Progress in investigations of sphingolipidoses

Manifestation of infantile GM1 gangliosidosis in the fetal eye. An electron microscopic study

GM1 gangliosidosis in the infantile form is a rapidly fatal storage disease produced by deficiency of acid beta-galactosidase. Ultrastructural studies of the eyes from two fetuses affected with GM1 gangliosidosis were performed in an effort to assess tissue-specific distribution of storage inclusions in the different ocular components derived from neuroectoderm, surface ectoderm, and mesoderm. Two major configurations of inclusions were observed: electronlucent vacuoles and pleiomorphic osmiophilic membranes. Although the latter changes mainly affected the retinal neurons, they were occasionally found in cells of epithelial and mesenchymal origin. The findings indicate that the lysosomal storage process in GM1 gangliosidosis, type 1, has a wide morphologic spectrum that is already present in the early period of fetal life.

N-acetyl-beta-hexosaminidase beta locus defect and juvenile motor neuron disease: a case study

A patient with partial deficiency of N-acetyl-beta-hexosaminidase (Hex) developed a progressive motor neuron syndrome beginning at age 7, characterized by dysarthria, muscle wasting, fasciculations, and pyramidal tract dysfunction. Minor clinical features have included tremor and late distal sensory abnormalities. Rectal biopsy at age 24 demonstrated membranous cytoplasmic bodies in submucosal ganglion cells. Biochemical evaluation revealed nearly absent Hex B activity in serum, leukocytes, and fibroblasts, with partial Hex A activity in serum and leukocytes, and low normal Hex A activity in fibroblasts. Motor neuron disease can be a presentation of a Hex beta locus defect, in addition to the previously recognized Hex alpha locus defects.

Tay-Sachs disease with conspicuous cranial computerized tomographic appearances

An autopsy case of a 3-year-old female infant with Tay-Sachs disease was presented. A cherry red spot in the fundus and a deficiency of N-acetyl-beta-hexosaminidase A in the white blood cells were revealed soon after admission at the age of one year. Her parents and sister were found to be healthy carriers. The patient showed a typical clinical course with marked cranial swelling. In addition to the marked ballooning of neurons on light microscope, membranous cytoplasmic body (MCB) on electron microscope and abnormal accumulation of GM2 ganglioside in the cerebral cortex by thin layer chromatography were confirmed in the autopsy specimens. In the late stage of her clinical course, the cranial computerized tomography (CT) demonstrated symmetric and deep-wavy hyperdense cerebral cortical zones, diffuse hypodensity and diminished volume of cerebral white matter, mild to moderate ventricular dilatation, and a small cerebellum and brainstem. These conspicuous appearances of the cranial CT seem to be characteristic of Tay-Sachs disease in the late stage, and they are derived from abnormal accumulation of GM2 ganglioside in the cerebral cortex, and diffuse intense demyelination (dysmyelinating demyelination) of the cerebral white matter.

Heritable metabolic storage diseases

During the last decade, examinations of skin biopsies have gained increasing importance in the search for a better understanding and facilitated diagnosis of metabolic storage diseases. In addition to biochemical and tissue culture techniques, light- and electron-microscopic investigations have been recommended in a number of such disorders (1-6). There are, however, a large number of different and inhomogeneous conditions to be identified in this group. At present, approximately 300 diseases can be identified as inborn errors of metabolism by the determination of a biochemically well-established underlying defect. Moreover, a yet undetermined number of pathological conditions is accompanied by the deposition of more or less defined storage materials in cutaneous tissue elements. It appears, therefore, premature to propose a systematic dermatopathology of metabolic storage diseases, and the following contribution should be understood as an attempt to indicate possibilities and chances by quoting some representative examples.

Neuropathological findings of an autopsy case of adult beta-galactosidase and neuraminidase deficiency

An autopsy case of a Japanese male with familial beta-galactosidase and neuraminidase deficiency is reported. The clinical picture was characterized by adult onset, a gargoyle-like face, cerebellar ataxia, myoclonus, convulsions, retinal degeneration and cortical blindness. Histopathologically, most neurons seemed to have become degenerated in the whole cerebral cortex. Moreover, the calcarine cortex appeared spongy with depopulation of nerve cells. Stuffed neurons or neuronal storage changes were found throughout the brain, especially in the motor nuclei of the spinal cord and brain stem. The inclusions in the stuffed neurons revealed various profiles on the electron microscope. They were composed of membranous lamellar and/or multilamellar structures, often accompanying vacuoles and reminiscent of lipofuscin-like profiles.

Two siblings, including a fetus, with Tay-Sachs disease

This report consists of a morphological study on two siblings of Tay-Sachs disease. One is a girl of 3 years of age and the other is a 23-week fetus. In the first case, the nerve cells in the cerebral cortex showed histochemically abnormal accumulation of glycolipids and electron microscopically numerous membranous cytoplasmic bodies characteristic to gangliosidosis. In the fetal case, the nerve cells in the brain stem were well differentiated and here abnormal inclusions were found by histochemical study. The cortical neurons were immature in structure and inclusions were not demonstrated by histochemical study. In electron microscopic study, the cortical neurons also showed a small number of intracytoplasmic inclusions which contained electron dense granules and/or membranous structures. Causes of the differences in amount of abnormal lipid accumulation in the brain stem and the cerebral cortex were discussed.

Neuropathology of various types of Niemann-Pick disease

A comparative neuropathological and histochemical study was performed on the brains of seven cases of NPD. In type A (two cases), besides the neuronal storage of SM, a widespread endothelial storage of a neutral glycosphingolipid was found. In one case a pseudosystemic lesion of the pallido-nigral system was observed. In type B (one case) the only finding was the endothelial storage of SM. In type C (four cases) the degree of neuronal storage distension contrasted considerably with a very low amount of lipid demonstrable histochemically in fixed brains. Only in one case, focal neuronal storage of a phosphoglyceride could be proved. However, in peripheral neurons (of unfixed appendix) the phosphoglycerides were clearly predominating (one case). A remarkable and constant finding in each case of the series was a widespread neuroaxonal dystrophy with various topical maxima (thalamus, dentate nuclei). The significance of the findings are discussed in relation to the present status of knowledge of this type.

The AB-variant of GM2-gangliosidosis. Clinical, biochemical, and pathological studies of two patients

Clinical, neuropathological, and biochemical studies are reported in two children with the AB-variant of GM2-gangliosidosis. One patient had become symptomatic by 1--1.5 years, initially showing cerebellar signs, and then progressive psychomotor retardation, with hypotonia, spasticity, dementia, and macular cherry red spots, until death at the age of 4.5 years. The second patient showed an earlier onset of retardation and a more rapidly progressive course. At postmortem, the brains were of normal or near normal weights and displayed grossly only mild cerebral cortical and cerebellar atrophy, and mild pallor or attenuation of the white matter. Neuronal storage was widespread throughout the CNS, and both neurons and glia contained a variety of abnormal, membranous inclusions. Visceral organs were not involved. Ganglioside sialic acid was increased several fold in gray matter, with GM2 the predominant ganglioside species. N-acetyl-beta-glucosaminidase activities in serum, leukocytes, fibroblasts, and postmortem gray matter, assayed with an artificial, fluorogenic substrate, were normal, as were activities of other lysosomal hydrolases.

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.