An unusual case of phospholipidosis

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.

Liver findings in Niemann-Pick disease type C

A complex analysis of liver from a series of eight cases of Niemann-Pick disease type C showed practically generalized storage of glycolipids and phosphoglycerides by chemical and histochemical techniques. In six of the eight cases the storage process was of low degree, barely recognizable by routine histology, but well recognizable by histochemistry and electron-microscopy. In two cases it was marked and led to early functional impairment of the liver. Changes in various enzyme activities and in ultrastructural features of the storage process are described. Sphingomyelin was found to participate to a very low low degree and its accumulation was not proportional to the extent of overall storage. In two cases with prominent involvement of the liver normal levels of sphingomyelin were found. In other cases sphingomyelin was found, by lipid histochemistry, to be stored only in macrophages. To stress that the storage process in Niemann-Pick disease type C is qualitatively different a comparison was made with liver findings in sphingomyelinase-deficient patients. This feature is of practical as well as theoretical importance.

Hepatic storage of bis(monoacylglycerol) phosphate without concomitant storage of sphingomyelin in a 72-year-old patient with a partial deficiency of sphingomyelinase

A 72-year-old patient with marked splenomegaly and low sphingomyelinase (6% of lowest control value) in peripheral blood leukocytes is described. Much higher but variable residual sphingomyelinase activity was observed in cultured skin fibroblasts (40-67% of lowest control value); reduced activity was also found in a liver biopsy sample. Excess storage of sphingomyelin was not observed in a liver biopsy; instead, a lipid tentatively identified as bis(monoacylglycerol) phosphate was present in amounts at least 20 times greater than in age-matched control livers. The biochemical relationship of this patient to patients with sphingomyelin storage disease (Niemann-Pick disease) and phospholipidosis Type II is 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.