Generalized accumulation of neutral glycosphingolipids with GM2 ganglioside accumulation in the brain. Sandhoff's disease (variant of Tay-Sachs disease)

A clinical review on megalencephaly: A large brain as a possible sign of cerebral impairment

Megalencephaly and macrocephaly present with a head circumference measurement 2 standard deviations above the age-related mean. However, even if pathologic events resulting in both megalencephaly and macrocephaly may coexist, a distinction between these two entities is appropriate, as they represent clinical expression of different disorders with a different approach in clinical work-up, overall prognosis, and treatment. Megalencephaly defines an increased growth of cerebral structures related to dysfunctional anomalies during the various steps of brain development in the neuronal proliferation and/or migration phases or as a consequence of postnatal abnormal events. The disorders associated with megalencephaly are classically defined into 3 groups: idiopathic or benign, metabolic, and anatomic. In this article, we seek to underline the clinical aspect of megalencephaly, emphasizing the main disorders that manifest with this anomaly in an attempt to properly categorize these disorders within the megalencephaly group.

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 β-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.

Neurological and cardiac responses after treatment with miglustat and a ketogenic diet in a patient with Sandhoff disease

Sandhoff disease is a progressive neurodegenerative disorder characterized by accumulation of GM2 gangliosides. We describe a 6-year-old male with coarse facial features, developmental delay, refractory seizures, hypertrophic cardiomyopathy, who was later found to have Sandhoff disease. Previous studies have revealed that caloric restriction in combination with miglustat increased survival and motor behavior in mouse model of Sandhoff disease. These findings suggest that combination therapy may result in improved outcomes for patients with Sandhoff. Initiation of treatment with miglustat and a ketogenic diet was followed by improvement of the patient's seizure control and cardiac function. Further clinical investigation is required to better determine the benefit of management in late-onset forms of Sandhoff disease.

GM2 gangliosidosis in a UK study of children with progressive neurodegeneration: 73 cases reviewed

AIM

To report the demographic, phenotypic, and time-to-diagnosis characteristics of children with GM2 gangliosidosis referred to the UK study of Progressive Intellectual and Neurological Deterioration.

METHOD

Case notification is made via monthly surveillance card, administered by the British Paediatric Surveillance Unit to all UK-based paediatricians; children with GM2 gangliosidosis were identified from cases satisfying inclusion in the UK study of Progressive Intellectual and Neurological Deterioration and analysed according to phenotypic and biochemical categories.

RESULTS

Between May 1997 and January 2010, 73 individuals with GM2 gangliosidoses were reported: 40 with Tay-Sachs disease, 31 with Sandhoff disease, and two with GM2 activator protein deficiency. Together they account for 6% (73/1164) of all diagnosed cases of progressive intellectual and neurological deterioration. The majority (62/73) were sporadic index cases with no family history. Children of Pakistani ancestry were overrepresented in all subtypes, particularly juvenile Sandhoff disease, accounting for 10 of 11 notified cases. Infantile-onset variants predominated (55/73); the mean age at onset of symptoms was 6.2 and 4.7 months for infantile-onset Tay-Sachs and Sandhoff disease respectively, and 26.2 and 34.7 months for the corresponding juvenile-onset variants. Time to diagnosis averaged 7.4 months and 28.0 months in infantile- and juvenile-onset disease respectively.

INTERPRETATION

GM2 gangliosidosis is a significant cause of childhood neurodegenerative disease; timely diagnosis relies upon improved clinical recognition, which may be increasingly important as specific therapies become available. There is a potential benefit from the introduction of screening programmes for high-risk ethnic groups.

Natural history of infantile G(M2) gangliosidosis

OBJECTIVE

G(M2) gangliosidoses are caused by an inherited deficiency of lysosomal β-hexosaminidase and result in ganglioside accumulation in the brain. Onset during infancy leads to rapid neurodegeneration and death before 4 years of age. We set out to quantify the rate of functional decline in infantile G(M2) gangliosidosis on the basis of patient surveys and a comprehensive review of existing literature.

METHODS

Patients with infantile G(M2) gangliosidosis (N = 237) were surveyed via questionnaire by the National Tay Sachs & Allied Diseases Association (NTSAD). These data were supplemented by survival data from the NTSAD database and a literature survey. Detailed retrospective surveys from 97 patients were available. Five patients who had received hematopoietic stem cell transplantation were evaluated separately. The mortality rate of the remaining 92 patients was comparable to that of the 103 patients from the NTSAD database and 121 patients reported in the literature.

RESULTS

Common symptoms at onset were developmental arrest (83%), startling (65%), and hypotonia (60%). All 55 patients who had learned to sit without support lost that ability within 1 year. Individual functional measures correlated with each other but not with survival. Gastric tube placement was associated with prolonged survival. Tay Sachs and Sandhoff variants did not differ. Hematopoietic stem cell transplantation was not associated with prolonged survival.

CONCLUSIONS

We studied the timing of regression in 97 cases of infantile G(M2) gangliosidosis and conclude that clinical disease progression does not correlate with survival, likely because of the impact of improved supportive care over time. However, functional measures are quantifiable and can inform power calculations and study design of future interventions.

High-sensitivity analysis of glycosphingolipids by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight imaging mass spectrometry on transfer membranes

Glycosphingolipids are ubiquitous constituents of cells. Yet there is still room for improvement in the techniques for analyzing glycosphingolipids. Here we report our highly sensitive and convenient analytical technology with imaging mass spectrometry for detailed structural analysis of glycosphingolipids. We were able to determine detailed ceramide structures; i.e., both the sphingosine base and fatty acid, by MS/MS/MS analysis on a PVDF membrane with 10 pmol of GM1, with which only faint bands were visible by primuline staining. The limit of detection was approximately 1 pmol of GM1, which is lower than the value in the conventional reports (10 pmol).

Quantitative dysmorphology assessment in Fabry disease

PURPOSE

1) To identify morphometric characteristics in hemizygous patients with Fabry disease a treatable lysosomal storage disorder caused by the deficiency of alpha-galactosidase A where morphological abnormalities have occasionally been mentioned, but have never been investigated systematically. 2) To devise a quantitative method to evaluate dysmorphic abnormalities in Fabry disease.

METHOD

Cross-sectional, single center, independent dysmorphology assessment by a panel of three clinical geneticists, based on standardized medical photography.

POPULATION

consecutive hemizygous patients with Fabry disease (N = 38) unselected for the features assessed, mean age 38 +/- 10.8 years (range: 10-60), recruited for neuropathic pain into enzyme replacement therapy trials.

RESULTS

The following dysmorphic features were identified (in order of descending frequency): periorbital fullness, prominent lobules of the ears, bushy eyebrows, recessed forehead, pronounced nasal angle, generous nose/bulbous nasal tip, prominent supraorbital ridges, shallow midface, full lips, prominent nasal bridge, broad alar base, coarse features, posteriorly rotated ears, and prognathism. Extremity features included broad fingertips, short fingers, prominent superficial vessels of hands, 5 digit brachydactyly, and 5 digit clinodactyly. Narrow anterior-posterior chest diameter was noted. Ten core features were statistically defined. Cronbach's alpha measuring internal consistency was 0.62. Light's kappa for global inter-rater variability was 0.26 while Cohen's kappa allowing pair-wise rater comparison varied between 0.08-0.48.

CONCLUSIONS

Patients with Fabry disease share common morphological characteristics of the face, trunk, and extremities. Some of these features are subtle as documented by the inter-rater variability. Awareness of these features may facilitate the diagnosis of patients with Fabry disease, and identification of affected family members.

Characterization of the testis and epididymis in mouse models of human Tay Sachs and Sandhoff diseases and partial determination of accumulated gangliosides

Beta-hexosaminidase (Hex) is an essential lysosomal enzyme whose activity is higher in the epididymis than in other tissues. The enzyme is also present in sperm and has been postulated to be required for fertilization. To better understand the role of Hex in reproduction, we have examined the testes and epididymides of mouse models of human Tay Sachs and Sandhoff diseases, produced by targeted disruption of the Hexa (alpha-subunit) or Hexb (beta-subunit) genes, respectively, encoding the enzymes Hex A (structure, alphabeta) and Hex B (betabeta). Testis weight, morphology, and sperm counts were unaffected in Hex-deficient mice. In the epididymis of the Hex A-deficient Hexa-/- mice, there was a large increase in the size and number of lysosomes in the initial segment/intermediate zone. In Hexb-/- mice (Hex A and B-deficient), the epididymal defects were much more extensive and the cytoplasm of all cell types throughout the efferent ducts and epididymis was filled with pale, uncondensed, enlarged lysosomes. In contrast to the brain where GM2 ganglioside accumulates, both mutant mice accumulated two non-GM2 gangliosides in the epididymis. The major accumulated species was characterized by electrospray ionization tandem mass spectrometry. The Hexa-/- male mice were fertile; however, litter sizes were reduced. The Hexb-/- males were able to sire normal sized litters up to nine weeks of age and remained healthy until 16-20 weeks of age. The extensive abnormalities in the Hexb-/- mice, in contrast to region-specific effects in the Hexa-/-mice, indicate an important and novel role for the Hex B isozyme in the epididymis and a region-specific role for Hex A in the initial segment/intermediate zone. In contrast to other reports, our results indicate that Hex is not essential for fertilization in young adult male mice. To explain the extensive epididymal abnormalities in the Hexb-/- mice, we propose that substrates for Hex, such as testis-derived glycolipids, cannot be catabolized and accumulate in lysosomes, leading to epididymal dysfunction and abnormalities in the epididymal luminal environment that supports sperm maturation.

Sandhoff disease

An autopsy case of Sandhoff disease in a 2-year-old boy is reported. Diagnosis was established by enzyme assay, which demonstrated total deficiency of hexosaminidase in the serum. Histochemical examination, using hematoxylin-eosin (H & E) and Luxol fast blue (LFB) stain, showed accumulation of LFB-positive material not only in cells of the cerebrum, cerebellum, spinal cord, and peripheral nervous system, but also in reticuloendothelial cells of the lymph nodes, spleen, thymus, and liver, in podocytes of renal glomeruli, in all types of renal tubular cells, in endothelial cells of small vessels, in fibroblasts, and in epithelial cells of the epididymis and ductus deferens. Electron microscopic examination showed that these deposits contained electrondense membranous bodies. Lipid analysis demonstrated a marked elevation of ganglioside GM2 and its asialo derivative in the brain and liver. Accumulation of globoside was found in the liver, kidney, and spleen. There was complete absence of hexosaminidase in the brain and liver.

Biochemistry and genetics of gangliosidoses

The gangliosidoses comprise an-ever increasing number of biochemically and phenotypically variant diseases. In most of them an autosomal recessive inherited deficiency of a lysosomal hydrolase results in the fatal accumulation of glucolipids (predominantly in the nervous tissue) and of oligosaccharides. The structure, substrate specificity, immunological properties of and genetic studies on the relevant glycosidases, ganglioside GM1 beta-galactosidase and beta-hexosaminidase isoenzymes, are reviewed in this paper. Contrary to general expectation, only a poor correlation is observed between the severity of the disease and residual activity of the defective enzyme when measured with synthetic or natural substrates in the presence of detergents. For the understanding of variant diseases and for their pre- and postnatal diagnosis, the necessity of studying the substrate specificity of normal and mutated enzymes under conditions similar to the in vivo situation, e.g., with natural substrates in the presence of appropriate activator proteins, is stressed. The possibility that detergents may have adverse affects on the substrate specificity of the enzymes is discussed for the beta-hexosaminidases. The significance of activator proteins for the proper interaction of lipid substrates and water-soluble hydrolases is illustrated by the fatal glycolipid storage resulting from an activator protein deficiency in the AB variant of GM2-gangliosidosis. Recent somatic complementation studies have revealed the existence of a presumably post-translational modification factor necessary for the expression of ganglioside GM1 beta-galactosidase activity. This factor is deficient in a group of variants of GM1-glangliosidosis. Among the possible reasons for the variability of enzyme activity levels in heterozygotes and patients, allelic mutations, formation of hybrid enzymes, and the existence of patients as compound heterozygotes are discussed. All these may result in the production of mutant enzymes with an altered specificity for a variety of natural substrates.

The pathology of Sandhoff's disease

We have presented the morbid anatomy of a case of Sandhoff's disease and have attempted to outline morphologic differences which distinguish this entity from other GM2 gangliosidoses. Yet, it may be well to maintain a sceptical eye. The anatomic differences among Tay-Sachs disease and its variants are more quantitative than qualitative and are overshadowed by the similarities. For these reasons, a definitive diagnosis must rest with the biochemist. Nevertheless, if many bizarre MCB's are encountered, the enzyme defect may be expected to differ from that of classical Tay-Sachs disease and, when seen in endothelial cells, they favour Sandhoff's disease. More importantly, if prominent visceral storage is found, and especially if it extends beyond the reticuloendothelial system to involve such selective sites as the kidneys and pancreas, Sandhoff's disease should immediately come to mind. For the pathologist, it is this latter point which more readily sets apart Sandhoff's disease from related GM2 gangliosidoses.

Aspartylglucosaminuria: unique biochemical and ultrastructural characteristics

The observation of vacuolated lymphocytes in a coarsely featured two year old female with hepatosplenomegaly, mitral insufficiency, and mild psychomotor retardation led to the first diagnosed case of aspartylglucosaminuria in the United States. Although physical characteristics and bone roentgenograms were consistent with a mucopolysaccharide disorder, analysis of the urine showed no mucopolysaccharide elevation. The chromatographic, enzymatic, and ultrastructural studies confirming the diagnosis are presented.