Magnetic resonance imaging and spectroscopy in late-onset GM2-gangliosidosis.

OBJECTIVE: Our study aimed to quantify structural changes in relation to metabolic abnormalities in the cerebellum, thalamus, and parietal cortex of patients with late-onset GM2-gangliosidosis (LOGG), which encompasses late-onset Tay-Sachs disease (LOTS) and Sandhoff disease (LOSD). METHODS: We enrolled 10 patients with LOGG (7 LOTS, 3 LOSD) who underwent a neurological assessment battery and 7 age-matched controls. Structural MRI and MRS were performed on a 3 T scanner. Structural volumes were obtained from FreeSurfer and normalized by total intracranial volume. Quantified metabolites included N-acetylaspartate (NAA), choline (Cho), myo-inositol (mI), creatine (Cr), and combined glutamate-glutamine (Glx). Metabolic concentrations were corrected for partial volume effects. RESULTS: Structural analyses revealed significant cerebellar atrophy in the LOGG cohort, which was primarily driven by LOTS patients. NAA was lower and mI higher in LOGG, but this was also significantly driven by the LOTS patients. Clinical ataxia deficits (via the Scale for the Assessment and Rating of Ataxia) were associated with neuronal injury (via NAA), neuroinflammation (via mI), and volumetric atrophy in the cerebellum. INTERPRETATION: The decrease of NAA in the cerebellum suggests that, in addition to cerebellar atrophy, there is ongoing impaired neuronal function and/or loss, while an increase in mI indicates possible neuroinflammation in LOGG (more so within the LOTS subvariant). Quantifying cerebellar atrophy in relation to neurometabolic differences in LOGG may lead to improvements in assessing disease severity, progression, and pharmacological efficacy. Lastly, additional neuroimaging studies in LOGG are required to contrast LOTS and LOSD more accurately.

Abnormal epiphyseal development in a feline model of Sandhoff disease.

Sandhoff disease (SD) is caused by decreased function of the enzyme ß-N-acetylhexosaminidase, resulting in accumulation of GM2 ganglioside in tissues. Neural tissue is primarily affected and individuals with the infantile form of the disease generally do not survive beyond 4 years of age. Current treatments address neurometabolic deficits to improve lifespan, however, this extended lifespan allows clinical disease to become manifest in other tissues, including the musculoskeletal system. The impact of SD on bone and joint tissues has yet to be fully determined. In a feline model of infantile SD, animals were treated by intracranial injection of adeno-associated virus vectors to supply the central nervous system with corrective levels of hexosaminidase, resulting in a twofold to threefold increase in lifespan. As treated animals aged, signs of musculoskeletal disease were identified. The present study characterized bone and joint lesions from affected cats using micro-computed tomography and histology. All affected cats had similar lesions, whether or not they were treated. SD cats displayed a significant reduction in metaphyseal trabecular bone and markedly abnormal size and shape of epiphyses. Abnormalities increased in severity with age and appear to be due to alteration in the function of chondrocytes within epiphyseal cartilage, particularly the articular-epiphyseal complex. Older cats developed secondary osteoarthritic changes. The changes identified are similar to those seen in humans with mucopolysaccharidoses. Statement of clinical significance: the lesions identified will have significant implications on the quality of life of individuals whose lifespans are extended due to treatments for the primary neurological effects of SD.

Natural History of Adult Patients with GM2 Gangliosidosis.

OBJECTIVE: GM2 gangliosidoses are lysosomal diseases due to biallelic mutations in the HEXA (Tay-Sachs disease [TS]) or HEXB (Sandhoff disease [SD]) genes, with subsequent low hexosaminidase(s) activity. Most patients have childhood onset, but some experience the first symptoms during adolescence/adulthood. This study aims to clarify the natural history of adult patients with GM2 gangliosidosis. METHODS: We retrospectively described 12 patients from a French cohort and 45 patients from the literature. RESULTS: We observed 4 typical presentations: (1) lower motoneuron disorder responsible for proximal lower limb weakness that subsequently expanded to the upper limbs, (2) cerebellar ataxia, (3) psychosis and/or severe mood disorder (only in the TS patients), and (4) a complex phenotype mixing the above 3 manifestations. The psoas was the first and most affected muscle in the lower limbs, whereas the triceps and interosseous were predominantly involved in the upper limbs. A longitudinal study of compound motor action potentials showed a progressive decrease in all nerves, with different kinetics. Sensory potentials were sometimes abnormally low, mainly in the SD patients. The main brain magnetic resonance imaging feature was cerebellar atrophy, even in patients without cerebellar symptoms. The prognosis was mainly related to gait disorder, as we showed that beyond 20 years of disease evolution, half of the patients were wheelchair users. INTERPRETATION: Improved knowledge of GM2 gangliosidosis in adults will help clinicians achieve correct diagnoses and better inform patients on the evolution and prognosis. It may also contribute to defining proper outcome measures when testing emerging therapies. ANN NEUROL 2020;87:609-617.

THE LYSOSOMAL STORAGE DISEASE GM2 GANGLIOSIDOSIS IN CAPTIVE BANDED MONGOOSE SIBLINGS ( MUNGOS MUNGO).

This study reports the occurrence of the lysosomal storage disease GM2 gangliosidosis (Sandhoff disease) in two 11-mo-old captive-bred, male and female mongoose siblings ( Mungos mungo). The clinical signs and the pathological findings reported here were similar to those reported in other mammalian species. Light microscopy revealed an accumulation of stored material in neurons and macrophages accompanied by a significant neuronal degeneration (swelling of neuronal soma, loss of Nissl substance, and neuronal loss) and gliosis. Electron microscopy of brain tissue identified the stored material as membrane-bound multilamellar bodies. An almost complete lack of total hexosaminidase activity in serum suggested a defect in the HEXB gene (Sandhoff disease in humans). High-performance thin-layer chromatography and mass spectrometry confirmed the accumulation of GM2 ganglioside in brain and kidney tissue, and the lectin staining pattern of the brain tissue further corroborated the diagnosis of a Sandhoff-type lysosomal storage disease.

FcRγ-dependent immune activation initiates astrogliosis during the asymptomatic phase of Sandhoff disease model mice.

Sandhoff disease (SD) is caused by the loss of ß-hexosaminidase (Hex) enzymatic activity in lysosomes resulting from Hexb mutations. In SD patients, the Hex substrate GM2 ganglioside accumulates abnormally in neuronal cells, resulting in neuronal loss, microglial activation, and astrogliosis. Hexb-/- mice, which manifest a phenotype similar to SD, serve as animal models for examining the pathophysiology of SD. Hexb-/- mice reach ~8 weeks without obvious neurological defects; however, trembling begins at 12 weeks and is accompanied by startle reactions and increased limb tone. These symptoms gradually become severe by 16-18 weeks. Immune reactions caused by autoantibodies have been recently associated with the pathology of SD. The inhibition of immune activation may represent a novel therapeutic target for SD. Herein, SD mice (Hexb-/-) were crossed to mice lacking an activating immune receptor (FcRγ-/-) to elucidate the potential relationship between immune responses activated through SD autoantibodies and astrogliosis. Microglial activation and astrogliosis were observed in cortices of Hexb-/- mice during the asymptomatic phase, and were inhibited in Hexb-/- FcRγ-/- mice. Moreover, early astrogliosis and impaired motor coordination in Hexb-/- mice could be ameliorated by immunosuppressants, such as FTY720. Our findings demonstrate the importance of early treatment and the therapeutic effectiveness of immunosuppression in SD.

Early cardiac involvement in an infantile Sandhoff disease case with novel mutations.

INTRODUCTION: Hepatosplenomegaly is often present in infantile Sanshoff disease. However, cardiac involvement is extremely uncommon. CASE REPORT: We describe a 14-month-old female baby who exhibited mitral regurgitation and cardiomegaly at the age of 2months, dilation of the left atrium and left ventricle at age of 6months, followed by regression of developmental milestones after an episode of minor infection at age of 14months. Brain magnetic resonance imaging revealed signal changes over the bilateral thalami, bilateral cerebral white matter and left putamen. An examination of the fundus showed presence of cherry-red spots in both macular areas. The lysosomal enzymatic activities showed a marked reduction of ß-hexosaminidase B (HEXB) activity. Two novel mutations of HEXB gene were identified. One of the mutations was a c.1538 T>C mutation, which predicted a p.L513P amino acid substitution of leucine to proline; the other was a c.299+5 G>A mutation, which was a splice site mutation. CONCLUSION: Cardiac involvement might occur prior to neurological symptoms in infantile Sandhoff disease, and it should be included in the differential diagnoses of metabolic cardiomyopathies in the infantile stage.

Circadian profiling in two mouse models of lysosomal storage disorders; Niemann Pick type-C and Sandhoff disease.

Sleep and circadian rhythm disruption is frequently associated with neurodegenerative disease, yet it is unclear how the specific pathology in these disorders leads to abnormal rest/activity profiles. To investigate whether the pathological features of lysosomal storage disorders (LSDs) influence the core molecular clock or the circadian behavioural abnormalities reported in some patients, we examined mouse models of Niemann-Pick Type-C (Npc1 mutant, Npc1(nih)) and Sandhoff (Hexb knockout, Hexb(-/-)) disease using wheel-running activity measurement, neuropathology and clock gene expression analysis. Both mutants exhibited regular, entrained rest/activity patterns under light:dark (LD) conditions despite the onset of their respective neurodegenerative phenotypes. A slightly shortened free-running period and changes in Per1 gene expression were observed in Hexb(-/-) mice under constant dark conditions (DD); however, no overt neuropathology was detected in the suprachiasmatic nucleus (SCN). Conversely, despite extensive cholesterol accumulation in the SCN of Npc1(nih) mutants, no circadian disruption was observed under constant conditions. Our results indicate the accumulation of specific metabolites in LSDs may differentially contribute to circadian deregulation at the molecular and behavioural level.

Mucopolysaccharidosis-like phenotype in feline Sandhoff disease and partial correction after AAV gene therapy.

Sandhoff disease (SD) is a fatal neurodegenerative disease caused by a mutation in the enzyme ß-N-acetylhexosaminidase. Children with infantile onset SD develop seizures, loss of motor tone and swallowing problems, eventually reaching a vegetative state with death typically by 4years of age. Other symptoms include vertebral gibbus and cardiac abnormalities strikingly similar to those of the mucopolysaccharidoses. Isolated fibroblasts from SD patients have impaired catabolism of glycosaminoglycans (GAGs). To evaluate mucopolysaccharidosis-like features of the feline SD model, we utilized radiography, MRI, echocardiography, histopathology and GAG quantification of both central nervous system and peripheral tissues/fluids. The feline SD model exhibits cardiac valvular and structural abnormalities, skeletal changes and spinal cord compression that are consistent with accumulation of GAGs, but are much less prominent than the severe neurologic disease that defines the humane endpoint (4.5±0.5months). Sixteen weeks after intracranial AAV gene therapy, GAG storage was cleared in the SD cat cerebral cortex and liver, but not in the heart, lung, skeletal muscle, kidney, spleen, pancreas, small intestine, skin, or urine. GAG storage worsens with time and therefore may become a significant source of pathology in humans whose lives are substantially lengthened by gene therapy or other novel treatments for the primary, neurologic disease.

AAV-mediated gene delivery in a feline model of Sandhoff disease corrects lysosomal storage in the central nervous system.

Sandhoff disease (SD) is an autosomal recessive neurodegenerative disease caused by a mutation in the gene for the ß-subunit of ß-N-acetylhexosaminidase (Hex), resulting in the inability to catabolize ganglioside GM2 within the lysosomes. SD presents with an accumulation of GM2 and its asialo derivative GA2, primarily in the central nervous system. Myelin-enriched glycolipids, cerebrosides and sulfatides, are also decreased in SD corresponding with dysmyelination. At present, no treatment exists for SD. Previous studies have shown the therapeutic benefit of adeno-associated virus (AAV) vector-mediated gene therapy in the treatment of SD in murine and feline models. In this study, we treated presymptomatic SD cats with AAVrh8 vectors expressing feline Hex in the thalamus combined with intracerebroventricular (Thal/ICV) injections. Treated animals showed clearly improved neurologic function and quality of life, manifested in part by prevention or attenuation of whole-body tremors characteristic of untreated animals. Hex activity was significantly elevated, whereas storage of GM2 and GA2 was significantly decreased in tissue samples taken from the cortex, cerebellum, thalamus, and cervical spinal cord. Treatment also increased levels of myelin-enriched cerebrosides and sulfatides in the cortex and thalamus. This study demonstrates the therapeutic potential of AAV for feline SD and suggests a similar potential for human SD patients.

Characterization of the mutant ß-subunit of ß-hexosaminidase for dimer formation responsible for the adult form of Sandhoff disease with the motor neuron disease phenotype.

The adult form of Sandhoff disease with the motor neuron disease phenotype is a rare neurodegenerative disorder caused by mutations in HEXB encoding the ß-subunit of ß-hexosaminidase, yet the properties of mutant ß-subunits of the disease have not been fully determined. We identified a novel mutation (H235Y) in the ß-sheet of the (ß/α)8-barrel domain, in addition to the previously reported P417L mutation that causes aberrant splicing, in a Japanese patient with the motor neuron disease phenotype. Enzyme assays, gel filtration studies and immunoprecipitation studies with HEK293 cells transiently expressing mutant ß-subunits demonstrated that the H235Y mutation abolished both α-ß and ß-ß dimer formation without increasing ß-hexosaminidase activity, whereas other reported mutant ß-subunits (Y456S, P504S or R533H) associated with the motor neuron disease phenotype formed dimers. Structural analysis suggested that the H235Y mutation in the ß-sheet of the (ß/α)8-barrel domain changed the conformation of the ß-subunit by causing a clash with the E288 side chain. In summary, H235Y is the first mutation in the ß-sheet of the (ß/α)8-barrel domain of the ß-subunit that abolishes α-ß and ß-ß dimer formation; the presented patient is the second patient to exhibit the motor neuron disease phenotype with P417L and a non-functional allele of HEXB.

Infantile Sandhoff's disease with peripheral neuropathy.

Sandhoff's disease is a rare autosomal-recessive disorder of sphingolipid metabolism that results from a deficiency of lysosomal enzyme beta-hexosaminidase A and B. The resultant accumulation of GM2 gangliosides within both grey matter and the myelin sheath of white matter results in essential, severe neurodegeneration. We describe a 14-month-old boy with seizures and severe neurodegeneration. His diagnosis was confirmed by neuroimaging and enzyme assay. In addition to the classic features of Sandhoff's disease, the child's clinical features were suggestive of neuropathy as supported by nerve conduction studies indicating that the bilateral median, ulnar, and common peroneal nerves were affected. Peripheral nervous system involvement is not consistently observed in infantile Sandhoff's disease, prompting us to report this case.

Substrate deprivation therapy in juvenile Sandhoff disease.

Substrate deprivation therapy has been successfully applied in a number of lysosomal storage diseases, such as Gaucher disease. So far only limited experience is available in Sandhoff disease. We initiated substrate deprivation therapy in one male patient, who initially presented at the age of 3.5 years with epilepsy and regression in motor skills and speech development. Juvenile Sandhoff disease was diagnosed on the basis of a decreased hexosaminidase activity in leukocytes and a homozygous HEXB gene mutation. After the epilepsy was controlled, the clinical course remained stable for years, defined by a mild proximal myopathy and stable mental retardation. At 14 years of age the patient experienced a second episode with progressively worsening general condition with diminishing muscle power and progressive ataxia. Treatment was started with the N-alkylated imino sugar miglustat, inhibiting the glucosylceramide synthase, an essential enzyme for the synthesis of glycosphingolipids. Diarrhoea was treated with lactose restriction. We performed detailed biochemical investigations, motor and mental development analysis, brain imaging, organ function studies and quality of life score prior to and at different time points after start of the treatment. Two years after the initiation of therapy the patient has a stable neurological picture without further regression in his motor development, ataxia or intelligence. There is a subjective improvement in the fine motor skills and walking up the stairs but no change in the quality of life score. Under treatment with miglustat the clinical course in our patient with Sandhoff disease did not further deteriorate.

Molecular and functional analysis of the HEXB gene in Italian patients affected with Sandhoff disease: identification of six novel alleles.

We report the molecular characterization of 12 unrelated Italian patients affected with Sandhoff disease (SD), a recessively inherited disorder caused by mutations in HEXB gene. We identified 11 different mutations of which six are novel: one large deletion of 2,406 nt, (c.299+1471_408del2406), one frameshift mutation c.965delT (p.I322fsX32), one nonsense c.1372C>T (p.Q458X), and three splicing mutations (c.299G>T, c.300-2A>G and c.512-1G>T). One allele was only characterized at the messenger RNA (mRNA) level (r = 1170_1242del). Real-time polymerase chain reaction analysis of the HEXB mRNA from fibroblasts derived from patients carrying the novel point mutations showed that the presence of the premature termination codon in the transcript bearing the mutation c.965delT triggers the nonsense-mediated decay (NMD) pathway, which results in the degradation of the aberrant mRNA. The presence of the c.299G>T mutation leads to the degradation of the mutated mRNA by a mechanism other than NMD, while mutations c.300-2A>G and c.512-1G>T cause the expression of aberrant transcripts. In our group, the most frequent mutation was c.850C>T (p.R284X) representing 29% of the alleles. Haplotype analysis suggested that this mutation did not originate from a single genetic event. Interestingly, the common 16-kb deletion mutation was absent. This work provides valuable information regarding the molecular genetics of SD in Italy and provides new insights into the molecular basis of the disease.

Early deficits in motor coordination and cognitive dysfunction in a mouse model of the neurodegenerative lysosomal storage disorder, Sandhoff disease.

Mouse models of lysosomal storage diseases, including Sandhoff disease, are frequently employed to test therapies directed at the central nervous system. We backbred such mice and conducted a behavioral test battery which included sensorimotor and cognitive assessments. This is the first report of short-term memory deficits in a murine model of Sandhoff disease. We also document early onset of motor deficits using the balance beam test.

N-butyldeoxygalactonojirimycin reduces brain ganglioside and GM2 content in neonatal Sandhoff disease mice.

Sandhoff disease involves the CNS accumulation of ganglioside GM2 and asialo-GM2 (GA2) due to inherited defects in the beta-subunit gene of beta-hexosaminidase A and B (Hexb gene). Accumulation of these glycosphingolipids (GSLs) produces progressive neurodegeneration, ultimately leading to death. Substrate reduction therapy (SRT) aims to decrease the rate of glycosphingolipid (GSL) biosynthesis to compensate for the impaired rate of catabolism. The imino sugar, N-butyldeoxygalactonojirimycin (NB-DGJ) inhibits the first committed step in GSL biosynthesis. NB-DGJ treatment, administered from postnatal day 2 (p-2) to p-5 (600 mg/kg/day)), significantly reduced total brain ganglioside and GM2 content in the Sandhoff disease (Hexb(-/-)) mice, but did not reduce the content of GA2. We also found that NB-DGJ treatment caused a slight, but significant elevation in brain sialidase activity. The drug had no adverse effects on viability, body weight, brain weight, or brain water content in the mice. No significant alterations in neutral lipids or acidic phospholipids were observed in the NB-DGJ-treated Hexb(-/-) mice. Our results show that NB-DGJ is effective in reducing total brain ganglioside and GM2 content at early neonatal ages.

Neuronal and glial accumulation of alpha- and beta-synucleins in human lipidoses.

A number of the lysosomal storage diseases that have now been characterized are associated with intra-lysosomal accumulation of lipids, caused by defective lysosomal enzymes. We have previously reported neuronal accumulation of both alpha- and beta-synucleins in brain tissue of a GM2 gangliosidosis mouse model. Although alpha-synuclein has been implicated in several neurodegenerative disorders including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy, its functions remain largely unclear. In our present study, we have examined a cohort of human lipidosis cases, including Sandhoff disease, Tay-Sachs disease, metachromatic leukodystrophy, beta-galactosialidosis and adrenoleukodystrophy, for the expression of alpha- and beta-synucleins and the associated lipid storage levels. The accumulation of alpha-synuclein was found in brain tissue in not only cases of lysosomal storage diseases, but also in instances of adrenoleukodystrophy, which is a peroxisomal disease. alpha-synuclein was detected in both neurons and glial cells of patients with these two disorders, although its distribution was found to be disease-dependent. In addition, alpha-synuclein-positive neurons were also found to be NeuN-positive, whereas NeuN-negative neurons did not show any accumulation of this protein. By comparison, the accumulation of beta-synuclein was detectable only in the pons of Sandhoff disease cases. This differential accumulation of alpha- and beta-synucleins in human lipidoses may be related to functional differences between these two proteins. In addition, the accumulation of alpha-synuclein may also be a condition that is common to lysosomal storage diseases and adrenoleukodystrophies that show an enhanced expression of this protein upon the elevation of stored lipids.

Peripheral nervous system manifestations in a Sandhoff disease mouse model: nerve conduction, myelin structure, lipid analysis.

BACKGROUND: Sandhoff disease is an inherited lysosomal storage disease caused by a mutation in the gene for the beta-subunit (Hexb gene) of beta-hexosaminidase A (alphabeta) and B (beta beta). The beta-subunit together with the GM2 activator protein catabolize ganglioside GM2. This enzyme deficiency results in GM2 accumulation primarily in the central nervous system. To investigate how abnormal GM2 catabolism affects the peripheral nervous system in a mouse model of Sandhoff disease (Hexb-/-), we examined the electrophysiology of dissected sciatic nerves, structure of central and peripheral myelin, and lipid composition of the peripheral nervous system. RESULTS: We detected no significant difference in signal impulse conduction velocity or any consistent change in the frequency-dependent conduction slowing and failure between freshly dissected sciatic nerves from the Hexb+/- and Hexb-/- mice. The low-angle x-ray diffraction patterns from freshly dissected sciatic and optic nerves of Hexb+/- and Hexb-/- mice showed normal myelin periods; however, Hexb-/- mice displayed a approximately 10% decrease in the relative amount of compact optic nerve myelin, which is consistent with the previously established reduction in myelin-enriched lipids (cerebrosides and sulfatides) in brains of Hexb-/- mice. Finally, analysis of lipid composition revealed that GM2 content was present in the sciatic nerve of the Hexb-/- mice (undetectable in Hexb+/-). CONCLUSION: Our findings demonstrate the absence of significant functional, structural, or compositional abnormalities in the peripheral nervous system of the murine model for Sandhoff disease, but do show the potential value of integrating multiple techniques to evaluate myelin structure and function in nervous system disorders.