Isoenzymes of sphingomyelinase and the genetic defect in Niemann-Pick disease, type C

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Niemann-Pick disease

Results of the investigation carried out during this decade brought unambigous evidence of biochemical heterogeneity inside the complex of Niemann-Pick disease according to which two entirely different metabolic disorders can be recognized. 1. Niemann-Pick sphingomyelinosis, a clear-cut enzymopathy, the pivotal lesion of which is the deficiency of lysosomal spingomyelinase leading to widespread lysosomal deposition of sphingomyelin liquid crystals. Two main allelic variants are known. The first one, neuronopathic (former type A) known as infantile with rapid course, may also manifest considerably prolonged course or an atypical course with predominantly visceral symptomatology. Patients with the second, visceral, variant (former type B), display mainly slow clinical course and often reach adulthood. With rare exceptions the neuronopathic variant can be biochemically recognized from the visceral one by much lower values of the in vivo sphingomyelin degradation test in the former. 2. The rest of the complex comprising types C-D differs substantially from the sphingomyelinase deficiency group by the remarkable heterogeneity in the lysosomal stored lipid pattern given by differences among the affected cell populations. Sphingomyelin storage could be proved histochemically solely in the histiocytic population together with cholesterol, neutral glycosphingolipids and lysobisphosphatidic acid, whereas the brain neurons displayed only neutral glycosphingolipid storage. There is an increasing evidence of the crucial biochemical lesion in this group being an altered intracellular traffic of exogenously derived cholesterol caused probably by its deficient translocation from lysosomes to other intracellular membrane sites. This leads to decreased cholesterol esterification rate which is the basis of the newly developed diagnostic test. Inconstant depression of sphingomyelinase activity is considered to be a secondary phenomenon. The so-called lactosylceramidosis is a rare variant pertinent to this group. The biochemical nature of type E still awaits clarification. Both groups of Niemann-Pick disease display clinical and especially histochemical features which allows to establish diagnosis in a highly efficient way already at the clinicopathological level.

Purified rat brain microvessels exhibit both acid and neutral sphingomyelinase activities

Purified rat brain microvessels have been shown to hydrolyze radiolabeled sphingomyelin by means of two different enzyme systems. Enzymatic activity was detected at pH 7.4 and was strongly stimulated by magnesium or manganese and inhibited by calcium. Activity at pH 5.1 could also be found and was not dependent on any of these cations. At neutral pH and in the presence of magnesium, the rate of sphingomyelin hydrolysis did not exhibit a linear relationship with protein concentration. In contrast, increasing the protein concentration from 0.05 to 0.5 mg/ml resulted in a constant increase of sphingomyelin hydrolysis at pH 5.1. Kinetic parameters of both neutral and acid activities have been determined and were similar in magnitude to values reported previously for neural sphingomyelinases. This work demonstrates the occurrence of a neutral sphingomyelinase activity in purified rat brain microvessels, an observation raising the question of its role at the level of the blood-brain interface.

Dot immunodetection for sphingomyelinase with monoclonal antibody

An assay for the detection of sphingomyelinase with monoclonal antibodies is described. The assay takes advantage of nitrocellulose membranes as antigen adsorbent on which a dilute sample can be concentrated as a spot, using a specially designed 96-well filtration device which is commercially available. The method requires only 6 micrograms of the extracts from leukocytes and liver, and it is 10 times more sensitive than the colorimetric assay. This reduced amount of sample material also has the merit of requiring only a 0.5-ml blood sample from patients. The combination of this dot immunoassay with the monoclonal antibody allows a sensitive and a specific assay, and is also applicable as a screening test on a large number of samples. Furthermore, the possibility of differential diagnosis of Niemann-Pick disease types by detecting isoenzymes by this method was examined after isoelectric focusing of placental sphingomyelinase.

Alterations in cholesterol metabolism in cultured fibroblasts from patients with Niemann-Pick disease type C

Cholesterol synthesis, esterification and efflux were investigated in cultured fibroblasts from patients with Niemann-Pick disease type C. Sterol synthesis from sodium acetate was markedly increased in the two Niemann-Pick disease type C strains as compared to controls, either in the presence or absence of exogenous cholesterol supply by low-density lipoproteins. By contrast, cholesterol esterification was about 2-3-fold reduced when measured by oleic acid incorporation into cholesteryl esters and 10-15-fold reduced when measured with labelled free cholesterol as precursor, although acylcoenzyme-A:cholesterol acyltransferase activity was normal when studied in vitro on cell homogenates. Chase experiments with 14C-cholesterol demonstrated that the rate of cholesterol efflux was decreased by about 3-4-fold in fibroblasts from patients with Niemann-Pick disease type C. These results provide further evidence for alterations of sterol metabolism in Niemann-Pick disease type C and support the hypothesis of a trapping of exogenous cholesterol, which cannot enter the regulatory intracellular pools.

Biochemical and ultrastructural studies on an Epstein-Barr virus-transformed lymphoid cell line from a Niemann-Pick disease type C patient

Human lymphoid cell lines established from normal subjects and from a Niemann-Pick disease type C patient were investigated from a triple point of view of enzymology, metabolism and ultrastructure: Sphingomyelinase activities, isoenzyme electrofocusing profiles and properties of the major enzyme were quite similar in type C and normal lymphoid cell lines. Similarly, no significant difference was observed in non-specific phosphodiesterases hydrolysing bis(methylumbelliferyl)phosphate and bis(methylumbelliferyl)pyrophosphate. The study of the lipid composition of type C cells showed no obvious accumulation of sphingomyelin or other phospholipid, but only a higher amount of glycolipids (mainly GlcCer and GbOse3Cer), as visualized by bidimensional thin-layer chromatography. Ultrastructural studies demonstrated, in type C cells, the presence of an obvious lysosomal storage of amphiphilic lipids quite similar to that observed in tissues of type C patients. These studies, which demonstrate the validity of lymphoid cell lines as an experimental model system for type C disease, agree with the current opinion that an impairment of sphingomyelin catabolism is not the primary defect in type C disease.

Juvenile dystonic lipidosis (variant of Niemann-Pick disease type C)

In two siblings affected with dementia, epilepsy and vertical supranuclear ophthalmoplegia, foam cells and sea-blue histiocytes were found in the bone marrow. Electron microscopy of skin and neuromuscular biopsies gave presumptive evidence in favour of a storage disorder. Postmortem examination of both cases revealed an intraneuronal polymorphous lysosomal storage in the central nervous system (in the cortex and in many nuclei e.g. the substantia nigra and the reticular formation of the brain stem). In the visceral organs with the spleen most severely affected, the inclusions had a different ultrastructure, being composed of tightly apposed leaflets. The biochemical study revealed accumulation of sphingomyelin and other lipids in liver and spleen, with normal sphingomyelinase activities, which is consistent with the diagnosis of Niemann-Pick disease type C. In the brain, the most striking abnormalities involved the glycolipids. Sphingomyelinase activities were unchanged in cultivated skin fibroblasts. These data compared with those of reported cases, allowed the following conclusions to be made: (1) although the combination of clinical features appears to be unique, none of them, when considered separately, is pathognomonic for juvenile dystonic lipidosis; (2) diagnosis during life can be suggested by careful examination of nerve bundles and fibroblasts with the electron microscope, although the method of choice appears to be the study of bone marrow; but final assessment of the diagnosis, in the absence of demonstrable enzymic deficiency, requires in most cases a study of the lipid profile in a liver biopsy (or better, spleen tissue whenever available); (3) the intralysosomal storage is different, both morphologically and biochemically, in the central nervous system and in the spleen; (4) juvenile dystonic lipidosis represents a juvenile variant of Niemann-Pick disease type C, pending the discovery of the primary defect responsible for this disorder.

A progressive neurologic disorder with supranuclear vertical gaze paresis and distinctive bone marrow cells

Nine patients with a progressive neurologic disorder that was characterized by mental deterioration, supranuclear vertical gaze paresis, and foam cells or sea-blue histiocytes in the bone marrow are described and compared with patients who were previously described as having " neurovisceral storage disease with vertical supranuclear ophthalmoplegia" and "dystonic lipidosis." The clinical manifestations of our patients and those described by others and the pathologic findings and profiles of lipid analysis reported by others are similar to those in patients with Niemann-Pick disease, type C. Sphingomyelinase activities in leukocytes and skin fibroblasts were normal in our patients and in more than half of the reported cases; these findings are also compatible with those in patients with Niemann-Pick disease, type C. Until the biochemical and genetic abnormalities of Niemann-Pick disease, type C are clearly defined, it is justifiable to classify the disorder under discussion as a subgroup of Niemann-Pick disease, type C because it seems to be a heterogeneous group. From the clinical point of view, the diagnosis is difficult to establish in the absence of abnormalities in the bone marrow in patients who are older than 20 years; repeat examinations of the bone marrow are necessary in such patients. Clinicians should be aware of this disorder not only in patients in the first and second decades of life, when this disorder usually becomes symptomatic, but also in patients in the fourth and fifth decades.

Niemann-Pick disease: lipid storage in bone marrow macrophages

A histochemical study of lipids in bone marrow smears was performed in a series of 15 cases of Niemann-Pick disease (NPD). It revealed significant differences in the amount of lipids stored in macrophages of sphingomyelinase (SMase) deficiency (types A, B) and type C. Early deposition of uniform, anisotropic droplets of sphingomyelin (Maltese-cross birefringence) in lysosomes was a feature of a 9-member group of SMase deficiency (types A, B). The type C group (six cases) was characterized by a remarkable difference in the degree of phospholipid, mainly sphingomyelin, deposition. The total amount of phospholipids was small on average, and very often inversely proportional to pronounced structural storage changes. This indirect relationship was most prominent in the early phase of the disease and grew less prominent as the disease progressed further. The stored lipid was primarily isotropic. In longer lasting cases of both categories (SMase deficiency and type C) a considerable part of the storage cell population displayed ceroid deposition giving the appearance of a 'sea-blue histiocyte' independent of the type of NPD, but with definite predominance in SMase deficiency. The diagnostic value of the findings is discussed, and some pathogenetic conclusions suggested, particularly as regards type C. Lipid histochemistry of bone marrow smears is highly recommended as it represents a simple but highly efficient approach, capable of yielding valuable diagnostic information.

Studies on sphingomyelinase and beta-glucosidase activities in Niemann-Pick disease variants. Phosphodiesterase activities measured with natural and artificial substrates

Cultured fibroblasts were studied from 12 cases of Niemann-Pick disease group C. In 11, sphingomyelinase and glucocerebrosidase (and beta-glucosidase) activities were reduced to around 50% of those of controls. On isoelectric focusing, all 12 strains lacked sphingomyelinase activity in the major cathodic region (pI 8.0). The defect was also demonstrated with the artificial phosphodiester substrates bis(4-methylumbelliferyl) phosphate and 4-methylumbelliferyl pyrophosphate diester. In control fibroblasts and those heterozygous for types A or B or group C Niemann-Pick disease, the major sphingomyelinase peak electrofocused at pI 8.0. No direct interaction could be demonstrated by mixing experiments between group C Niemann-Pick extracts and those of type A disease or Gaucher disease. Profiles for beta-glucosidase activity appeared normal in Niemann-Pick group C fibroblasts. No reduction of sphingomyelinase or glucocerebrosidase activities was found in Niemann-Pick group C liver, nor any attenuation of cathodic sphingomyelinase activity in the affected tissue. Results suggest that sphingomyelinase expression differs in fibroblasts and liver. Enzyme defects associated with Niemann-Pick disease group C were only observed in cultured cells.

Biochemical studies in Niemann-Pick disease. I. Major sphingolipids of liver and spleen

In liver and spleen specimens of 12 patients with Niemann-Pick disease types A or B, sphingomyelin was increased 15-45-fold, total phospholipids 4-10-fold and cholesterol 3-6-fold over the normal values. The storage pattern was qualitatively similar in both types but the degree of accumulation was less in type B. In Niemann-Pick disease type C (16 cases), sphingomyelin was increased 3.5-fold in liver and 6-fold in spleen. In all forms of Niemann-Pick disease, bis(monoacylglycero)phosphate was markedly elevated. Glycosphingolipids were studied in six cases with type C, three cases with type B and two cases with type A. Glucosylceramide showed the largest increase from the normal pattern in all types of Niemann-Pick disease. Highest values were recorded in type C, 14- and 35-fold normal concentrations in liver and spleen, respectively. Other neutral glycosphingolipids, particularly lactosylceramide, were also elevated, and a 2-4-fold increase of ganglioside GM3 occurred. The fatty acid profiles of the sphingolipids showed only minor alterations. In contrast to the largely dominating sphingomyelin storage found in liver and spleen of Niemann-Pick disease types A and B, the major characteristic of the lipid storage in Niemann-Pick disease type C was the absence of any prevailing accumulation and, thus, the concept of this disorder as a primary sphingomyelin storage disease is not founded.

Niemann-Pick disease type C. Pathological, histochemical, ultrastructural and biochemical studies

Two sisters with Niemann-Pick Disease Type C suffered from a progressive CNS degenerative disease which ended with death at 8 and 7 years. Light microscopic and histochemical studies revealed storage of lipid (principally sphingomyelin) in the viscera and in the central nervous system (predominantly ganglioside). Complex lipid cytosomes containing stacked membranes, concentric laminated bodies with central dense cores and pleomorphic profiles were seen. Biochemical analysis showed an elevation of sphingomyelin in liver and spleen with normal total sphingomyelinase levels. However, by isoelectric focusing, there was a marked reduction of sphingomyelinase activity in the range of pI 4.6--5.2, whereas normal amounts of more acidic components were found. These data are compatible with autosomal recessive inheritance of a sphingomyelin lipidosis associated with deficiency of isoelectric forms of sphingomyelinase.

Morphological diagnosis of Niemann-Pick disease type C by skin and conjunctival biopsies

Skin and conjunctival biopsies were performed in six children with mental deterioration, incoordination, involuntary movements and discrete visceromegaly. Two main types of inclusions were observed: 1) intracytoplasmic bodies containing membranous profiles loosely disposed in concentric or parallel arrays, lying in clear cells of eccrine sweat glands, hair follicles and cells of the basal layer of skin and 2) pleomorphous membrane bound bodies with a multivesicular aspect which are formed by vacuoles, stacks of lamellae and amorphous electron dense material. Subsequent biochemical studies showing a slight increase of sphingomyelin in liver and normal sphingomyelinase in leukocytes supported the morphological diagnosis of Niemann-Pick disease type C. The qualitative regional diversity of storage is stressed and the interest of both skin and conjunctival biopsies in the diagnosis of this affection is discussed.

Somatic cell hybridisation studies showing different gene mutations in Niemann-Pick variants

Cultured skin fibroblasts from patients with different clinical types of Niemann-Pick disease were hybridized and sphingomyelinase activities were measured in the heterokaryon cell population. Both the natural substrate (3H-choline) sphingomyelin and the chromogenic analogue hexadecanoylamino-4-nitrophenylphosphorylcholine were used in the complementation analysis. In fusions between cells from type C Niemann-Pick disease with those from type A or B a clear restoration of sphingomyelinase activity occurred, whereas no complementation was found in other fusion combinations. The results indicate that at least two different genes are involved in the mutations leading to the different Niemann-Pick variants.

Neutral and acid sphingomyelinases: somatotopographical distribution in human brain and distribution in rat organs. A possible relationship with the dopamine system

Acid and neutral sphingomyelinase activities have been measured in 22 regions of human brain, and in several rat organs. In general, acid sphingomyelinase activity was similar in most brain regions examined. By contrast neutral sphingomyelinase activity decreased 30-fold between the globus pallidus and white matter. In grey matter structures activity decreased in the order globus pallidus greater than substantia nigra greater than or equal to putamen greater than head of caudate greater than thalamus greater than cortical structures. Under the conditions of assay and in the presence of several possible donors or acceptors, there was no evidence of transfer of phosphoryl-choline to other lipid acceptors. Acid sphingomyelinase was ubiquitously distributed in all rat tissues examined, highest in liver and lowest in adipose tissue. Neutral sphingomyelinase activity was highest in brain; activity from 25 to 10% of that in brain was observed in testis, adrenal gland and aorta. Activity in the other organs examined was less than 10% of that in brain. We suggest that the neutral enzyme serves a special function in brain, perhaps related to the dopaminergic systems.

Basic findings and current developments in sphingolipidoses

Sphingolipidoses are caused by recessively inherited deficiencies of lysosomal hydrolases. The clinical backgrounds of and current biochemical and genetic approaches to the different forms and variants of gangliosidoses, trihexosylceramidosis (Fabry's disease), galactosylceramidosis (Krabbe's disease), sulfatidoses (metachromatic leukodystrophies), glucosylceramidosis (Gaucher's disease), sphingomyelinoses (Niemann-Pick disease) and ceramidosis (Farber's disease) are presented.

Sphingomyelinase activities in cultured skin fibroblasts from patients with Niemann-Pick Disease

Sphingomyelinase activity in cultured skin fibroblasts from a fetus affected with infantile-type Niemann-Pick disease was 0.5% of control activity; the activities in cells from two patients with adult-type disease (Cases 2 and 3) were 5.0% and 59.0%. Sphingomyelinase activiy was separated into three peaks (I-III) by isoelectric focusing. The isoelectric points were 4.5, 4.9, and 5.2 for peaks I, II, and III, respectively. The three peaks in the Case 2 cells were drastically reduced; only a very small peak could be distinguished (pI of 4.7). On the other hand, three peaks were observed in the Case 3 cells. Peak I had a pI of 4.4, peak II a pI of 4.7, and peak III a pI of 5.2. Peak I was found at near normal level, but both peaks II and III were markedly reduced. Sphingomyelinase in the peak I fraction obtained from isoelectric focusing in Case 3 cells was found to have the same Km value as that in control cells.

Sphingomyelinase activity levels in human peripheral blood leukocytes, using [3H]sphingomyelin as substrate: study of heterozygotes and homozygotes for Niemann-Pick disease variants

Patients and heterozygous carriers of Niemann-Pick disease types A and B as well as the primary (genetic) sea-blue histiocyte syndrome were investigated for their leukocyte sphingomyelinase activity. In parallel, glucocerebrosidase activity was determined in all cases studied. [3H]Sphingomyelin and [14C]glucocerebroside served as substrates for sphingomyelinase and glucocerebrosidase activity measurements, respectively. Conditions for these enzymes' assays are discussed. Sphingomyelinase activity was completely absent in three cases of Niemann-Pick disease type A and significantly diminished in one patient with Niemann-Pick disease type B and two with the sea-blue histiocyte syndrome. Sphingomyelinase activity in obligatory heterozygotes of all variants investigated represented about 40 to 70% of normal activity. Nevertheless, some overlapping with normal values occasionally occurred. Interestingly, glucocerbrosidase activity was elevated in patients with Niemann-Pick disease variants.

An unusual case of phospholipidosis

We present the results of a structural, histochemical and lipid-chromatographic study of tissues obtained at postmortem from an unusual case of phospholipidosis. A previous biopsy of the appendix and liver (Elleder et al., 1975a) had revealed a predominance of phosphoglyceride storage, principally of lysobisphosphatidic acid (LBPA) postmortem material showed that this lipid was stored exclusively in central neurons. In the spleen and the lymph node, however, sphingomyelin (SP) was shown, histochemically and chromatographically, to be the main lipid stored. Total sphingomyelinase (SPase) activity in the appendix was reduced to about 50% of normal. Neuroaxonal dystrophy (NAD) and a conspicuous discrepancy between the degree of distension of some neurons and their lipid content deserve special mention. The case is contrasted with classical sphingomyelinosis; the complexity of the Niemann-Pick group of diseases is discussed as an indication of the difficulties of classification of any atypical case.

The isolation and characterization of sphingomyelinase from human placental tissue

Human placental sphingomyelinase activity was eluted as a single symmetrical peak from Sephadex G-200 with a molecular weight of 290000; however, the enzyme behaved heterogeneously on ion exchange chromatography. A specific species of sphingomyelinase was purified approx. 10 000-fold to a constant specific activity of 274 000 nanomol of sphingomyelin hydrolyzed per mg protein per h. When the purified enzyme was examined on sodium dodecyl sulfate disc gel electrophoresis, two distinct protein bands in approximately equal proportions with molecular weights of 36 800 and 28 300 were found. The specificity of the enzyme is directed towards both the hydrophilic phosphocholine and the hydrophobic ceramide moieties of sphingomyelin. Possible interrelationships between the heterogenous forms of placental sphingomyelinases are discussed.

Niemann-Pick disease type D: lipid analyses and studies on sphingomyelinases

Lipids and sphingomyelinase activity were studied in spleen, liver, and brain tissues of a 13-year-old boy with Niemann-Pick disease type D (NPD-D). The greatest lipid changes occurred in spleen; cholesterol, cholesterol esters, total phospholipids, sphingomyelin, and bis-(monoacylglyceryl)phosphate were increased above normal range. In liver, striking increases were observed in cholesterol and bis-(monoacylglyceryl)phosphate. Minor changes in neutral and acidic glycolipid patterns occurred in liver, spleen, and brain. Sphingomyelinase activity (optimal at pH 5.0) was elevated above mean control levels in liver and spleen, but not in brain, kidney, or leukocytes. Enzyme properties were generally normal. Activity of NPD-D liver crude homogenate, but not that of normal liver homogenates, was inhibited at high protein concentrations. Activity levels of a second sphingomyelinase, optimal at pH 7.4, in NPD-D brain were apparently normal. These findings are generally consistent with the classification of NPD-D as a sphingomyelin lipidosis.

A potential source of error in the enzymatic diagnosis of the neurolipidoses when radiolabelled sphinogolipids are used as substrates

High specific activity 3H-labelled glucocerebroside, galactocerebroside and sphingomyelin but not 3H-labelled ceramide, have been found to bind to the wall of glass scintillation vials thereby greatly decreasing the counting efficiency. The binding of the lipids was largely eliminated by counting samples in scintillation fluid containing methanol (6-10%, v/v). To avoid possible errors in the enzymatic diagnosis of the neurolipidoses, it is suggested that the latter solvent should be routinely incorporated into scintillation fluid used for counting labelled sphingolipids.

Krabbe's globoid cell leucodystrophy. Studies on galactosylceramide beta-galactosidase and non-specific beta-galactosidase of leucocytes, cultured skin fibroblasts, and amniotic fluid cells

Galactosylceramide beta-galactosidase (cerebrosidase) and nonspecific beta-galactosidase activities were measured in both cultured skin fibroblasts and leucocytes from a family with Krabbe's globoid cell leucodystrophy (GLD). The activities of these enzymes were also determined in cultured skin fibroblasts of a patient with GM1 gangliosidosis and in cultured amniotic fluid cells. While cerebrosidase activity was deficient in GLD fibroblasts and leucocytes, its activity in GM1 gangliosidosis fibroblasts was increased. Two forms of each enzyme were found on isoelectric focusing, but in the GM1 gangliosidosis fibroblasts, cerebrosidase activity occurred as a single but intermediate peak. The use of cultured cells in assessing isoenzyme abnormalities associated with certain neurolipidoses is discussed.

The cerebral lipidoses

The disorders presented consist of those clinical entities in which a reasonably well defined lipid storage material accumulated within nervous tissue. Many other progressive, degenerative disorders are suspected of being storage disorders, but their chemical pathology remains unclear. Collectively this group could be designated the sphingolipidoses. In each case, the disease is a genetic disturbance and transmitted as an autosomal recessive. Sphingolipid storage in each disorder is associated with deficient activity of a specific degradative enzyme or enzyme system, and these deficient enzymes are all lysosomal hydrolases. Lysosomal hydrolases catalyze the breakdown of complex molecules in digestive vacuoles (phagocytic or autophagic) within the cells. Lysosomes show structural latency (requiring osmotic shock or freeze thawing in vitro); their enzymes show maximal activity at acidic pH ranges, and on electron microscopic examination they appear as small, electron-dense intracellular bodies. These hydrolytic enzymes seem to have some form of biological vulnerability in terms of their genetic expression, and this vulnerability underlies the sphingolipidoses. Diagnosis in each case is primarily a clinical problem. The presentation of these disorders, especially in intermediate or advanced forms, is sufficiently distinctive to permit a reasonably accurate diagnosis on the basis of history, physical examination, and routine laboratory data. Patients seen in early stages may be more difficult to recognize but follow-up evaluations usually clarify the problem. Specific enzyme assays are now available for confirmation of the diagnosis in these disorders. A frequent finding in this connection is an increase in the activities of noninvolved lysosomal hydrolases in the storage disorders. Once a case is clinically diagnosed, the clinician has the responsibility of ensuring that proper genetic counseling is made available to the affected families. Considerable supportive care is needed in each case. These patients can survive for prolonged periods, and great stress is placed on their families by these prolonged, hopeless illnesses. Since the disorders affect infants or young children, their parents are usually young adults in their early reproductive years. It is essential that they receive information concerning the risk of subsequent pregnancies. Specific diagnosis of the fetus in early pregnancy can be made now by amniocentesis and enzyme assays on cultured fibroblasts. If the fetus is a homozygote on the basis of enzyme assays, the option of therapeutic abortion should be discussed with the family. For many parents there will be considerable sensitivity to the ethical implications of this course and, if any doubt arises, ethical or pastoral consultation should be sought. Although there are no specific therapeutic approaches, a considerable degree of supportive care can and should be given. In the gangliosidoses and late in the course of the leukodystrophies, seizures will present management problems...

[Sphingolipid storage disease as an example of a molecular neuropathology (author's transl)]

A short survey on the sphingolipid storage diseases is presented. The chemical nature of the accumulated substances is related to the genetically induced enzymic blocks on their biodegradation. Two disorders are stressed with alter the nervous system: metachromatic leukodystrophy and familiar infantile amaurotic idiocy (GM2-gangliosidosis). The difficulties in the causal interpretation of three variants of the latter disease due to the involvement of isoenzymes are dealt with. The relationship between the enzyme defect in these disorders and their time of clinical onset is discussed. Finally, the diagnostic possibilities are presented which are a prerequisite for preventing a further dissemination of these therapy-resistent inborn errors of metabolism.

Niemann-Pick disease (Crocker's type C): A histological study of the distribution and qualitative differences fo the storage process

A histochemical study is reported of regional differences of the lipid storage in a case of Niemann-Pick disease (NPD) type C. Besides tissues known to be affected (reticulo-endothelium, hepatocytes, nervous system), storage was demonstrated in adrenal cortical spongiocytes, sweat glands, renal glomerular and tubular cells, smooth muslce, excretory tubules of some salivary glands, ependyma and in choroid plexus. In most tissues were stored sphingomyelin, cholesterol and a small amount of a glycosphingolipid. In the endothelium of cerebral and spinal vessels the main stored lipid was a glycosphingolipid. The significance of these regional differences are discussed and their study is recommended as a useful counterpart to the biochemical investigation.