Niemann-Pick type C (NP-C) is a rare neurovisceral genetic disorder caused by mutations in the NPC1 or the NPC2 gene. NPC1 is a multipass-transmembrane protein essential for egress of cholesterol from late endosomes/lysosomes. To evaluate impacts of NPC1 mutations, we examined fibroblast cultures from 26 NP-C1 patients with clinical phenotypes ranging from infantile to adult neurologic onset forms. The cells were tested with multiple assays including NPC1 mRNA expression levels and allele expression ratios, assessment of NPC1 promoter haplotypes, NPC1 protein levels, cellular cholesterol staining, localization of the mutant NPC1 proteins to lysosomes, and cholesterol/cholesteryl ester ratios. These results were correlated with phenotypes of the individual patients. Overall we identified 5 variant promoter haplotypes. Three of them showed reporter activity decreased down to 70% of the control sequence. None of the haplotypes were consistently associated with more severe clinical presentation of NP-C. Levels of transcripts carrying null NPC1 alleles were profoundly lower than levels of the missense variants. Low levels of the mutant NPC1 protein were identified in most samples. The protein localised to lysosomes in cultures expressing medium to normal NPC1 levels. Fibroblasts from patients with severe infantile phenotypes had higher cholesterol levels and higher cholesterol/cholesteryl ester ratios. On the contrary, cell lines from patients with juvenile and adolescent/adult phenotypes showed values comparable to controls. No single assay fully correlated with the disease severity. However, low residual levels of NPC1 protein and high cholesterol/cholesteryl ester ratios associated with severe disease. The results suggest not only low NPC1 expression due to non-sense mediated decay or low mutant protein stability, but also dysfunction of the stable mutant NPC1 as contributors to the intracellular lipid transport defect.

中文翻译：

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皮肤成纤维细胞中的转录本、蛋白质、代谢物和细胞研究证明了 NPC1 突变的不同致病影响。

Niemann-Pick C 型 (NP-C) 是一种罕见的神经内脏遗传疾病，由 NPC1 或 NPC2 基因突变引起。NPC1 是一种多通道跨膜蛋白，对于胆固醇从晚期内体/溶酶体的排出至关重要。为了评估 NPC1 突变的影响，我们检查了 26 名 NP-C1 患者的成纤维细胞培养物，其临床表型从婴儿到成人神经系统发病形式不等。用多种测定法对细胞进行了测试，包括 NPC1 mRNA 表达水平和等位基因表达比率、NPC1 启动子单倍型评估、NPC1 蛋白水平、细胞胆固醇染色、突变 NPC1 蛋白在溶酶体中的定位以及胆固醇/胆固醇酯比率。这些结果与个体患者的表型相关。总的来说，我们确定了 5 个变异启动子单倍型。其中三个显示报告活性降低到控制序列的 70%。没有一种单倍型始终与更严重的 NP-C 临床表现相关。携带无效 NPC1 等位基因的转录本水平远低于错义变体的水平。在大多数样品中鉴定出低水平的突变 NPC1 蛋白。在表达中等至正常 NPC1 水平的培养物中，该蛋白质定位于溶酶体。患有严重婴儿表型的患者的成纤维细胞具有较高的胆固醇水平和较高的胆固醇/胆固醇酯比率。相反，来自青少年和青少年/成人表型的患者的细胞系显示出与对照组相当的值。没有单一的检测与疾病严重程度完全相关。然而，与严重疾病相关的 NPC1 蛋白残留水平低和胆固醇/胆固醇酯比率高。结果表明，不仅由于无义介导的衰变或突变蛋白稳定性低导致的 NPC1 表达低，而且稳定突变 NPC1 的功能障碍也是细胞内脂质转运缺陷的原因之一。