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Updated: Nov 6, 2025

In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila
Published on: August 20, 2019
Additive effect of frequent polymorphism and rare synonymous variant alters splicing in twin patients with
Igor Bychkov1, Alexandra Filatova2, Grigory Perelman2
1Research Centre for Medical Genetics, Moscow, Russia. bychkov.nbo@gmail.com.
Abstract:
Niemann-Pick disease type C (NP-C) (OMIM#257220) is a rare lysosomal storage disorder caused by pathogenic variants in either the NPC1 or NPC2 genes. It manifests with a wide spectrum of clinical symptoms and variable age of onset. We studied the impact of the frequent polymorphic variant c.2793 C > T (p.Asn931 = ), located in the donor splice site (SS) of NPC1 exon 18 on the penetrance of the rare synonymous variant c.2727 C > T (p.Cys909 = ), identified in two 55 y.o. twins with an adult onset form of NP-C. The patients' diagnosis was supported by biochemical analysis and positive filipin test. Analysis of the patients' cDNA showed that the c.2727 C > T variant leads to cryptic donor SS activation and frameshift deletion in the NPC1 exon 18. However, the minigene assay demonstrated that this exon shortening takes place only in the presence of the frequent polymorphic variant c.2793 C > T. Results of the transcript specific qPCR showed that only the presence in the NPC1 exon 18 of both variants leads to significant decrease of wild type (WT) transcript isoform.
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