An autopsy case of Sandhoff's disease

Thymic involution and corticosterone level in Sandhoff disease model mice: new aspects the pathogenesis of GM2 gangliosidosis

Sandhoff disease (SD) is a lysosomal disease caused by a mutation of the HEXB gene associated with excessive accumulation of GM2 ganglioside (GM2) in lysosomes and neurological manifestations. Production of autoantibodies against the accumulated gangliosides has been reported to be involved in the progressive pathogenesis of GM2 gangliosidosis, although the underlying mechanism has not been fully elucidated. The thymus is the key organ in the acquired immune system including the development of autoantibodies. We showed here that thymic involution and an increase in cell death in the organ occur in SD model mice at a late stage of the pathogenesis. Dramatic increases in the populations of Annexin-V(+) cells and terminal deoxynucletidyl transferase dUTP nick end labeling (TUNEL) (+) cells were observed throughout the thymuses of 15-week old SD mice. Enhanced caspase-3/7 activation, but not that of caspase-1/4, -6 ,-8, or -9, was also demonstrated. Furthermore, the serum level of corticosterone, a potent inducer of apoptosis of thymocytes, was elevated during the same period of apoptosis. Our studies suggested that an increase in endocrine corticosterone may be one of the causes that accelerate the apoptosis of thymocytes leading to thymic involution in GM2 gangliosidosis, and thus can be used as a disease marker for evaluation of the thymic condition and disease progression.

Thymic alterations in GM2 gangliosidoses model mice

Background

Sandhoff disease is a lysosomal storage disorder characterized by the absence of β-hexosaminidase and storage of GM2 ganglioside and related glycolipids. We have previously found that the progressive neurologic disease induced in Hexb^−/− mice, an animal model for Sandhoff disease, is associated with the production of pathogenic anti-glycolipid autoantibodies.

Methodology/Principal Findings

In our current study, we report on the alterations in the thymus during the development of mild to severe progressive neurologic disease. The thymus from Hexb^−/− mice of greater than 15 weeks of age showed a marked decrease in the percentage of immature CD4⁺/CD8⁺ T cells and a significantly increased number of CD4⁺/CD8⁻ T cells. During involution, the levels of both apoptotic thymic cells and IgG deposits to T cells were found to have increased, whilst swollen macrophages were prominently observed, particularly in the cortex. We employed cDNA microarray analysis to monitor gene expression during the involution process and found that genes associated with the immune responses were upregulated, particularly those expressed in macrophages. CXCL13 was one of these upregulated genes and is expressed specifically in the thymus. B1 cells were also found to have increased in the thy mus. It is significant that these alterations in the thymus were reduced in FcRγ additionally disrupted Hexb^−/− mice.

Conclusions/Significance

These results suggest that the FcRγ chain may render the usually poorly immunogenic thymus into an organ prone to autoimmune responses, including the chemotaxis of B1 cells toward CXCL13.

The fine structure of cytoplasmic inclusions in brain and other visceral organs in Sandhoff disease

This paper describes an 11-month-old male who died of Sandhoff disease. Diagnosis was based on detection of cherry red spots and total deficiency of hexosaminidase A and B activities. Sections of the brain revealed swollen neuronal cells and their degeneration and disappearance, leaving a distorted cortical architecture. Ultrastructurally, numerous inclusions showing concentric lamellar or stacked lamellar profiles were found in ballooned neuronal cells, astrocytes and histiocytes. The parafoveal retina in the region of the cherry red spot contained ballooned ganglion and amacrine cells filled with PAS and LFB positive granules. Electron microscopically, these cells showed a greater accumulation of inclusions with stacked lamellar profiles, than the concentric lamellar ones, of classically membranous cytoplasmic bodies (MCB). Hepatocytes and Kupffer cells and epithelial cells of renal glomeruli contained pleomorphic inclusions. Biochemical analysis by thin-layer chromatography of lipid extracts from the cerebral cortex showed a marked increment of the GM2 fraction, without an increase in globoside.

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.

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.

GM2-gangliosidosis, AB variant: clinico-pathological study of a case

Clinical and neuropathological studies of a case of AB variant GM2-gangliosidosis have been presented. The patient was a 14 months old black female infant who had "black cherry spot" in the retinas. The total activities of beta-galactosidase and N-acetyl-beta-hexosaminidase, as well as the proportion of hexosaminidase A and B components in her serum and leukocytes were normal when the assays were carried out with artificial fluorogenic substrate. Diagnosis of GM2-gangliosidosis AB variant was established by an abnormal increase of GM2-ganglioside in the biopsied brain tissue, similar to classical Tay-Sachs disease. Her clinical manifestation appeared to be similar but somewhat milder than those of classical Tay-Sachs disease. Light microscopic features of the cerebral biopsy were also closely similar to Tay-Sachs disease and Sandhoff disease but gliosis and neuronal loss were less pronounced. Electron microscopic study revealed numerous membranous cytoplasmic bodies (MCB) and zebra bodies in neurons. In addition, varieties of large intracytoplasmic inclusions in astrocytes, a feature distinctly different from classical Tay-Sachs disease, were observed. Numerous cytoplasmic inclusions were also present in oligodendroglia, pericytes and microglial cells.