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Genetic Heterogeneity of Niemann-Pick Disease Type C
Shinjiro Akaboshi and Kousaku Ohno*
Division of Child Neurology, Institute of Neurological Sciences and *Department of Neurobiology, Faculty of Medicine, Tottori University, Yonago 683, Japan
Niemann-Pick disease type C (NP-C) is an autosomal recessive neurovisceral lipid storage disorder, which is considered to have a defect in intracellular transport of unesterified cholesterol from lysosomes to other membrane sites, but the basic defect has not been clarified. Cultured cells from NP-C patients can be identified by accumulation of unesterified cholesterol in lysosomes, defective esterification of exogenously added cholesterol and normal lysosomal enzyme activities. The NP-C patients have been classified into four clinical groups depending on their clinical pictures, but the genetic heterogeneity among these groups was unknown. In this study, complementation analyses were performed by cell fusion between five patients with NP-C and SPM-3T3 cells derived from a mouse model of NP-C. Accumulation of intracellular cholesterol was not complemented in multinuclear cells fused between SPM-3T3 and each of four strains from the childhood type of NP-C, whereas a diminution in accumulation of intracellular cholesterol was found in multinuclear cells fused between SPM-3T3 cells and cells from a patient with the adult type of NP-C. The result indicates that a genetic heterogeneity exists in NP-C and that the model mouse belongs to the same complementation group of the childhood type. The adult type showed not only mild clinical features but also mild accumulation of intracellular cholesterol, when compared with cells from the childhood type. In addition, when cytoplasmic pH was measured under a laser scanning microscope, cells from the childhood type showed higher pH than cells from normal or the adult type in the presence of 10% fetal bovine serum. In the presence of lipoprotein-depleted serum pH in cells from an adult patient was significantly lower than those in normal cells or cells from childhood cases. When the intracellular acid granules were examined by acridine orange vital staining, acid granules were present in both types of NP-C, suggesting involvement of a defective cytoplasmic pH regulation and its severity in the pathogenesis and the genetic heterogeneity of NP-C, and not a defect in vacuolar type ATPase, a proton transporter into lysosomes.
Key words: complementation analysis; cytoplasmic pH; Iow density lipoprotein; Niemann-Pick disease type C