Reduced cellular cholesterol efflux and low plasma high-density lipoprotein cholesterol in a patient with type B Niemann-Pick disease because of a novel SMPD-1 mutation

Background Type A or B Niemann-Pick disease (NPD) is characterized by the accumulation of sphingomyelin in the lysosomes and cell membranes. This accumulation results because of a mutation in the sphingomyelin phosphodiesterase-1 ( SMPD-1 ) gene that causes a deficit in the acid sphingomyelinase (ASM). Objective Herein, we report on a new point mutation in the SMPD-1 gene that was discovered in a patient with type B NPD. Methods and Results A culture of the patient's fibroblasts demonstrated that the observed clinical symptoms and reduced plasma high-density lipoprotein cholesterol (HDL-C) were associated with a reduced efflux of cholesterol. Examination of the skin fibroblasts demonstrated that ASM activity was reduced to approximately 60% of that observed in control cells, and a newly identified point mutation was found in codon 494 [Gly (GGT) → Cys (TGT)] in the SMPD-1 gene. Furthermore, repeated measurements of the plasma HDL-C levels remained low (17.5-20.5 mg/dL), and the Apo A-I− or HDL−mediated cholesterol efflux from the patient's fibroblasts was significantly reduced as compared with control fibroblasts. Conclusion In summary, we identified a unique point mutation in a patient with type B NPD that was associated with various clinical findings, including a low plasma HDL-C level. This reduced cellular cholesterol efflux may be implicated, at least in part, in low plasma HDL levels.