Non-invasive and rapid diagnosis of Niemann-Pick disease type C1 by immunocytochemical detection of leaky lysosomes in squamous epithelial cells.

Niemann-Pick disease type C (NPC) is a rare lysosomal storage disorder characterized by impaired intracellular cholesterol trafficking, primarily caused by mutations in NPC1 or NPC2. Current diagnostic approaches mostly rely on invasive sampling, radiological imaging and complex biochemical analyses. Here, we report a rapid and non-invasive method for detecting type 1 NPC using exfoliated buccal squamous cells coupled with immunocytochemical identification of LGALS3 (Galectin-3)-positive leaky lysosomes, a hallmark of lysosomal membrane instability (leaky lysosome). In a cohort of three clinically and genetically confirmed NPC1 individuals, immunocytochemical analysis revealed a marked accumulation of LGALS3-positive puncta, indicating lysosomal leakage in proband-derived squamous cells. In contrast, no leaky lysosomes were observed in healthy control samples. This simple cell-based assay reliably discriminated NPC-affected individuals from unaffected controls without the need for next-generation sequencing or complex biochemical assays. Our findings demonstrate the feasibility of using buccal squamous cells for detecting lysosomal leakage, offering a rapid, low-cost, and non-invasive diagnostic platform. This approach has strong potential as a point-of-detection assay for early NPC diagnosis and for monitoring therapeutic responses in clinical settings.