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.

Infantile gangliosidoses: Mapping a timeline of clinical changes

BACKGROUND

Infantile gangliosidoses include GM1 gangliosidosis and GM2 gangliosidosis (Tay-Sachs disease, Sandhoff disease). To date, natural history studies in infantile GM2 (iGM2) have been retrospective and conducted through surveys. Compared to iGM2, there is even less natural history information available on infantile GM1 disease (iGM1). There are no approved treatments for infantile gangliosidoses. Substrate reduction therapy using miglustat has been tried, but is limited by gastrointestinal side effects. Development of effective treatments will require identification of meaningful outcomes in the setting of rapidly progressive and fatal diseases.

OBJECTIVES

This study aimed to establish a timeline of clinical changes occurring in infantile gangliosidoses, prospectively, to: 1) characterize the natural history of these diseases; 2) improve planning of clinical care; and 3) identify meaningful future treatment outcome measures.

METHODS

Patients were evaluated prospectively through ongoing clinical care.

RESULTS

Twenty-three patients were evaluated: 8 infantile GM1, 9 infantile Tay-Sachs disease, 6 infantile Sandhoff disease. Common patterns of clinical change included: hypotonia before 6months of age; severe motor skill impairment within first year of life; seizures; dysphagia and feeding-tube placement before 18months of age. Neurodevelopmental testing scores reached the floor of the testing scale by 20 to 28months of age. Vertebral beaking, kyphosis, and scoliosis were unique to patients with infantile GM1. Chest physiotherapy was associated with increased survival in iGM1 (p=0.0056). Miglustat combined with a low-carbohydrate ketogenic diet (the Syner-G regimen) in patients who received a feeding-tube was associated with increased survival in infantile GM1 (p=0.025).

CONCLUSIONS

This is the first prospective study of the natural history of infantile gangliosidoses and the very first natural history of infantile GM1. The homogeneity of the infantile gangliosidoses phenotype as demonstrated by the clinical events timeline in this study provides promising secondary outcome measure candidates. This study indicates that overall survival is a meaningful primary outcome measure for future clinical trials due to reliable timing and early occurrence of this event. Combination therapy approaches, instead of monotherapy approaches, will likely be the best way to optimize clinical outcomes. Combination therapy approaches include palliative therapies (e.g., chest physiotherapy) along with treatments that address the underlying disease pathology (e.g. miglustat or future gene therapies).

[Clinical characteristics of early juvenile GM2 gangliosidosis: a case report]

We describe the case of a 15-year-old male with early juvenile type GM2 gangliosidosis. He first manifested with progressive clumsiness in his extremities at the age of 1.5 years, followed by motor regression. Intellectual disability became evident as late as age 6 years. This discrepancy along with rapid motor deterioration after varicella infection, lack of startle response or macrocephaly, and paucity of myoclonus were thought to be characteristic of juvenile GM2 gangliosidosis. In contrast to the cerebellar atrophy as the initial finding in usual juvenile GM2 gangliosidosis, magnetic resonance imaging revealed initially cerebral, and subsequently cerebellar, progressive atrophy. Autistic behavioral problems, including phonophobia, during intellectual regression in this patient was also unusual in juvenile GM2 gangliosidosis. Thus, recognition of these features would prompt proper diagnosis and insights into the pathomechanisms of GM2 gangliosidosis.

The GM1 and GM2 Gangliosidoses: Natural History and Progress toward Therapy

The gangliosidoses are lysosomal storage disorders caused by accumulation of GM1 or GM2 gangliosides. GM1 gangliosidosis has both central nervous system and systemic findings; while, GM2 gangliosidosis is restricted primarily to the central nervous system. Both disorders have autosomal recessive modes of inheritance and a continuum of clinical presentations from a severe infantile form to a milder, chronic adult form. Both are devastating diseases without cure or specific treatment however, with the use of supportive aggressive medical management, the lifespan and quality of life has been extended for both diseases. Naturally occurring and engineered animal models that mimic the human diseases have enhanced our understanding of the pathogenesis of disease progression. Some models have shown significant improvement in symptoms and lifespan with enzyme replacement, substrate reduction, and anti-inflammatory treatments alone or in combination. More recently gene therapy has shown impressive results in large and small animal models. Treatment with FDA-approved glucose analogs to reduce the amount of ganglioside substrate is used as off-label treatments for some patients. Therapies also under clinical development include small molecule chaperones and gene therapy.

Substrate reduction therapy in juvenile GM2 gangliosidosis

Substrate reduction therapy (SRT) is considered to be a potential therapeutic option for juvenile GM2 gangliosidosis (jGM2g). We evaluated the efficacy of SRT in jGM2g, assessing neurological, neuropsychological and brain magnetic resonance imaging (MRI) outcomes over a 24-month period of treatment. In an open-label and single-center study, five jGM2g patients (mean age 14.6+/-4.5 years) received oral miglustat at doses of 100-200mg t.i.d. adjusted to body surface area. Patients underwent general and neurological examinations, neuropsychological, electrophysiological, and brain MRI studies. All patients showed neurological deterioration over the period of the study, with particularly notable worsening of gait, speech and coordination. One patient experienced acute psychosis, and another showed worsening of pre-existing epilepsy. Some neuropsychological tests showed no evidence of deterioration in the three patients with high enough cognitive functioning for reliable assessment. Profound cognitive impairment in two children precluded neuropsychological evaluation. In four patients, evaluation of brain MRI showed no changes in white matter signal abnormalities and cerebellar atrophy noted at baseline, while one patient showed progression of cerebellar and supratentorial brain atrophy. Transmission electron microscopy analysis of peripheral mononuclear cells showed reduction of intracytoplasmatic inclusions with treatment. SRT with miglustat of patients with jGM2g failed to ameliorate progressive neurological deterioration, but apparently no worsening of some areas of cognitive function tested and brain MRI lesions was noted over 24 months of treatment. The results must be interpreted with care owing to the small sample of patients and the lack of a control-arm.

The Natural History of Cognitive Dysfunction in Late-Onset GM2 Gangliosidosis

BACKGROUND

Late-onset GM2 gangliosidosis (LGG) is a rare disease that is often considered in the differential diagnosis of adolescents and young adults who present with multiple realms of neurologic dysfunction. Cognitive disturbances are common but have not been systematically studied.

OBJECTIVE

To determine the natural history of cognitive dysfunction in patients with LGG.

DESIGN

Case series and literature review.

SETTING

Urban tertiary referral clinic.

PATIENTS

Individuals with hexosaminidase A deficiency as the origin of LGG.

MAIN OUTCOME MEASURES

Cognitive dysfunction, psychiatric symptoms, and cerebellar, upper motor neuron, lower motor neuron, or extrapyramidal symptoms and signs.

RESULTS

Historical and examination data from 62 patients were found. Forty-four percent of LGG patients had some degree of cognitive dysfunction. Cognitive dysfunction was associated with a greater number of other elemental neurologic deficits. In 21 patients with acceptable longitudinal information, 8 (38%) had a static cognitive disorder, whereas progressive dementia was evident in 13 patients (62%), including 2 of our cases with serial neuropsychological testing. Neuroimaging often showed nonspecific cerebellar and/or cerebral atrophy.

CONCLUSIONS

Cognitive dysfunction is a frequent manifestation of LGG. Patients who experience cognitive dysfunction are more likely to have a greater number of other neurologic manifestations of the disease. Cognitive dysfunction may take the form of static encephalopathy, but progressive dementia is more often encountered. The pathogenesis of cognitive dysfunction in this disease is unknown, highlighting the need for further study.

What can cell biology tell us about heterogeneity in lysosomal storage diseases?

Lysosomal storage diseases are clinically heterogeneous with respect to their age of onset, progression of symptoms and the particular organs involved. Varying levels of residual enzyme activity, associated with different defective alleles that cause the respective diseases, are responsible in part for this clinical heterogeneity. In general, the higher the residual enzyme activity, the milder the phenotype. Enzyme activity in severe forms of disease is frequently zero, and in mild forms usually does not exceed approximately 5%. However, the correlation is not so strict as to allow prediction of the phenotype of individual patients. The molecular basis of the different levels of enzyme activity can only be revealed by biochemical investigations of the defective lysosomal proteins. Null alleles may be due to splice-site mutations or deletions. In the case of missense mutations, enzymes frequently fold incorrectly and are retained in the endoplasmic reticulum and subsequently degraded. As these enzymes do not reach the lysosome, they do not provide any functional residual activity. Residual enzyme activity is only observed in cases where the defective enzyme reaches the lysosome and has retained enzymatic activity. Patients carrying the same mutant alleles still show considerable phenotypic variability due to modifying genes and epigenetic factors. None of these has so far been elucidated. However, there are some indications that differences in splicing-factor machinery may influence the phenotypic expression of splice-site mutations and that hormonal modulation of secondary microglial activation in lipidosis may also influence the disease course.

CONCLUSION

Phenotypic variability is a frequent phenomenon in lysosomal storage diseases. Residual enzyme activity has been identified as one of the factors influencing the clinical outcome of disease; however, it is obvious that other genetic and epigenetic factors also affect phenotypic variability, particularly in patients with late onset disease.

Neuropsychological assessment of patients with late onset GM2 gangliosidosis

OBJECTIVE

To characterize cognitive status in a sample of individuals with late-onset GM2 gangliosidosis (commonly referred to as late-onset Tay-Sachs disease).

METHODS

Seventeen subjects (13 men, 4 women) diagnosed with GM2 gangliosidosis were evaluated. Subjects ranged in age from 18 to 56 years and were in various stages of disease progression. Subjects underwent comprehensive neuropsychological assessment. Impairment was defined as performance more than 1.6 SD below the normative mean.

RESULTS

Group mean performance was within the denoted normal range on all measures except on a task assessing visual sequencing and set shifting. Approximately one-half of the sample scored in the impaired range on measures of processing speed, visual sequencing, and set shifting. One-third of the sample also scored in the impaired range on measures of delayed verbal recall. Impairment tended to be restricted to a subset of the sample, as 5 of the 14 subjects able to undergo formal testing accounted for 70% of the total number of impaired scores. If the three subjects unable to participate in formal testing are also considered impaired, 47% of the current sample exhibited significant cognitive impairment in at least one cognitive domain.

CONCLUSION

In late-onset GM2 gangliosidosis, there is a risk of impairment in executive functioning and memory as well as cerebellar dysfunction. Dementia was not present in any subjects in the current sample.

GM2 gangliosidosis variant B1 neuroradiological findings

Variant B1 is a rare type of GM2 gangliosidosis. Clinically, it shows a wide spectrum of forms ranging from infantile to juvenile. We report the first magnetic resonance imaging (MRI) findings from three patients affected by GM2 gangliosidosis variant B1, two presenting with the infantile form and one with the juvenile form. The MRI appearances of the two patients with the infantile form disease are congruent with those reported for the early-onset type of both Tay-Sachs and Sandhoff diseases, and are characterized by early involvement of the basal ganglia and thalamus with cortical atrophy appearing later. In contrast, the patient with the juvenile form of variant B1 showed progressive cortical and white-matter atrophy of the supratentorial structures and, to a lesser extent, the infratentorial structures. No basal ganglia or thalamic anomalies were observed. Because in the adult forms of both Tay-Sachs and Sandhoff diseases a progressive cerebellar atrophy represents the only abnormality detectable, it appears that an MRI pattern peculiar to GM2 gangliosidosis can be defined. This pattern ranges from the basal ganglia injury associated with the early and severe demyelination process noted in the infantile form of the disease, to cerebellar atrophy with no supratentorial anomalies in the adult form. An "intermediate" MRI picture, with cortical atrophy and mild cerebellar atrophy, but without basal ganglia impairment, can be observed in the juvenile form. In addition, our investigations suggest that MRI abnormalities in GM2 gangliosidosis correlate with the clinical form of the disease rather than with the biochemical variant of the enzymatic defect.

Ectopic dendrite initiation: CNS pathogenesis as a model of CNS development

The neuronal storage diseases are a rare group of disorders with profound clinical consequences including severe mental retardation and death in early childhood. A subset of these disorders, those with elevated levels of GM2 ganglioside, are further characterized by the reinitiation of primary dendrites on mature cortical neurons. These ectopic dendrites are unusual as primary dendrite initiation is normally confined to a narrow developmental window. Thus, ectopic dendritogenesis appears to be a recapitulation of the normal developmental program temporally displaced. Consequently, understanding ectopic dendritogenesis should offer insights into both the pathogenesis of the neuronal storage diseases as well as mechanisms of normal CNS development. Using a feline model of GM2 gangliosidosis, we compared patterns of gene expression in normal newborn and mature diseased animals (both undergoing active primary dendritogenesis) with normal, mature controls (where primary dendritogenesis has ceased). From this work, we have identified two genes that appear to function in primary dendrite initiation. One, tomoregulin, is an integral membrane protein with both EGF- and follistatin-like motifs in its extracellular domain. The second, Tristanin, is a member of the positive regulatory domain (PRD) family of a zinc-finger transcription factors. Both genes are up regulated in the disease state, and both show a shift in their intracellular location to the nucleus in diseased animals that is not observed in age matched controls. In normal mouse brain, tomoregulin and Tristanin reveal developmental patterns consistent with a role in dendrite initiation and show changes in subcellular localization similar to that observed in the cat.

Promoter characterization and expression of the gene coding for the human GM2 activator protein

Genomic clones of the human GM2 activator protein have been isolated and analyzed. The 5' region of the gene demonstrated promoter activity as ascertained by its ability to drive luciferase gene expression in transfected COS cells. This sequence contains GC rich region and several putative promoter elements were present, including Sp1, AP2, cAMP-responsive element, and B-cell-specific activating protein. Analysis of tissue distribution of the GM2 activator protein gene revealed tissue-specific variations in transcript levels. Placenta, bone marrow, mammary gland, bladder, lymph node, and spleen had the highest mRNA levels.