Therapeutic advantages of combined gene/cell therapy strategies in a murine model of GM2 gangliosidosis

The GM2 gangliosidoses Tay-Sachs disease and Sandhoff disease (SD) are respectively caused by mutations in the HEXA and HEXB genes encoding the α and β subunits of β-N-acetylhexosaminidase (Hex). The consequential accumulation of ganglioside in the brain leads to severe and progressive neurological impairment. There are currently no approved therapies to counteract or reverse the effects of GM2 gangliosidosis. Adeno-associated vector (AAV)-based investigational gene therapy (GT) products have raised expectations but come with safety and efficacy issues that need to be addressed. Thus, there is an urgent need to develop novel therapies targeting the CNS and other affected tissues that are appropriately timed to ensure pervasive metabolic correction and counteract disease progression. In this report, we show that the sequential administration of lentiviral vector (LV)-mediated intracerebral (IC) GT and bone marrow transplantation (BMT) in pre-symptomatic SD mice provide a timely and long-lasting source of the Hex enzyme in the central and peripheral nervous systems and peripheral tissues, leading to global rescue of the disease phenotype. Combined therapy showed a clear therapeutic advantage compared to individual treatments in terms of lifespan extension and normalization of the neuroinflammatory and neurodegenerative phenotypes of the SD mice. These benefits correlated with a time-dependent increase in Hex activity and a remarkable reduction in GM2 storage in the brain tissues that single treatments failed to achieve. Our results highlight the complementary and synergic mode of action of LV-mediated IC GT and BMT, clarify the relative contribution of treatments to the therapeutic outcome, and inform on the realistic threshold of enzymatic activity that is required to achieve a significant therapeutic benefit, with important implications for the monitoring and interpretation of ongoing experimental therapies, and for the design of more effective treatment strategies for GM2 gangliosidosis.

Microglia-Specific Expression of HEXA and HEXB Leads to Poor Prognosis in Glioblastoma Patients

Glioblastoma multiforme (GBM) is one of the deadliest cancers in brain. There have been few treatment advances for GBM despite increasing scientific understanding of this disease. β-hexosaminidase (Hex) is an important enzyme system in human body, encoded by two genes, HEXA and HEXB, are closely related to central nervous system (CNS) diseases such as Sandhoff disease (SD) and Tay-Sachs disease (TSD). However, the expression pattern and function of HEXA and HEXB in GBM remains unclear. Here, we found that both the mRNA and protein expression levels of HEXA and HEXB were significantly upregulated in GBM patient samples. The results from single-cell RNA-sequencing (scRNA-seq) database and double immunostaining showed that HEXA and HEXB were specifically expressed in microglia in GBM patient samples. Furthermore, our in vitro experiments revealed that conditioned media from HEXA and HEXB knockdown-microglia cells could inhibit the proliferation and migration of GBM cells. Finally, according to survival analysis based on online database, higher expression of HEXA and HEXB was associated with poor prognosis in GBM patients. In conclusion, these results suggest that microglial HEXA and HEXB play fundamental role in GBM progression, and they will be potential biomarkers for GBM.

Investigating Immune Responses to the scAAV9-HEXM Gene Therapy Treatment in Tay–Sachs Disease and Sandhoff Disease Mouse Models

GM2 gangliosidosis disorders are a group of neurodegenerative diseases that result from a functional deficiency of the enzyme β-hexosaminidase A (HexA). HexA consists of an α- and β-subunit; a deficiency in either subunit results in Tay–Sachs Disease (TSD) or Sandhoff Disease (SD), respectively. Viral vector gene transfer is viewed as a potential method of treating these diseases. A recently constructed isoenzyme to HexA, called HexM, has the ability to effectively catabolize GM2 gangliosides in vivo. Previous gene transfer studies have revealed that the scAAV9-HEXM treatment can improve survival in the murine SD model. However, it is speculated that this treatment could elicit an immune response to the carrier capsid and “non-self”-expressed transgene. This study was designed to assess the immunocompetence of TSD and SD mice, and test the immune response to the scAAV9-HEXM gene transfer. HexM vector-treated mice developed a significant anti-HexM T cell response and antibody response. This study confirms that TSD and SD mouse models are immunocompetent, and that gene transfer expression can create an immune response in these mice. These mouse models could be utilized for investigating methods of mitigating immune responses to gene transfer-expressed “non-self” proteins, and potentially improve treatment efficacy.

Two patients from Turkey with a novel variant in the GM2A gene and review of the literature

Objectives GM2 gangliosidosis is a rare form of inborn errors of metabolism including Tay-Sachs disease, Sandhoff disease, and GM2 activator deficiency. GM2 activator protein deficiency is an ultra-rare form of GM2 gangliosidosis. To date, 16 cases of GM2 activator protein deficiency have been reported in the literature, and among them, 11 cases were the infantile form of the disease. Here we report the first two patients from Turkey with the infantile form of the disease with a novel likely pathogenic variant. Case presentation A boy of eight months old presented to the metabolic department with very mild neurological deterioration, although he had achieved early developmental milestones at the appropriate time. The parents also had a daughter who had lost skills progressively before one year of age. The boy was evaluated and bilateral cherry-red spots were found with no abnormality in either metabolic screening including β-hexosaminidase or cranial magnetic resonance imaging. A novel homozygous likely pathogenic variant in GM2A was detected in a next-generation sequence panel revealing GM2 activator protein deficiency. His sister was investigated after he was diagnosed with GM2 activator deficiency and it was found that she had the same variant as her brother. Conclusions This case report emphasizes that in the event of normal β-hexosaminidase activity, GM2 activator protein deficiency could be underdiagnosed, and further molecular analysis should be performed. To the best of our knowledge, this boy is one of the youngest patient diagnosed with very mild symptoms. With this novel pathogenic variant, these patients have expanded the mutation spectrum of GM2 activator protein deficiency.

Effect of Yuzu (Citrus junos) Seed Limonoids and Spermine on Intestinal Microbiota and Hypothalamic Tissue in the Sandhoff Disease Mouse Model

The effect of limonoids and spermine (Spm) extracted from yuzu (Citrus junos) seeds on the gut and the brain in a mouse model with Sandhoff disease (SD) was investigated. Wild-type and SD mice were fed a normal diet, or a diet supplemented with limonoid, Spm, or limonoid + Spm for 14–18 weeks, and then 16S rRNA gene amplicon sequencing with extracted DNA from their feces was executed. For SD control mice, intestinal microbiota was mostly composed of Lactobacillus and linked to dysbiosis. For SD and wild-type mice fed with limonoids + Spm or limonoids alone, intestinal microbiota was rich in mucin-degrading bacteria, including Bacteroidetes, Verrucomicrobia, and Firmicutes, and displayed a higher production of short-chain fatty acids and immunoglobulin A. Additionally, SD mice fed with limonoids + Spm or limonoids alone had less inflammation in hypothalamic tissues and displayed a greater number of neurons. Administration of limonoids and/or Spm improved the proportions of beneficial intestinal microbiota to host health and reduced neuronal degeneration in SD mice. Yuzu seed limonoids and Spermine may help to maintain the homeostasis of intestinal microbiota and hypothalamic tissue in the SD mouse model.

Genetic testing of leukodystrophies unraveling extensive heterogeneity in a large cohort and report of five common diseases and 38 novel variants

This study evaluates the genetic spectrum of leukodystrophies and leukoencephalopathies in Iran. 152 children, aged from 1 day to 15 years, were genetically tested for leukodystrophies and leukoencephalopathies based on clinical and neuroradiological findings from 2016 to 2019. Patients with a suggestive specific leukodystrophy, e. g. metachromatic leukodystrophy, Canavan disease, Tay-Sachs disease were tested for mutations in single genes (108; 71%) while patients with less suggestive findings were evaluated by NGS. 108 of 152(71%) had MRI patterns and clinical findings suggestive of a known leukodystrophy. In total, 114(75%) affected individuals had (likely) pathogenic variants which included 38 novel variants. 35 different types of leukodystrophies and genetic leukoencephalopathies were identified. The more common identified disorders included metachromatic leukodystrophy (19 of 152; 13%), Canavan disease (12; 8%), Tay-Sachs disease (11; 7%), megalencephalic leukodystrophy with subcortical cysts (7; 5%), X-linked adrenoleukodystrophy (8; 5%), Pelizaeus–Merzbacher-like disease type 1 (8; 5%), Sandhoff disease (6; 4%), Krabbe disease (5; 3%), and vanishing white matter disease (4; 3%). Whole exome sequencing (WES) revealed 90% leukodystrophies and genetic leukoencephalopathies. The total diagnosis rate was 75%. This unique study presents a national genetic data of leukodystrophies; it may provide clues to the genetic pool of neighboring countries. Patients with clinical and neuroradiological evidence of a genetic leukoencephalopathy should undergo a genetic analysis to reach a definitive diagnosis. This will allow a diagnosis at earlier stages of the disease, reduce the burden of uncertainty and costs, and will provide the basis for genetic counseling and family planning.