiology, but here we concentrate on three major channel classes: TRP (transient receptor potential channels), voltage-gated sodium channels (Nav), and voltage-gated calcium channels (Cav). Here, we first propose a conceptual framework binding together all three classes of ion channels, a "flow-of-excitation model" that takes into account the inputs mediated by TRP and other similar channels, the outputs invariably provided by Cav channels, and the regenerative transmission of signals in the neural networks, for which Nav channels are responsible. We use this framework to examine the function, structure, and pharmacology of these channel classes both at cellular and also at whole-body physiological level. Building on that basis we go through the pathologies arising from the direct or indirect malfunction of the channels, utilizing ion channel defects, the channelopathies. The pharmacological interventions affecting these channels are numerous. Part of those are well-established treatments, like treatment of hypertension or some forms of epilepsy, but many other are deeply problematic due to poor drug specificity, ion channel diversity, and widespread expression of the channels in tissues other than those actually targeted.