Clinical presentation and outcome in infantile Sandhoff disease: a case series of 25 patients from Iranian neurometabolic bioregistry with five novel mutations

Gene Therapy of Sphingolipid Metabolic Disorders

Sphingolipidoses are defined as a group of rare hereditary diseases resulting from mutations in the genes encoding lysosomal enzymes. This group of lysosomal storage diseases includes more than 10 genetic disorders, including GM1-gangliosidosis, Tay-Sachs disease, Sandhoff disease, the AB variant of GM2-gangliosidosis, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease, Farber disease, etc. Enzyme deficiency results in accumulation of sphingolipids in various cell types, and the nervous system is also usually affected. There are currently no known effective methods for the treatment of sphingolipidoses; however, gene therapy seems to be a promising therapeutic variant for this group of diseases. In this review, we discuss gene therapy approaches for sphingolipidoses that are currently being investigated in clinical trials, among which adeno-associated viral vector-based approaches and transplantation of hematopoietic stem cells genetically modified with lentiviral vectors seem to be the most effective.

Infantile Sandhoff disease with ventricular septal defect: a case report

Background

Infantile Sandhoff disease is a rare inherited disorder that progressively destroys nerve cells in the brain and spinal cord, and is classified under lysosomal storage disorder. It is an autosomal recessive disorder of sphingolipid metabolism that results from deficiency of the lysosomal enzymes β-hexosaminidase A and B. The resultant accumulation of GM2 ganglioside within both gray matter nuclei and myelin sheaths of the white matter results in eventual severe neuronal dysfunction and neurodegeneration.

Case presentation

We evaluated a 3.5-year-old Comorian girl from the United Arab Emirates who presented with repeated chest infections with heart failure due to ventricular septal defect, neuroregression, recurrent seizures, and cherry-red spots over macula. She had macrocephaly, axial hypotonia, hyperacusis, and gastroesophageal reflux. Organomegaly was absent. Brain magnetic resonance imaging, metabolic tests, and genetic mutations confirmed the diagnosis. Despite multidisciplinary therapy, the girl succumbed to her illness.

Conclusion

Though early cardiac involvement can be seen with novel mutations, it is extremely rare to find association of ventricular septal defect in infantile Sandhoff disease. Neuroregression typically starts around 6 months of age. We report this case because of the unusual association of a congenital heart disease with underlying infantile Sandhoff disease and symptomatic heart failure in the first month of life with eventual fatal outcome.

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.

Delineating the neuropathology of lysosomal storage diseases using patient-derived induced pluripotent stem cells

Lysosomal storage diseases (LSD) are inherited metabolic diseases caused due to deficiency of lysosomal enzymes, essential for the normal development of the brain and other organs. Approximately two-thirds of the patients suffering from LSD exhibit neurological deficits and impose an escalating challenge to the medical and scientific field. The advent of iPSC technology has aided researchers in efficiently generating functional neuronal and non-neuronal cells through directed differentiation protocols, as well as in decoding the cellular, subcellular and molecular defects associated with LSDs using two-dimensional cultures and cerebral organoid models. This review highlights the information assembled from patient-derived iPSCs on neurodevelopmental and neuropathological defects identified in LSDs. Multiple studies have identified neural progenitor cell migration and differentiation defects, substrate accumulation, axon growth and myelination defects, impaired calcium homeostasis and altered electrophysiological properties, using patient-derived iPSCs. In addition, these studies have also uncovered defective lysosomes, mitochondria, endoplasmic reticulum, Golgi complex, autophagy and vesicle trafficking and signaling pathways, oxidative stress, neuroinflammation, blood brain barrier dysfunction, neurodegeneration, gliosis, altered transcriptomes in LSDs. The review also discusses the therapeutic applications such as drug discovery, repurposing of drugs, synergistic effects of drugs, targeted molecular therapies, gene therapy, and transplantation applications of mutation corrected lines identified using patient-derived iPSCs for different LSDs.

Clinical Presentation and Genetic Heterogeneity Including Two Novel Variants in Sri Lankan Patients With Infantile Sandhoff Disease

Infantile Sandhoff Disease ( iSD) is a subtype of GM2 gangliosidosis, which is never been reported in Sri Lanka. Data of eight children, who were diagnosed with iSD during the period of 2017 to 2021, were analyzed retrospectively. The aim of this study was to analyze genotypic and phenotypic variations of native iSDs. Café-au-lait spots, mitral regurgitation and atrial septal defect were found in our patients but never reported in the literature. We found c.1417 + 5G>A and c.1303_1304insCT p.(Arg435Thrfs*10) novel variants of HEXB gene among the nine different gene mutations that were identified. The commonest HEXB gene variant identified in India was c.850 C4T (p.R284X) but was not noticed among Sri Lankan patients. In contrast to other studies, all our patients died within the age of two years. This is the first Sri Lankan study that expands the clinical and molecular basis of iSD with its novel findings.

Sphingolipid lysosomal storage diseases: from bench to bedside

Johann Ludwig Wilhelm Thudicum described sphingolipids (SLs) in the late nineteenth century, but it was only in the past fifty years that SL research surged in importance and applicability. Currently, sphingolipids and their metabolism are hotly debated topics in various biochemical fields. Similar to other macromolecular reactions, SL metabolism has important implications in health and disease in most cells. A plethora of SL-related genetic ailments has been described. Defects in SL catabolism can cause the accumulation of SLs, leading to many types of lysosomal storage diseases (LSDs) collectively called sphingolipidoses. These diseases mainly impact the neuronal and immune systems, but other systems can be affected as well. This review aims to present a comprehensive, up-to-date picture of the rapidly growing field of sphingolipid LSDs, their etiology, pathology, and potential therapeutic strategies. We first describe LSDs biochemically and briefly discuss their catabolism, followed by general aspects of the major diseases such as Gaucher, Krabbe, Fabry, and Farber among others. We conclude with an overview of the available and potential future therapies for many of the diseases. We strive to present the most important and recent findings from basic research and clinical applications, and to provide a valuable source for understanding these disorders.

A case of adult onset Sandhoff disease that mimics Brown-Vialetto-Van Laere syndrome

Sandhoff disease is a rare fatal infantile neurologic disorder. Adult onset Sandhoff is even rarer. Variability of clinical features in adult onset Sandhoff patients and overlaps between these and features of other neurologic diseases have sometimes led to mis-diagnosis. We describe an adult onset Sandhoff disease affected individual whose clinical presentation were also consistent with the Brown-Vialetto-Van Laere syndrome (BVVL) diagnosis. Screening of BVVL-causing genes, SLC52A3 and SLC52A2, did not identify candidate disease-causing mutations, but exome sequencing revealed compound heterozygous mutations in the known Sandhoff disease-causing gene, HEXB. Decreased blood hexosaminidase activity and evidence of cerebellar atrophy confirmed Sandhoff disease diagnosis. To the best of our knowledge, this is the first report of a Sandhoff disease case that mimics BVVL and that presents with prominent cranial nerve involvement. For differential diagnosis, measurement of hexosaminidase activity and MRI should quickly be performed. Genetic analysis can be done for confirmation of diagnosis.

Building the brain from scratch: Engineering region-specific brain organoids from human stem cells to study neural development and disease

Human brain development is an intricate process that involves precisely timed coordination of cell proliferation, fate specification, neuronal differentiation, migration, and integration of diverse cell types. Understanding of these fundamental processes, however, has been largely constrained by limited access to fetal brain tissue and the inability to prospectively study neurodevelopment in humans at the molecular, cellular and system levels. Although non-human model organisms have provided important insights into mechanisms underlying brain development, these systems do not fully recapitulate many human-specific features that often relate to disease. To address these challenges, human brain organoids, self-assembled three-dimensional neural aggregates, have been engineered from human pluripotent stem cells to model the architecture and cellular diversity of the developing human brain. Recent advancements in neural induction and regional patterning using small molecules and growth factors have yielded protocols for generating brain organoids that recapitulate the structure and neuronal composition of distinct brain regions. Here, we first provide an overview of early mammalian brain development with an emphasis on molecular cues that guide region specification. We then focus on recent efforts in generating human brain organoids that model the development of specific brain regions and highlight endeavors to enhance the cellular complexity to better mimic the in vivo developing human brain. We also provide examples of how organoid models have enhanced our understanding of human neurological diseases and conclude by discussing limitations of brain organoids with our perspectives on future advancements to maximize their potential.

GM2 Gangliosidoses: Clinical Features, Pathophysiological Aspects, and Current Therapies

GM2 gangliosidoses are a group of pathologies characterized by GM2 ganglioside accumulation into the lysosome due to mutations on the genes encoding for the β-hexosaminidases subunits or the GM2 activator protein. Three GM2 gangliosidoses have been described: Tay-Sachs disease, Sandhoff disease, and the AB variant. Central nervous system dysfunction is the main characteristic of GM2 gangliosidoses patients that include neurodevelopment alterations, neuroinflammation, and neuronal apoptosis. Currently, there is not approved therapy for GM2 gangliosidoses, but different therapeutic strategies have been studied including hematopoietic stem cell transplantation, enzyme replacement therapy, substrate reduction therapy, pharmacological chaperones, and gene therapy. The blood-brain barrier represents a challenge for the development of therapeutic agents for these disorders. In this sense, alternative routes of administration (e.g., intrathecal or intracerebroventricular) have been evaluated, as well as the design of fusion peptides that allow the protein transport from the brain capillaries to the central nervous system. In this review, we outline the current knowledge about clinical and physiopathological findings of GM2 gangliosidoses, as well as the ongoing proposals to overcome some limitations of the traditional alternatives by using novel strategies such as molecular Trojan horses or advanced tools of genome editing.

Clinical and Molecular Characteristics of Two Chinese Children with Infantile Sandhoff Disease and Review of the Literature

Infantile Sandhoff disease is an autosomal recessive inherited disease primarily characterized by cherry red spots in the retina, muscle weakness, seizure, truncal hypotonia, hyperacusis, developmental delay and regression. The pathogenic genetic defects of the HEXB gene, which encodes the β subunit of the hexosaminidase A (ɑβ) and hexosaminidase B (ββ) enzymes, cause deficiency of both the Hex A and Hex B enzymes, resulting in the deposition of GM2 ganglion glycerides in the lysosomes of the central nervous system and somatic cells. The aim of this study was to discover disease-causing variants of the HEXB gene in two Chinese families through the use of exome sequencing. By characterizing three novel variants by molecular genetics, bioinformatics analysis, and three-dimensional structure modeling, we showed that all these novel variants influenced the protein structure. The results broaden the variant spectrum of HEXB in different ethnic groups. Furthermore, not all patients diagnosed with infantile Sandhoff disease had characteristic cranial imaging findings, which can only be used as supplementary information for diagnosis. The results of this study may contribute to clinical management, genetic counseling, and gene-targeted treatments for Sandhoff disease.

Utility of Seizure Pattern and Related Clinical Features in the Diagnosis of Neurometabolic Disorders

OBJECTIVES

The current study aimed at identifying the role of seizure types and related clinical features in differentiation between neurometabolic disorders and other causes of seizure.

MATERIALS & METHODS

The current cross sectional study was conducted at two referral children hospitals in Tehran, Iran, from 2011 to 2018. The study population included 120 patients presenting with seizure due to neurometabolic disorders and 120 cases due to other causes. The types of seizure and related clinical findings were assessed in both groups.

RESULTS

There was a significant difference in the frequency of seizure types in the two groups. Tonic and myoclonic seizures as well as infantile spasm were observed more commonly in the patients with neurometabolic disorders, while atonic, partial and generalized tonic-clonic seizures were more common in the control group. In addition, frequency of refractory seizure, age at onset of seizure, and pattern of involvement in brain imaging were helpful for differentiation.

CONCLUSION

The pattern of seizure and related findings varied in patients with metabolic disorders, and was helpful for diagnosis. Thus, these factors can contribute to early diagnosis and treatment.

Brain Organoids as Tools for Modeling Human Neurodevelopmental Disorders

Brain organoids recapitulate in vitro the specific stages of in vivo human brain development, thus offering an innovative tool by which to model human neurodevelopmental disease. We review here how brain organoids have been used to study neurodevelopmental disease and consider their potential for both technological advancement and therapeutic development.